Big Muff, little sound :(

[carboncomp]

The caps in question are 100nf ceramics, and on the layout it has R8 omitted on the rams head.

[Jdansti]

I'm certain the missing R8 on the schematic you're looking at is an error. I've looked at several schematics for the Ram's Head and they all have a 100k on Q2 where your R8 is. Here's one example. The resistor on this schematic is labeled R16.



If you drop a 100k in the R8 holes, that sucker should work.

[carboncomp]

put in the 100k and the Q2 collector has jumped from 1.2v to 3.5v, but there is still no noticeable effect on the output, just a little more gain  

[Jdansti]

Ok. I went to the Tonepad site and it appears that you're doing the "triangle" muff. You're correct that there is no R8. I don't understand how Q2 is supposed to bias without R8, but apparently it's supposed to work. I noticed that this version also omits C2, but it looks like you've decided to keep it. The other difference between the stock and triangle versions is many of the resistors and capacitors have different values.



Going back to one of your first statements that it was working and it stopped working after you boxed it, I think the next thing I'd do is reflow all of the solder joints including the pots and jacks, clean off the flux, and look for solder bridges. If that doesn't help, I'd replace Q2 (I can't recall if you said that you've already done this.  This is a tuff one!!!

[DiscoVlad]

Ok. I went to the Tonepad site and it appears that you're doing the "triangle" muff. You're correct that there is no R8. I don't understand how Q2 is supposed to bias without R8, but apparently it's supposed to work.

The base hopefully gets pulled up to bias by the 470k resistor between the base and collector. It lets a very small current flow into the base of the transistor, and out through the emitter (and emitter resistor to ground) which lets the transistor turn on.

The bias point is arrived at from a lot of assumptions:
Transistor gain, estimating the base current from that, then guessing at a voltage drop across the resistor from those...

The problem with this way is that the bias point becomes dependent on the transistor's Hfe which can vary a lot (the Art of Electronics has a schematic [pg. 72] illustrating this way of biasing with the caption "Don't do this!").

Adding in the 100k to ground makes the bias point the same regardless of what transistor you use.

[Pyr0]

ok, going back to your voltages  -
   Q1
    C 4.33v
    B 3.49v
    E 4.18v

Q1 is wrong, the base should be higher then the emitter. You also have a 3.6k resistor on the base and schematic says it should be 3.3k, but I doubt that would make such a big difference.
I noticed your using solid core wire, this can put stress on the copper pads and can cause hairline cracks where the pad joins the rest of the track, so it might be worth checking continuity from the pots to the next component in the schematic. i.e dont just check continuity from the pot to where the wore goes into the board, but check it to the adjacent component.
When using an audio probe on it, there should be a noticeable increase in sound on the collector of Q1, it's configured as a clean boost stage, if the volume is not getting boosted from Q1 then the problem lies there, again Q1 voltages are not correct - unless you mixed up the B and E voltage readings when you first took them.
What transistors are you using ? 2N5088's ?
There are also a few dodgy looking solder joints, base and emitter of Q1 look like they could do with a reheat, and the 100k resistor ground connection on the base of Q4 looks suspect.

c'mon man get this working - you can do it.