Muff build, getting 0v all across one of the transistors?

Started by carboncomp, February 12, 2015, 06:57:44 PM

Previous topic - Next topic

carboncomp

Having a little trouble with this Muff build, getting 0v all across one of the transistors, and can see any shorts?


carboncomp

#1
Solved, the 20K resistor was duff!

Turns out that was not the problem, still getting 0v

Seljer

The emitter is connected to ground over the 100ohm resistor

Theres the 470kohm feedback/bias resistor between the base and the emitter.

There should a resistor from the collector to your +9V supply (value allegedly 12k or 15k but there are a bunch of big muff variants). I don't see this one at all on the layout. The 20k that is there connected to the collector next to the diodes is already part of tone control.

CodeMonk

Quote from: Seljer on February 12, 2015, 08:16:04 PM
The emitter is connected to ground over the 100ohm resistor

Theres the 470kohm feedback/bias resistor between the base and the emitter.

There should a resistor from the collector to your +9V supply (value allegedly 12k or 15k but there are a bunch of big muff variants). I don't see this one at all on the layout. The 20k that is there connected to the collector next to the diodes is already part of tone control.
This.
The Collector doesn't seem to have a voltage source.
12k or 15k is "normal", although I have seen 10k or 22k depending on which muff version it is.

carboncomp

So, i can just slap a  10k to 22k from VCC to the Collector and im good?

Any other fults on this layout? 

antonis

If you're still getting 7.2mV at Q1 & Q2 Bases the Q3 Collector resistance will not help...
(it's necessary for powering Q3 but it has nothing to do with other transistors biasing..)
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

GibsonGM

Quote from: CodeMonk on February 12, 2015, 08:38:02 PM

This.
The Collector doesn't seem to have a voltage source.
12k or 15k is "normal", although I have seen 10k or 22k depending on which muff version it is.

See why layouts are nowhere near as good as a schematic??   It LOOKS to me (and Rob) like Q3 has no collector resistor.   If resolved, THEN you have to look at what Antonis said about improper biasing on  Q1 and Q2.

Is this layout 'approved', as in - tested and known to work?  There seem to be a few issues...
  • SUPPORTER
MXR Dist +, TS9/808, Easyvibe, Big Muff Pi, Blues Breaker, Guv'nor.  MOSFace, MOS Boost,  BJT boosts - LPB-2, buffers, Phuncgnosis, FF, Orange Sunshine & others, Bazz Fuss, Tonemender, Little Gem, Orange Squeezer, Ruby Tuby, filters, octaves, trems...