“Correct Leakage Numbers”

There you go, you answered your own question. Sometimes a leaky transistor needs to be used in order to bias the transistor correctly in the circuit so the transistor "turns on" and conducts in order to pass signal. MK2 is an example of this. Cathode-base resistors can be used but I feel it's a "cheat" and a deviation of the original circuit.

It doesn’t take much though. Like I said, 15 microamps is all it takes to get a no-bias Q1 like the MK II to work.
 
Back to my OP.

Let’s take a circuit I know pretty well: The Classic Tonebender MK II.

If you take 3 middle of the road OC75s with medium to high leakage, that stock circuit will bias up to vintage spec almost as an afterthought. The OC75 does have a desirable and definite upper frequency thing going on. Let’s bookmark that.

Now you can pretty much take any low leakage Germanium transistor in a reasonable gain range (60-100 hFE) and tweak the circuit for bias and get most of the way there. What you can them do is tweak the input, treble bleed and emitter caps to get back some of that OC75 “zing”.

What you get with the tweaked circuit that you don’t with the vintage spec is temperature stability. You can make the tweaked circuit sound like the Vintage spec but the Vintage spec will never have the bias stability that the tweaked circuit will.

That’s my whole beef with leakage in a nutshell.
As with anything, the answer is always: it depends.

High leakage, low leakage, high hFE, low hFE....really depends on the circuit itself and what you're going for. Personally, I haven't paid too much attention to leakage. I tend to focus more on hFE which gives me an indication of how much gain I can expect. Now, some of the circuits I've tried run the gamut of either being the typical sputtery fuzz or something that's more tame and yields more of an overdrive quality. One thing I've noticed is that there can be quite a difference in circuits that default to PNP transistors as opposed to NPN ones.
 
It's funny - I've made a heap of great fuzz pedals. Some of them I really like, some are just meh, some I have taken apart and used the bits for other things or given to guys who like them.

But I never use one on my board. I have zero use for them. Maybe one day!
 
HFE and AC signal gain are not the same thing. I discussed this at length in The Boneyard.
Some circuits are sensitive to HFE and most are not.
Some circuits need high leakage, some need low leakage and some don't care. Big Monk is right about leakage biased circuits being inherently unstable thermally. The TB Mk 1 is the only leakage-biased Fuzz that I've bonded with, it just sounds right to me. But I know it will drift all over the place if it gets hot. There are ways to make a circuit insensitive to leakage variation. I did that with my FET-Ge Boost. The Ge transistor has a large emitter resistor and smallish base bias resistors. That's all it takes. The emitter resistor is bypassed with a cap so I don't lose gain with the emitter resistor. I'm more interested in building a circuit that sounds good than building a circuit that is an exact duplicate of something else. If I want to get fancy and stabilize the bias without emitter resistors, then a servo is in order.

Vintage PNP Ge transistors are lower leakage and lower noise than vintage Ge NPN. Because they performed better, they were more desirable and more plentiful. That is why so many vintage Ge circuits, not just guitar pedals, used PNP. The difference in PNP & NPN performance was a consequence of the manufacturing process at the time. The Ge transistors manufactured in the 70s & later had much better performance and there was less difference between the NPN & PNP transistors. My experience with the Russian transistors I've used (mainly MP38A & P28) is that the PNPs have significantly lower leakage.
 
I say the same thing all the time. I can love riffing on a fuzz alone but in my personal playing I find it hard to use. I have built so many that I realized it's for certain occasions. I generally find my RAT to be easier to use and gives more favorable results tonally.

This is a pretty key point I think.

For starters, I don’t play in bands so my Fuzz knowledge is all personal (plus some feedback from a handful of commission builds I’ve done) and also confined to me riffing in my bonus room.

I always seem to think of Fuzz as this wild sound but all my favorite recorded fuzz sounds (barring a few wild ones like on The Stooges records, etc.) are really more refined and/or modified to provide a sort of fuzzy overdrive sound.
 
Most fuzz that has the fuzz sound is scooped in the mids. Unless your playing in a dou or using the right gear in a trio, I find fuzz doesn't work well if you want to be heard in the mix. I find the adding a mids knob to a fuzz makes it easier to cut thru but changes the tone of the fuzz in an unpleasant way. It takes away all the fuzz character and turns it into an overdrive on steroids.

It always seems to a study in compromises. I always have a Pre-Gain pot (input resistance) on my MK II/Supa/MK 1.5/Fuzz Face builds.

When you get them so your power chords crunch instead of mush out, the lead sound is gone and vice versa.

It’s still such a compelling sound though. It’s so much fun to play and maybe that’s because I’m simply a hobbyist and I don’t have to sit in a mix anywhere.
 
Most fuzz that has the fuzz sound is scooped in the mids. Unless your playing in a dou or using the right gear in a trio, I find fuzz doesn't work well if you want to be heard in the mix. I find the adding a mids knob to a fuzz makes it easier to cut thru but changes the tone of the fuzz in an unpleasant way. It takes away all the fuzz character and turns it into an overdrive on steroids.

I tried to use a Bass Big Muff in a live setting a couple of times. I might as well have just unplugged, it just dropped right out. Sounded good at home, though!
 
This is the problem with fuzz. Sounds awesome alone at home or when your doing corrective EQing in a daw but live shit just disappears. Also why I don't understand the love of full frequency boosts and drives. Everything turns to mush and gets lost in a mix. Then all the mod threads to cut bass lol
I've been preaching the church of the Vario Boost to everyone who plays guitar or bass. It's one of the most useful pedals a person can have, IMO.
 
I tried to use a Bass Big Muff in a live setting a couple of times. I might as well have just unplugged, it just dropped right out. Sounded good at home, though!
This is why Skreddy adds a flat or pushed mids switch to so many of his Muffs. They work. When making a Skreddy fuzz I generally leave the switch off and just build the version with more mids.

The Marshall Supa Fuzz was made for Marshall by Sola Tone. It uses bigger caps and has a huge sound, not unlike a Big Muff. But it has plenty of mids, so should be heard.

This all relates to why I love Gretsch guitars so much. For a long time I would turn up to rehearsal with my Tele or Strat all dialled in with whatever new Fender amp I had and use the onboard dirt on the Fender amp. (This was a long time ago - think Rivera-era Fender amps) And my sound would be soooo thin in the band context. So I would try a 335 or something and my sound would be all mids and no cut. Tiny little sound, even though at home it sounded like Angus Young.

Then one day I took a '64 Gretsch 6120. At home it sounded a bit rough but in the band all of a sudden I had this broad, expansive tone which sat beautifully in the mix but still sounded huge. It cut though like a Fender but retained the body of the sound - heavenly!

Ever since I have used Gretsches. I still have some wonderful Gibsons but for gigs it's usually a Gretsch. Sometimes a Gibson with P90s.
 
The Marshall Supa Fuzz was made for Marshall by Sola Tone. It uses bigger caps and has a huge sound, not unlike a Big Muff. But it has plenty of mids, so should be heard.

What's interesting about the Supafuzz is that when it was produced by Sola Sound, it was just a re-branded MK II. Same circuit.

When Sola Sound ended the contract to produced them for Marshall, Marshall took over production in-house. That's when the 10 uf Input and Emitter caps came in. Interestingly enough though, they also removed the treble bleed cap at some point. However, it seems there was a period where they were still built with the treble bleed cap.

I've breadboarded both many, many times. The 10 uf/0.01 uf combo has a lot of "Ass" (for lack of a better term) and it should considering the treble rolloff at the input from the 0.01 uf. The 10uf/no treble bleed combo is interesting because it is actually a little brighter than the stock MK II but also just a touch fatter because of the bigger input and emitter caps.
 
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