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!

 

[BuddytheReow]

Clean your board with some isopropyl alcohol and repost your pics. Be careful not to get any inside the pots. You may have some bad solder joints that need retouching.

 

[Mcknib]

What's Q2 collector voltage when you say the vrefs are correct do you mean transistor voltages

 

[PangeaDestructor]

What's Q2 collector voltage when you say the vrefs are correct do you mean transistor voltages

I wasn't sure what to call them here, since vref is usually half the supply. I meant the points on the schematic in the build doc that say voltage should be 9v or -9v are measuring approximately those values.

q2 collector voltage is right around 9v, trimpot increases and decreases it by a max of about 0.2v.

 

[jwin615]

Did you try it with the sundial pot turned to both extremes?
It's in series with Q2 bias.
Do you have an audio probe?

 

[jwin615]

Resistors all check out
Can't see the cap value.

 

[PangeaDestructor]

Did you try it with the sundial pot turned to both extremes?
It's in series with Q2 bias.
Do you have an audio probe?

I'll fiddle with the sundial pot again, I was trying to bias with that set at noon - but the bias trimmer doesn't really change much.

I do have an audio probe, but it seems like there's a substantial volume drop after every component and the "loops" in the circuit always throw me a bit when trying to follow the signal.

 

[PangeaDestructor]

Resistors all check out
Can't see the cap value.

I confirmed that all cap values and orientations are correct

 

[Harry Klippton]

I built some pedals recently using the sunflower schematic as a starting point and found that I needed to switch to a 10k bias trimmer to get the bias where I wanted it. You still haven't told us what your collector voltages are

 

[PangeaDestructor]

I built some pedals recently using the sunflower schematic as a starting point and found that I needed to switch to a 10k bias trimmer to get the bias where I wanted it. You still haven't told us what your collector voltages are

I'll check those transistor voltages tonight after work and post them up here, meant to include them in my original post.

q2 collector is right around 9v.

 

[Harry Klippton]

q2 collector is right around 9v.

Well that's not right at all

 

[Harry Klippton]

You should have a negative voltage on the collectors, and you want q2 to be around -4.5v. if you're getting "9v" whether it's + or -9, that can often be a missing ground connection through the emitter(s)

 

[jwin615]

Fuzz pot should be B1k and is B5*¿
That's going to shift both resistance to ground and the filter corner frequency.
I'd check that bias trimmer for proper functionality as well.
Pin 2 3 will be zero ohms
Pins 2/3 to 1 should sweep from near zero to 5kohm.

 

[Mcknib]

Q2 collector voltage should be anything from minus 4.5 to minus 7v or whatever sounds good to you

What I'd do is set the bias trim to maximum resistance (fully CW) check you get max resistance across pins 1 and 3 to make sure it isn't faulty as @jwin615 says

Set sundial to minimum resistance fully CCW to get as close to the original 8K2 collector resistance as you can, the bias trim, R3 and 4 would give you around 6K5 you can check resistance obviously with no power to the circuit from -9v side of R4 to Q2 collector and turn the sundial up if you want exactly 8K2

R4 isn't part of the audio path because it goes to a reference voltage you'd obviously only get audio one side, again I don't know but perhaps C1 neg side audio being low is because the transistors aren't biased correctly and it's having a knock on effect

Edit: basic audio path: you will get audio
in places like R2 bottom side etc but it's not part of the audio path

 

[PangeaDestructor]

You should have a negative voltage on the collectors, and you want q2 to be around -4.5v. if you're getting "9v" whether it's + or -9, that can often be a missing ground connection through the emitter(s)

With all the pots at max, transistor voltages are

Q1 E 0.00, B -0.072, C -0.255
Q2 E -0.273, B -0.247, C -9.02

 

[PangeaDestructor]

Fuzz pot should be B1k and is B5*¿
That's going to shift both resistance to ground and the filter corner frequency.
I'd check that bias trimmer for proper functionality as well.
Pin 2 3 will be zero ohms
Pins 2/3 to 1 should sweep from near zero to 5kohm.

Using the pinout in the bottom left of this image (https://i.pinimg.com/736x/d4/1e/99/d41e99c7407ae218cfbe7ef4b2d57f5c.jpg), i get the sweep from ~0 to 4.7k between pins 1-3 and 2-3, and 0 ohms from 1-2.

 

[Mcknib]

With all the pots at max, transistor voltages are

Q1 E 0.00, B -0.072, C -0.255
Q2 E -0.273, B -0.247, C -9.02

Voltages should be more like

Q1 C. -1.4v
B. - 0.6v
E. - 0v

Q2 C. - 4.5 up to around - 7v
B. - 1.4v
E. - 0.8v

Your transistors aren't conducting correctly

Check what resistance you get from R4 to Q2 collector the points in red with sundial and bias fully CW then CCW

Again don't power the circuit for resistance checks

 

[Big Monk]

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.

 

[jwin615]

Fuzz pot should be B1k and is B5*

 

[PangeaDestructor]

Voltages should be more like

Q1 C. -1.4v
B. - 0.6v
E. - 0v

Q2 C. - 4.5 up to around - 7v
B. - 1.4v
E. - 0.8v

Your transistors aren't conducting correctly

Check what resistance you get from R4 to Q2 collector the points in red with sundial and bias fully CW then CCW

Again don't power the circuit for resistance checks

View attachment 80914

with sundial and bias fully CW, resistance is 9.06k ohms. Fully CCW it's 1.416k ohms.