Low-Draw Devi Fuzz Needs More Than 9v... Why?

[GAStan]

Is Q1 base biased  too high? It looks like Q1 is fully conducting (on). This would indicate too high of voltage on the base. this will give very asymmetrical clipping. What kind of clipping is desired? For symmetrical shouldn't the collector be at ~4.5 - 5 volts?

But the pedal sounds good with the current Q1 and Q2 setup.

As far as checking voltages I see the biggest change in Q4 (2N2222A), the next biggest at Q3 (MPSA18).

@Ginsly what do you have available for test equipment?

 

[PedalBuilder]

Tried a bunch - 180k, 100k, 47k... not a huge difference when it comes to the "low" 9v behavior. Hmm.


Yep! No clue. The breadboarded circuit works great, it's just odd that it quiets/fades so severely with a voltage that's still around 9v... Since the stripboard pedal and this breadboard (one based on a layout, one on the schematic) exhibit the same behavior, I have to assume it's normal for the circuit... ??? 2mA power consumption, but starts to lose tons of volume/texture at like 9.2v...

If you're powering the circuit with a 9v power supply and have the negative side of the power supply connected to ground, it's not possible that there is a negative voltage at the base of Q3. As an additional matter, are you sure that you have the pinout of Q3 correct? The collector voltage is way too high.

Huh, that's very strange about the first 2N2222A... why the heck is it there?? I take it the US sounded good when you breadboarded it based on the above schematic.

It's being used as a diode, similar to the Bazz Fuss.

 

[Ginsly]

I wonder if you aren't getting some sort of high frequency oscillation. By any chance do you or anyone close to you have an o'scope?

I don't hear any high frequency oscillation. I just got a crappy little portable o-scope but haven't used it yet! I also have a couple multimeters, of course.

If you're powering the circuit with a 9v power supply and have the negative side of the power supply connected to ground, it's not possible that there is a negative voltage at the base of Q3. As an additional matter, are you sure that you have the pinout of Q3 correct? The collector voltage is way too high.

I agree, it's very strange. The pinouts on all transistors looks to be correct - double checked on the breadboard and vero pedal (via TC-1) just to make sure. Both circuits work and sound as they should...

I just took some new measurements, and I don't know what to make of it. I'm leaving the first 2N2222A out of the equation, as like you said, it's a diode here. I also swapped out the metal can 2N2222A in Q4 for a 2N3904 of similar hfe just to see what happened. They sounded pretty much identical.

Used the same Truetone CS-6 9v supply for both:

Breadboard Version:

Q1 (MPSA18) - 0 / .53 / .72
Q2 (MPSA18) - 0 / .6 / 3.14
Q3 (2N2222A) - 0 / -1.6 / 9.2

Vero Version:

Q1 - 0 / .55 / .67
Q2 - 0 / .6/ 2.6
Q3 - 0 / 0 / 9.1

 

[pbrommer]

I don't hear any high frequency oscillation. I just got a crappy little portable o-scope but haven't used it yet! I also have a couple multimeters, of course.


I agree, it's very strange. The pinouts on all transistors looks to be correct - double checked on the breadboard and vero pedal (via TC-1) just to make sure. Both circuits work and sound as they should...

I just took some new measurements, and I don't know what to make of it. I'm leaving the first 2N2222A out of the equation, as like you said, it's a diode here. I also swapped out the metal can 2N2222A in Q4 for a 2N3904 of similar hfe just to see what happened. They sounded pretty much identical.

Used the same Truetone CS-6 9v supply for both:

Breadboard Version:

Q1 (MPSA18) - 0 / .53 / .72
Q2 (MPSA18) - 0 / .6 / 3.14
Q3 (2N2222A) - 0 / -1.6 / 9.2

Vero Version:

Q1 - 0 / .55 / .67
Q2 - 0 / .6/ 2.6
Q3 - 0 / 0 /

I’m stumped, but vested in helping. That Q3 negative voltage is making me question what’s going on. Maybe try a new cap that lead to the 100k resistor. [edit: try the cap from your board in the breadboard first - it will change the voltages if it’s bad in your working verision]Also, did you pull that second 100k that is attached to the Collector of Q3 (the red text asterisk)? Again, still spitballing places to look

 

[Ginsly]

I’m stumped, but vested in helping. That Q3 negative voltage is making me question what’s going on. Maybe try a new cap that lead to the 100k resistor. [edit: try the cap from your board in the breadboard first - it will change the voltages if it’s bad in your working verision]Also, did you pull that second 100k that is attached to the Collector of Q3 (the red text asterisk)? Again, still spitballing places to look

I pulled BOTH C-B 100k resistors for the last transistor, as it seems that’s the correct setup- I tried putting one in (which the “multi-schematic” seems to indicate), but it sounded awful and squealed like crazy! The guy who did the Vero layout did some digging and Devi said to leave both off for the US.

I’m not sure which cap you’re suggesting I swap- There’s only one 100k resistor, and it connects the final transistor’s C to power. That transistor’s 1nf cap is omitted for the US Fuzz version, according to the schematic. So I have nothing connecting B and C and no cap to power.

 

[PedalBuilder]

Used the same Truetone CS-6 9v supply for both:

Breadboard Version:

Q1 (MPSA18) - 0 / .53 / .72
Q2 (MPSA18) - 0 / .6 / 3.14
Q3 (2N2222A) - 0 / -1.6 / 9.2

You should post a picture of the breadboard and show us where you are connecting the red and black probes on your multimeter. It's not possible that you connected everything properly and ended up with a negative voltage on the base of Q3.

I breadboarded the third stage, and you should be getting something like E= 0v, B=0.56v, C= 0.7v on Q3.

 

[pbrommer]

I pulled BOTH C-B 100k resistors for the last transistor, as it seems that’s the correct setup- I tried putting one in (which the “multi-schematic” seems to indicate), but it sounded awful and squealed like crazy! The guy who did the Vero layout did some digging and Devi said to leave both off for the US.

I’m not sure which cap you’re suggesting I swap- There’s only one 100k resistor, and it connects the final transistor’s C to power. That transistor’s 1nf cap is omitted for the US Fuzz version, according to the schematic. So I have nothing connecting B and C and no cap to power.

I missed the asterisk on the schematic! D’oh

 

[Ginsly]

You should post a picture of the breadboard and show us where you are connecting the red and black probes on your multimeter. It's not possible that you connected everything properly and ended up with a negative voltage on the base of Q3.

I breadboarded the third stage, and you should be getting something like E= 0v, B=0.56v, C= 0.7v on Q3.

I must be measuring incorrectly, at very least. I was under the impression that I connect MM black to ground and then touch red to each leg of each transistor (with circuit powered and "on"). Please correct me if that's wrong - haven't done this kind of troubleshooting much.

I just re-checked the Q3 (now 2N3904 instead of 2N2222A) base of both the breadboard and stripboard pedal. -2.83 on BB and -.61 on pedal. Not a clue. The black MM lead at the bottom of the first pic goes to ground, and you'll see the red lead touching the Q3 (followed by the MM reading). It's also wild that I'm getting the full 9v at Q3 C whereas you are getting .7v.

Also - when you set yours up, what exactly was connected to Q3 (2N2222A)? According to DE's multi-schematic, the 1nf-to-power is omitted for the US Fuzz and even though it says to omit only one of the B-C 100k resistors, it seems that neither one should be there in the US Fuzz - so now nothing connects them, as in the vero layout - no cap to power either. I have a 10nf cap between Q2 C to Q3 B, Q3 E to ground, 100k from Q3 C to power, and a 20nf cap leads to the Volume pot.


Pedal:

 

[Ginsly]

View attachment US Fuzz.mp3
Something may very well be off, but still... they both sound pretty good! This is the pedal I built about a year ago. Bad Iphone recording through my little Boss desktop amp.

 

[GAStan]

I don't hear any high frequency oscillation.

I was actually at a frequency too high to hear, that's why I was asking about an o'scope.