Triangle Big Muff Clone - Very Low Output Problem

[SeymourDunk]

I have already built a "Stock Big Muff" from Tonepad which works, yet for some reason this Triangle Big Muff wont work.

The signal works fine when bypassed and I can hear my guitar fine but when the effect is engaged the sound is hardly audible... have to crank my amp to a stupid level to hear anything.

Thought the issue might have been with R8 and C2 being blank so i ran a jumper but that didnt help

Q1
E - 0.16V
B - 0.74V
C - 4.45V

Q2
E - 0.095V
B - 0.70V
C - 1.20V

Q3
E - 1.19V
B - 1.77V
C - 3.70V

Q4
E - 7.48V
B - 8.26V
C - 7.49V

[nocentelli]

Thought the issue might have been with R8 and C2 being blank so i ran a jumper but that didnt help



Q2
E - 0.095V
B - 0.70V
C - 1.20V

From the tonepad layout pdf, R8 appears to be the base-to-ground resistor for Q2 (usually 100k), I think it is needed for correct biasing of this stage. BMP collectors tend to sit around 4-5v, with Q1-3 all fairly similar.

[antonis]

Q4 measurements are all wrong..
(don't stand even for a saturated BJT..)

[anotherjim]

The emitter resistor for Q4 is either missing or very much too high in value. Check your resistor colour bands.

[SeymourDunk]

(blank)

[SeymourDunk]

The emitter resistor for Q4 is either missing or very much too high in value. Check your resistor colour bands.

Are you referring to the 2K7 resistor near Q4?

I measured it with a multimeter and it is correct

[SeymourDunk]

Tonight i went through every resistors colour band and every capacitor value - all match as per tonepad schematic. all transistors are in correct position as well as diodes

only explanations i can think of is faulty transistors, faulty foot switch, faulty pot, solder bridge/cold joint (cant see any), or layout for 'triangle big muff is incorrect.

Pulled apart my other 'original big muff pi' pcb and everything looks the same (postion wise) except for the electrolytic 1uf caps

[antonis]

Whta's the purpose of wire jumper between upper end of "blank" resistor and "somewhere" near bottom end of 22k & 390k..??

[anotherjim]

I don't know what schematic you are working off. For BMP, the transistors are numbered in reverse order with Q4 the first stage.
I now see that this is numbered backwards and Q4 is the last stage.

Q4
E - 7.48V
B - 8.26V
C - 7.49V

This can't be right. The emitter should be at a lower voltage. If the resistor is good, then the connection to ground from that 2k7 resistor might be an open circuit or the transistor is fried. Q4 emitter should be at a much lower voltage.
With a home etched pcb, there is always the chance of a fine break in trace continuity. Using a DMM that has a continuity beep/buzzer built-in is a powerful way to test that point A really does connect to point B and not just look like it does.

[SeymourDunk]

I managed to find a post on a forum from August 21, 2008 which stated there were problems with schematic i was using. This lead me to search and find other schematics.

Tonepad schematic



Schematic from other source




What I have learnt is that the schematic ive been using is horribly wrong, there are so many component values which are incorrect.

I subbed in the correct components and their was a much better result (effect volume was louder) although im still experiencing some issues. I am going to etch a new board and restart it now that i know what issues are.

Thanks for all the help, greatly appreciated!

[GibsonGM]

I subbed in the correct components and their was a much better result (effect volume was louder) although im still experiencing some issues. I am going to etch a new board and restart it now that i know what issues are.

Better result when that bottom schematic calls for PNP transistors, but you're using NPN???      

I would've used an audio probe, personally.  Tonepad is known for being a reliable resource.  It's almost ALWAYS a build error on our side... 

[MaxPower]

Both schematics have the same resistor values in the final stage. If you don't want to use ohm's law to figure out the base voltage at the least, there's ltspice or tina-ti to simulate the circuit and see what voltages you should have.

[MaxPower]

Base should be about 1.8v. Emitter voltage about 1.2v. Those are ballpark figures. The collector, I'm guessing, is biased to be close to 1/2 the power supply (4.5v).

[anotherjim]

The Kit Rae schematics are generally accurate. You happen to have chosen a rare PNP version. Apart from PNP versus NPN transistors - it has a positive ground power supply.
Note the polarity of the battery. In the original EXH production, these pedals were always battery power only, so a PNP version only needed the battery wires reversing. Test voltage readings will be negative.

There is no such thing as a single defining build standard for the Triangle Big Muff! The only thing that makes it Triangle is the panel layout.