Losing signal through darlingtons (in Scrambler)

[mark2]

I have an 250/Dist+ overdrive going into a Scrambler, and I'm struggling to get a signal through Q1.

I tried an MMBTA14 and a BC517. I double checked the pin orientation (perhaps should triple check?).

I can hear a signal loud and clear going into the base, but nothing from the emitter.  Any advice on what to look for or what to change?

Update: Voltages are
C: 8.45V
E: 5mv
B: jumping around, often hovering around 200mV

[iainpunk]

you forgot the input cap.
should go in front of the two 1M resistors, after the volume control of the previous pedal

cheers, Iain

[antonis]

Check for R11 very low value (4R7 or so..) 

[mark2]

Check for R11 very low value (4R7 or so..) 

Unfortunately that wasn't the case. It's 4k7

you forgot the input cap.

I didn't think I needed one, but will certainly add one on the next iteration. I just measured and there's only a tiny DC offset so I'd guess it's not related to this problem. Though of course worth fixing, thanks!

Any other ideas? This seems so odd to me.

[antonis]

Iain is right..!! 
(my bad about R11..)

LEVEL pot wiper-lug1 is effectively set in parallel with R10, dramatically lowering Base bias..
(even with pot set FCW, Base DC level is lower than Darlington V_BE..)

[mark2]

Thank you both. Sounds like I was too quick to assume it was an unrelated problem.

I'll clip that pot leg and stick a cap in there and see how it behaves, and report back.

[iainpunk]

Quote from: iainpunk on Today at 14:47:20
you forgot the input cap.

I didn't think I needed one, but will certainly add one on the next iteration. I just measured and there's only a tiny DC offset so I'd guess it's not related to this problem. Though of course worth fixing, thanks!

that is 100% the cause of the problem, i bet my whole salary of this year on that

cheers, Iain

[mark2]

that is 100% the cause of the problem

Thanks again! I should not have made assumptions that it was unrelated and will definitely fix it and see if it works (or more likely, what the next problem turns out to be  )