EA Tremolo Help

[zocochico]

I've had an unfinshed EA Trem on my bench for about a year. I started the project back up but am having some issues. Bypass works fine but when the pedal is engaged I get a drop in volume and no effect. I am working off the old PCB from GGG, not the current one on the site. I am also using the original plans for the 2 25k Log pots (Volume and Speed) and the 1M linear Depth pot. I am also using 2 j201 instead of the 2 2n5457 transistors. All pinouts have been confirmed as well as polarity of the electrolytic caps. Here are my readings:

V+: 9.2

Q1:
C: 9.2
B: 1.9
E: 1.4

Q2:
G: Varies between 0 and -1.7
S: 0
D: 0

Q3:
C: Varies 0 - 6.3
B: .5
E: 0

Q4:
G: 4.4
S: 4.7
D: 9.2

Also my audio probe gets no sound at the Q1 Collector but I don't know if it should or not.

Thanks for your help.

[zocochico]

I thin I may have spotted the problem. After R5 (180ohm) there is no signal. Turns out I don't have a 180ohm resistor on there. I also don't have one in my box. If I add some up in series I can get close.

Can anyone tell me how close is close?

[Paul Perry (Frostwave)]

170 to 190 should not be a problem.
You could probably go a bit wider than that.. but I don't advise using widely different components, until after you have got something working.

[gez]

Hint: it helps if you link to a schematic.  I can't be the only one here who hates schematic chasing (I usually skip posts that don't link to them).

I'm going by the schematic at GGG now, so hopefully it's the same one (seems to be going by your voltages).  You seem to have shorted/connected Q1's collector to V+.  Its junction with R4 (the 4k7 collector resistor) should sit at around 4.6V.

[zocochico]

Thanks for the help fellas. Sorry about not posting a link to the schematic, GGG has updated the one on their site so I only have build instructions to go off of for my old 2006 pcb version. I put it that new set of resistors (it called for a 180ohm and I had something crazy in there) and now my numbers look closer. I now have a boosted signal but don't get any tremolo sound... yet. Going to use my audio probe to see if I can find the problem.

[gez]

Zocochico.  Is the schematic you used the same as this one:

http://www.generalguitargadgets.com/pdf/ggg_eat_sc_improved.pdf?phpMyAdmin=4a28f86a515b7883e7bc35a68d4e7b6d

If the schematic isn't the same, could you compare it with what you've used and tell us which transistors on the current GGG schematic correspond with the labelling you used in your initial post (my Q1 = GGG?, my Q2 = GGG? , etc.)

If it is the right one, the collector of Q1 should be at around half voltage, not V+.  You've either wired it up to V+ by accident, there's a short, or you've used a small value collector resistor (R4) by mistake.  If you've subsequently sorted this out and now have boost at the output, then concentrate on the LFO and the modulating element.  Your readings were intermittent, which suggests that the LFO is working, so perhaps the  FET is wired incorrectly.  Check its pinout.

[zocochico]

That schematic is close it just uses different values for it's speed and depth pots. When I use the audio probe I can hear sound pulsing when I'm in the LFO section. It is a bit faint but you can hear it. I believe your right when you mention that there may be an issue there. I also looked up the pinout on those FETs and they seemed correct but I will double check. This may be another thing I have taken for granted but could the J201 pinouts be different from the diagrams I found on the net?

I'm soooo close to getting it to work.

[zocochico]

HAHA! It's working now! I swapped out the FET at Q2 and viola! Tremolo! This thing sounds sweet too.

Thanks for the help fellas! Now to get started on my Seventh Circle preamps!