Artemis Labs PH-1 Schematic
Technical Features of the
2
1
3
V4
1/2 5687
V4
V5
Power
Rig ht
Out puts
1
2
5
4
8
5
4
8
+160V +250V
+250V
+6V
+163V r eference
Muting relay
control
Lundahl
500H
choke
V2V1
V3
5
5
4
4
8
5
4
8
Power Supp ly
(unre gulat ed)
40 se cond
Delay
4 sec ond
Delay
Lin e volt ages
ava ilable :
100 V,
110V,
120 V,
220 V,
230 V,
240 V
50 or 60H z
Fea tures:
- E lectro stati callyshi elded trans former
- H igh-sp eed r ectifi ers
- High-t emper ature
(10 5°C) e lectr olytic s
Lef t
Out puts
1
2
+160V
GainRIAA Equaliz ationGain Muting & Ou tput Low-G ain R egulati on Power Supply & Ti me De lays
PH- 1 Ph ono P re am p
Simpl ified Sch ematic
Artemis Labs
Rig ht
Inp ut
47.5K
1.5V
N or AM-5
2
3
1
V2
1/2 12AX7
V1
6N1 P
2
3
1
7
9
6
V5
1/2 5687
Lundahl
500H
choke
Lef t
Inp ut
47.5K
1.5V
N or AM-5
7
8
6
V3
1/2 12AX7
7
8
6
TexTool®
"ZI F" Soc ket
for R or C
loa ding
Artemis Labs PH-1
Phono
Preamp
Low-noise rst preamp stage with battery bias
With typical signals at the microvolt level, the rst
amplier stage is extremely critical. Parts are chosen
carefully for low noise and minimum low-level nonlinearities. To get around the problems of cathode
biasing and the typical electrolytic capacitor, xed bias
using a single “N” alkaline cell is employed. Being in
the grid path, virtually no current is drawn, letting the
battery last for at least several years. Unlike circuits
where the battery is in the cathode, any imperfections
or non-linearities in the battery are not manifested by
the tube’s current ow.
The plate supply for the rst stage is ltered by an
R-C lter using a 15µF polypropylene capacitor. This
insures minimum noise without the sonic degradation
Extended high-frequency response
of electrolytic capacitors.
Many phono preamps’ response drops quickly above
20KHz. The PH-1 maintains its RIAA equalization to
above 40KHz, important for high-resolution playback
systems and for use with 96KHz digital systems.
Passive RIAA equalization using hand-selected
capacitors
By using passive equalization the problems of feedback
equalization are eliminated: slew-rate distortion, deviation of equalization curves at high frequencies, and
instability problems. To permit at equalization to
within +/-0.2dB, the capacitors in the equalization
network are pairs that are hand-selected on a precision
impedance bridge to better than +/-0.5% accuracy.
Single-triode output stage with choke loading
The Artemis Labs PH-1 uses a single 5687
medium-mu, low resistance triode as the nal amplifying device for each channel. The 5687, originally
designed by Tung-Sol for military and industrial uses,
has excellent linearity, and in the mil-spec version,
excellent unit-to-unit consistency. Its low plate resistance allows it to drive heavy loads without the use of a
cathode follower stage.
The use of an inductor (choke) load instead of a
conventional plate resistor offers several signicant
advantages to the PH-1 design. A good-quality audio
choke is essentially a perfect current source, allowing
the triode to operate into an innite-resistance load,
giving the lowest distortion. Unlike semiconductor
constant-current devices, an inductor is an energystorage device. This allows the plate voltage to swing
100% above the B+ plate supply voltage, doubling the
“head-room” and allowing a lower B+ supply voltage
to be used, reducing power consumption. This permits
an output of over 40 volts rms before clipping.
The audio chokes used in the PH-1 are made by Lun-
dahl, a Swedish rm that uses a proprietary core material that has low distortion. Two windings are used on
a common “C-core”, which reduces pick-up of hum
and noise.
Modest feedback stabilizes gain without hurting
sonic quality
Modest feedback is used across the last two stages.
This stabilizes the gain and makes the frequency
response less sensitive to loading. The inherent distortion of the 5687 with choke loading is already very low,
so the high-order harmonics that can be generated by
excessive feedback are minimal.
Can drive 8K ohm (aggregate) or higher loads
Despite the lack of a cathode-follower output stage,
the PH-1 can drive loads as low as 8K while still
meeting specications. This is important when driving some pro audio equipment which can have input
impedances as low as 10 or 15K ohms.
Each channel individually voltage regulated
Each channel has its own MOSFET source-follower
low-gain regulator. This insures there is no coupling
between the two channels through the power supply.
The source follower regulator gives good regulation
without the “transistor sound” typical of high gain regulators using op-amps. Protection resistors and diodes
help prevent burn-out of the MOSFETs.
True voltage regulation minimizes noises and changed
operating conditions due to power line shifts. Since
the impedance of the power supply, as seen by the
preamp, is low and at, the bass response is even and
solid.
Cool-Swap™ tube connections let tubes run cooler,
provides built-in spare
Many dual triodes, such as the 12AX7 and 5687, have
split heaters, allowing them to run from either 6.3V or
12.6V. This heater set-up allows only one of the two
triodes to be heated. In the Cool-swap conguration
used in the Artemis Labs PH-1, one tube is used for
each channel, each with one half heated. The right
channel uses triode #1 and the left channel uses triode
#2. Since the main failure mode in modern tubes is
cathode wear-out, the unused triode in each tube is
essentially a spare. By swapping the two tubes, the
unused spare is brought into use. Thus Cool-Swap
essentially doubles tube life, and since only half the
tube is heated, the tube runs cooler, an important
factor in the normally hot-running 5687. A side benet is reduced cross-talk between channels, since each
channel has its own tube. The rst stage, a 6N1P,
does not use the Cool-Swap conguration. Its internal
shield minimizes coupling between channels.
DC heater supply
A well-ltered DC heater supply helps keep hum low
and allows the use of tubes that would otherwise have
too much hum in AC-heated systems.
Delayed high-voltage with delayed muting relay
The high voltage plate supply is applied to the tubes
after a delay of about 40 seconds. This gives the
tubes ample chance to warm-up without the chance
of “cathode stripping” (degradation of the cathode by
bombardment by positive ions before it is hot enough
to build-up a protective space charge around the cathode.) This helps extend tube life. A muting relay
shorts the audio outputs until about 4 seconds after
the high voltage is applied. This allows start-up transients to die away.
No troublesome integrated circuits
All time delay and regulation circuits use time-proven,
simple discrete semiconductor devices.
Critical audio circuits point-to-point wired with
military-style terminal boards
Conventional ber-glass PC boards are used for the
power supply and for the rear panel jacks and switching. All critical circuits in the audio path use point-topoint wiring on military-style terminal boards using
silver-plated turrets. This technique minimizes the
sonic effects of PC boards and allows easy component
replacement.
High-speed rectiers and electrostatically-shielded
power transformer
Power supply noise is minimized by the use of a
custom power transformer with electrostatic shielding
between the primary and secondaries. High speed
rectiers are used for both the plate and heater supplies.
Available mains voltages (wired at factory): 100V,
110V, 120V, 220V, 230V, 240V, 50 or 60Hz
Virtually all the power systems of the world can be
accommodated by the PH-1 transformer connections.
These are set at the factory or can be re-wired by a
qualied technician.
Artemis Labs products
are distributed by:
AYDN Vacuum Tube Audio
679 Easy Street, Unit E
Simi Valley, California 93065 USA
www.aydn.com
Tel: +1 818 216-7882
email: info@aydn.com
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