http://www.ozvalveamps.org/repairs/circuitbin.htm | Created: 5/06/11 |
Last update: 20:25 20/04/2012
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Circuit Bin

From down the back of the filing cabinet at AVA.

These circuits have been aquired over time, downloaded for repairs in hand,
to answer repair questions, or exploring design ideas (an all electronic Lesley rotating
speaker effect for one). They are here because they are not of ANZ
manufacture and there is no other specific place for them, but they are fairly
typical of the sort of thing an amp tech will have coming across the bench.

This is not intended to be exhaustive but only to provide representative
examples, particularly for stomps and Fx.

Anyone who wants to add, attribute or remove a circuit should e-mail;

Amplifier Circuits

Acoustic

Acoustic 360/361 Service Manual. Caution: 11Mb
PDF

Ampeg

svt6146b-circuit

BOSE

bose-1801-preamp

input-circuit

Fender

bl_delux - Blues Deluxe

fbassman - Bassman

fchamp - Champ 12

fndr60a - 60-Series part-A, fndr60b
- 60-Series part-B

fstudio85 - Studio 85 Fully solid-state

concert_6g12.pdf 6G12 circuit and layout, 2x 6L6's,
“Harmonic Vibrato”

concert_6g12a.pdf 6G12 circuit and layout, 2x 5881's,
“Harmonic Vibrato”

showman_6g14.pdf 6G14 circuit and layout, 4x 6L6's,
“Harmonic Vibrato”

showman_6g14a.pdf 6G14 circuit and layout, 4x 5881's,
“Harmonic Vibrato”

Gem

Super Deluxe Reverb 50r (rev1.02bis)

Grant Wills

Poor mans Plexi

HAG

HAG 39 - 2x ELC84/6GW8's

Marshall

1987 Power

1987pre

2204pre

2205pow

2205pre

2210pow

2550 Amp

2550 Power supply

j9po1002 - JCM900 100W

j9pow100 - JCM900 100W (2100, 2101, 4100, 4101, 4102)

j9pow50 - JCM900 50W (2500, 2501, 2502, 4500, 4501,
4502)

j9pr_mv2 - JCM900 Power (2500, 2501, 2503, 2100,
2101)

j9pre_mv - JCM900 Pre (2500, 2501, 2502, 2100, 2101)

jcm900du - JCM900 (4500, 4501, 4502, 4100, 4101,
4102)

marshal_1-2205-preamp

marshal_2-2205-op+psu

Rockit

Rockit Super Sustain 130 - power stages

Titano

Custom 314

Stomp and Fx Circuits

Note: LDR = Light Dependent Resistor, Cadmium Sulphide (CdS) cell

6BM8 Single Tube Reverb - by Eric Barbour.

biphase - Bi-Phaser

The original used 4558 and 741 op-amps. Today we could use the TL07x or
TL08x single, dual or even quad FET input op-amps and improve the distortion
and residual noise. While there are super-dooper quiet op-amps available, the
LM833 is an almost perfect dual audio amplifier at a very cheap price.
Effects oscillators are normally not critical since they aren't in the signal
path.

Each of the sections of the chain introduces a phase shift determined by
the capacitor and the FET, and this phase shift accumulates down the chain.
This basic phase shifting chain is applied in various ways in different
effects, ranging from a single shifter to produce a very subtle frequency
shift, then adding feedback and multiple paths (plain, or itself shifted as
here) and summed to produce selective cancellation at the output, resulting in
Vibrato, Phasing, or Flanging.

The little FET matching test circuit in the middle measures the individual
FET Idss (Drain current, gate shorted to Source) and applies generally
to matching FET's in any phase-shifting network. This matching is needed
because most common FET's (such as the common MPF102/2N3819) have a very wide
spread of Idss characteristic, often as much as 10:1. The exact value
isn't critical, but the Idss should be matched to better than 2:1, and we
would generally aim for better than root2 or 1.5:1. Once matched the “trim”
control is used to bring them all into an acceptable operating range.

comp1 - valve compressor.

DOD 595 phasor - a six stage phase-shifter using LDR's and
LED's.

enhancer

With typical Elektor overkill this circuit has three areas of
interest.

The first is the input section which allows the insertion of small
capacitances across the guitar output. With a naked pickup this will allow
manipulation of the pickup self-resonance. This is discussed on the pickups
page, and could be used ahead of a valve rather than the FET shown.

The input amplifier or impedance converter around the FET is an example of
an idealised stage using a current source and current sink.

The enhancer itself allows a controlled small amount of distortion due to
diode D1 to be added to the clean signal. While this looks similar to a fuzz
circuit the signal level across the diode is quite small and only works it
across its initial non-linear curve, producing only a light distortion.

An indicator is also provided to assist in the correct setting of the
enhancer controls.

Exciter - extracts higher frequencies and allows them to
be mixed back into the main signal with controllable proportion and phase.

function-gen - ECELab.com

Four op-amp fixed frequency function generator/oscillator with square,
triangle and sine output.

funcgen-natsemi

Two op-amp tuneable function generator with square and triangle output.
The main attraction of this sort of function generator is that it is tuned
with a single resistive element which may be a FET or LDR. Switch selecting
values for C1 allows range switching.

fxboxsch-hfj - Hi-Fi John Fuzz, 4x PNP, diode
clipper, easy mod to NPN silicon

fxloop1-valvewizard - Fx loop send/return using valves.

fxschem-hfj - Hi-Fi John Boost/Distortion clipper,
any op-amp, +/-9V

Harmoniser - More Elektor overkill with this
circuit that is a stereo form of the enhancer

This extracts higher frequencies from the signal passing through and using
diode distortion adds harmonics to it, but is gated so this only happens when
the signal is above a set level.

ibnzbe10 - Ibinez five one octave band equaliser

The rank of op-amps on the right side are configured as gyrators or
simulated inductors. These act as series-resonant LC circuits with C10
etc taking the role of the C and the op-amp and C9 etc setting the value of
the simulated inductance L. Each acts as an acceptor resonator in its
band, and the dip in impedance is fed via the control to the main amp feedback
circuit, giving boost or cut.

This gyrator circuit element is important to understand since it is used
almost univerally in multi-band graphic equalisers, so common in fact that
there are specific multi-section IC's specifically for this
application.

ibnzpt90 - Ibinez Phaser, MP-P01001A - a four stage phase
shifter using FET's

Jen Wah-Volume pedal

JFET Bass Preamp - by Albert Kreuzer. albertkreuzer.com

jordan_bosstone N.B. value corrections. Values on the
circuit disagree with values in the parts list. R2 should be 150k, C3 should
be 47 or 50pF, R7 should be a 10k pot. R2 is quite “tweekable” and trying
different values down to 68k may be profitable. I'm also inclined to think
that R6 should be between +9V and the emitter of Q2 since the circuit seem
unstable and prone to self oscillation as drawn.

This is a fairly conventional high gain amplifier followed by a diode
clipper, but note carefully that the two back-to-back diodes are not the same
type. This is deliberate so that the signal clipping is slightly different
for the positive and negative signal peaks, as it would be in an overdriven
valve preamp.

korgngt1 - Korg Noise Gate

korgoct1 - Korg Octave Divider

IC4d - high impedance input buffer, IC4a - signal polarity inverter, IC6b -
three pole low pass filter, IC6b + IC3c +IC3? - signal slicer, the first
flip-flop IC1 is a squarer, the second flip-flop is the actual frequency
divider. This divided signal is injected into the gain control port of an OTA
IC2f, 13600, which is also fed with the unconditioned signal input, which is
therefore modulated by the divided signal.

korgpeq1 - Korg Parametric EQ (Devices IC1-3 with the
unique circuit symbol, TX-429D, are Dual Gate MOSFET's, similar to the MPF131.)

korgphs1 - Korg Phaser (Devices IC1-4 with the unique
circuit symbol, TX-429D, are Dual Gate MOSFET's, similar to the MPF131.)

korgtnb1 - Korg EQ/buffer (KLM690)

Latching switch - push on, push off. Hackaweek.com

m2000b

A fairly conventional valve guitar preamp with gain, volume, treble, bass
and middle controls, but also featuring a “sweep” control that allows some
adjustment of the hinge, or turnover, point of the tonestack from around 500Hz
to around 800Hz.

Sweep at minimum 10k

Sweep at maximum 110k

Response graphs from Tone
Stack Calculator

mu-tron3

Op-amps A2, 3 and 4 comprise a state variable filter that has
low-pass, band-pass and high-pass outputs, and can be tuned with two series
resistance elements.

The mystery component, “OB05” or “O805”, is a LED to dual LDR opto-coupler.
One of the LDR's goes between A2 and A3, and the other between A3 and A4.

The light is a LED or LEDs (because filament lamps are polarity
insensitive). R23 should be selected to give a LED current of 20mA or less.

mxrdistp - MXR Distortion

A very straight forward distortion pedal suitable for beginner
construction, can use just about any available op-amp and the diode clamp can
be tweeked to taste. Note: the input tip and ring contacts are drawn
transposed; ring is power, tip is signal.

octavia - Bob Starr's Octavia frequency doubler.

Uses a common LM386 audio power amplifier, a common transistor radio
transformer, and full-wave rectifier.

Preamp/buffer - by Rod Elliot, ESP

Phase Shift Oscillators - by Bill Bowden

purple - The Purple Pedal by C.Steele

Four stages of heavily clipped gain

reverb-hfj - Hi-Fi John Stand alone reverb, valve

reverb - springline drive and recovery by Robin
Tomtlund

Note: the springline driver uses current feedback so the outer of the
RCA connectors driving the line must be isolated from ground.

Three simple boosters - bass/treble Big Muff style
control, bass booster, and presence control. All of these have quite low
input impedance and will seriously damp an unbuffered pickup.

triangle-to-sine converter - Driven by the function-gen above this should provide a variable
frequency audio function generator with square, triangle and sine output.
While diode wave shapers of this sort can produce a reasonable approximation
of a sine output they aren't perfect and contain distortion that may be
significant in some applications. Their main attraction is very good
amplitude stability when used for frequency sweeping applications.

uniflash Bob Starr again with a complex way to
flash a small globe, unless you want tight control for LDR's.

Valve Vibraton - a stand-alone version of the vibrato
effect used in Vox AC30's and as Fender's “Harmonic Vibrato”. This design
produces selectable vibrato (phase/frequency modulation) and tremolo
(amplitude modulation). It is contended by some booters for Magnatone that
they produced the first and only genuine frequency shifters. “First” is a
matter of history and patent applications which I don't dispute, but “only” is
simply a failure of proper circuit analysis since circuits such as this one
(apparently inspired by the Vox) do indeed produce a shift in
frequency.

Vari-tone-p1 and Vari-tone-p2 - an article by Tim de Whalley on the Gibson
Vari-tone which is a passive tunable notch filter that can be applied as a
modification to other guitars.

Valve vibrato unit - from RTV&H. Actually an
amplitude modulation tremolo unit using a single 12AX7 and neon/LDR.

Z.Vex SHO (Super Hard On) - MOSFET guitar buffer/booster.
Layouts by Andrew Carrell for printed circuit, dab-board, or Veroboard
construction.
The circuit thanks to Gottfried Divos.

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