Another distortion. This one offers crunchy vintage dirt. Like MFZ-1.

[brett]

Hi
after getting help from RG Keen about improving the Maestro MFZ-1, I've come up with this design.  It's called the Hidrosis, which is the medical term for excessive sweating.  The sound is quite like what you hear on Black Keys albums (Dan uses an MFZ-1), but the maximum gain is a bit higher, the noise (hiss) is a lot less, and the tone is a little darker.

Here's the schematic:


A key component is the 120pF cap in the feedback network of the second op-amp stage.  Substituting 47pF makes the tone sharper, while 220pF is softer/darker.  I found it hard to choose between 100pF, 120pF and 150pF.  150pF is what I used in mine, but I only play at home and don't need any highs to cut through a backing band.

Here's a pcb and an overlay:
http://gmm.bigblog.com.au/data/1/9576/image/HidrosisPCB3319620061030094340.JPG
http://gmm.bigblog.com.au/data/1/9576/image/HidrosisOverlay3319520061030094340.JPG

While I try to design things so that component values aren't critical, there's lots of components in this one that can't be varied too much, so it would be best to stick with the schematic wherever possible.
For people who want even greater "crunch", they might want to try LEDs instead of the 1N4148s.

that's about it.
cheers

[Dragonfly]

very cool Brett...i'm gonna have to add this to my "must build" list....

AC

[MartyMart]

Nice Brett, reminds me a bit of a Dist+ on steroids!! 

Marty.

[MartyMart]

Just breadboarded it Brett, sounds FAB !!
Very much a Fuzz/Distortion tone
Once I corrected my VB mistake ( 10k from9v to 1M !! ) it worked a treat !
Thanks,
Marty.

[brett]

Thanks MartyMart
I'm a major fan of the Black Keys, so I like pedals that gives me that kind of sound.
you've built a lot of stuff.  For people who might be interested in building this, but have no reference point, how would you compare it to other distortion/fuzz pedals, and how would you describe the tone?
cheers

[MartyMart]

For people who might be interested in building this, but have no reference point, how would you compare it to other distortion/fuzz pedals, and how would you describe the tone?

Tough one "describing" the sound.
Somewhere between a "Little Big Muff" and a "Dist+"
It has a nice "Rubber fuzz" sort of middle honk to it, it's a good sound for sure and
is unlike anything else that I have.
Stick to Bretts values as close as poss, my only changes were 12k's for all the 10k's
and a 25k B gain pot, but with a 22k r across 1 & 3 , so about a 12k pot ... close !!
100pf also " all I had "

MM.

[Nashtir]

You said you 've put a 25k pot..where did you put it? in the layout I can only see 1 10kB pot and a 100k for the volume..

[Seljer]

You said you 've put a 25k pot..where did you put it? in the layout I can only see 1 10kB pot and a 100k for the volume..

he used a 25k pot and a 22k resistor parallel to it (bringing it down to about 12kohms) because he didn't have a 10k pot available for the gain

[Nashtir]

oh, ok, thank you

[David]

So could the 10K resistor in the feedback loop of the first op-amp be successfully increased to produce more gain?

[MartyMart]

So could the 10K resistor in the feedback loop of the first op-amp be successfully increased to produce more gain?

Not really, all the gain is in stage two, from the pot and the 1M feedback resistor/2k2 & 2u2 cap !!
Trust me, having built one, you dont need any more gain 
If you made the first stage more af a gain stage it would just wipe out stage two and become uncontrolable MUSH !

MM.

[yeeshkul]

Brett i am gonna build this one, i was checking the schematics and have one question: what is the reason for having 2 parallel filtering caps (2u2 and 10n)? I mean those on TL072 lug no.8
thanks
Jan

[~arph]

Any sound samples? 

[gutsofgold]

It's a very gainy fuzz sound. My only problem was I felt it needed to be thicker and more bassy, but I always feel that way. I changed all the 2.2u filter caps to 10u at brett's suggestion and it definitely fattened up a bit.