Input cap alternatives in the Tonebender Mk II

[mordechai]

I'm wondering if anybody has experimented with different input caps in this thing.  I like the sound of the standard 4.7uf but if I have transistors that have a bit of a higher gain than the typical/common 70/70/100 (more or less) in the original circuit, what types of variations would you try for the input cap?  For the record, I've got a good set of 2n1309s, low leakage, with Hfe's of 90/112/125.  So it's not a LOT higher than the usual ratings on the transistors small bear usually offers, but with the aggregate hike in gain, I'm wondering if I can take some of the mud but changing the input cap, but not changing it so much that it detracts from a good, strong low end.

[blooze_man]

Try an input cap blend control.

[Derringer]

Try an input cap blend control.

this

or, socket the input cap and try progressively smaller input caps till you find the one that sounds best to you
pretty much everything I build now has the in, out and any other character altering caps socket-ed for just this reason

[jpiddy118]

2.2uF did the trick for me, as well as .047uF on the output. currently on the breadboard waiting for a permanent home.

[mordechai]

Didn't the 2.2uf cut down on the lows a little too much, though?  What sort of volume pot did you use?

[jpiddy118]

Didn't the 2.2uf cut down on the lows a little too much, though?  What sort of volume pot did you use?

Not at all... in fact, i think it helped by preventing too much unnecessary low end from mucking things up (wish i could validate that scientifically, but i just listen for what works best with my rig & my ears ). Using the larger output cap gave me back the balls i needed. 500k audio pot. Also have a 10k linear on Q1 C instead of the fixed resistor.

[Electric Warrior]

I'm wondering if anybody has experimented with different input caps in this thing.  I like the sound of the standard 4.7uf but if I have transistors that have a bit of a higher gain than the typical/common 70/70/100 (more or less) in the original circuit, what types of variations would you try for the input cap?  For the record, I've got a good set of 2n1309s, low leakage, with Hfe's of 90/112/125.  So it's not a LOT higher than the usual ratings on the transistors small bear usually offers, but with the aggregate hike in gain, I'm wondering if I can take some of the mud but changing the input cap, but not changing it so much that it detracts from a good, strong low end.

so you finally got it working properly?
125 is not a particularly high gain for an OC75. In fact the Mullards that Sola Sound used in the original units were very high gain. David Main dared to unsolder the transistors from his Sola made Supa Fuzz and they hfes were 174 (Q1), 208 (Q2), 194 (Q3).
The MKII circuit can produce a very muddy low end indeed, but by choosing the right transistor combination you should be able to tighten it up considerably. Don't limit yourself to a 70/70/100 pattern.

[mordechai]

Yes, I did fix the problem (well, there were a few, but c'est la vie) when I breadboarded everything.  That's really interesting about the gains of David's original circuit that you mentioned.  But I still can't figure out why having Q2 possess a higher gain than Q3 works.  If this stage in the circuit is essentially a FF at heart, how could operate well?  How would it benefit the signal flow?

[Electric Warrior]

Great to hear!
I have no idea how, but it can work. The interplay between different hfes and leakages is really complex. It's whatever works, really. Three stages interacting with each other are much harder to tune than the two stages of the Fuzz Face.

[LucifersTrip]

125 is not a particularly high gain for an OC75. In fact the Mullards that Sola Sound used in the original units were very high gain. David Main dared to unsolder the transistors from his Sola made Supa Fuzz and they hfes were 174 (Q1), 208 (Q2), 194 (Q3).

did David ever note what the leakages were for those high gain transistors?

[twabelljr]

did David ever note what the leakages were for those high gain transistors?

Good question, I was wondering the same thing.
Good luck mordechai. I hope you can find the sound you seek.

[Electric Warrior]

If he did I can't remember it. But OC75s have plenty of leakage in general. I've got some high gainers (though Valvos, not Mullards; hfes mostly between 115 and 215) and most of them leak between 250 and 500µA. Got a bunch of really nice Philips OC75s for a friend and the hfes were up to 150, leakages up to 300µA.

[mordechai]

If he did I can't remember it. But OC75s have plenty of leakage in general. I've got some high gainers (though Valvos, not Mullards; hfes mostly between 115 and 215) and most of them leak between 250 and 500µA. Got a bunch of really nice Philips OC75s for a friend and the hfes were up to 150, leakages up to 300µA.

How much leakage can the TBMkII circuit tolerate?  I think that it's alright for Q1 to be fairly leaky (right?) but what about Q3?  If it's too leaky (more than 300uA) wouldn't it be too unstable to bias properly?

[Electric Warrior]

I don't have any issues out of the ordinary. Guess it can take a lot of leakage.