What would you recommend for a 'low' gain transistor?

[Guitarfreak]

I know there isn't such a thing as 'low' gain, and that twenty or so years ago it wouldn't have been considered quite so low.  What I am looking for is something to replace the high gain transistors in my NYC Muff with something lower gain and a bit warmer.  What I've got now is 4 transistor stages of 2N5088's all NPN.   I am basically going for the Ram's Head Muff sound if that helps.  I understand that those models used 1970's 2N5133's, and it has been brought to my knowledge that they don't make those anymore.  Is there anything within the spec range that can offer me similar results?

[trjones1]

I'm not sure what the specs of the 2N5133 is, but I've used PN2369A transistors in fuzz faces with excellent results.  The ones I've gotten are consistently right around 120 hfe.  I've been meaning to try them in different circuits.  They might be right for your needs.

[soggybag]

2N3053 and 2N3019

[John Lyons]

There isn't going to be much difference in a big muff.
The high gain transistors 500-800 will have a little more fizz but that's about it.
Anything around 300-500 is going to sound about the same.
The big muff is set up so the gain does not matter much.

John

[Guitarfreak]

There isn't going to be much difference in a big muff.
The high gain transistors 500-800 will have a little more fizz but that's about it.
Anything around 300-500 is going to sound about the same.
The big muff is set up so the gain does not matter much.

John

Is this due to the Muff having such a huge ratio of C/E resistance?  Or something else?

[R.G.]

I know there isn't such a thing as 'low' gain, and that twenty or so years ago it wouldn't have been considered quite so low.  What I am looking for is something to replace the high gain transistors in my NYC Muff with something lower gain and a bit warmer.  What I've got now is 4 transistor stages of 2N5088's all NPN.   I am basically going for the Ram's Head Muff sound if that helps.  I understand that those models used 1970's 2N5133's, and it has been brought to my knowledge that they don't make those anymore.  Is there anything within the spec range that can offer me similar results?

The clipping stages of the muff can be looked at as very low-gain opamps. They're set up as inverting feedback clippers. You can lower the effective gain of the transistors by inserting bigger emitter resistors, increasing the incoming series base resistors, lowering the collector-to-base feedback resistors, or lowering the collector resistors. Of these, changing the collector resistor or colector-to-base resistors change the bias a lot, so changing the incoming base resistor or emitter resistor is going to be simpler, as you won't get biasing results which are way different.

Transistor gain does not translate directly into circuit gain. Instead, transistor gain is a *capability* which limits the ultimate gain you can get. The resistors around the transistor determine the actual voltage gain you get, within the capability the transistor has.

[Guitarfreak]

I know there isn't such a thing as 'low' gain, and that twenty or so years ago it wouldn't have been considered quite so low.  What I am looking for is something to replace the high gain transistors in my NYC Muff with something lower gain and a bit warmer.  What I've got now is 4 transistor stages of 2N5088's all NPN.   I am basically going for the Ram's Head Muff sound if that helps.  I understand that those models used 1970's 2N5133's, and it has been brought to my knowledge that they don't make those anymore.  Is there anything within the spec range that can offer me similar results?

The clipping stages of the muff can be looked at as very low-gain opamps. They're set up as inverting feedback clippers. You can lower the effective gain of the transistors by inserting bigger emitter resistors, increasing the incoming series base resistors, lowering the collector-to-base feedback resistors, or lowering the collector resistors. Of these, changing the collector resistor or colector-to-base resistors change the bias a lot, so changing the incoming base resistor or emitter resistor is going to be simpler, as you won't get biasing results which are way different.

Transistor gain does not translate directly into circuit gain. Instead, transistor gain is a *capability* which limits the ultimate gain you can get. The resistors around the transistor determine the actual voltage gain you get, within the capability the transistor has.

Incredibly wise, thank you for the assessment.  Exactly where does the Muff get its 'sizzle'?  I've been trying to track this down.  Is it due to the amount of gain in each gain stage, is it due to the feedback resistors, or due to a bias being set too low?

[R.G.]

Exactly where does the Muff get its 'sizzle'?  I've been trying to track this down.  Is it due to the amount of gain in each gain stage, is it due to the feedback resistors, or due to a bias being set too low?

It is likely that it's from the cascading of three gain stages, the last two of which include explicit clippers. The first stage amplifies the signal and gives you a control to back that down. The second stage both amplifies and clips with its feedback diodes. The third stage does the same again, amplify and clip. Lots of gain, and a clipping stage to keep the final clipping stage from being pushed so far off its bias point that it dissolves in blocking/farting sounds.

[Guitarfreak]

What exactly do those collector to base feedback resistors do for the sound of the pedal?  Does that increase the sustain?

[IvIark]

2n3903s are great for low gain silicon.  The ones I've got are all around 70 - 140hfe and sound great in a Fuzz Face type circuit.

[R.G.]

What exactly do those collector to base feedback resistors do for the sound of the pedal?  Does that increase the sustain?

It's difficult to say that one part does X or Y to the sound. Generally, any one part can only effect the sound in concert with the others. Sometimes it does one thing, but mostly not.

The collector to base feedback resistors:
1) change the biasing point of the transistor; this can effect sound because if it's misbiased, you get the sound of the transistor running out of voltage instead of just the feedback diodes clipping
2) change the AC gain of the transistor in concert with the collector resistor, emitter resistor and any other resistors connected to the base; this changes the sound by changing how hard the feedback clipping diodes are driven into clipping
3) change the frequency response of the transistor and clipping in concert with the capacitances connected to it and with the overall AC gain of the circuit
4) change the input and output impedance of the circuit in concert with other resistors connected to the base and collector respectively

Sustain in the context of a distortion pedal means "how little input signal can give an audibly similar level clipped signal before the input signal decays below the clipping threshold?"  This is determined by the overall gain of the circuit before clipping, the relative size of the clipping thresholds, and the size of the input signal. Transistor gain gets into it, yes; but so does the size of the clipping threshold and a lot of other things. Does it change the gain? Yes. Does it change sustain? Yes. Does it change other things? Yes.

[Guitarfreak]

I ended up going with the 2N3019, couldn't resist.  I'll post back and let you know how it goes.

[R.G.]

I ended up going with the 2N3019, couldn't resist.  I'll post back and let you know how it goes.

That's cool. If it works, do it.

[edvard]

Aren't most power transistors rather low gain?
Looking up the "Power Transistor" category on Mouser shows lots of hFE's in the 10-100 range.
I always thought it'd be funny to build a Fuzz Face with a couple of those gigantic TO-3 cans.
It's got so few parts, there's plenty of room... 

[Lurco]

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