GGG Big Muff Clone Volume Problem

[ymjon]

Hey all,

I built a Big Muff Russian Green Clone from Generalguitargadgets and it sounds like a Big Muff but there is no volume to it.
There is very little output when turning the volume knob until the last 1/4 of the turn where it goes from very little to little output.
I've gone through it and it looks that everything is hooked up correctly so hopefully you can point me in the right direction to get it working right.

Here are the links to the schematic and layout:

schematic
http://www.generalguitargadgets.com/pdf/ggg_bmp_grus_sc.pdf
layout
http://www.generalguitargadgets.com/pdf/ggg_bmp_grus_lo.pdf
wiring
http://www.generalguitargadgets.com/pdf/ggg_bmp_wiring.pdf

and here are measurements I took:

V+8.81v

all 4 transistors are 2n5089s

q1
e .141v
b .722v
c 4.43v

q2
e .141v
b .722v
c 4.42v

q3
e .129v
b .708v
c 4.34v

q4
e .902v
b 1.47v
c 8.76v

Thanks for the help,

Jon

[reveriesof]

i had this exact problem when i built my ggg muff.  it turned out to be one of the resistors toward the end of the signal chain, just before the output.  i didnt catch it til the 2nd time i looked them all over but i used the wrong value by a factor of 10.  those 5 band blue resistors are easy to misread if both ends have a brown band.  i fixed my friend's attempted ggg orange squeezer finding the exact same problem. 

[gigimarga]

For sure you have some problems on Q4's collector.
The voltages on all 4 collectors must to be around 4.5V (half of the power supply), as you can see in the instructions:
http://www.generalguitargadgets.com/pdf/ggg_bmp_instruct.pdf.

I've just finished one couple of weeks ago and it worked from the beginning very well.

Good luck!

[destriaero]

As said above recheck your resistor and capacitor values making sure you didn't do a mistake. Also check that everything grounds correctly.

[ymjon]

i had this exact problem when i built my ggg muff.  it turned out to be one of the resistors toward the end of the signal chain, just before the output.  i didnt catch it til the 2nd time i looked them all over but i used the wrong value by a factor of 10.  those 5 band blue resistors are easy to misread if both ends have a brown band.

Will re-check this, you are definitely right about the 5-band with brown on both ends.

For sure you have some problems on Q4's collector.
The voltages on all 4 collectors must to be around 4.5V (half of the power supply), as you can see in the instructions:
http://www.generalguitargadgets.com/pdf/ggg_bmp_instruct.pdf.

yeah, I saw that but wasn't sure because I didn't know if the difference in versions would give different readings.

Thanks for the suggestions, will check and then report back.

[petemoore]

  Collector toward the middle of the PS rails gives it room to swing to + and - from there without hitting a rail.
  Base needs to be 1 diode drop above emitter.
  [all four transistor stages in the BMP being voltage gain]
  When things are 'right, the voltages will reflect fairly closely with these statements.

[ymjon]

  Collector toward the middle of the PS rails gives it room to swing to + and - from there without hitting a rail.
  Base needs to be 1 diode drop above emitter.
  [all four transistor stages in the BMP being voltage gain]
  When things are 'right, the voltages will reflect fairly closely with these statements.

I wish I could understand this...


anyways, I checked all the resistors and caps, and they all look to be the right values.
Didn't de-solder and measure any of the resistors but I calculated what the reverse read values were for the resistors in the output section and they weren't values that were included in the kit.

I audio probed the circuit from output to q4 and the volume drop looks to be between Q4's base and collector (loud at base, quiet at collector).
Is Q4 supposed to be like that or could that be that be the problem, could Q4 be bad?

[ymjon]

So is Q4 bad, or is it supposed to behave like that? Or is there something else I can check?

[slacker]

Q4 could be bad. Like other people have said the voltages should be similar to the other 3 transistors.
So you've either got a short somewhere or an incorrect part value or something not connected right. If you've double checked all those things then Q4 might be bad, or it could be in the wrong way round.
If you've used sockets just swap it with one of the other ones and then check the voltages for Q4, if they're now correct then the transistor was bad. If not you've got another problem. If you've soldered the transistors in, then I would replace Q4 and see what happens.

Welcome to the forum

[ymjon]

Q4 could be bad. Like other people have said the voltages should be similar to the other 3 transistors.
So you've either got a short somewhere or an incorrect part value or something not connected right. If you've double checked all those things then Q4 might be bad, or it could be in the wrong way round.
If you've used sockets just swap it with one of the other ones and then check the voltages for Q4, if they're now correct then the transistor was bad. If not you've got another problem. If you've soldered the transistors in, then I would replace Q4 and see what happens.

Welcome to the forum

Thanks,

Traded out Q4 and got the same result so I guess it's back to checking component values and looking for shorts

[gigimarga]

Recheck the resitors values...I had a lot of troubles with a Triangle because I used a 10K instead of 120 ohms (same colors!!!)

[ymjon]

Recheck the resistors values...I had a lot of troubles with a Triangle because I used a 10K instead of 120 ohms (same colors!!!)

Finally fixed it, you were exactly right. I had a 120 ohm resistor where I needed a 10k resistor (R24 btwn V+ and Q4's collector).

Thanks everyone so much for the help,

Jon

[gigimarga]

Glad to help you!