help Debugging GGG EA Tremolo

Started by Dylfish, December 01, 2010, 08:40:05 AM

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Dylfish

Hey Guys, finished my first build tonight.

its (obviously) the GGG Tremolo w/ footswitched boost. I plugged her in and the bypass works well, the boost seems to work via the volume pot, but so far no tremolo effect!

Ive gone over the Transistor voltages and these were my results.

one spot power supply : 9.46v ( I know i should be using a battery for debugging but at the moment im yet to grab a fully charged one)

Recommended voltages first, then followed by my readings after the -

Q1
Collector
6.0v - 6.62v
Base
1.4v - 1.452v
Emitter
0.8v - 0.833v

Q2
Drain
0.0v - 0v
Source
0.0v - 0v
Gate
variable - 0v

Q3
Collector
variable (with Speed Knob) 0v
Base
0.6v - 0.643v
Emitter
0.0v - 0.0v

Q4
Drain
8.8v  - 9.47v
Source
5.0v - 4.69v
Gate
4.1v - 4.5v

Im a little worried about no voltages on Q2's Gate and Q3's Collector. I searched the forum and i saw a similar problem but with no outcome.

please, any words of wisdom will help a lot., Cheers.

Dylfish


PRR

> Anyone?

Please (if possible) give a link to the the specific circuit.

Maybe http://www.generalguitargadgets.com/pdf/ggg_eat_sc_improved.pdf  ??

Did you get the complete kit-of-parts from GGG or other reliable source, or collected them yourself?

> Q3 Collector ... 0v

That's not the right answer.

Q3 C should try to come up to a steady 2V, then wobble violently. DVMs may give a confused reading, not zero.

Short R10, is it still zero?

Is R9 really 2.2 Meg?

Check for missing or mis-soldered R8 or transistor leg.

Check for solder-bridges around Q3 C4 R9
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Dylfish

sorry!

ok ive gone over it again and found this, i have a variable voltage on q3 but no voltage whatsoever on q2 where it is meant to be variable. 

my question is what voltage should q2 have and would DC voltage get through at all with c3 filtering out all the DC components?

im still getting a wicked boost but no actual trem effect at all.

http://www.generalguitargadgets.com/pdf/ggg_eat_sc_improved.pdf  this is the related schematic and below are my revised obersvations

First are the recomended GGG Voltages followed by my results

9 volt power supply
9.45v

Q1
Collector
6.0v - 6.62v
Base
1.4v - 1.45v
Emitter
0.8v - 0.83v

Q2
Drain
0.0v - 0v
Source
0.0v - 0v
Gate
variable - 0v

Q3
Collector
variable (with Speed Knob) - i get around 2-3v which moves around alot

Base
0.6v - 0.57
Emitter
0.0v - 0v

Q4
Drain
8.8v - 8.1v
Source
5.0v - 5.0
Gate
4.1v - 4.1v





Dylfish

oh and i almost forgot, it was the proper GGG kit purchased off the website.

PRR

#5
> i have a variable voltage on q3 but no voltage whatsoever on q2

I have water at the cellar sink but no water at the upstairs sink. How to debug? Look for the pipe clog between the cellar and the upstairs.

In electricity a "clog" is usually a broken wire, a bad solder joint, a mis-wiring. (Often easier to see than the clot of silt and gravel I get inside my water pipes.)

Follow the PATH from Q3 collector to Q2 gate.



In practice you check both ends of every part along the path. My red dots. At Q3 side of C4 you have an average few-Volts DC +plus+ a big wobble which confuses your DMM. At the other side of C4 you have an average zero-Volts DC +plus+ a big wobble which confuses your DMM. It may be confused different, but you can tell something's happening.

Follow through R7 R13 to Q2 gate. The wobble will get weaker (Q3 makes more wobble than Q2 can take) but it should be unsteady. If it gets steady, you found the break. Fix it.
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