EA Tremolo (GGG) not working

[deke99]

Hi all,

I recently built the EA Tremolo from General Guitar Gadgets and I'm having a problem with it.  It is a standard build with the only exception being that I have the LED wired to pulse with effect.  I adusted R8 from 15K to 10K to compensate for this (per ROG).  The bypass signal is fine, but I get no sound when I engage the effect.  The LED does pulse correctly and the rate changes with the speed knob.  When engaged, I just hear some hiss that gets louder/softer with the volume adjustment.  I've checked my pinouts on the transistors and everything seems to be fine.  I can't find any wrong part installations and there are no solder shorts.

Here are my voltages at the transistors:

9.3 Supply voltage

Q1 (2N3904)
C  9.09V
B  .614V
E  69.6mV

Q2 (J201)
D  .9V
S  0V
G  275mV

Q3 (2N5088)
E  0V
B  .4-.6V this fluctuates
C  3-6V this fluctuates

Q4 (J201)
D  9.3V
S  8.55V
G  8.55V

When the effect is on the source and gate of Q4 measure full continuity.  When I disengage the effect, that continuity disappears.  Any help that you can provide would be greatly appreciated.  Please let me know if there is any additional information that you need to help.

Thanks!
Derek

[deke99]

Well, I've made some progress.  As it turns out, I had the 2 J201s reversed, so I have corrected that issue and now I get a tremolo signal through the pedal, but the signal is weak (i.e. more quiet than the bypassed signal even with volume maxed).  This sound is also very metallic/overdriven.  My updated voltages are below with the changes bolded . . . any help is appreciated!!

9.28 9V source signal:

Q1 (2N3904)
C  9.09V
B  .62V
E  0V

Q2 (J201)
D  0V
S  0V
G -1V - 0V fluctuates

Q3 (2N5088)
E  0V
B  .62V
C  3-6V this fluctuates

Q4 (J201)
D  9.28V
S  4.85V
G  4.4V

[MohiZ]

Hi!

Based on the schematic, the Q1 voltages seem off... The transistor seems to be barely conducting. The base voltage should be higher, as should the emitter voltage. Check that the connections are made correctly around that transistor (the resistors to ground and +9V from the base and emitter).

[deke99]

Thanks for your input MohiZ, I'll check that out and report back.  Again, I really appreciate the help!

[deke99]

It turns out I'm an idiot and had the pinout of the 2N3904 backwards.  It's funny how you check and double check something and can get it wrong every time.  Thanks for pointing me in the right direction, the pedal is fully operational now!

[MohiZ]

Glad to hear it!  The pinouts should have some kind of a standard, I'm sure that would solve many problems before they were ever made.

[VeridisQuo]

Hi I'm having the same problem that you described in the first post on this thread. Bypass works, but no effect signal except for some hiss with pulse. All the right transistors are in the right spot, I have no clue what could be causing this problem.

[nomorebetts]

Do you have a digital multimeter to take some voltage readings at the transister pins like deke99 has done?
There are directions on how to do this in the debugging thread.
Once you have the readings compare them to the values that GGG specified and investigate from there.
Good luck!