Tonebender MKII hum/whine question

[benny_profane]

I've built a Tonebender Mkii on the Aion Deimos board with a matched set of PNP transistors from Small Bear. I'm running the circuit with a voltage inverter (TC1044S) to get a positive ground from a standard wall wart. My voltages from the inverter look good. I've also been able to get a good bias (Q3=-4.5v from the SBE recommendations and Q3=-8.5v as well).

When I turn the attack knob past 3 o'clock, though, I get a hum/whine that sounds like a slightly sputtering D#4 with or without a guitar plugged in, both in and out of the enclosure, and from the wall wart and a battery.

I tried a 10pf capacitor between the Q2 and Q3 emitters. This didn't change much. I tried increasing the value to 100pf and the whine lowered in tone a bit.

Any ideas as to what could be going on/how to address this?

Thanks

[Netnnk]

  I built the same project yesterday that also whined, but swapping the charge pump solved it. You say you used a battery, but it still passed through the voltage inverter section to make negative ground, right?

[benny_profane]

That's a good idea. I might be able to swap one out from another build. Were you getting the same whine with the fuzz control nearing maximum?

And yes, the battery passed through the inverter circuit as well. I didn't move to removing the whole inverter circuit and replacing the diode to a 1n4001 yet.

[Netnnk]

Yes, my build was a Flesh Head, which is a TB MKii with fuzz hardwired at max.  The first charge pump  made a faint squeal, the second was very loud. The third was silent.   

[benny_profane]

Glad to hear that you were able to get it working! Unfortunately, I just swapped it out with one I haven't had any issues with and the same thing happened. Any other thoughts?

[pickdropper]

If it only happens with the fuzz on max, try a stopper resistor in-line with the fuzz control.  I would socket it (or put a 250R trim pot).  100 ohms often is about right, but it varies. 

[benny_profane]

If it only happens with the fuzz on max, try a stopper resistor in-line with the fuzz control.  I would socket it (or put a 250R trim pot).  100 ohms often is about right, but it varies.

I was thinking attenuating the pot might be a good workaround. If that's the case, though, I might just leave it as-is and stay off from maxing it out.

I'm still wondering what could cause this, though? If it's the nature of the circuit or if there's something that can be done to tame it. In other words, I would like to be able to reduce the noise and be able to get the full sweep of the pot rather than take the last bit of the range away if that's a possibility.

I still haven't taken the voltage inverter completely out of the circuit yet and tried to see if running it with a non-inverted positive ground fixes the issue.

[Bret608]

I built one on vero with no chargepump and it oscillated at max fuzz as well, sort of a hum like you mentioned. It's apparently a common problem with this circuit, based on what I saw over at DIYSB. Electric Warrior noted that some versions of the MkII attenuated the pot exactly as Pickdropper described. This was on the earlier versions before Sola added power supply filtering. So I would say it's the circuit, not your charge pump.

One important thing to note with this circuit as well is that the Q2 bias will influence how much gating or hiss is present. Try getting Q2 down under about 0.2 volts on the collector and then get Q3 up to 8 volts or more, and see if this helps.

[benny_profane]

I built one on vero with no chargepump and it oscillated at max fuzz as well, sort of a hum like you mentioned. It's apparently a common problem with this circuit, based on what I saw over at DIYSB. Electric Warrior noted that some versions of the MkII attenuated the pot exactly as Pickdropper described. This was on the earlier versions before Sola added power supply filtering. So I would say it's the circuit, not your charge pump.

One important thing to note with this circuit as well is that the Q2 bias will influence how much gating or hiss is present. Try getting Q2 down under about 0.2 volts on the collector and then get Q3 up to 8 volts or more, and see if this helps.

Thanks for the reply! I'll give the Q2 adjustment a shot. Right now the Q2 collector voltage is registering -.52v. I'll report back if/when I'm able to get that voltage to -.2v while retaining good bias on Q3.

Otherwise, I suppose I'll either leave it as-is with the oscillation or attenuate the pot.

[pickdropper]

I built one on vero with no chargepump and it oscillated at max fuzz as well, sort of a hum like you mentioned. It's apparently a common problem with this circuit, based on what I saw over at DIYSB. Electric Warrior noted that some versions of the MkII attenuated the pot exactly as Pickdropper described. This was on the earlier versions before Sola added power supply filtering. So I would say it's the circuit, not your charge pump.

One important thing to note with this circuit as well is that the Q2 bias will influence how much gating or hiss is present. Try getting Q2 down under about 0.2 volts on the collector and then get Q3 up to 8 volts or more, and see if this helps.

Yeah, on my recent layouts I just put a 250R pot in there.  It can be dialed totally out of the circuit if it isn't needed.

[wbgarman]

I was able to address a squeal on the same build by using a 47uf cap on C8.

More details here: https://www.diystompboxes.com/smfforum/index.php?topic=119638.0


Sent from my iPhone using Tapatalk

[benny_profane]

I was able to address a squeal on the same build by using a 47uf cap on C8.

More details here: https://www.diystompboxes.com/smfforum/index.php?topic=119638.0


Sent from my iPhone using Tapatalk

Thanks for the link! That's pretty similar to what I'm experiencing (except yours was starting way earlier on the turn...yikes).

I'm going to 1) Re-bias and see if I can get my voltages in line, 2) Try the C8 swap, and then try 3) Attenuate the signal leading to the pot.

I'll report back with my results. Thanks for everyone's input here!

[benny_profane]

Okay. So I was able to get bias voltages in range. I still had the hum near the end of the pot's sweep, though. I then swapped out the 10uf cap at C8 for 47uf. That completely got rid of the hum, but it also clamped down on higher frequencies from the guitar (specifically, and oddly, the first octave of the high E string but not the second octave). I should note all of this is with humbucker pickups. At that point I switched over to a 22uf cap. There's still a faint hum audible, but the frequency attenuation on the E string is not nearly present. I think this is where I'm going to keep it.

Thanks for everyone's help here! This was quite maddening sorting it out by myself so I really appreciate the help.

[Bret608]

Cool! Glad to hear this worked. That 47uf cap that comes before the charge pump is the normal MkII value (at least after Sola dropped that 100r resistor in line with the fuzz pot). I wonder then if bumping up that 10uf that comes at the -9v out for the pump is essentially adding some additional power supply filtering? I don't know too much about charge pumps if I'm being honest.

[benny_profane]

Cool! Glad to hear this worked. That 47uf cap that comes before the charge pump is the normal MkII value (at least after Sola dropped that 100r resistor in line with the fuzz pot). I wonder then if bumping up that 10uf that comes at the -9v out for the pump is essentially adding some additional power supply filtering? I don't know too much about charge pumps if I'm being honest.

I have the exact same question because I too have little knowledge of inverters/charge pumps. The DIYSB thread actually ends with a similar (unanswered) question.