Tonebender MKII negative ground problem

[Johnny Lemonhead]

Hello,

I've built a GGG Tonebender MKII using the negative ground layout with matched PNP germanium transistors from small bear, and although it
operates flawlessly with a battery, it's unusable when connected to a common 9v adapter.
After reading several threads concerning this issue, I'm still somewhat confused about the different solutions for this problem.
The hum is more than just a regular hum - it dwarfs any other sound coming out of the pedal. I realize that an adapter has a great influence over this, but this sort of hum never occurred with the other pedals I've built.

I tried adding a 100uf elec. capacitor between - and +, but it didn't seem to change anything and I'm not entirely sure where to connect the other suggestions, such as a 150ohm resistor.

Here is the layout with the added capacitor. It would be greatly appreciated if you could add any suggestions to the actual picture and re-post it. Not being a native English speaker sometimes makes verbal instructions a bit confusing, especially for neophytes such as myself.

Thank you!

[petemoore]

  I've built a GGG Tonebender MKII using the negative ground layout with matched PNP germanium transistors from small bear, and although it
operates flawlessly with a battery
  Some who worked with that reported having good results, others report intractable rpoblems.
  It might be worth to give a voltage regulator a shot, however this might not cure it either.
  Pos. Gnd. PNP can be debugged.

[MikeH]

Any minute now RG will come through and give the usual speech about why PNP negative ground is a bad idea.   

Seriously though, if it's anything like a PNP neg ground fuzz face, sometimes they're just more trouble than they're worth.

[Johnny Lemonhead]

Thank you both for the information. I wanted it to work with a shared power supply, but I guess a conversion to positive-ground is inevitable.
IMO, it's better to have it run on its own power supply than just being able to use a battery.

I have some distaste of batteries. Don't like rechargeable drills either

Thanks again.

[MikeH]

There's a bipolar power supply project at tonepad, which you could use to just supply the negative voltage you need.  It's tiny, so I'm sure you could fit it into your enclosure,

[R.G.]

Thank you both for the information. I wanted it to work with a shared power supply, but I guess a conversion to positive-ground is inevitable.
IMO, it's better to have it run on its own power supply than just being able to use a battery.

Why don't you use an LT1054 charge pump converter inside the pedal and make -9V out of +9V? That lets you use the same power supply for the cost of one 8 pin chip and several electro capacitors.

[MikeH]

Thank you both for the information. I wanted it to work with a shared power supply, but I guess a conversion to positive-ground is inevitable.
IMO, it's better to have it run on its own power supply than just being able to use a battery.

Why don't you use an LT1054 charge pump converter inside the pedal and make -9V out of +9V? That lets you use the same power supply for the cost of one 8 pin chip and several electro capacitors.

Same thing as the tonepad +/- power- which uses a MAX1044(?) chip.  Although I don't know what the price difference is; the MAX chip is about 3 and a half bucks.

[chi_boy]

Johnny,

Since you're talking about noise, how quiet is yours when on a battery?  I built the TonePad version and it is noisy all the time, and sounds the same with the wall wart. It's the noisiest pedal I have, but I don't know if it's normal for the pedal, or if I need to try troubleshooting. Just wondering. Thanks, and good luck with the debug.
Cheers,
George

[R.G.]

Since you're talking about noise, how quiet is yours when on a battery?  I built the TonePad version and it is noisy all the time, and sounds the same with the wall wart. It's the noisiest pedal I have, but I don't know if it's normal for the pedal, or if I need to try troubleshooting. Just wondering. Thanks, and good luck with the debug.

It is critical with the MAX1044 to use the "boost" function by connecting pins 1 and 8, and by using good decoupling of the incoming and outgoing power to/from the 1044 so switching noise doesn't get carried into the effect.

Is your pedal noisy on the battery?

[chi_boy]

R.G.,

I don't use the MAX on this one.

I have a couple of positive ground boxes that share a power supply.  No negatives are attached.  And yes, it sounds exactly the same on the battery.

Like I said, just curious if it is the nature of the beast, or if it should be better. If it should be better, I'll pursue the trouble shooting.

Thanks again!

[R.G.]

Ah, OK. I understand now. Noisy even with batteries probably means you have some noisy transistors.

Germanium was mankind's "learner semiconductor". It's easier to refine and process than silicon, and can be processed at lower temperatures. As in any learning experiment, the first trials are crude, and they get better as you understand more. It was from processing germanium that we learned that we needed clean rooms to do the processing in, and that we needed to keep all kinds of crud, even molecular level, off the surface of semiconductors.

Early germanium transistors were inconsistent and suffered from excess noise from surface contamination, which could manifest itself even years later. This does not affect the gain characteristics, it's just excess noise in the signal it passes. In a high gain distortion pedal, noise may change with every new input transistor you sub in.

It might possibly be RF oscillation, but I'd guess a noisy transistor.

You didn't use carbon composition resistors did you? 

[mharris80]

You didn't use carbon composition resistors did you? 

But I thought those came loaded with mojo.  *ducking*

[Scruffie]

Lol I harvested some carbon comps from 3 radio full of mojo transistors (all of them were fine! bonus) I measured the resistors though, I was getting 130k from 100k resistors and decided i'd just stick to the unleaky OC mullards for my tone bender clone

[chi_boy]

You didn't use carbon composition resistors did you? 

Nope, no carbon comps.  All 1% metal films, and Panasonic and Xicon caps.

I'll try swapping out the transistors and see if it changes.

Thanks for the non-trouble shooting trouble shooting!

GP

[smallbearelec]

I have been building stock of NPN germanium over the last years, and I now have enough to comfortably market for awhile. OC140 FF pairs are available, and I will be adding more matched pairs and sets over the summer. Not cheap, but you do get quality, and it's the simplest way technically to deal with this problem.

[chi_boy]

It might possibly be RF oscillation, but I'd guess a noisy transistor.

You didn't use carbon composition resistors did you? 

R.G.

I think you are right.  I swaped in some different Ge transistors and the noise level changed for the better.  With the transistors I have on hand I couldn't get the noise down and get Q3 to bias at the same time, but I think it proved that the trannies are the problem.  I suspect Q2 is the culprit.  These were a matched set from SB too.  I'll probably just pick up a whole new set and be done with it.  I hope.

Thanks again for the tip.

Cheers,
George

[smallbearelec]

I swaped in some different Ge transistors and the noise level changed for the better.I suspect Q2 is the culprit.  These were a matched set from SB too.

Drop us a message at smallbearelec@ix.netcom.com and refer to this exchange. Matched sets carry my warranty, and we will replace noisy devices. We do our best to weed out the hissy ones when auditing, but the process isn't perfect, and these devices are Old; they do sometimes poop without warning. Note to others: Please use transistor sockets, and do not clip leads until you have tested thoroughly!

Regards
SD

[Johnny Lemonhead]

Johnny,

Since you're talking about noise, how quiet is yours when on a battery?  I built the TonePad version and it is noisy all the time, and sounds the same with the wall wart. It's the noisiest pedal I have, but I don't know if it's normal for the pedal, or if I need to try troubleshooting. Just wondering. Thanks, and good luck with the debug.
Cheers,
George

On a battery, it's surprisingly quiet. No hum whatsoever and the hiss is unnoticeable. Current +9v adapter makes it unusable, though.
The germanium transistors are a matched set from Small Bear (Q1 is Hitachi 2sb77 and the other two are 3ax31c) and the resistors are metal film (except R6 that was swapped with a 10k trimpot).

There's a bipolar power supply project at tonepad, which you could use to just supply the negative voltage you need.  It's tiny, so I'm sure you could fit it into your enclosure,

Why don't you use an LT1054 charge pump converter inside the pedal and make -9V out of +9V? That lets you use the same power supply for the cost of one 8 pin chip and several electro capacitors.

I was unaware of this solution and it sounds like a good one. I'll try to get one of those IC's and until then just use the pedal with a battery. Thanks!
GGG should add an extra layout with the conversion already incorporated to the circuit. Does that make sense?