Hi all,
Out of sheer coriosity and driven by interest
I tried to see, how this pedal works.
Head room 30V?
==============
Sorry, I guess, differences between AC30 and AC15 are ment.
E.g., AC15 with 2xEL84 runs with a cathode resistor of 130Ohms,
and AC30 runs with 4xEL84 runs with a cathode resistor of
50Ohms, so AC15 runs colder (more class AB than class A).
So no charge pump for 30V I guess, pedal runs on 9V.
Screen Shots and Resistor Values:
=================================
For explorirng schematic a photograph of other side of PCB would
be very usefull;-)
Resistor color codes on video seems to be strange, for instance:
Emitter of 2N5089 (pre-booster) is connected to ground via 100
Ohms (value printed on “naked” PCB) or something like 590 k
(color rings on video). Assuming 10 Ohms here, like displayed on
PC board printing seems to make more sense.
Foot switch:
============
Mounted on extra circuit boards
Normal true Bypass for Buffer and for device:
—Left switch layer switches effect in (SND) between input jack
(JI+I2) and X-to-ground (G1, G2 etc.).
—Middle switch layer switches ground from LED- (L-) to
X-to-ground (G1,G2 etc.).
—Right switch layer switches effect out (O2) from Return (O,
RET) to input jack (J2).
On main PCB L- go to an 10k resistor to LED.
Boost-Stage:
============
2N5089,
Input circuit 100pF to Ground
Input circuit 10nF in series to Input (Bass cut) ?
Operation point 4,5-5Volts, nothing like Treblebooster 6-7Volts
operation point.
100Ohms Emitter to Ground
Collector 5.6k to 9V; 470nF --> to Out (Pot 100k log?).
Tone Stack
==========
Like VOX tone Stack
(2*1Meg, 47pF, 22n, 22nF, Bass taper 10k to Ground)
Really scrambled routing (look, where 47pF is)
Last? Cliping stage—the cliping LED
============================================
Seems to be an MOSFET cliping stage like hard one alike booster,
22k drain resistor, 2.2k || 47n source resistor. High drain
resistor, stage seems to run cold (low current). LED is between
gate and source, clipps high positive input peaks. Capacitor 1n
between gate and source, lowpass cliping peaks of LED as well
as enlarges input impedance by bootstraping.
Transistors and ICs:
====================
From top to right:
—bs170: ???
—J113: drain on 9V, buffer or mu-Amp with bs170 ?
—2N5089: Gain Booster.
—J201: drain on bias resistor, cliping stage before tonestack?
—bs170: Cliping stage with LED.
—J113: drain on 9V, source on 10k to ground, buffer ?
—11P06: P-Channel-MOSFET—seems to be a series resistor for 9V.
4 x OPA
from 4.5V, one OPA is biased with 1Meg (input buffer?), two (at
least) are biased with 100k.
12 resistors, 9 capacitors. Could be, this is a filter or a
gyrator circuit to simulate interaction of power amp and speaker
inpedance of an real VOX?
Generally said,
===============
looks like, there is a 3-5 transistor pedal oriented on the
AC15/AC30 schematic. Distortion seems to be realized with FET
(JFET/MOSFET) cliping. OPA seems to be used for some additional
filtering, not for cliping.
cheers.
Torsten
P.S.:
Screenshot of PCB (youtube video) and (possible) cliping stage with
MOSFET and LED: