help with FuzzDog Deep Vibes Optical Vibe Machine

[m7b52000]

Hope someone can help with debugging this beast. It is apparently similar to the Earthquaker Devices "the Depths". Info here: http://pedalparts.co.uk/docs/DeepVibes.pdf



My build is unmodified from BOM with no substitutions.
Power supply is steady at 9.25V, confirmed at ribbon cable V entering PCB
Tested unboxed, in my reliable testing rig, it does as follows:

There is no vibe effect
Audio path seems OK and responds to Vol knob
Intensity knob does alter brightness of LED but LED not flashing/pulsing
All other knobs have no effect
Soldering all looks OK. I have reflowed what I can still reach.
IC's and transistors all in sockets

Voltages as follows:

IC2 TL074

1 4.63V
2 4.63V
3 4.63V
4 9.23V
5 4.62V
6 4.62V
7 4.62V
8 4.63V
9 4.63V
10.4.63V
11 0.3 mV
12 4.63V
13 4.63V
14 4.63V

IC1 TL072

1 4.63V
2 4.63V
3 4.02V
4 0.2mV
5 4.56V
6 4.63V
7 4.64V
8 9.23V

Q1 MPSA18

E 0.2 mV
B 1.013V
C 1.124V

Q2

E 144mV
B 1.267V
C 1.87V

D1

K 9.23V
A 0.1mV


D2 Yellow LED

flat side 1.87V
other side 3.81V

I hope all of this is helpful. If I have missed something, please let me know!

cheers,

Tony

[11-90-an]

Pictures plez...

The LFO seems to be the one not working here...

[m7b52000]

[PRR]

> Q1 MPSA18
> B 1.013V
> C 1.124V

Q1 may not be a MPSA18 transistor. If it truly is, then it isn't connected as it should be.

[m7b52000]

Damn my aging eyes. Q1 and Q2 were indeed MPSA13. Now they are MPSA18 but still no flashing LED. Any other suggestions?

[11-90-an]

Now that it's MPSA18... voltages of that trannie pls.. 

[m7b52000]

OK

Q2
E .88V
B 1.58V
C 2.93V

Q1
E .2mV
B .61V
C 2V

[Marcos - Munky]

Your collector voltages are very low. Ho's the voice pot adjusted for those readings? Check Q2 collector voltages with the pot set to both extremes.

Also, that R26... are you sure you used the correct value for it? It seems to me you used a 150K resistor (brown green black orange, for a 5 band resistor), while the effect calls for a 15K resistor (brown green black red, for a 5 band resistor). Those coloured resistors sometimes have the color of some band blending with the color of the resistor, making it very confusing to read using the eyes. The best would be to measure them with a multimeter with them out of the board.

[Eb7+9]

It is apparently similar to ...

as drawn, that LED drive ckt is asking for trouble ...

first you need a device with the same specs they used, otherwise that circuit won't bias like theirs did ... the variable "voice" resistor in series with LED is also not a good idea, after all they are both being driven by a current source, so variable R sets cutoff point of current source ... why do that ??

you can keep your present LED driver device and cut to the chase simply by replacing R22 and R23 by a 100k-to-250k trimpot going between +9 and GND (sweeper to Base) ... don't go to bottom of the LED like the schematic shows, go to +9 instead ... that's a bad mistake (makes adjustments almost impossible when done in tandem with said variable R above LED) ... and set variable R to zero at first, maybe remove entirely ... see if it really does anything that useful

now, you can manually bias your (any) LED to a useful idling value ... and go from there

** basically the same as my Univibe Bulb Driver OFFSET/BIAS MOD

[m7b52000]

Your collector voltages are very low. Ho's the voice pot adjusted for those readings? Check Q2 collector voltages with the pot set to both extremes.

Q1 C voltage steady at 1.9 V over range of Voice pot
Q2 C voltage from 1V to 6.9 V over range of Voice pot

will check that resistor shortly...