# Tonebender with sputtery/gates fuzz



## aefpv (May 10, 2022)

I was making a Guitarpcb Pump'd up Tonebender, v4. I am able to get fuzz, but it is sputtery/gated and at a lower volume. Below are my voltages for the IC and germanium  transistors. I am worried that I blew two transistors (Q1 and 2). My father, who is a EE, walked me through the process to test the transistors with a volt meter, comparing the resistance of the B to each C and E. I am confused how the pedal can potentially have two blown transistors and still work, creating fuzz (yet bad fuzz). The transistors were matched for Q1 and Q2. Q 3 has the highest hFe. To test, I swapped out all the transistorss with a 2n3906 (PNP) transistors, but I still received poor fuzz. 

Do these symptoms appear consistent with blow transistors or could the problem be elsewhere? To me, it sounds like a biasing issue. Any suggestions are appreciated. Thanks for your time. -Andrew

Power supply: 8.85 V
IC 1: 8.66 2: 4.59 3: 0 4: -3.97 5: -8.51 6: 2.53 7: 1.43 8: 8.66

Q1 B: -0.01 C: -8.43 E: 0

Q2 B: -0.16 C: -8.43 E: 0

Q3 B: -5.04 C: -0.44 E: -0.32


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## Coda (May 10, 2022)

Use the trimpot to set the bias of Q3: with the pedal powered on, put the positive from your multimeter on the leg of the collector at Q3, and place the negative probe to anything that ground (negative lug of power jack for example). Next, start turning the trimmer until the voltage reads around 4.5v. Doesn’t have to be perfect. You may even want to get it closer to 5v.


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## aefpv (May 10, 2022)

Yes. I played around with the trimmer. It does help to adjust the voltage, but the fuzz is still gated (even at lower voltages). The gating is most notable when plucking single notes on the high E and B strings. With chords, the fuzz is not terrible.


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## aefpv (May 10, 2022)

Another added question: If the transistors are bad, would the pedal be able to produce fuzz or operate?

I am trying to avoid another purchase of transistors, but suspecting that I might be forced to do so. Thanks


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## Mcknib (May 10, 2022)

If you got a matched set of transistors make sure you put the correct hFE in the correct transistor spot

Your charge pump voltages look fine and should be quiet if it's a 7660S the S being critical for a whine less charge pump

Q3 collector as @Coda says needs to be biased anywhere from - 4.5v to - 8v or whatever sounds best to you

I find when I use those Russkies I bias them at a higher voltage obviously depending on hFE

Your Q2 collector and Q3 base voltages don't look correct to me

Doubtful your transistors are damaged it looks like you've socketed them?

Your pics out of focus can't quite make out your 1Ms multiplication band if it's green all good


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## aefpv (May 10, 2022)

Yes. The transistors for Q1 and 2 were matched. Any suggestions to rectify the Q2 and 3 voltages?


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## Bret608 (May 10, 2022)

I see you have a couple of Russian transistors there. Make sure you have the correct legs in the correct positions. Guitar PCB's board is set up for and EBC pinout, but I think a lot of the Russians are something like ECB. That could explain the odd voltages. In particular, the Q2 collector should be less than -0.50v, and the Q3 collector should be at least -5v (and historical ones could be up to -8v due to leaky transistors).


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## Mcknib (May 10, 2022)

I wondered why Q1 looked different tone bender matched sets are all 3 matched

Did you put the correct hFE transistor in the correct spot for the matched one's

If you look at Q2 and 3 part of the schematic it's a fuzz face set up

So you'd want hFEs of Q1 60 to 70, Q2 60 to 70 Q3 100 to 120, hFE value isn't absolutely critical more you want the lower values for Q1 and 2, higher for Q3 to make biasing easier


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## aefpv (May 10, 2022)

I just saw a typo. Below was my actual readings for Q 2. Sorry for the confusion. 

Q2 B: -0.16 C: -0.44 E: 0


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## Big Monk (May 10, 2022)

Are we using the correct term? Gating would be voltages near the power rail, while sputter/Velcro tends to be undervolted. 

I’m not familiar enough with this circuit to quote correct voltages but just want to be sure we are using the same language.


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## Mcknib (May 10, 2022)

Here's voltages from a man that knows fuzz Electric Warrior

Voltages from his original




This using the same as the gpcb schematic with 100K resistors on Q1 base and Q2 collector

Your Q3 voltages aren't correct base  - 5.04? it should be the same as Q2 collector voltage which in turn should be much lower

Did you measure your resistors are R2,4 and 5 definitely 100K read the other way they'd be 130R might explain why Q2 collectors voltage is so high etc


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## aefpv (May 10, 2022)

I would characterize it best as sputtering and Velcro. 

As for Q 3 base, I can get close to -8v by using the trimmer. 

Based on the above voltages, my Q2’s C looks higher than the above values. I guess that I could raise the 100 k resistor on Q2. Would that be wise?

So- I think my evenings work will focus on making sure that the transistors are placed correctly for each lead. Double check the locations of the transistors based on reported hFe. 

If there are other “to do” ideas, let me know.


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## Mcknib (May 10, 2022)

Make sure R2, 4 and 5 are indeed 100K see last comment

With no power to the circuit measure resistance from ground to the base of Q1 or top side of R2 and from Q3 emitter to Q2 base with attack turned up


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## Big Monk (May 10, 2022)

I thought from your OP that this was a MK IV!

Yes, something is up with your transistor voltages if this is a MK II. 

I would focus on Q2. You should not have anything g higher than around 300 mV at the collector of Q2. Get Q2 voltages in line and Q3 should fall into place. 

Also, if you are gating, try dropping the voltage of Q1 as well


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## aefpv (May 10, 2022)

Would trying a 150 K resistor for R4 be a good starting point to help bias Q2?


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## Big Monk (May 10, 2022)

Can you re-measure all your voltages and and source voltage and post them?


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## aefpv (May 11, 2022)

I think I have got it fixed!  Thanks for all with the help. The issues were as follows- Attack potentiometer was faulty and Q 3 was poorly seated in the socket. I also rebiased it with the trimmer and found the best sound with Q3 C near -7V.  

Regarding one of Big Monk’s replies, I still have Q2’s C at -0.39, so it is higher than he proposed. I think it sounds great, so I will likely leave it (unless there is a compelling reason to lower it). 

I can’t thank you all enough. It is helpful to have this support and camaraderie.


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## Bret608 (May 12, 2022)

Your Q2C should be fine with -0.39v. If it's in that range or ever a little higher, you will have better volume knob cleanup from your guitar (just maybe with a bit more background hiss). It should pair well with that -7.0v you have on Q3C as well. Anything below -0.20v on Q2C and you will hear more gating when you turn down your guitar volume. But it pushes Q3C up to -8v or higher, which is a great vintage sound which some say sounds ideal with humbuckers.

Glad you're liking it now! It is a cool circuit to learn from. Electric Warrior's information helped me quite a bit.


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## Big Monk (May 12, 2022)

Adjusting Q1c voltage down will also help cleanup, as will a Pregain control on the input. 

I like Q1c in the 7.8 vDC range and Q3c in the 7.6 vDC range but that brings more noise so you’ll need a combination (or all) of feedback bypass cap and base to collector caps on the transistors. 

I usually get my voltages where I want them, listen to the noise level, then do a
mixture of noise suppression caps and finally, tweak the input, output and emitter caps to get the frequency content I want back in line.


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## aefpv (May 15, 2022)

This is good information.  I like the sound, but I still might breadboard a second circuit and play around with the bias of the transistors.  I would be a good learning opportunity to learn how each piece interacts.  Thanks again


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## aefpv (May 10, 2022)

I was making a Guitarpcb Pump'd up Tonebender, v4. I am able to get fuzz, but it is sputtery/gated and at a lower volume. Below are my voltages for the IC and germanium  transistors. I am worried that I blew two transistors (Q1 and 2). My father, who is a EE, walked me through the process to test the transistors with a volt meter, comparing the resistance of the B to each C and E. I am confused how the pedal can potentially have two blown transistors and still work, creating fuzz (yet bad fuzz). The transistors were matched for Q1 and Q2. Q 3 has the highest hFe. To test, I swapped out all the transistorss with a 2n3906 (PNP) transistors, but I still received poor fuzz. 

Do these symptoms appear consistent with blow transistors or could the problem be elsewhere? To me, it sounds like a biasing issue. Any suggestions are appreciated. Thanks for your time. -Andrew

Power supply: 8.85 V
IC 1: 8.66 2: 4.59 3: 0 4: -3.97 5: -8.51 6: 2.53 7: 1.43 8: 8.66

Q1 B: -0.01 C: -8.43 E: 0

Q2 B: -0.16 C: -8.43 E: 0

Q3 B: -5.04 C: -0.44 E: -0.32


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## HamishR (May 18, 2022)

Bret608 said:


> I see you have a couple of Russian transistors there. Make sure you have the correct legs in the correct positions. Guitar PCB's board is set up for and EBC pinout, but I think a lot of the Russians are something like ECB. That could explain the odd voltages. In particular, the Q2 collector should be less than -0.50v, and the Q3 collector should be at least -5v (and historical ones could be up to -8v due to leaky transistors).


Every Russian transistor I have is CBE. If looking from underneath with the pins making a V shape (B being the point at the bottom of the V) they are C-B-E. I've never had a Russian transistor in a different configuration, although it is of course possible that they exist!


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