Glass Ware Janus User Manual

Download

Page 1

GlassWare

AUDIO DESIGN

Shunt Regulator

Low- & High-Voltage Regulators

USER GUIDE

Contents

Page 1

10 11 12 13 17 19 20 21 22 23 23 24

Rev. A

Janus PCB Overview Introduction to Power Supplies

Standard Power Supplies

The Function of a Power Supply

Wall Outlet Voltage Problems

The Parts of a Power Supply

Rectifiers

Capacitors

Types of Electrolytic Capacitors

Capacitor Safety Rectifier Circuits Voltage Doubler Circuits Voltage Regulators Janus Shunt Regulator Schematic & Part Values Transformers & Rectifiers Heater Power Supply & Regulator Assembly and Testing Modifications & Part Upgrades Operation Janus PCB Dimensions

10/19/2008

Page 2

DANGER!

—

Ideally, a variac should be used to slowly power up the

oriented electrolytic

sistor blow at low voltages,

rather than at high voltages. Remember that the danger

increases by the square of the voltage; for example, 200

and 400

, be cautious at all

even when the power supply is disconnected

capacitors will have

. If you are not

attaching the

have someone who is

well

loving solder slingers left; we cannot

This PCB holds a high-voltage power supply; thus, a real and possibly—lethal shock hazard exists.

regulator, as it is better to have a miscapacitor or a mis-located re

volts is four times more dangerous than 100 volts volts is sixteen times more dangerous.

Once the power supply is powered up times. In fact, or shut down, assume that power-supply retained their charge and, thus, can still shock an experienced electrical practitioner, before transformer windings to the board,

-experienced in electronics review your work.

There are too few tubeafford to lose any more.

GlassWare

AUDIO DESIGN

www.glass-ware.com

www.tubecad.com

[email protected]

Page 3

GlassWare Audio Design

voltage and a high

its own raw power

In other words,

PCB holds all that is needed to make a

voltage

bridge rectifier arrangement or

ler configuration, allowing for more latitude in power

voltage regulator uses

bridge

voltage electrolytic capacitors now

bypass capacitors; in addition, the heater

the

Which helps explain why

ubtleties of creating

heater may be powered by either an AC or DC

power supply, a DC power supply is always necessary, as the remaining portion of the

voltage power supplies are at once both the easiest and the

most challenging element of tube electronics. Requiring as little as one transformer,

diode, and capacitor, what could be simpler? Or utilizing as much as a several power

bridges, a score of

individual

With audio circuits

in output

that power supply is

that the audio gear is the film in a movie projector

the power supply; the whiter and steadier the light,

Although the conventional, simple, transformer

capacitor power supplies can

, they

far from perfect, as a varying wall voltage results in a varying output voltage

Thus,

Janus PCB [Rev. A]

The Janus circuit board makes life quite a bit easier for the tube fancier. On this small by 6 inch, extra thick (0.094), 2oz-copper traces, USA-made PCB resides both a low

-voltage regulator, with each regulator finding supply, including the rectifiers and power-supply reservoir capacitors. except for the power transformers, the Janus superb tube- circuit power supply.

The low- voltage regulator is meant to supply the tube heaters; the highregulator, the rest of the tube circuit. The low- voltage regulator’s power supply flexible enough to allow either a conventional full-wavea two-rectifier voltage-doub transformer selection; this regulator can be set to either 6.3V or 12.6V. The high

a pure-tube, feedback-and- feedforward shunt regulator achieve a quiet AC regulated B+ voltage, which can span from 200V to 300V Furthermore, both a full-wave-center- tapped configuration or a full- waverectifier arrangement can be used with the high-voltage portion of the circuit.

Revision A changes to the PCB are an one inch increase in height and all four high

hold

regulator can now employ a bigger heatsink.

Introduction to Power Supplies

For most modern electronic products— printers, alarm clocks, LCD photo frames— power supply is the least important portion of the package. cheap, small, switching, universal, wall-wart power supplies fill every available outlet most houses. All proficient tube-circuit designers must master the s a clean DC voltage. For although a

tube circuit requires solely DC voltage.

Paradoxically enough, high-

transformers, many precision voltage references, twelve rectifier high-voltage MOSFETs, a fistful of OpAmps, dozens of capacitors, a cup of diodes, and several hundred resistors, what could be more complex?

, the cleaner, the steadier, the lower and the flatter impedance across the audio band of frequencies, the better suited for audio use. A good metaphor is and the high-intensity light source is the better the picture.

-rectifiersbe bolstered by increased capacitance and the addition of RC and LC and pi filters are quite and their output impedance is anything but flat across the audio spectrum.

oltage regulators are both the obvious and usual solution to these failings.

Page 4

A “standard power supply” is one that is not regulated. A standard power supply can

be simple or complex, unipolar or bipolar, low voltage or high voltage, low current or

the only disqualification is having a regulator. As most regulated supplies must also

incorporate a standard power supply as their voltage source, an understanding of the

Obviously, a power supply’s purpose is to provide a power source for a circuit.

However, we should take one step back and consider why the wall outlet cannot serve

since it does so for a lamp or toaster. The

simple answer is that the wall outlet provides an AC voltage and audio tube circuits

that a power supply not only

C, additionally, it converts the value of the AC voltage

and it modifies the resulting DC voltage by smoothing, stabilizing, current limiting,

and removing much of the radio frequency interference (RFI) from it. All of these

amp or toaster, but are essential for a tube circuit.

Actually, the only safe assumption concerning the wall voltage is that its time base is

he wall voltage varies from

t has slowly risen over the

ruly old transformers bear stickers that specify a 110Vac or

112Vac input voltage; whereas, a newer transformer sticker might read 117Vac or

;

or less, because of

varying

, thus

ility company is

But these

A standard power supply’s output voltage will

+ voltage

volts is a lot of voltage variation; in fact, it might be more than half the voltage drop

GlassWare Audio Design

Standard Power Supplies

high current, vacuum tube rectified or solid state rectified, choke-free or choke-filled—

standard power supply is primary to understanding voltage regulation.

The Function of a Power Supply

directly as a power supply for a tube circuit,

require a DC voltage. A more complete answer is converts the AC voltage into D

functions are not needed by a l

accurate. Beyond frequency, there is much latitude—sadly, too much latitude.

Wall outlet voltage problems:

• Voltage varies

• RFI contamination

• AC voltage may contain a DC component

The wall voltage is not as fixed as you might imagine, as t city to city, and within the same city, from hour to hour. I decades. For example, t

120Vac. In many new developments, the wall voltage runs hot, at 122Vac or hotter whereas in an old Victorian apartment, it can run cold, at 110Vac the long skinny wall wiring used. The wall voltage varies depending on the load presented to the power line feeding your house. During peak use it drops and when unburdened, it climbs. (Indeed, if a power line on the street is ruptured unloading the load down from the break, the voltage can climb to scary heights.)

Although a power-supply designer would disagree, as far as the ut concerned, +/-10Vac variations in wall voltage are perfectly acceptable. voltage variations can cause trouble. vary with the change in wall voltage. For example, a power amplifier’s B could drop or rise 50 volts from being used in one city versus another. Now, +/-

across a pass device in a high voltage regulator.

Page 5

GlassWare Audio Design

A reasonable guess on the absolute upper

, as the

which could be held liable for damaging your microwave oven, if

voltage. The lower limit is

. You can, however, choose to design

Radio frequency

interference comes from more than just radio stations. Light dimmers, computers,

all can pollute

voltage is moderately

Sometimes

adding a small shunting capacitor after the fuse on the primary is all that is needed; at

AC Plus Some DC

Every electronic student knows that the wall outlet provides AC

voltage; few, however, know that it might carry a DC component as well. This DC

ndustrial power

feeding some DC into the line. Since the power supply contains a

transformer, we imagine that this DC voltage can have no effect on our power supply.

ctly AC use, which means that its core was not

passes through a

transformer winding, the core will tend to polarize, that is the molecules within the

orientation into one unified

direction. The result of polarization of the core is that the transformer begins to

resemble an electromagnet, which can quickly saturate the core material and radically

ords, the presence of DC across a winding

of a normal AC transformer will make the transformer much less effective at

Paradoxically, the better the transformer, the worse the saturation problem. A toroidal

sitive to a DC current, as it is a much tighter inductive

core transformer is a looser inductive design and

this looseness allows it to sustain a greater amount of saturation. What is going on

ers contain some sloppiness in their electromagnetic circuit,

as their physical construction is not perfect, and this sloppiness constitutes a parasitic

air gap. This air gap works like the purposeful air gap in a single ended transformer by

component on the wall voltage? Here is a possible scenario: you have just built a

er, an amplifier so sweet and bewitching that

if Shakespeare had heard it, he would have been compelled to write an additional

bring it to your friend’s house, it sounds unbelievably

s wall connection contained a unhealthy

amount of DC and this so saturated the core of the power transformer that its

secondary voltage dropped, its ripple component increased, its ability to contain its

input circuitry

Maximum and Minimum Wall Voltages

limit of sustained higher line voltage would be around 127vac in the USA power company— the voltage became too hot—is very quick to prevent an overusually set to around 108vac here in the USA around an even wider variation, say 100-130vac.

RFI The art and science of stripping away RFI can fill a large book.

cable TV, hair dryers, switching power supplies, industrial electronics— the wall voltage with RFI. In general, assume that the wall contaminated with RFI and provide some means for scrubbing it clean.

other times, many complex RF filters are required on both the primary and secondary.

voltage can be as great as a few volts and it is usually the result of an i supply back-

Unfortunately, we are not that lucky.

The transformer was designed for a stri designed to be used in the presence of a DC current. If a DC current

iron core material will move from their flexable

decrease its effective inductance. In other w

transferring energy.

transformer is much more sen design. In contrast, the standard EI-

here is that all transform

increasing the saturation threshold of the transformer’s core.

Beyond reduced efficiency and poorer regulation, what are the ramifications of a

supremely wonderful single ended amplifi

twenty sonnets. Yet, when you noisy and harsh. What happened? Probably hi

magnetic field reduced to the point of radiating the field across the and output transformer, which then coupled it to the speakers.

Page 6

Power transformers are used to isolate, to convert, and to filter the wall

voltage. A transformer is made up at least two tightly coupled coils, which usually

cally close and

electromagnetically coupled. By means of the electromagnetic induction, AC voltage is

transformed from one voltage to another from one coil to another, while the

the transformer is called an isolation transformer. If the voltage increases, the

down transformer.

if the

primary winding, the winding that is connected to the wall outlet, has a hundred

turns and the secondary winding, the winding that feeds the rectifying circuit, has a

thousand turns, the winding ratio will be 1 to 10, or 1:10, which means that the

As there are no free

lunches in physics, if the voltage increased by tenfold on the secondary, the current

must decrease by tenfold. In other words, the winding ratio specifies the voltage ratio

core

transformer. The outer appearance of this transformer may be an industrial looking

open frame construction or classic tube amplifier end bell style or a shiny potted case.

internal to each is an ferromagnetic core, which is made up of flat, thin,

pieces of soft iron called laminations that come in two shapes: an E and an I. These

two shapes are placed side by side so as to define a closed H shape. One E is followed

on the layer, but on the next layer an I is followed by an E, then back to an

E followed by an I for the next layer and on and on…until the desired thickness is

almost

metal instead of the many

laminations? The answer lies in the fact that a solid core would suffer from a

rob the

transformer of efficiency. Imagine a doughnut made of iron, around a section of

which several turns of wire have been wound. Now, if a DC current is applied to the

b’s

in a hula hoop, which is what we desire. But the same circling induces an

electromagnetic field within the core itself, which creates perpendicular currents in

GlassWare Audio Design

The Parts of a Power Supply

Transformers

enshroud a ferromagnetic core. The coils are both physi

frequency remains the same. If the voltage on the primary and the secondary equal

transformer is called a step-up transformer; if it decreases, a stepThe ratio of turns in each winding determines the ratio of voltage change. Thus,

transformer will step up the wall voltage by a factor of ten.

and the inverse of the current ratio.

Standard EI-Core Transformers Most tube power supplies use an EI-

Nonetheless,

by one I

achieved. This interlacing of E’s and I’s makes for an electromagnetic circuit as tight as a core made of solid iron.

This begs the question: Why not use a core of solid

deleterious effect known as Eddy currents. These electrical currents

winding, the induced lines of magnetic flux will circle the around the core, like b

the core material. These currents, as they only generate heat within the core material drag down the power transfer.

Page 7

GlassWare Audio Design

Fortunately, Eddy currents are proportional to the square of the core thickness.

Therefore, if the core is made thin enough, we can ignore the Eddy currents. This what

the laminations do, as they are very thin and electrically insulated from each other by

suited to modern sleek and

slender enclosures. Additionally, they present relatively higher winding DC resistances

Their greatest failing,

however, is the large radiated magnetic fields that emanate from the bell sides of the

transformer. In other words, placement of this type of transformer within a chassis is

placed

core transformers often set the standard in

on printed circuit boards, these fairly

ack a good amount of power in a small package. Wider and longer

made up of E and I laminations and

four bobbins of wire. This last feature is what most interests us. Most transformers

sitting on top the other, as it helps to

further couple them. The disadvantage of such an arrangement lies the increased

capacitive coupling afforded by the closeness of the windings. This capacitance will

, the flat

pack’s greater distance between the primary and the secondary greatly reduces the

capacitive coupling between windings; thus, greatly reducing the RFI transference. (The

one of best choices of the easily

difficult. First,

radiated magnetic fields, better regulation, smaller, lighter, and

cooler running. The obvious downside is higher cost. Where a conventional EI power

transformer can be easily and quickly assembled by simple machines, toroids require

oroids

can be dreadfully noisy, not in terms of magnetic fields, but in terms of mechanical

noise toroid can be

onally, toroids often pass much more RFI than a comparable

clunky EI power transformer would. Because the toroid’s primary and secondary lie

wax or shellac.

Large and heavy, typical EI-core transformers do not seem

and, as a result, deliver a more load-dependent secondary voltage.

critical, as hum can be injected into an otherwise quiet circuit by a illtransformer. Yet, in spite of all of this, EIaudio gear and should not be demised out of hand.

Flat Pack Transformers Often mounted modern designs p than they are tall, the flat pack transformer is also

have one winding, primary and secondary,

couple undesirable RFI noise from the primary to the secondary. In contrast

core is just too slow to react to the extreme high frequencies of the RFI.)

Flatpack Toroidal

Toroidal Transformers Theoretically, the toroid is available transformers. But, like so many good theories, practice proves the attributes: low

much more labor and elaborate machines. The next disadvantage is surprising: t

buzzing. Even the wire itself can buzz. Finding a low-mechanicalquite difficult. Additi

next to each other, there is more capacitive coupling between the windings.

Page 8

Furthermore, toroids easily saturate in the presence of a sustained DC current through

a winding. Because the magnetic circuit is so tight in a toroid, any DC current flow

s. In

other words, toroids are perfect, except that they aren’t. My recommendation is to only

use a toroidal power transformer when you have no other choice because of space

needed in converting AC

age power supplies, but

the vacuum tube’s limited current rating and high voltage drop prohibits its use in a

re slow to conduct, however);

usually win in shootouts, but

Just as a resistor is the practical embodiment of pure resistance, a capacitor is the

practical embodiment of pure capacitance. Unfortunately, a perfect embodiment is

nd electrodes/plates have some resistance and all

The dielectric material acts as an amplifier of sorts, as it “amplifies” the small capacity

allowing a small

rfections are also

Since most materials change both in shape and in resistance with

degrade in performance with

changes in temperature and they do. In other words, a perfect capacitor could be made

used in its construction, just as perfect society could be formed if it

fore, the dielectric makes for the biggest

In a power supply, the capacitor stores and smoothes the rectified DC voltage. In

ignal while isolating

the different DC levels. As can be expected, each function demands its own preferred

capacitor style, with the power supply capacitor relying on its quantity of capacitance

he quality of the capacitor.

A capacitor has four frequently published specifications: its amount of capacitance, its

voltage limit, its temperature limit, and its tolerance. An added piece of information is

Voltage Limits

Capacitors often bear two voltage ratings on their bodies: a DC rating

and an AC rating. The AC rating will be the lower of the two. A sinusoidal wave peaks

capacitor only bears one

rate the capacitor when

can magnetize the toroidal core, thereby robbing the transformer of its effectivenes

limitations. And when you do use one, be sure to use it conservatively (which mean that much of the smaller size benefit will be lost because of larger toroid being used).

Rectifier only allow unidirectional current flow, an attribute into DC. Tube and solid-state rectifiers can be used in high-volt

low-voltage power supply. One great advantage the tube rectifier holds over its solid state brother is its slow turn on (not all tube rectifiers a additionally, tube rectifier can more often survive high-voltage surges from the wall socket or inductive kickbacks. Sonically, tube rectifiers the best solid-state rectifiers, such as HEXFREDs, easily beat the worst tube rectifiers.

GlassWare Audio Design

Rectifiers

Capacitors

difficult to produce. The lead wires a physical dielectrics (the stuff between the electrodes/plates) have some conductance.

to hold a charge that would otherwise exist in its absence. By capacitor to hold a large charge, however, the dielectric’s impe “amplified.” temperature, we would expect many actual capacitors to

if no material were were not populated with people. There deviation between the perfect capacitor and the actual capacitor.

between audio stages, a coupling capacitor freely passes the AC s

and the AC signal transferring capacitor relying heavily on t

the polarity indicator on polarized capacitors, such as electrolytics.

at 1.4 times its equivalent DC voltage. Consequently, if the voltage rating, assume that it refers to the DC rating and deusing it in an AC application.

Page 9

GlassWare Audio Design

frequency noise on the power supply’s

valued capacitor across the power transformer’s

µF. But as the power supply

transformer arrangement, the capacitor sees not

volts! Even worse, if a large choke connects directly to the

volts. Considering that the wall voltage may hold momentary peaks of much higher

a temperature limit to every capacitor, as no

survive on the Sun’s surface for example. With film capacitors, such as

limit is seldom printed on their bodies,

tor.

at a much lower temperature than do glass, mica, porcelain,

1% capacitor

can easily be thrown off a few percent by such an overheating, as the heat causes the

lectrolytic capacitors always (well, almost

e limit. This limit should never be approached let alone

life expectancy is shortened drastically with

(the electrolyte) evaporates with heat, leaving the capacitor

as an

ost

are made with metal, thin metal at that, so we

from the leads, the electrodes, and the

the

film capacitors, as foil has a lower resistance. Placing multiple

. So keeping a capacitor cool is important and ESR

resistor

would facing the same currents. A capacitor’s construction, unfortunately, limits its

Like ESR, ESL represents the inductance in

on for

frequency applications as well.

Placing multiple capacitors in parallel lowers the effective ESL, but the best plan

. DF is much more important in

DF is used in

Here’s an extreme example. Fearing ultra-highoutput, an audiophile places a smallsecondary. Now, since the power supply yields a nominal 400-volts, a 400-volt high frequency-shunting capacitor is soldered in place, say 0.1comprises a full-wave center-tapped400-volts, but 800-peakdiodes (choke loading), then the peak voltage across the leads is 1130-volts, not 400

voltages, a safe rating might be 1600-volts, quite a distance from 400-vdc.

Temperature Limits There has to be capacitor can Mylar or polystyrene, the temperaturealthough this limit can be found in the manufacture’s spec sheet for the capaci Because plastic films melt or ceramic, care should be taken not to momentarily overheating film capacitors during soldering, particularly with polystyrene capacitors. For example, a

plastic to change in shape. In contrast, e always) display a temperatur exceeded, as the capacitor can be easily damaged and it just might rupture. addition, an electrolytic capacitor’s useful excess heat, as the wet part greatly reduced in capacitance.

Equivalent Series Resistance (ESR) Ideally, a capacitor should hold no ESR, ideal capacitor dissipates no heat and loses no voltage across its leads, but m capacitors do both. Real capacitors should expect some resistance due to the metal, slight resistance from the solder that binds the leads to the electrodes, but not dielectric effective residual resistance. Plastic film-foil capacitors display a lower ESR than metalizedcapacitors in parallel lowers the effective ESR.

Heat is the capacitor’s enemy works against us. High ripple current causes a capacitor to self-heat, just as a

heat transfer to its surroundings. The heat dissipation in a capacitor is equal to I

ESR, where I is the RMS ripple current.

Equivalent Series Inductance (ESL)

series with the capacitance in the capacitor. This is an important considerati high-frequency power supply filtering and other high-

might be to use specially-designed high-frequency electrolytic capacitor instead.

Dissipation Factor (DF) DF is equal to ESR/X

power supply applications than it is in signal-coupling applications. predicting the amount of heat a capacitor will dissipate.

Quality Factor (Q) The inverse of DF is the quality factor (Q). Thus, Q = ESR/XC.

Page 10

temperature

stability, the most leakage, the most noise, and the shortest lifespan of any capacitor.

and

The reason we put up with the

electrolytic is because of its volumetric efficiency; we hunger for capacitance, lots of

state

µF of polypropylene would be

hugely expensive (more than most cars) and hugely bulky (about the size of a small

lytic

All electrolytic capacitors belong to the polarized group and none should ever be

reversed biased, i.e. hooked up backwards, as the capacitor conducts extremely well in

verse direction. In fact, as little as 0.4 volts (depends on capacitor temperature)

of reversed voltage can damage an electrolytic permanently. This bring up the issue of

hrs. Why so short a lease on life?

ereo

equipment, stereo equipment filled with electrolytics, stereo equipment that still

hour life span means. The life rating spells

out how long the capacitor will survive under its maximum voltage and temperature

ratings. Reducing the applied voltage by only 20% increases its lifespan by threefold

and reducing the applied voltage by 50% increases its lifespan by 8 times. The formula

o if

a reduced voltage, the

capacitor lifespan should exceed the useful life of the piece of equipment.

state

volt power supply rail would most likely use a 50v electrolytic

voltage is only 60% of the capacitor’s maximum

volt

a 450v or 500v

t be used so as not to go bad. When left

uncharged, the electrolytic capacitor loses capacitance over time and must be

GlassWare Audio Design

Electrolytic Capacitors This type of capacitor displays the poorest

NASA prohibits the use of electrolytics in space flight, because of high failure rate their possible venting of noxious fluids and gases.

capacitance. A tube power amplifier’s power supply needs at least 50-µF and solidamplifier’s need closer to at least 10,000-µF. 10,000-

car). So instead we make do with the electrolytic. And it must be admitted: electro capacitors have increased in quality substantially over the last decade.

the re

the electrolytic’s short life span, which is measured in thousands of hours, as in 2,000 hrs. Long life electrolytics might be good for 4,000Basically, the volumetric efficiency came at a price. No doubt some are thinking that lifespan of just 2,000 hours sounds far to short, as they own 40 year old st

works. The answer lies in what the 2,000-

for estimating electrolytic capacitor life is:

L = LR x (ER/EO)3 x 2

(T/10)

where,

L = the estimated resulting lifespan LR = the life at rated limits ER = rated voltage limit EO = operating voltage T = rated temperature minus core temperature in C

Capacitor life roughly doubles for each 15°C reduction in operating temperature; s the electrolytic capacitor is used in a cool environment at

Unfortunately, with tube equipment that turns out to be a big “IF,” as the high voltage and many heat radiating parts work against us. For example, a solidamplifier with a 30capacitor, which means that the B+ rating. On the other hand, to make the same ratio, a tube amplifier with a 450rail would need a 750v capacitor, which is unlikely. More than likely, capacitor would be used, giving only a 0% to 10% voltage safety margin.

Paradoxically, electrolytic capacitors mus

“reformed” to restore its full capacitance and reduce its leakage.

Page 11

GlassWare Audio Design

current limited voltage to the

ohmage resistor,

meg, is placed in series with the capacitor and a variable voltage power supply

set to the capacitor’s maximum voltage. Once the voltage drop across the resistor falls

to a reasonable level, the capacitor will have been reformed. This can take as little as

ast

throwing away any capacitor that takes over 10 minutes to form. The resistor will get

hot, so avoid touching it and wear safety goggles when you form old electrolytic

in and turn on an old piece of electronic equipment that

asn’t been used for decades or even years, as the electrolytic capacitors might vent or

even explode. Instead, plug the equipment into a variac and slowly bring up the

state equipment or

state rectifiers, but less well with tube rectifier based gear. The

state rectifier across the tube rectifier’s

100%

state rectifiers yield higher voltages); then

e, but not all electrolytic capacitors are equal. The

capacitor manufacturers have developed several optimized electrolytic capacitors that

Big and blue, these capacitor stand out. The computer grade

acitor gives up volumetric efficiency for reliability. This capacitor is

designed to take a beating from high ripple currents. Their use is limited to the power

Panasonic and others make electrolytic capacitors that trade some

metric efficiency for improved high frequency behavior. ESL is reduced in these

capacitors, making them effective at higher frequencies than a generic electrolytic

capacitor. Highly recommended for cathode resistor bypassing, power supply use, and

ing capacitors in OTL amplifiers. Unfortunately, they are usually only

ESR and high current do not go together. Consequently, low

acitor must

A special type of electrolytic capacitor, these capacitors were designed

voltage electric

ckly, which handsomely suits the needs of a

flash bulb. What about audio; how well do these capacitors work with tube

equipment? Fairly well is the quick answer, if a few key provisions are followed. The

betrays that these capacitors cannot

tolerate a steady and heavy use. Using them near their rated voltage or rated

temperature is sure to shorten their life. So too using them in a power supply, as the

Reforming of the dielectric requires applying a capacitor, until the excessive current draw falls off. Usually, a highsay 1-10-

one minute or hours. I recommend not using old electrolytic capacitors or at le

capacitors. And never plugh

voltage over a few minutes. This procedure works well with solidtube gear with solidwork around is to tack solder high-voltage solidsocket pins and slowly bring up the voltage to about 80% of the wall voltage ( could damage the capacitors, as the solidturn off the unit and discharge the capacitors before removing the solid-state rectifiers

Types of Electrolytic Capacitors

Electrolytic capacitors are a headach

are worth looking into:

Computer Grade

electrolytic cap

supply.

HF Electrolytic

volu

as coupl available up to 100-volts.

Low ESR Electrolytic

ESR capacitors are useful as a power supply reservoir capacitor, as this cap see a high ripple current.

Photo Flash

for use with a camera’s flash unit. They store a relatively large highcharge and they can deliver the charge qui

photo flash capacitor’s large volumetric efficiency

main filter capacitor, is sure to kill them.

Page 12

, after being

ling

capacitor in an OTL amplifier. In fact, one OTL manufacturer found that they

worked perfectly in that position. Wouldn’t the high current demands of the

No, although the current peaks can be quite high,

exclusively listening to organ music at high volumes, you are not

Because the power supply workhorse known as the electrolytic

quality

any

electrolytic capacitors present a large amount of inductance (ESL), which will oscillate

e, which many bypass capacitor approach. The

workaround is to place a resistor in series with the bypass capacitor (usually equal to

voltage capacitor can be hard to find,

cularly if the voltage rating needs to be over 450V. This predicament can be

voltage capacitor in series, which effectively doubles the

voltage rating, but halves the total capacitance. The danger in trick lies in the

s not uniformly charging up, which will expose one to excessive voltage,

ohmage (100k to 1M) resistor in parallel with each

These added resistors will work to prevent dissimilar voltage

Always assume that capacitor holds charge and you will never be shocked to

ct it did. Oil capacitors are notorious for retaining a large

Always use a resistor to short out a capacitor and never short the capacitor’s

leads together, as the capacitor’s own lead wire can melt and sputter from a

Always observe a polarized capacitor’s orientation, as some polarized

capacitors have gone off like little hand grenades after being inserted

voltage capacitors to reduce possible

watt resistor, as an unsupported heavy capacitor will bounce and jiggle with

of one its leads. This is particularly

true with power supply capacitors, as the constant vibration from the power

So what good are photo-flash capacitors? These capacitors are quite suitable for low ripple power supply use; say for the first stage of an amplifier’s RC filter fed by a high-ohmage voltage-dropping resistor. Another use is as the output coup

loudspeaker ruin this capacitor? unless you are actually delivering very much steady current into the loudspeakers.

Bypass Capacitors

capacitor is so clunky, many advocate bypassing it with a smaller-valued, highfilm or oil capacitor. This can work supremely well, but it can also backfire. M

in combination with a pure capacitanc

the electrolytic capacitor’s ESR).

Two high-voltage capacitor in series Highparti overcome by placing two high-

GlassWare Audio Design

capacitor thereby destroying or damaging the capacitor. The workaround is to place a high voltage, high-wattage, highcapacitor in the series. drops across either capacitor, dividing the DC voltage equally between capacitors.

Capacitor Safety

•

find that in fa charge after having been discharged.

•

heavy discharge without the current limiting that the resistor imposes.

•

backwards.

• Always shroud the exposed leads of high-

shorts or shocks.

• Always ensure adequate clamping of any axial capacitor much larger than 5

vibration or movement and break free

transformer can cause the capacitor’s leads to fatigue and snap.

Page 13

GlassWare Audio Design

chained to AC wall

. In other words, all power supplies that plug into wall sockets, must convert

and there

This is the classic tube

only half

two rectifiers, saving two

wave bridge configuration. On

will see twice the

in a

wave bridge configuration, which can greatly limit

voltage power

is only about 75%

as effectively utilized in this configuration compared

for

, this

voltage

diode voltage drop greatly

most popular

The entire

This configuration is seldom

used with tube rectifiers, as the rectifier

cathodes cannot be heated by just a single

drops

voltage power supply,

voltage power

supply

used with tube

When designed correctly, this power supply

topology yields the flattest output voltage

over a wide range of current draw, as the

power supply capacitor is charged by a near

square waveform. On the other hand, the

large choke will be expensive, heavy, and

This circuit

valued bleeder

from

Rectifier Circuits

Tube equipment was born to run on DC and everywhere it is sockets AC voltage to DC voltage. This conversion requires rectifiers and capacitors; are several ways that the rectifiers can be configured.

Full-Wave Bridge This is the power supply configuration. primary winding is used and four rectifiers are required.

heater winding. The two diode voltagemean little in a highbut are a big liability in lowsupplies.

Full-Wave Center-Tap

amplifier power supply configuration. It uses of secondary winding at a time and requires a center tapped winding and compared to the fullthe other hand, the two rectifiers peak reverse voltage that four rectifiers would see fullthe use of solid-state rectifiers in highsupplies; in addition, the primary

Iac / 1.8

out

Vdc =

(Vac x 1.4) - 2V

out

Vdc =

Iac / 1.27 Vac* / 1.43 - V *entire primary

diode

to the FW bridge circuit. Paradoxically enough what many consider a purely high-voltage circuit rectifier circuit is often used in extremely lowpower supplies, as the singleincreases this circuit’s efficiency.

Full-Wave Choke Input This powerconfiguration is often rectifiers and requires quite a bit of tuning

given to loud mechanical noise. requires a relatively lowresistor to keep the output voltage peaking dangerously high at turn on.

(60Hz) L (50Hz) L

out

Vdc =

/ I

out

(mA)

out

/ I

(mA)

out

diode

≈

1.2 x V

≈

Iac / 0.707

Vac* / 2.2 - V *entire primary voltage

- R

inductor

x I

Page 14

Although

there is

power supply

wave voltage

circuit doubles the voltage that a

wave bridge rectifier circuit would

y half the output

he ripple is at the

120 Hz frequency as in the

charges one capacitor during one half of

or.

Because these capacitors are in series with each other, the voltages and frequency of

power supply is that the current

of the AC cycle

and then it flows in the other direction the other half of the cycle: up, down, up,

wave voltage rectified power supply, the current will flow

cycle and then

it not flow on the other half of the cycle: up, off, up, off. These repeated single

direction conduction cycles are similar in effect to hooking up a DC voltage source

tize the

wave rectifier circuits should only be used where

little current draw is expected, such as in establishing a negative bias voltage power

The

wave

voltage doubler, however, is different from

wave rectified power

wave

wave"

noise frequency and

capacitor,

but not because of the conduction cycle

wave voltage doubler's transformer conducts through both halves of the AC

On the first half of the cycle, the

itor

receives no charging. On the second half, the both capacitors are charged

simultaneously. So the transformer's secondary experiences a current conduction on

wave voltage doubler circuit, while it does experience conduction

GlassWare Audio Design

Voltage Doublers

Full-Wave Voltage Doubler

B+

often shunned by tube fanciers, nothing wrong with this configuration. The full-

load

B+/2

doubler fullprovide, but with onl current capability. And t same 100Hz or full-wave bridge rectifier circuit.

In this circuit, the transformer core is not partially magnetized as it is in simple half wave power-supply circuits, as the primary

Iac / 3.6

out

Vdc =

(Vac x 2.8) - 2V

diode

the cycle and then in the second half of the cycle, it charges the second capacit

the noise double.

Now, what normally happens in a full-wave-bridge flows through the secondary winding in one direction on one half

down. But in the simple halfthrough the secondary winding in one direction on one half of the AC

across the transformer's secondary, which would definitely work to magne transformer’s core. Thus, simple half-

supply.

Half-Wave Voltage Doubler principle of operation for a half-

that of the simple half-

B+

load

supply, being much closer to the fullrectifier circuit. They share the "halfname because of same half cycle charging of the output

Iac / 3.6

out

Vdc =

(Vac x 2.8) - 2V

C2 =

C1 / 2

through the secondary.

The halfcycle just like the full-wave bridge rectifier circuit. capacitor attached to the transformer's secondary is charged and the output capac

both halves of the cycle and is thus not subject to the magnetizing of its core. contrast, the fullthrough both halves of the cycle, works differently from the half-wave version.

diode

Page 15

GlassWare Audio Design

A voltage regulator is an electronic circuit that strives to maintain a constant output

in spite of variations in either the wall voltage or the current drawn by the

r battery does by

brute force: it maintains a steady and accurate output voltage over a large range of

Regulators fall into two groups: switching and linear. In terms of sales,

he switching regulator

end audio

. Switching regulators operate at

high frequencies can easily

, on the other hand, are relatively inefficient; but

are also lower in noise, require fewer parts, and are usually much less complex and

volt linear regulator

pin package that requires few supporting parts can be had for less than a

voltage

B amplifier: it does not

dissipate power unless it required to. For example, if the tubes are pulled from an

voltage regulator stops conducting until the tubes are

plugged in again. When the amplifier is drawing full current from the power supply,

A amplifier: it is

always on, it dissipates the most power at idle, and it is unburdened when power is

shifted into the load. For example, if the tubes are pulled from an amplifier, the shunt

on (and thus its dissipation) to

compensate for the current that the tubes had drawn. When the amplifier is drawing

es regulators; they usually find a

shorter and cleaner path to the ground reference, and they absorb noise rather than

transmit it, but at the cost of decreased efficiency. Inefficiency, however, is something

accept and some believe to be virtue:

The principle of operation of a shunt regulator in AC terms is simple enough: the

he shunt

resistor or

ail voltage is

compared to a voltage reference and the idle current through the shunt regulator is

Like the series

device with a

ground, and a

feedback mechanism to control the flow of current through the shunt regulator.

Voltage Regulators

voltage— load. A voltage regulator does with complex circuitry what a ca

load current.

flexibility, conversion efficiency, and weight to power output, t beats the linear regulator. Yet, the switching regulator is rarely used in highproducts. Why? Because of noise, high-frequency noise supersonic frequencies, 40kHz and much higher; and these escape and pollute the rest of the circuit.

Linear Regulators Linear regulators

finicky than a switching regulator. For example, an excellent 1A, 5in a threequarter. Linear voltage regulators further subdivide into series and shunt regulators.

Series Regulators The series regulator is the overwhelmingly most used regulator—for good reasons. A series regulator is like a class-

amplifier, the series high-

the series regulator is at peak dissipation.

Shunt Regulators In contrast, the shunt regulator is like a class-

high-voltage regulator must increase its conducti

full current from the power supply, the shunt regulator is at its lowest dissipation.

Shunt regulators offer many sonic advantages over seri

with which tube audio designers have learned to “the less efficient, the better the sound,” as they say.

noise signal on the output is compared to ground, then the current through t regulator’s active current shunting device is varied in response to that signal, and then in turn, this current develops a varying, inverting voltage across a series choke that cancels this same signal. In DC terms: the power supply r

varied to bring the power supply voltage in line with the reference. regulator, the shunt regulator needs three elements to work: a shunting variable conductance, a voltage reference that is AC bypassed to

Amazingly enough, the triode comprises all three elements at once.

Page 16

cathode voltage, which is why the

cathode voltage creates a soft

oltage.

This occurs because a triode, unlike a pentode or a transistor or MOSFET, exhibits

plate resistance (rp). For example, a 4k resistor attached to a power supply of 400 volts

p and

cathode voltage, the

portant difference:

if we move the power supply voltage up and down, current will increase and decrease

much more severely than it did through the resistor, because the rp of the triode

rd element, we can see that a triode gives us all we need to

how few parts are required.

Still this regulator is only adequate at maintaining a constant output voltage. A

decrease in current draw of 1 mA at its output that would in the absence of the triode

ause a 1 volt increase in output voltage. But with the triode in place, the rp is

effectively in parallel with the 1k resistor, which yields an equivalent resistance of only

e in

plate voltage. True, this is only a modest improvement in regulation, but the triode

The amplification factor or mu of a triode is

the measure of the degree that the grid is

more effective than the plate in controlling

the flow of current through the tube. Here is

our missing feedback mechanism to control

unt

regulator. By delivering the change in output

voltage of the regulator to the grid of the

reases by

The triode's current can be varied by varying grid-totriode is called a "valve" in England. The same grid-tovoltage reference, as the triode's plate will buck or fight any change in plate v

will experience a current flow of 100 mA. Moving the power supply voltage u down will increase and decrease the current flow through the resistor, as

?I = ?V / R.

If we replace the resistor with a triode with the correct grid-tosame current would flow as did with the resistor. But here is the im

might only 400 ohms,

?I = ?V / rp.

Before going on to the thi make a simple shunt regulator.

GlassWare Audio Design

+200V

out in

-4V

R R

+300V

+200V

out in

+4V

+300V

These two examples of a simple shunt regulator show just

285 ohms and 1 mA multiplied against this value results only a 0.285 volt increas

has that third element that greatly increases the regulation.

+200V

out

+300V

+4V

the flow of current through the sh

triode, the amount of regulation inc the mu of the triode.

Page 17

GlassWare Audio Design

For example if the mu of the triode is 35, then the 1 mA current decrease would only

So we see that what really matters is Gm (transconductance), as the greater the Gm,

mpedance. One triode might have a mu of 10 and an rp of

1000; and another, a mu of 100 and an rp of 10000. But each triode would still have

The remaining weak link in our shunt regulator design is the voltage reference. What

independent voltage reference.

Precision IC voltage references come immediately to mind, but they are seldom

le in high voltages. Zeners do come in higher voltages, but are neither precise

nor low noise. Of course, their noise can lessened by bypassing them with a large

value capacitor. Furthermore, if the absolute value of the output voltage is not critical,

n the zener might fill the need. A possible circuit using a zener voltage reference is

A related regulator design is the feedforward noise

canceling circuit. Like a conventional shunt regulator, the feedforward shunt regulator

dropping resistor. But unlike the conventional shunt

, the feedforward shunt regulator receives its error signal from the other side

series resistor must equal the inverse of the tube’s

right

’s grid in its

entirety, provoking an increase in conduction equal to 1V times the tube’s

transconductance. If, for example, the transconductance equals 10mA per volt, a

result in a 0.0011 volt, as the output impedance of the regulator is about 11 ohms:

Zo = (Ra||rp) /Gain

but as

Gain = µRa / (Ra + rp)

and

Ra||rp = Ra•rp / (Ra + rp)

thus

Zo = [Ra•rp / (Ra + rp)] / [µRa / (Ra + rp)] Zo = rp / µ or Zo = 1 / Gm.

In this case

Zo = 400 / 35.

the lower the output i

an equal Gm of 10 mA/v or as it is often expressed in micromhos, 10,000 µmhos, as

Gm = µ / rp.

is needed is a stable, precise, low noise, temperature-

availab

the shown below.

290k

20mA

80mA

+30V

Z=30V

1.4k

+410V

+300V

1µF

+10V

10k

Feedforward Shunt Regulator

employs a series voltageregulator of the series resistor. The transconductance. For example, assume that a 1-volt positive pulse appears at the of the series resistor shown below. This pulse will be relayed to the triode

10mA increase in current will flow through the tube.

Page 18

0mA drawn by the load and the

. When the added 10mA increase

in current travels through the series resistor, whose value equals 1/0.01, or 100 ohms,

esistor will develop an increased voltage drop of 0.01 against 100, or 1V, forcing

going pulse raised the B+ voltage

nlike the conventional shunt regulator that samples the power supply noise after the

series resistor and that can never completely eliminate all the noise, the feedforward

based circuit. (Feedback requires that an error exist so that it can counter it. If you

causal, you are right, as the feedback system needs an

ry; it

knows what the error looks like before it appears at the output, so it sends a

countervailing signal to cancel the error when it arrives. Try thinking of a negative

but

sense; and think of

? Well, in the

a power supply

with no feedforward shunt regulator, except that the ripple’s phase would be inverted.

going pulse on the raw power supply rail, would induce

going pulse on the other side of the series resistor, but as the other end

of the resistor was going up by 1 volt, the output side of the resistor goes down by

o halve the triode’s input signal, then the triode would

going pulse at the output, thereby canceling the

resistor voltage

GlassWare Audio Design

This surge in current will then combine with the 8 existing idle current flowing through the tube, 20mA

the r the B+ downward by 1 volt, except that the positiveby 1 volt. In other words, a perfect null. Very Aikido, indeed.

100

0.1µf

-20V

+310V

80mA

+300V

20mA

shunt regulator can completely null out the noise, as it is not a negative-feedback

think that this sounds a bit antierror to be made so that it can unmake it.) A feedforward system is anticipato

feedback system as being reactive, not so much in the electrical-engineering sense, in the current psychological—Seven Habits of Highly Effective People— feedforward systems as being proactive.

But what if we were to use a series resistor twice the 1/gm rule, e.g. 2/gm stock circuit, as shown above, the ripple voltage would equal that of

For example, a 1Vpk positivea positive 10mA increase in current conduction in the triode, which would yield a 2 volt negative-

only 1 volt. Now, if we were t respond with only a 5mA negativepositive-going pulse. So how do we lose half of the input signal? A twodivider is the easiest solution.

80mA

+300V

20mA

200

-20V

1µf

100k

-20V

100k

+310V

Page 19

GlassWare Audio Design

based

supply noise from its output. In the simplified circuit shown below, we

see the rightmost triode doing the double duty of voltage dividing the raw power

supply ripple by a fixed amount and by amplifying the error signal at the regulator's

tput, and then passing the correction signal to the leftmost triode's grid, which then

the leftmost triode inverts the input signal at its plate, thereby nulling the error signal

error

Shunt Regulator

The Janus shunt regulator made its first appearance in 2007, in the Tube CAD Journal In a nutshell, the Janus shunt regulator uses both feedforward- and feedbackshunt regulation to reject both the rectifier-induced power-supply noise and the signal induced power-

at the regulator's output.

Vout

Raw B+

load

current

Rk2

The schematic below displays how the Janus shunt regulator uses feedforward correction to null the rectifier-induced power-supply noise from the output.

+300V

20mA

no ripple

+0.5V

1500

11mA

12AU7*

31mA

+104.5V

ripple

+347V

200k

1.2mA

+109V

10k

* or 1/2 12DW7 or 7247

12AX7*

300

Page 20

ince the Janus regulator

state rectifiers can be

. Also note the lack of DC voltages in the schematic. This

ementation of the Janus regulator was designed to deliver between +250V to

a DC voltage

regulator, as it cannot maintain a fixed B+ voltage; instead, it works to eliminate any

filled power supply that bucks quick changes in output voltage, but allows slow DC

with the Janus

voltage will depend on the input voltage and the current

, which in this example is 1500 ohms. For

example, given a raw power supply voltage of +350Vdc after the rectifiers and a

he leftmost triode), the output voltage will

be +300Vdc, as 33mA against 1500 ohms equals a voltage drop of 50V. In other word,

filled power

supply noise created by audio signals circulating through the B+

GlassWare Audio Design

Looking at the powerconnection, we see how the Janus regulator erases much of the offending noise.

1500

+300V

20mA

+0.5V

10k

12AU7

+109V

200k

+104.5V

12AX7

300

+347V

The Janus regulator PCB holds the following implementation of the regulator.

D10

D11

R13

R12

Vout

to heater PS Neg

C5 C4

12AU7*

C17

5Vac

R9C15

*7247 or 12DW7 or ECC832

C16

12AX7*

C1 C2

Note the use of a tube rectifier, either a 5AR4, 5R4, or 5Y3. S uses solely tubes, why not go all tube. Or, if you choose, solidused exclusively impl +300V worth of B+ voltage. The Janus regulator is not, however,

AC perturbations on its output voltage. In this way it is similar to a large inductor

voltage to vary with the wall voltage variations. In other words,

regulator, the output drawn through the key series resistor

current draw of 28mA (plus 5mA through t

do not expect this realization of the Janus circuit to power a KT88amplifier. A line stage amplifier or phono stage is a better match.

Page 21

GlassWare Audio Design

film

capacitors, and leftmost triode’s plate dissipation. The power transformer’s selection is

somewhat critical, as too high a primary voltage will create too high a B+ voltage.

, offering

The limiting factors are the 5W 1500-ohm series resistor, the 4.7µF/400V

Unfortunately, most high-voltage power transformers are truly high-voltage far too much secondary voltage.

High-Voltage Schematic & Part Values

Vout

to heater PS Neg

C5 C4

R9C15

Typical Part Values

C1, C3, C4 =

C2, C5, C16, C17 =

½V1

C6 =

C15 =

C17

C16

33µF - 450V

4.7µF - 400V 220µF - 160V

0.33µF 160V

½V1

C1 C2

D10

D11

V2 Heater Schematic

H+ H-

J2 J3 J4

5Vac

R13

R12

D1, D8, D9, D10, D11 =

R1, R2, R12, R13 =

R3, R7 =

Heater Vac =

(B+) Full-Wave CT Vac =

(B+) Full-Wave Bridge Vac =

1N4007 or better 100 1W

300 200k

R4 =

1.5k 3W

R5 =

10k 3W

R6 =

300k 1W

R8 =

100k 1W

R9 =

5AR4 or 5R4 or 5Y3

V1 =

7247 or 12DW7 or ECC832

V2 =

If heater regulator output 6.3V, use J2 & J4 If heater regulator output 12.6V, use J3 only

5V@2A 400Vac to 550Vac (requires center-tap)* 200Vac to 275Vac (requires using D8 & D9)*

V2 Heater

*Current rating depends on load. Usually, 50mA to 100mA is adequate.

With center-tapped transformer, do not use diodes D8 & D9 or resistors R12 & R13. WIth non-centertapped transformer, use

use R12, R13, D10, D11 (and R1, R2, D8, D9, if non-center-tapped transformer is used).

diodes D8 & D9 and resistors R12 & R13. If only solid-state rectifiers are used, then

Chassis Ground

Use jumper J1 to ground the chassis to the PCB ground.

Page 22

can use either a conventional

power

ified DC yield, while

transformers deliver

oth power

power

circuit uses only two rectifiers,

will be exposed to twice the peak inverse voltage than the circuit on

lost across

the rectifiers and a much lower internal resistance, the last advantage may not prove to

resistance tube rectifiers, such as the WE274,

state rectifiers is

state

rectifiers do not need a heater winding and can be left on continuously, which is

GlassWare Audio Design

Transformers & Rectifiers

Transformers As shown below, the Janus regulator tube-intended, high-voltage, center-tapped transformer or a non-center-tapped transformer. The leftmost transformer’s current rating is in rect the rightmost transformer, in AC current yield; nonetheless, both the same amount of power for the power supply. Note that the circuit on the right a hybrid affair that uses both tube and solid-state rectifiers. Nonetheless, b supplies will exhibit a slow turn on, due to the tube rectifier.

5Vac

R13

R12

D10

D11

C1 C2

R13

R12

480Vct @ 75mA 240Vct @180mA

C1 C2

D10

D11

Solid-State Rectifiers The Janus regulator PCB can also accept just solid-state high voltage rectifiers instead of a tube rectifier. Once again, either a conventional tube intended, high-voltage, center-tapped transformer or a non-center-tapped transformer, as shown below on the right. The leftmost but the rectifiers the right. Solid-state rectifiers present at least two advantages: less voltage is

be an actual advantage, as the high-plateseem to offer the best sonics. One certain advantage to using solidthat they do not age and wear away as the tube rectifiers do. In addition, the solid-

useful in setups wherein the heaters are switch on and off instead of the B+ voltage.

5Vac

D10

D11

C1 C2

R13

R12

C1 C2

D10

D11

5Vac

R13

R12

Page 23

GlassWare Audio Design

Below is

the heater power supply schematic used on the Janus PCB. As can be seen, the power

wave voltage doubler

wave bridge rectifier circuit, the two power

supply filtering capacitors are oriented with their positive leads pointing to the top of

red as a voltage doubler, these capacitors are

Heater Power Supply & Regulator

The Janus PCB also holds a low-voltage power supply and voltage regulator.

supply can accept either full-wave bridge rectifier circuit or a fullrectifier configuration. When used as a full-

the PCB, where the heatsink sits; configu rotated 90 degrees clockwise, so the positive leads point to the right edge of the PCB.

Heater+

C14

Heater-

Heater+

C14

Adj

InOut

C12

Regulator

R10

C13

R11

Capacitor C11 & C12 positive leads pointing to heatsink

Fullwave-Bridge Rectification. Raw DC voltage = 1.414Vac - 2V

AC voltage is applied to pads A and C only.

Regulator

R10

InOut

Adj

C11

C12

D3C8

D4 C7

D2 C10

D4 C7

R10 = R11 =

C11

1000pF - 50V 1800µF - 16V 680µF - 16V MUR410G 124 499 ohm for 6.3Vdc

R11

Heater-

Fullwave-Volatge-Doubler Rectification. Raw DC voltage = 2.828Vac - 2V

AC voltage is applied to pads A & B only; D2, D4, C7, C10 are left off PCB.

Typical Part Values

C13

Capacitor C11 & C12 positive leads pointing to tube rectifier

C7, C8, C9, C10 =

C11, C12 = C13, C14 =

D2, D3, D4, D5 =

1.13k for 12.6Vdc

Regulator =

Vac Input =

LM350 or LT1085 7-8Vac @ 5A for 6.3Vdc (FW Bridge)

12-12.6Vac @ 2.5A for 12.6Vdc (FW Bridge)

6.3-8Vac @ 5A for 12.6Vdc (Voltage Doubler)

D2 C10D5C9

Page 24

Assembly

Before soldering, be sure to clean both sides the

looking solder; solder

If the resistor leads look in the least gray, clean away the

oxidation with either steel wool or a wire sniper’s sharp edges. Admittedly, with new

ts have sat in your

rectifiers,

stors; keep all the tolerance

bands on the resistor’s body at the right side as you face the resistor straight on. This

in the wrong

ces and pads on each side, it is

the PCB is so overbuilt, it is

Be sure to confirm all the

olarized capacitor can easily vent (or

to its heatsink first and

the PCB at once, rather than

supply capacitor will spray hot

h the other hand behind

voltage gear, as a current flow

soled shoes and work in

lowly bring up the AC voltage, while looking for smoke or

output voltage without and with a load. If the

voltage, try either

12V instead of 12.6V, as the

ch of the four

bypass capacitors, C2, C5, C16, C17. No voltage should exceed 400V and the

voltage across capacitor C5 should never exceed 160V. The tube rectifier is

the AC voltage on

both sides of Resistor R5; on the regulator output side, the AC voltage

Only after you are sure that both regulators are working well, should you attach the

GlassWare Audio Design

Assembly & Testing

Cleanliness is essential. PCB with 90% to 99% isopropyl alcohol. Do not use dullshould shine. If it doesn’t, first clean away the outer oxidation with some steel wool a copper scouring pad.

resistors and a fresh PCB, such metal dulling is rare; but if the par closet for a year or two, then expect a good amount of oxidation to have developed.

First, solder all the small diodes in place, and then solder the resistors, capacitors, and heatsinks. Be consistent in orienting the resi

will pay dividends later, if you need to locate a soldered a resistor location. Because the board is double sided, with tra easier to solder the resistors from their top side. As extremely difficult to remove an incorrectly placed part. electrolytic capacitor orientations, as a reversed p even explode) when presented with high-voltage. Confirm twice, solder once.

It is often easier to attach the LD1085 (low-voltage regulator) then to solder both the heatsink and regulator to attaching the heatsink first and then attaching the regulator to the heatsink.

Testing Wear safety eye goggles, as a venting powercaustic chemicals. Make a habit of using only one hand, wit your back, while attaching probes or handling highacross your chest can result in death. In addition, wear rubberdry environment. Remember, safety, first, second, and last.

1. Attach only the heater power supply’s transformer winding, leaving the high-

voltage transformer leads unattached and electrical tape shrouded.

2. Use a variac and s

part discoloration or bulging.

3. Measure heater regulator’s

heater regulator fails to regulate or provide enough DC lowering the heater voltage a tad, for example

0.6V difference might be enough to bring the regulator back into regulation.

4. Next, power down the heater regulator and attach the high-voltage windings

5. Attach the power transformer to a variac and slowly bring up the AC voltage

6. Measure the output voltage and the voltages present at ea

slow to conduct, so be patient.

7. Once the regulator has warmed up and stabilized, measure

should be substantially lower than on the resistor’s other lead.

line stage amplifier (or phono stage, etc.).

Page 25

GlassWare Audio Design

are

production

example, old 5Y3 rectifiers

and 12DW7/7247/ECC832 tubes are still available at somewhat reasonable prices. The

rectifier offers the widest choice of suitable replacements, such as the 5AR4/GZ34,

can be used, such

as the 12BH7 or ECC99. Using a different regulator tube will require, however, an

using a tube

(V2)

heater regulator is set to an

The range of prices for resistor and capacitor is huge, with

resistors costing as little as $0.02 and as much as $25. Fortunately, the Janus regulator

is quite economical in its number of critical parts. Resistors R4, R5, R7 and capacitors

a single power transformer, but using two

voltage B+

power supply will

can easily couple to the B+

winding, as the two share the same core. But when you use two power transformers,

separate

power transformers allow a staggered turn on, wherein

the heater power supply can be turned on first before applying the B+ voltage.

four 6SN7s with

, due

Laying out the ground wires in an audio piece of equipment is both a

y using a single star

attach

io circuits

Usually a fuse is placed in series with the power transformer’s primary, but

both the B+ output and the heater output can receive a fuse as well. Use a slow blow

while powered, as it

addition, give the Janus regulator lots of room and

good air flow to wick away heat.

Modifications & Part Upgrades

Tubes The tube rectifier (V1) and the dissimilar twin-triode regulator tube (V2) new production stock. Several Janus regulator users have used long-out-ofNOS tube replacements and gotten excellent results. For

5R4GB (avoid the version with the large bulbous base), and even the WE274.

For the truly advanced practitioner, a different regulator tube (V2)

entirely different set of part values, which can only be found through manual and calculator and much experimentation. And bare in mind that a tube with a 6.3V heater can only be used when the Janus’ output voltage of 6.3V. Nonetheless, the sonic rewards can be large.

Resistors & Capacitors

C2, C5, C16, C17 are the most sonically important.

Power Transformer Most will desire using power transformers, one for the heater power supply and one for the highpower supply, holds real merit. Why two? Imagine a single power transformer; the low voltage solid-state rectifiers and large-valued capacitors in the heater allow huge current surges that occur for in only brief spurts, while charging its power supply capacitors. These large current-conduction spikes

the heater power supply’s current spikes are isolated, applying to only its transformer. In addition, two

Moreover, the single power transformer that was adequate to power AC on the heaters, may longer prove adequate when it must deliver rectified DC to the losses involved in rectification and regulation.

Operation

Grounding

science and an art. The best procedure is to avoid ground loops b ground, which may hold several ground spurs, say one for each channel in a dual mono setup, with two sets of hookup wire leading to the Janus PCB. Be sure to only the ground pad (and the B+ pad) at the top of the PCB to the aud being powered, using tightly twisted wires.

Fusing

fuse for the heater and quick blow fuse with the B+ output.

Caution Do not touch the heater regulator’s exposed metal tab will be both extremely hot and charged to 1/4 the B+ voltage; it is a shock hazard.

Page 26

GlassWare Audio Design

5.0 in

4.50 in

5.50 in

Janus PCB (5" by 6")

Layout & Dimensions