Dirt Transmitter clone no signal / sputtery at low bias

[tefanone]

Hi all, had a few successful builds after a shaky start and helpful advice on here.  I've an issue with my latest though:

1. Dirt Dealer Fuzz (based on EQD Dirt Transmitter), PCB from Fuzzdog.
2. All build as per schematics, images plus schematic attached.
3.  No modifications
4.  Polarity as per schematic
5.  At low bias there is no signal at all. As it gets to about 9 o clock, it's faint and very sputtery (much moreso than it should be), improving as the Bias is maxed.  The other controls work fine.

I've checked my soldering and redone connections, not sure what the issue is. Faulty / overheated 2N1711s? I had them flush with the board but redid and gave them a mm or so clearance.

Voltages below:

Dirt 1,2,3 - 0V

Bias  1: 4.7   2: 4.7  3: 1.69

Vol 1,2,3 : 0

Tone 1,2,3: 0

V+: 9.3
G: 0
IN: 0
OUT: 0

Q1: min to max bias

B: 0.76 - 0.90
C: 1.75 - 2.05
E: 0.19 - 0.31

Q2: min to max bias

B:  1.75 - 2.05
C: 1.14 - 4.7
E: 1.11 - 1.41

D1:  0, 9.3

C1: 0, 0
C2: 0, 0.9
C3: 0, 0.9
C4: 1.66, 2.04
C5:  0,  0.31
C6: 0, 1.66
C7: 0,0
C8: 0, 0
C9: 0, 1.4
C10: 0, 9.3

R1: 0,0
R2: 0,0
R3: 2.04,  9.3
R4: 0.86, 1.4
R5: 0, 1.4
R6: 0, 0.31
R7: 4.7, 9.3
R8: 0, 0
R9: 0, 0

[antonis]

Bias  1: 1.46   2: 4.9  3: 4.9

Q1 E: 2.04  B: 0.9  C: 0.31
Q2 E: 0 B: 2.04 C: 1.4

C4: 1.66, 2.04

You've mixed Bias pot 1 & 3..
(1 & 2 should have the same voltage and 3 should have the lower one ..)

Q1 seems to be OK (more or less)  but Q2 is out of order..
(Q1 Collector & Q2 Base should exhibit the same voltage.. Q2 Emitter should stand on 1.4V, like upper leg of R5.. C4 right leg should exhibit the same voltage of Collector, instead of Base..)

[tefanone]

Well spotted! Thanks. I was mixing up the legs on the schematic vs the physical image of the transistor.  Figures revised - the 0 value was erroneous.

[nocentelli]

So the bias control is not useful over the lower range but sounds ok as it maxes out? What range of voltages do the collectors move between as you twiddle the bias?

[tefanone]

So the bias control is not useful over the lower range but sounds ok as it maxes out 4.7 volts?

Yes, that's correct.

[tefanone]

What range of voltages do the collectors move between as you twiddle the bias?

Good pointer, thank you; I'll check in the morning.

[tefanone]

So the bias control is not useful over the lower range but sounds ok as it maxes out? What range of voltages do the collectors move between as you twiddle the bias?

EDIT - got Q1 and Q2 mixed up, correction as below.

Just checked, came up with the following:

Q1: min to max bias

B: 0.76 - 0.90
C: 1.75 - 2.05
E: 0.19 - 0.31

Q2: min to max bias

B:  1.75 - 2.05
C: 1.14 - 4.7
E: 1.11 - 1.41

[tefanone]

After fiddling around I now have 9.3V across R7 and cannot figure out why.  Tried tracing continuity across the circuit but nothing untoward. Think this is one for the bin and redo with new components.

[duck_arse]

if you're going to bin it anyway, you might as well convert it to positive ground, if for no other reason than practise. it should have been pos ground from the start, anyway.

[tefanone]

Well, after further analysis I think there was an issue with the circuit by the bias knob (unsurprisingly). After further swearing, bit of extra wiring and testing.... it works! Rather good it is too. And somewhat cheaper than the £170 for a new one :-)

Thanks folks again for the assistance.  Further lessons learned on this one and getting more au fait with layouts.