Tonebender Mark II Fuzz Mods

[Giglawyer]

I have an old BYOC Tonebender Mark II with 3 OC72 transistors.  I was thinking about modding it (why not, right?).  More specifically, I was thinking about some of the mods on Beavis Audio Research's site (  http://www.beavisaudio.com/Projects/FuzzLab/FuzzCloneMods_V2.gif), like the transistor switching mod.  If I do this, I am thinking I need 3 low gain silicon transistors like 2n2369s or 2n3440s or some similar low-gain NPN silicon transistor.  

Any suggestions?  Thoughts?  

[RandomGlitch]

I've liked the 2n2222 in the fuzzes I've made.

If you like 'messed up' or gritty sounds then give the voltage sag and bias mods a go (especially if you are switching transistors)

[Solidhex]

The first stage in a MkII won't work with a silicon transistor. Having a switchable silicon/germanium Q2 can be help on hot days. An external bias control of either Q2 or Q3's collector resistor can be handy. You could remove the 470 ohm resistor and replace it with a 1Kpot and 220 ohm resistor in series like the Fulltone 69' mids control...

[Giglawyer]

Thanks for the pointers.

[AnalogPackrat]

The first stage in a MkII won't work with a silicon transistor.

Sure it will.  You just have to add a bias resistor from B to C on Q1 to make up for the lack of leakage.  I used 470k in mine and a low gain Si Q1 (Hfe = 46) which drastically reduced the hiss over Ge for Q1.  Try it!  I've got a Ge in Q3 and might swap one into Q2 as well.  Good luck with it.

[Gus]

AnalogPackrat good see your post

Giglawyer another schematic to look at might be the input of the Hot Silicon Doug H. The input is a controlled gain of about X10 with a nice input resistance for a distortion/fuzz,  Now if you want to change the bias point(collector voltage) you can adjust the two input resistors voltage divider values.

[Giglawyer]

The first stage in a MkII won't work with a silicon transistor.

Sure it will.  You just have to add a bias resistor from B to C on Q1 to make up for the lack of leakage.  I used 470k in mine and a low gain Si Q1 (Hfe = 46) which drastically reduced the hiss over Ge for Q1.  Try it!  I've got a Ge in Q3 and might swap one into Q2 as well.  Good luck with it.

Would I add bias resistors for BOTH the Ge and the Si transistors at Q1, or just for the Si?  (I am starting to feel that this is heading above my paygrade...LOL...) 

[drewl]

That's my favorite of all fuzzes, I've built NPN and PNP versions, but all germanium. That's what gives it it's wonderful sound.
If you must mod it, maybe try some diode clipping on the output? Switchable of course.
Maybe add a ringer or other type of octave circuit?

[Giglawyer]

There's no "must" about modding it...LOL...just a desire to experiment.  Its great all on its own, but...COULD IT BE BETTER?   We'll see...

[Solidhex]

The first stage in a MkII won't work with a silicon transistor.

Sure it will.  You just have to add a bias resistor from B to C on Q1 to make up for the lack of leakage.  I used 470k in mine and a low gain Si Q1 (Hfe = 46) which drastically reduced the hiss over Ge for Q1.  Try it!  I've got a Ge in Q3 and might swap one into Q2 as well.  Good luck with it.

Yeah obviously if you change the biasing on the first stage you can use a silicon but Giglawyer was referring to a transistor switching mod. That's fine for Q2 and 3 but you need different biasing depending on what you're using on the first stage. Throwing a 470K pull up on the germanium will just make things hissy. At that point would just make more sense to make an all silicon bender from scratch...

[jrod]

The first stage in a MkII won't work with a silicon transistor.

Sure it will.  You just have to add a bias resistor from B to C on Q1 to make up for the lack of leakage.  I used 470k in mine and a low gain Si Q1 (Hfe = 46) which drastically reduced the hiss over Ge for Q1.  Try it!  I've got a Ge in Q3 and might swap one into Q2 as well.  Good luck with it.

Would I add bias resistors for BOTH the Ge and the Si transistors at Q1, or just for the Si?  (I am starting to feel that this is heading above my paygrade...LOL...) 

The first stage requires some leakage to bias correctly. If you swap out Q1 with a silicon transistor you will need to add a bias resistor. You shouldn't need to add a bias resistor with a germanium transistor in the first stage as long it has some leakage.

[Giglawyer]

The first stage in a MkII won't work with a silicon transistor.

Sure it will.  You just have to add a bias resistor from B to C on Q1 to make up for the lack of leakage.  I used 470k in mine and a low gain Si Q1 (Hfe = 46) which drastically reduced the hiss over Ge for Q1.  Try it!  I've got a Ge in Q3 and might swap one into Q2 as well.  Good luck with it.

Yeah obviously if you change the biasing on the first stage you can use a silicon but Giglawyer was referring to a transistor switching mod. That's fine for Q2 and 3 but you need different biasing depending on what you're using on the first stage. Throwing a 470K pull up on the germanium will just make things hissy. At that point would just make more sense to make an all silicon bender from scratch...

So, if I understand you correctly, better to leave Q1 alone and save teh switching for Q2 and Q3? 

[AnalogPackrat]

Set it up on a breadboard and try all the options out.  Only you can determine what you like.  I built and NPN version with Si-Si-Ge using the modified bias on Q1.  I also added a bias control on Q3 and a bright switch so I could use it with my SF Fender amps (lots o' treble).  I tried a pile of different transistors, variable bias on Q2, and a couple of other things before settling on my final build.  I like it.  Different transistors make a big difference IMO.  I ended up with a relatively recent 2N2369 (Hfe = 46) in Q1, an early NS 2N5856 (Hfe = 94) in Q2, and a 2N1306 (Hfe = 133, 58uA leakage) in Q3.  I might try a Ge in Q2 at some point, but all that I currently have are too high Hfe or very leaky.

[AnalogPackrat]

AnalogPackrat good see your post

Thanks, Gus.  I still lurk around the DIY forums and occasionally find time to build something...

[Solidhex]

The first stage in a MkII won't work with a silicon transistor.

Sure it will.  You just have to add a bias resistor from B to C on Q1 to make up for the lack of leakage.  I used 470k in mine and a low gain Si Q1 (Hfe = 46) which drastically reduced the hiss over Ge for Q1.  Try it!  I've got a Ge in Q3 and might swap one into Q2 as well.  Good luck with it.

Yeah obviously if you change the biasing on the first stage you can use a silicon but Giglawyer was referring to a transistor switching mod. That's fine for Q2 and 3 but you need different biasing depending on what you're using on the first stage. Throwing a 470K pull up on the germanium will just make things hissy. At that point would just make more sense to make an all silicon bender from scratch...

So, if I understand you correctly, better to leave Q1 alone and save teh switching for Q2 and Q3? 

You know what you can do actually. If using a 3pdt switch to go between the two transistors place a 470K resistor across the base and collector of the silicon being used. That way the biasing only affects the silicon

[Giglawyer]

SOlidhex - I am trying to envision how that would be wired up, but I think I understand it in principle. 

[Solidhex]

Oh sorry didn't see this reply. Picture a 3pdt switch with the "pole" lugs in the middle and the two rows of "throw" lugs on either side. The poles would be wired to the circuit board. On one row of the "throw" lugs you would solder a germanium transistor with its emitter, base, and collector corresponding to the related wires on the "pole" lugs. On the other side you would solder a silicon transistor in the same manner except you would add a 470K between the base and collector. That way the germanium maintains its regular biasing scheme and when you switch to the silicon it now has biasing scheme independent of the germanium side.

[Giglawyer]

SolidHEx - This makes sense.  THanks!