Glass Ware Janus User Manual
GlassWare
AUDIO DESIGN
Shunt Regulator
Low- & High-Voltage Regulators
USER GUIDE
Contents
Page 1
10
11
12
13
17
19
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21
22
23
23
24
Rev. A
Janus PCB Overview
Introduction to Power Supplies
1
Standard Power Supplies
2
The Function of a Power Supply
2
Wall Outlet Voltage Problems
2
The Parts of a Power Supply
4
Rectifiers
6
Capacitors
6
Types of Electrolytic Capacitors
9
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
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
sales@glass-ware.com
Copyright © 2008
All Rights Reserved
GlassWare Audio Design
5
-
voltage and a high
its own raw power
In other words,
PCB holds all that is needed to make a
voltage
is
bridge rectifier arrangement or
ler configuration, allowing for more latitude in power
-
voltage regulator uses
to
.
bridge
-
voltage electrolytic capacitors now
bypass capacitors; in addition, the heater
the
Which helps explain why
in
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,
v
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.
2
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
50
volts is a lot of voltage variation; in fact, it might be more than half the voltage drop
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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.
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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
DC
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.
3
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.
4
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
,
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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.
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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,
5
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.
6
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
s
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.
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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.
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