Tranny Gain/Leakage Recommendations Tonebender MKII

[fuzzy645]

I acquired some OC44 transistors.  I measured gain/leakage with a PEAK unit.  I'm wondering which ones you think will work best in Q1, Q2 and Q3 of a Tonebender MKII.

A = HFE 113 / LKG 40

B = HFE 89 / LKG 40

C = HFE 91 / LKG 40

D = HFE 125 / LKG 60

E = HFE 117 / LKG 60

F = HFE 90 / LKG 0 (yes, this one shows no leakage on repeated measurements)

Recommendations?  I have heard that Q1 and Q2 in particular require some leakage, but not sure how much??

Thanks!

[Buzz]

I made a tonebender MKII with AC125s sourced from Chromesphere.

It is an absolute pearler of a pedal.

His recommendations are as follows:

Gains
Q1 - 60-80 hfe | < 300ua leakage
Q2 - 60-80 hfe | < 300ua leakage
Q3 - 100-120 hfe | <300ua leakage

Use sockets, mix and match.

For a first attempt try B as Q1, C as Q2 and E as Q3.

Good luck, if you get this going well it's the best fuzz you can make ( IMHO )

[fuzzy645]

Thanks for your recommendation.  I will try to socket them and mix and match to see what sounds best. I'll start off with your recommendation (B,C, E) .  I'm curious what will happen when I try out the tranny with zero leakage.

[LucifersTrip]

I think the best thing to do is look at good working voltages from originals and see if yours are in the ballpark.

for instance, here's some from DAM

Battery -9.01
Q1 c -8.50 b -0.038 e 0
Q2 c -0.13 b -0.076 e 0
Q3 c -8.29 b -0.13 e -0.08

OC81D MkII #1 (100K on Q1 base, 100K on Q2 collector)
Battery -9.55
Q1 c -8.51 b -0.06 e 0
Q2 c -0.13 b -0.068 e 0
Q3 c -8.72 b -0.13 e -0.07

OC81D MkII #2 (100K on Q1 base, 100K on Q2 collector)
Battery -9.50
Q1 c -8.76 b -0.062 e 0
Q2 c -0.22 b -0.075 e 0
Q3 c -8.13 b -0.22 e -0.14

You most likely won't get these with the low leak ones you mentioned above.

[fuzzy645]

You most likely won't get these with the low leak ones you mentioned above.

Thank you.  To achieve the voltages (and hopefully tone) along the lines of what you mentioned about the DAM site, would you say one should be looking for trannys with higher leakage (say 150 - 250) for all 3 transistors?

[LucifersTrip]

most i've seen usually leak 100uA+, but of course there are exceptions.   I saved some hfe's from ones reported (also from DAM, I think):

Q1 - hfe - 38 / Ic - 0.00mA
Q2 - hfe - 27 / Ic - 0.04mA
Q3 - hfe - 227 / Ic - 0.34mA

Q1 - hfe - 25 / Ic - 0.04mA
Q2 - hfe - 31 / Ic - 0.04mA
Q3 - hfe - 335 / Ic - 0.10mA

I'm not sure what the voltages would be and I haven't tried this yet.

do some experiments. you'll probably find out that with the low leak ones you have, you'll be closer to Fuzz Face voltages. experiment with a higher leak Q2. it'll lower the collector voltage and Q3 B, which will raise Q3C closer to the 7.5V+ that you want.

it's also common to use a 100K trimmer in place of Q2's C resistor.

[nocentelli]

You can use a high value resistor (like 100k and up) from base to collector, especially for Q2, to simulate leakage. This definitely works well for silicon which barely leaks, if at all. Not sure how well it might work withlow leakage germanium transistors, but it's worth trying on the breadboard.

[Electric Warrior]

most i've seen usually leak 100uA+, but of course there are exceptions.   I saved some hfe's from ones reported (also from DAM, I think):

Q1 - hfe - 38 / Ic - 0.00mA
Q2 - hfe - 27 / Ic - 0.04mA
Q3 - hfe - 227 / Ic - 0.34mA

Q1 - hfe - 25 / Ic - 0.04mA
Q2 - hfe - 31 / Ic - 0.04mA
Q3 - hfe - 335 / Ic - 0.10mA

I'm not sure what the voltages would be and I haven't tried this yet.

Those were Impex S3-1Ts. Voltages should be in the same ballpark, at least for Q3. I found it hard to get it to behave nicely with low leakage transistors, even when I set them up like these. Noise and oscillation can be a real pain.

With too little leakage (I tried to make a MKII with 2SB175s once) and a more even hfe selection it kinda works, but it's usually hissy and not fuzzy enough. It usually lacks low end, too and it will sound like crap when you get it to gate.

High leakage types like OC75s (most of mine leak betweeen 250µA and 500µA, but I've had some that leaked less, too) make things much easier. I can pick any three transistors and it will work and sound like a MKII. Sure, it still needs some tweaking, but the perfect amount of clean up/gating and a tonal balance that I like are just a couple of transistors swaps away. The hiss is easy to manage. And a bit of gating sounds awesome with these.
Hfe range doesn't seem to matter all that much. I've had Philips OC75s in the 50 to 120 range and some Valvo made ones that were between 130 and 220. Both types quite leaky, both work really well. The Valvos were just a tad brighter. I've also had some Valvo AC125s that were perfect.

Of course you still have to pick a set that works well for you. Just ignore the "formulas" and use your ears.