JMI MK III TONE BENDER SCHEMATIC

[tonefactory]

I am looking for more detailed information about the JMI MK III Tone Bender.
I am wanting to know is it an exact duplicate of another version by someone else and are there any schematics available.
re there any clones of the JMI.


                   Thank You for your help......

[LucifersTrip]

they probably cloned the big one...sola sound or less possibly a vox?

http://fuzzcentral.ssguitar.com/3knob.php

here's an early one;

http://forum.musikding.de/cpg/albums/userpics/16602/earlyMKIIIschematic.png

[Electric Warrior]

The Vox MKIIIs were mostly built by Sola Sound and used the exact same circuits as the Solas.

They did make a couple of changes to it over the years. JMI went for the last (1972 onwards) variant with the 220k/47k bias string iirc.

[LucifersTrip]

There's tons of voltages reported for vintage mkii's, but there's a general lack for the mkiii

Does anyone have voltages from an original?

If I remember correctly, the mkiii and variants I've built have lower voltages for Q3C than many fuzzes...usually around 1.5 - 2V

[Electric Warrior]

Sounds about right. But nothing is set in stone. They can vary a lot iirc.
I didn't even worry about voltages when I built mine. It's not hard to make a three knob Tone Bender sound good.

[LucifersTrip]

you're correct...it's one of the easiest fuzzes to get to sound good since you really just have to worry about 1 transistor, Q3.  Q1/Q2 are so easy to choose, since darlington. You just need to pick a couple with low leakage...

But, to sound great is a different story. The sound really changes a lot with Q3 leakage, so always best to try a bunch before finalizing...like the Buzzaround.

[LucifersTrip]

if it helps, I just finished one of my best sounding ones

Q1/Q2 hfe 63, leak ~ 50uA
Q3 hfe 94, leak ~400uA

Q1/2 collector = -6.7V
Q3 collector = -2.06V

the higher Q3C voltage is, the bassier it will be

higher leakage will drop Q3C voltage

higher hfe Q3 is more gain (and I think also treble), even if leakage is constant

don't worry about higher amounts of treble since
1) there's a tone control
2) 220pf on Q1/2 really smoothens it out

a good mod would be to simply put a switch on the 220pf
(a lower gain Q3 sounds cool with the 200pf removed. I almost used a hfe 50 with 80uA leakage for Q3 [4.2V on collector], but later added the 220pf which smoothed it out so much, I put something in there [hfe 94, leak ~400uA] which gave me more treble and gain

edit:
forgot to mention I made only 1 change to the circuit. I changed the 220K between the vol & tone to 15K for more volume. removing it altogether was not cool since it seemed to get a bit boomy at high volume.