Glass Ware Aikido Stereo 5687 PCB User manual

Aikido Stereo 5687 PCB
USER GUIDE
Introduction
Overview
Schematics
Recommended Configurations
Tube Lists
Assembly Instructions
lass are
G W
AUDIO DESIGN
Dec 16 2011

DANGER!
This PCB holds a high-voltage power supply; thus, a real
—
and possibly—lethal shock hazard exists.
Ideally, a variac should be used to slowly power up the
regulator, as it is better to have a mis-
oriented electrolytic
capacitor or a mis-located re
sistor blow at low voltages,
rather than at high voltages. Remember that the danger
increases by the square of the voltage; for example, 200
volts is four times more dangerous than 100 volts
and 400
volts is sixteen times more dangerous.
Once the power supply is powered up
, be cautious at all
times. In fact,
even when the power supply is disconnected
or shut down, assume that power-supply
capacitors will have
retained their charge and, thus, can still shock
. If you are not
an experienced electrical practitioner, before
attaching the
transformer windings to the board,
have someone who is
well
-experienced in electronics review your work.
There are too few tube-
loving solder slingers left; we cannot
afford to lose any more.
AUDIO DESIGN
www.glass-ware.com
www.tubecad.com
[e-mail]
Copyright © 2009-2011
All Rights Reserved
GlassWare

Warning!
This PCB contains a high-voltage power supply; thus, a real and lethal
shock hazard
exists. Once the power transformer
is attached, be cautious at all times. In fact, always
assume that the high voltage capacitors will have retained their charge e
ven after the
power supply has been
disconnected or shut down. If you are not an experienced
electrical practitioner, before applying the AC
voltage have someone who is
experienced review your work. There are too few tube-
loving solder slingers left; we
cannot afford to lose any more. Overview
Thank you for your purchase of the GlassWare Aikido 5687 All in One 9-
pin stereo
PCB. This FR-
4 PCB is extra thick, 0.094 inches (inserting and pulling tubes from their
sockets won’t bend or break this board), double-sided, with plated-through heavy
2oz
copper traces. In addition, the PCB is lovingly an d expensively
made in the USA. The
board is 7 by 6 inches, with five mounting holes, which helps
to prevent excessive PCB
bending while inserting and pulling tubes from their sockets.
Each PCB holds two Aikido line-
stage amplifiers; thus, one board is all that is needed
for stereo unbalanced use (or one board for one channel of balanced amplification).
By
including the necessary components for the heater and high volta
ge B+ power supplies
on the PCB, the5687 All in One board makes building a standard-
setting line stage
amplifier a breeze. This assembled board with a chassis, volume control, selector
switch, power transformer, and a fistful of RCA jacks is all that is needed.
PCB Features
B+ and Heater Power Supplies On the 5687 All in One board, two power su
pplies
reside, one for the high-voltage B+ for the tubes and a low-
voltage power supply for the
heaters. The high-voltage power supply uses an RC filter to smooth
away ripple, while
the low-voltage power supply uses an LDO
voltage regulator to provide a stable and
noise-
free voltage output. The power supplies require an external power transformer(s)
with two secondary windings, one for the B+ voltage and one for the heater
power
supply.
Redundant Solder Pads This board holds two sets of differently-
spaced solder pads
for each critical resistor, so that radial and axial resistors can easily be used (
radial
bulk-foil resistors and axial
film resistors, for example). In addition, most capacitor
locations find many redundant solder pads, so wildly differing-
sized coupling
capacitors can be placed neatly on the board, without excessively bending their leads.
Two Output-Stage Topologies The output stage can
be configured either as the classic
Aikido line amplifier or as an Aikido headphone amplifier. The 5687 is a robust
triode
that can deliver a lot of current at relatively low voltage
s, making it ideal for driving
headphones or other low-impedance loads.
Power-Supply-Decoupling Capacitors The 5687 All in One
PCB provides space for
two sets of capacitors to decouple both Aikido gain stages from the B+ connection and
each other. This arrangement allows a large-valued electrolytic capacitor and small
-
valued film capacitor to be used in parallel, while a series voltage-
dropping resistor
completes the RC filter.

GlassWare Audio Design

2
The
Aikido
amplifier delivers the sonic goods. It offers low distortion, low output
impedance, a great PSRR figure, and feedback- free amplification. The secret to it
s
superb performance— despite not using global feedback—
lies in its internal symmetry,
whic
h balances imperfections with imperfections. As a result, the Aikido circuit
works
at least a magnitude better than the equivalent SRPP or grounded-cathode amplifier.
Aikido Amplifier
B+
Rk
Rk
in
out
R2
R1
Rk
Rk
C
5687
Rg
Rgs
Rgs
Introduction to the Aikido
Universal Topology
In
the schematic
above
, the
5687
triodes are
specified
as an
example only, as 300B
and 845 triodes could be used to make an Aikido amplifier.
The circuit does not rely on these triodes or any other specif
ic triodes to work
correctly. It’s the topology, not the tubes that make the Aikido special. (Far too m
any
believe that a different triode equals a different topology; it doesn't. Making this
mistake would be like thinking that the essential aspect of being a seeing-
eye dog
rested in being a Golden Lab.)
Low Distortion For example, the Aikido
circuit produces far less distortion than
comparable circuits by using the triode’s own nonlinearity against itself
. The triode is
not as linear as a resistor so,
ideally, it should not see a linear load, but a
corresponding, complementary, balancing non-
linear load. An analogy is found in
someone needing eye
glasses; if the eyes were perfect, then perfectly flat (perfectly
linear) lenses would
be needed, whereas imperfect eyes need counterbalancing lenses
(non-linear lenses) to see clearly. Now, loading a triode with the same triode—
under
the same cathode-to-plate voltage and idle current and with the same cathode resistor—
works well to flatten the transfer curve out of that triode.
PSRR The
Aikido circuit sidesteps power supply noise by incorporating the noise into
its normal operation. The improved PSRR advantage is important, for it greatly
unburdens the power-supply. With no tweaking or tube
selecting, you should easily be
able to get a -30dB PSRR figure (a conventional grounded-
cathode amplifier with the
same tubes and current draw yields only a -6dB PSRR); and
with some tweaking of
resistor R1’s value, -60dB—or more—is possible. Additionall
y, unless regulated power
supplies are used for the plate and heater, these critical voltages will vary as
the power
line’s voltage falls and climbs with your house’s and neighbors’ house’s use
, usually
throwing the supposedly fixed wall-voltage askew. Nev
ertheless, the Aikido amplifier
will still function flawlessly, as it tracks these voltage changes symmetrically.
Aikido 5687 Stereo All-In-One PCB
5687
56875687

GlassWare Audio Design 3
Age
Tolerant
Remember
, tubes are not yardsticks, being more like car tires
—
they
wear out. Just as a tire’s weight and diameter decrease over time, so does a
tube’s
conductance. In other words, a fresh 5687 is not the same as that same 5687
after
2,000 hours of use. But as long as the two triodes within the 5687
age in the same
way—which they are inclined to do—
the Aikido amplifier will always bias up
correctly, splitting the B+ voltage between the triodes.
No Negative Feedback Loop The Aikido topology d
oes not use any negative
feedback, other than the local degenerative feedback because of the unbypassed
cathode resistors in the input stage and the active load presented by the bottom
triode of the output stage. In fact, the Aikido topology makes use of f
eedforward
noise canceling at the output. Unlike negative feedback that has to
wait until
something goes wrong
before it can work to undo the damage, feedforward feedback
anticipates what will go wrong before it does. It is proactive, not reactive, to borr
ow
the terms of pop-psychology.
The Aikido circuit eliminates power-supply noise from its
output, by
injecting the same amount of PS noise at the inputs of the top and bottom tube
s in
the two-tube cathode-follower circuit. Since both of these signals are
equal in
amplitude and phase, they cancel each other out, as each triode
sees an identical
increase in plate current—imagine two equally stron g men in a tug of war contest.
So,
shouldn’t resistors R1 and R2 share the same value, thereby also splitting the power
-
supply noise at 50%? No. If triode did not present a low plate resistance, then the
50% ratio would apply. Because of the low rp, the correct relationship between
resistors R1 and R2 is given by the following formula:
R1 = R2[(mu - 2)/(mu + 2)]
Low Output Impedance The
Aikido topology uses a modified cathode follower
circuit as the output stage. Cathode followers
are famous for providing low
distortion and low output impedances, but no voltage gain. This modified cathode
follower scrubs away the power-
supply noise from its output and provides a
complementarily non-
linear load for the top triode’s cathode. The top triode’s
capacitor resistor is in series with the output, so its resistance must be added to the
cathode follower output impedance. Had the output connection been
taken from the
top triode’s cathode, then the
output impedance would be slightly l ower, but the
symmetry would be broken and the PSRR enhancement would be lost.
Gain Calculating the gain from an Aikido amplifier is easy, as it roug
hly equals half
the mu of the input triode used. The gain from a simple grounded-
cathode amplifier
(with an un-bypassed cathode resistor) is
Gain = muRa/[Ra + (mu + 1)Rk + rp]
In the Aikido, the resistance presented by the top tube and its cathode r
esistor is
R' = (mu + 1)Rk + rp. So if you substitute R' for Ra in the above
equation and
simplify you get
Gain = mu[(mu + 1)Rk + rp ] / [(mu + 1)Rk + rp +(mu + 1)Rk + rp] = mu/2
Of course there is a slight loss though the Aikido’s modified-cathode-
follower output
stage
, whose gain usually falls between 0.93 to 0.98.

4Aikido 5687 Stereo All-In-One PCB
Heater Issues
The 5687 All in One PCB holds the heater's raw power supply and its DC
voltage
regulator. The regulator is an LD1085 low-
dropout adjustable voltage regulator. The
regulator can be set to an output voltage of 12V or 12.6V. The
advan tage of running a
slightly low heater voltage
(12Vdc) is that it extends tube life and can lower distortion a
tad. All the 5687 tube's heaters are placed in parallel, so a 6.3V or 25.2V heater
voltage
cannot be used. Be sure use jumpers J1 and J2.
54
J1
+H
-H
Filament Jumper Wire Schedule
V2
54
J2
54
V3
V4
54
C18
AC
LD1085
Adj
InOut
Heater +
Heater -
C15
C14
R20
D6
D5
D8 C10D7C9
D10 C12D9C11
R21
{
C18
+
+
+
+
AC
CT
C13
C16
to B+ heater
bias voltage
A
s can be seen, the power supply can accept either
a
full
-
wave
-
bridge
-
r
ectifier circuit or
a full-wave-voltage-doubler-rectifier configuration. When used as a full-
wave bridge
rectifier circuit, the two power-supply filtering capacitors are placed in paralle
l by
orienting their positive leads to where the heatsink sits;
and the secondary attaches to
the two encircled AC pads. Configured as a voltage doubler, these capacitors
placed in
series by being rotated 90 degrees clockwise, so the positive leads point to the center
-
tap ("CT") pad at the bottom of the PCB; the secondary attaches to single "AC"
pad in
between capacitors C13 and C14 and AC pad number 2 that feeds rectifier D7
and
D9; and D8, D10, C10, C12 are left off the PCB. If used as a full-wave center-tap
circuit, the two power supply filtering capacitors are placed in parallel by orienting
their positive leads to where the heatsink sits;
and the secondary attaches to the two
encircled AC pads (1 & 2) and the secondary center-tap attaches to the CT pad
and
C11, C12, D9, and D10
removed
.
See the inside back cover for more information.
V1
Filament Regulator

GlassWare Audio Design 5
The
heater’s PS
reference
bias
voltage to
target is
one quarter of the
B
-
plus
voltage
that the Aikido’s tubes use, not the initial raw B-plus
voltage at the high voltage
rectifiers. Alternatively, you might experiment with floating the heater power supply,
by “grounding” the heater power supply via only a 0.1µF film or ceramic capacitor
,
leaving resistors R19 and R18s off the board
. The capacitor will charge up through
the leakage current between heater and cathodes. Not only is this method cheap, it is
often quite effective in reducing hum with certain tubes.
DC
Heater
Regulator 300k 1W
47k 1W
[L] B+
AC
R18
R19
Final B+
4
Since one triode stands atop another, the heater
-
to
-
cathode voltage experienced differs
between triodes. The safest path is to reference the heater power supply to a voltage
equal to one fourth the B+ voltage; for example, 75V, when using a 300V power
supp
ly. The ¼ B+ voltage ensures that both top and bottom triodes see the same
magnitude of heater-to-
cathode voltage. The easiest way to set this voltage relationship
up is the following circuit:
Heater Voltage =
R21 =
R20 =
D7 - D10 =
D5, D6 =
C9, 10, 11, 12 =
C13, C14 =
C15, C16 =
C18 =
Regulator =
Vac Input =
12V 12.6V
1.07k 1.13k
124 124
MUR410G "
1N4007 "
0.1µF / 50V "
10kµF* "
1kµF / 16V "
1k-3900µF* "
LD1085, LT1085
12Vac or 12.6Vac @ 3.5A for or 12Vdc or 12.6Vdc
*Capacitor voltage must exceed 1.414 x Vac input voltage
Typical Part Values
Resistors
R
20
and
R
2
1
set the voltage regulator’s output voltage. The formula is
V
0
= 1.25(1 + R
21
/ R
20
)
Heater
Elements
+
-
[R] B+
R18
C17

6Aikido 5687 Stereo All-In-One PCB
R3
R2
R1
R4
R12
R5
R6
R9
R10
R8
R7 R11
C5C4
C6
C3
L-in
L-out
V1 V3
1
2
3
6
7
91
2
3
9
7
6
B+
R22
C23
Configuring the PCB as a Headphone Amplifier
The standard Aikido is a thoroughly single-
ended affair, nothing pulls while
something else pushes. Unfortunately, wonderful as single-
ended mode is sonically, it
cannot provide the larger voltage and current swings that a push-
pull output stage can.
Single-ended stages can only deliver up to the idle current into a load, whereas class-
A
push-pull stages can deliver up to twice the idle current into the load
. For a line stage,
such big voltage and current swings
are seldom required; headphones, on the other
hand, do demand a lot more power; really, a 32-
ohm load is brutally low impedance
for any tube to drive. Fortunately, the
PCB can be configured with an optimal White
cathode-follower stage, which will both ret
ain much of the Aikido’s great PSRR and
allow up to twice the idle current to be delivered into low-
impedance loads. All that is
required is to include resistor R22 and capacitor C23 and replace resistors R6 & R
10
with jumper wires.
Headphones require big current swings and little voltage swings, so we should lower
the B+ voltage and raise the idle current, say 160Vdc and 24mA for the output tube
s
(Rk = 47 ohms). A coupling capacitor of at least 30µF is required when driving 300
-
ohm headphones; 330µF for 32-ohm headphones. Capacitor C3
can be bypassed by
using a small film or PIO capacitor on bottom of the PCB.
In the optimal White cathode follower, the critical resistor is R22
. This resistor is used
to sense current flow variations through the top triode and to create an anti-
phase
signal that is relayed to the bottom triode's grid. In other words, it sets the
dynamic
current
balance between top and bottom tubes. A value that is too high or too low will
compromise performance. Finding the correct value for resistor R22 is easy:
R22 = (rp + 2Rload)/mu,
where rp equals the plate resistance and Rload
equals the load impedance. From a quick
inspection, we see that the lower the load impedance, the closer the formula comes to:
Ra = rp/mu. On the other hand, when the load impedanc
e is as much as 600 ohms
and the rp as low as
the 5687's 16
00 ohms, then the difference is fairly large.

GlassWare Audio Design 7
C1, C2 =
C3* =
C4* =
C5 =
C6* =
C7, C8 =
C23 =
0.01-0.33µF (optional) Same Same Same
0.1 - 4µF Film or PIO " " "
0.01 - 1µF Film or PIO " " "
270µF 200V 270µF 200V 150µF 400V 150µF 400V
0.1 - 1µF Film or PIO Same Same Same
220µF 200V 220µF 200V 47µF 450V 47µF 450V
None None None None
*Voltage rating must equal or exceed B+ voltage
*High-quality resistors essential in this position. All resistors 1/2W or higher
Typical Part Values
() Parentheses denote recommended values
Configuring the PCB as a Line Amplifier
The Aikido topology makes a
perfect line amplifier, as it offers low distortion, low
output impedance, and excellent power-supply noise rejection—
all without a global
feedback loop. The key points are to replace resistor
R22 with a jumper wire and leave
capacitor C23 off the PCB. The following
table list four recommended
configurations, but actually there are in infinite number of possible setups.
B+ Voltage =
AC Secondary =
AC Current =
Heater Voltage =
Heater Current =
R1,11 =
R2,5,8* =
R3,4* =
R6,7* =
R9 =
R10 =
R22 =
5687 & 5687 5687 & 5687 5687 & 5687 5687 & 5687
100V 150V 200V 250V
150 - 170Vac 230 - 250Vac 200 - 250Vac 115 - 120Vac
50mA 60mA 80mA 60mA
6.3V or 12.6V 6.3V or 12.6V 12.6V 6.3V or 12.6V
2A or 1A 2.5A or 1.25A 0.75A 1.5A or 0.75A
1M 1M 1M 1M
100 - 1k (300) Same Same Same
100 - 470 (300, 5.5mA) 300 - 1k (390, 7mA) 300 - 1k (390, 10mA) 300 - 1k (845, 7mA)
200 - 340 (150, 8mA) 200 - 470 (240, 10mA) 200 - 470 (300, 12mA) 300 - 1k (680, 10mA)
100k Same Same Same
78.7k 78.7k 78.7k 78.7k
Jumper Same Same Same
R3
R2
R1
R4
R12
R5
R6
R9
R10
R8
R7 R11
C5
C4
C6
C3
L-in
L-out
V1 V3
1
2
3
6
7
91
2
3
9
7
6
B+
R22
C23
Tubes =

8Aikido 5687 Stereo All-In-One PCB
5687
Specifications
Heater Voltage 6.3V & 12.6V
Heater Current 900mA & 450mA
Maximum Plate Voltage 330V
Maximum Plate Dissipation 4.2W
Maximum Cathode Current 65mA
Maximum Cathode-to-heater Voltage 100V
Amplification Factor 18.5
Transconductance 11.5mA/V
Plate Resistance 1600 Ohms
Grid-to-Plate Capacitance 0.75pF
RETMA 9H
Bottom View
Pin 1: Plate, triode 2
Pin 2: Grid, triode 2
Pin 3: Cathode, triode 2
Pin 4: Heater
Pin 5: Heater
Pin 6: Cathode, triode 1
Pin 7: Grid, triode 1
Pin 8: Heater center-tap
Pin 9: Plate, Triode 1