Celica Fuzz - Tone Bender MkII build - Thank You & a couple remaining questions

[valcotone]

hi all,

I finished building up a modified Tone Bender MkII and wanted to post some info on it. Yowza, it sounds spectacular! Compares well to a recent DAM/Sola Hybrid Mk2 I have.

First up, I want to pass along a big THANK YOU to previous discussion threads and posters about Tone Bender builds. When searching for details on MkII's, threads from DIYSB consistently came up and were always useful. In particular, posts by Electric Warrior (thank you!) on voltages and biasing really helped me dial things in. I learned a lot.

Below are some pics of the 3 pedals I've build in the last month, including the MK II (Celica Fuzz) and the schematic for that one. My goals were to build up some classic circuits and rely mostly on parts from my shelves... just ended up having to order transistors, 1K RA pots, and 5uF caps.

I did have a couple of remaining questions or uncertainties I hoped to clarify, if anyone is interested:

1. I used a 10K base resistor for Q1 as it seemed to put the collector voltage in the right spot. The voltage was too low with 100K -- does that sound like what you'd expect?

2 .Has anyone noticed any change in tone/response when swapping out the 470R resistor for a higher value (to get more output)? I used an 880R here as I wanted a little more output when engaging a tone control circuit (modded flat-response Big Muff style) which is pretty lossy.

3. I used a 250K volume pot as I didn't have any 100K... I temporarily tried a 220K resistor to ground on the output (to simulate 100K), but couldn't hear a difference in output or high-end vs. the 250K. This doesn't seem to align with things I've read about using 100K pots for Fuzz Faces to get more high end.

4. I see some of the high-end fuzzes often have shielded coax to/from the jacks and switch. Things are relatively OK with noise now, but do you see much benefit in doing that in your experience?

The voltages drift with temperature as expected with germainium devices, but I'm surprised by how much!

Any additional comments on the schematic, voltages, etc, are welcome. Thanks.

cheers!

[percyhornickel]

With 10K resistor in my build (pnp) Q1b is around -7.1V / -7.3V (9.0V P.S.) so I set the bias like -7.3V at Q3c.  If I set a higher bias starts to gathe too much. My transistor are so leaky so I am pretty happy with the sound.

Your Q1b seems to be a little high but is ok cause your -9.4V P.S.

Nice pictures, great components, great build!!!...      Looks incredible!

Saludos

P.H.

[valcotone]

Thanks P.H. !

For interests sake, I measured the Q1 collector voltage of the Sola/DAM Hybrid Mk2, and it reads 9.27V with a 9.38V supply. This is with a CV7112 Ge transistor in that position.

[valcotone]

A couple of updates on the Celica / MkII:

I ended up adding an external bias pot for Q2, as it's more effective in achieving velco/gated sounds than just adjusting Q3 bias by itself. The hi/lo switch now toggles between a normal fixed 'Mk II' bias setting/sound for Q2, and the bias pot.

Also, I can't say enough about using a reverse-audio C-taper 1K pot for the Attack/Fuzz control... it really opens up more precision over the upper-end of the fuzz control.

The switchable tone control I used in this a flat-response Big Muff style... this works really well, but does load the signal and drop some output when it's engaged (I tried to compensate by using the 820R to increase the output level a little). I'm able to get some MkIII/IV style sounds with this setup.

cheers!