Sunflower Fuzz - Low, Gated Output, bias trim not working

[PangeaDestructor]

Such a simple build, I even got my Ge transistors as a selected pair (from Barry at guitarpcb). They are PNP, the pinout is correct, charge pump is from Tayda, everything looks right to me, the vrefs are correct. However, the bias trimpot does nothing (changes q2's range by about -/+ 0.2v), the output is low and gated - no sustain at all - with an audio probe I get a pretty substantial volume drop at the tail end of each component (e.g., signal is full volume entering c1 and barely audible leaving the capacitor, same with r4). Pics attached, including the charge pump voltage, any help appreciated!

 

[PangeaDestructor]

Check the connections to the fuzz pot.

This used to happen to me frequently on the breadboard and it was almost universally a poor connection to ground at the fuzz pot.

Start there.

Pin 1 is grounded, pin 2 i have continuity with c2, pin 3 i get continuity at both R1 and q1e

 

[Big Monk]

Pin 1 is grounded, pin 2 i have continuity with c2, pin 3 i get continuity at both R1 and q1e

Try 1k for the Fuzz Pot.

Also check the joints at C2. Especially the ground connection.

 

[PangeaDestructor]

Try 1k for the Fuzz Pot.

Also check the joints at C2. Especially the ground connection.

You mean replace the b5k with a b1k? Just making sure before i go digging for one, I may have that around somewhere.

I do get a ground connection on the + leg of c2.

Edit: I used a b5k when the fuzz pot should be a b1k. This is the kind of thing I do, so unsurprising to me but needed it called out by someone else. I see this noted in @jwin615 's comment earlier as well. Going digging, will report back - seems a likely culprit here.

 

[Harry Klippton]

You mean replace the b5k with a b1k? Just making sure before i go digging for one, I may have that around somewhere.

I do get a ground connection on the + leg of c2.

B5k for the fuzz pot is definitely wrong

 

[PangeaDestructor]

B5k for the fuzz pot is definitely wrong

Yep, I just replaced it with the correct value. Doesn't seem to have solved the issue, but it brought the q2c voltage down by about 1v (bias trim now adjusts it from about 7.2v up to 8.3v.

 

[Mcknib]

You could try tacking a 1K3 resistor in parallel across fuzz lugs 1 and 3 as a quick test to save you desoldering the pot

That'd change the pot resistance to just over 1K

*Edit too late haha, minus 7.2v bias should work especially with Russian transistors I usually bias some Russian transistors at around minus 7v on the collector for the best sound you are getting negative voltages aren't you?

 

[PangeaDestructor]

You could try tacking a 1K3 resistor in parallel across fuzz lugs 1 and 3 as a quick test to save you desoldering the pot

That'd change the pot resistance to just over 1K

Swapped out the pot for a b1k, since I had one in the pile. Doesn't seem to have solved the issue, but it brought the q2c voltage down by about 1v (bias trim now adjusts it from about 7.2v up to 8.3v.

 

[Mcknib]

Swapped out the pot for a b1k, since I had one in the pile. Doesn't seem to have solved the issue, but it brought the q2c voltage down by about 1v (bias trim now adjusts it from about 7.2v up to 8.3v.

Is that with the sundial pot fully CCW

 

[PangeaDestructor]

Is that with the sundial pot fully CCW

Yep, with sundial fully cw the bias range at q2c goes from 7.42 to 5.94

 

[Mcknib]

Yep, with sundial fully cw the bias range at q2c goes from 7.42 to 5.94

Fully ccw not cw, cw would be max resistance across the sundial

 

[PangeaDestructor]

Fully ccw not cw, cw would be max resistance across it

Right, but the numbers here are negative, so wouldn't the higher number range there actually be less voltage?

I attached a probe to q2c - turning the sundial ccw/left sent the reading to -8.3, turning it cw/right all the way was -7.2v.

 

[jwin615]

Just for a sanity check, what transistors did you purchase?Please reference the transistor, not the site/order email.

 

[jwin615]

Also, as asked before, do you have a probe? As far as I can tell, we are guessing here.
Just a pokey thing with a cap stuck in it.
I'm big on sanity checks, if you can't tell. But it would be good to know if you have audio into q2.

 

[Mcknib]

The bias trimmer and sundial are both wired as variable resistors with lugs 2 and 3 joined turning them clockwise should increase resistance across lugs 1 and 3 of both so they seem to be OK from your description

When I initially looked at your resistance values I thought R3 had a red multiplier band rather than brown but even zooming in I can't tell

Are R3 colour bands brown black black brown brown

 

[PangeaDestructor]

Just for a sanity check, what transistors did you purchase?Please reference the transistor, not the site/order email.

They're both MP21a

 

[PangeaDestructor]

Also, as asked before, do you have a probe? As far as I can tell, we are guessing here.
Just a pokey thing with a cap stuck in it.
I'm big on sanity checks, if you can't tell. But it would be good to know if you have audio into q2.

Sanity checks are necessary and appreciated, I have audio at all 3 legs of q2.

 

[PangeaDestructor]

The bias trimmer and sundial are both wired as variable resistors with lugs 2 and 3 joined turning them clockwise should increase resistance across lugs 1 and 3 of both so they seem to be OK from your description

When I initially looked at your resistance values I thought R3 had a red multiplier band rather than brown but even zooming in I can't tell

Are R3 colour bands brown black black brown brown

Under my magnifier it looks to me like brown black black brown brown, yes.

 

[Mcknib]

Those are normal CBE pinout how did you know the pinout where they marked or did you test them

Did you reflow any solder joints as @BuddytheReow said initially this one here on the bias trimmer doesn't look great

 

[PangeaDestructor]

Those are normal CBE pinout how did you know the pinout where they marked or did you test them

Did you reflow any solder joints as @BuddytheReow said initially this one here on the bias trimmer doesn't look great

View attachment 80946

Tested on my cheapo meter - even desoldered Q2 and put it back on the tester to make sure i had it right, because the output sounded like I'd reversed them. Didn't get a chance to reflow last night, but I'll hit that one today and see if it changes anything.

 

[Mcknib]

You can't really put them in the wrong way around I don't think the 2 inline pins would make it difficult

I'd reflow the bias trimmer joint first, check it, if it's still not right reflow every joint it's not that big a circuit