Sunflower and Gnat Fuzzes: Experimenting with PNP Trannies

[jeffwhitfield]

Got a bundle of a few GE trannies and wanted to try them out. So, I got the Sunflower and Gnat boards to experiment with. I ordered a set of MP20A's and a set of GT402B's. I had used some MP20A's on a few previous projects and liked them. However, they tend to be on the lower HFe side so I got the GT402B's to compensate. For a typical Fuzz Face type circuit, I figure the MP20A's can handle the 60-80 range with the GT402B's for the 120-ish range. After trying them out in these circuits, I think I was pretty much on mark. They definitely sound pretty darn good!

 

[Mentaltossflycoon]

I remember my first time experimenting with russian trannies, good job!

 

[Coda]

View attachment 19738

Mu-Tron makes a good phraser…

 

[MobyOctopad]

This is a dumb question, but how does the mismatched pair of transistors change the sound compared to two of either the MP20s or GT402s? I'm waiting on an order of Russian transistors and looking forward to experimenting with pairs myself.

 

[jeffwhitfield]

It's not a dumb question at all.

Really depends on the transistors in question. From my understanding, leakage differences are the main thing. If one is more leaky than the other then it impacts the sound more. I think the ones I have are fairly comparable though in terms of leakage...not exact but close enough to not cause any issues. Main thing I was aiming for was a set that was in the ballpark in terms of hFE. These are circuits that are pretty forgiving so, yeah, seems to work well.

That said, I have a Fuzz Face clone I'll be building soon. Gonna try the same approach. However, my understand is that a Fuzz Face is a bit more fussy so we'll see.

 

[JamieJ]

It’s an interesting question @MobyOctopad - GE transistor part numbers aren’t that important. Their gain and leakage characteristics are the main thing. So these transistors are match on their gain and leakage properties rather than getting two AC128s or NKT275s.

 

[jeffwhitfield]

Yeah, mixing and matching is sometimes necessary because its hard to find the same transistor in both high and low gain. The lower gain ones in the first stages is less important. It's that last one that's the really important one. Get that one right and the earlier ones are easier to deal with.

In my case, the MP20A is an easy one to match with a lower gain hFE. Leakage isn't bad either...pretty low leakage. But it's hard to get it upwards in the 110 to 120 range though. There is an MP20B that carries higher gain...but you still have to buy a batch in order to raise your chances of getting one that's in the ballpark that you want.

Which lead me to getting a batch of GT402B which, based on the bit of research I did on it, seemed to be easier to match for a 110-120 hFE range. So I figure that I could match this one for the high gain and the MP20B for the lower gain spots.

 

[Coda]

I have found that just because the numbers match up doesn’t mean it will sound good. In a Fuzz Face, you can sometimes get a pair of transistors that just don’t get along. I think this was the reason behind the variance between original units.

 

[MobyOctopad]

Yeah, definitely hear what you're all saying about the overall importance of gain and leakage in the circuit. I think my question came to mind because of the way Analogman writes about the different tonal qualities of transistors they offer for Sun Faces (e.g. the 2SBs are smoother than others they have in stock, BARTs are woolier, etc.) plus some other YouTube videos I've found socketing different transistors (though still in pairs of the same make), so was curious to see what it would mean to pair two different makes with potentially different sounds to them, if that makes sense.

Though I suppose it wouldn't necessarily be like for like in this case if the MP20As all topped out at lower gains than the GT402Bs.

Appreciate the responses, y'all!

 

[fig]

Nice looking builds as usual Jeff!

I've nothing really to add to the insightful responses to @MobyOctopad 's question, but I will pose a followup question to the responses..in another thread.

 

[Big Monk]

Yeah, definitely hear what you're all saying about the overall importance of gain and leakage in the circuit. I think my question came to mind because of the way Analogman writes about the different tonal qualities of transistors they offer for Sun Faces (e.g. the 2SBs are smoother than others they have in stock, BARTs are woolier, etc.) plus some other YouTube videos I've found socketing different transistors (though still in pairs of the same make), so was curious to see what it would mean to pair two different makes with potentially different sounds to them, if that makes sense.

Though I suppose it wouldn't necessarily be like for like in this case if the MP20As all topped out at lower gains than the GT402Bs.

Appreciate the responses, y'all!

One of the reasons using the breadboard to tune fuzz circuits is so important in my opinion is the ease in which you can swap not only the transistors, but supporting components like collector, base and emitter resistors as well.

 

[Coda]

One of the reasons using the breadboard to tune fuzz circuits is so important in my opinion is the ease in which you can swap not only the transistors, but supporting components like collector, base and emitter resistors as well.

I breadboarded my Sandspur build to swap out everything that I needed to…and I still ended up opening the pedal up and modding part of it. Of course, not all circuits are as simple to breadboard as a fuzz face…