Skreddy Cognitive Dissonance MKIII

mmolteratx · Post by **mmolteratx** » 06 Dec 2011, 19:21

Here's the schem, will post pics once my camera is charged.

mod edit: original schematic deleted. New one is posted below.

Diamond · Post by **Diamond** » 06 Dec 2011, 21:24

Excellent job! Btw, what's the function of C11? The 1n cap between lugs 2 and 3 of the sustain pot. It's not on other Big Muffs. There's also an extra 100pF cap (C18) between lugs 2 and 3 of the volume pot. The 200pF cap to ground after the tone pot (C15) is for smoothing out the highs a little, isn't it?

Nocentelli · Post by **Nocentelli** » 06 Dec 2011, 22:34

I think both C11+18 are there to allow some high-end to bypass the pots and retain some brightness at lower settings. I've seen the sustain pot bright cap in a few BMP variants, notably the Catalinbread Goat pedal (Manx Loughtan?)

bubstance · Post by **bubstance** » 06 Dec 2011, 23:29

Nocentelli wrote:I think both C11+18 are there to allow some high-end to bypass the pots and retain some brightness at lower settings.

Bingo.

mmolteratx · Post by **mmolteratx** » 06 Dec 2011, 23:35

Ya, the caps across lugs 2 and 3 allow everything above a certain frequency bypass the gain pot. The same set up is seen in a lot of tube amps, i.e. JCM 800 and derivatives. It doesn't really do much above half way and does nothing when the controls are dimed.

Photos can be found at https://www.photobucket.com/cognitivedissonancemkiii/. They're way too large to post in here but there's plenty of detail, though the color seems to be off a bit, particularly with greens. Didn't feel like messing around with taking the pots off but I'm confident on the routing underneath.

Skreddy · Post by **Skreddy** » 07 Dec 2011, 08:48

C18 is traced wrong; it's not a treble bleed but a simple cap to ground.

It should be pointed out that the particular gain range used in this series is in the 800 Hfe zone. That's really high for a Big Muff build; hence the 390k feedback resistors and the 560pf treble filters in the clipping stages, which compensate and bring things back down to a reasonable level. Also certainly not Fairchild but either Central or CDIL based on the "C" logo, but yeah; these are of probably a 70's or 80's vintage that I've found in surplus shops, first in Sacramento then through a friend at a Singapore shop.

This build doesn't target any particular recorded tone or artist's signature style. It's just meant to be a good balance of articulation (the small 200pf filter cap in the input stage along with the polyester film input cap and treble bleed on the sustain pot help with this) and power.

Greg · Post by **Greg** » 07 Dec 2011, 10:25

Kudos to Marc for coming and offering assistance with this..
Let's not get into the whole "cap type doesn't make a difference" argument again please.. it's been done to death.

mmolteratx · Post by **mmolteratx** » 08 Dec 2011, 00:53

Skreddy wrote:C18 is traced wrong; it's not a treble bleed but a simple cap to ground.

It should be pointed out that the particular gain range used in this series is in the 800 Hfe zone. That's really high for a Big Muff build; hence the 390k feedback resistors and the 560pf treble filters in the clipping stages, which compensate and bring things back down to a reasonable level. Also certainly not Fairchild but either Central or CDIL based on the "C" logo, but yeah; these are of probably a 70's or 80's vintage that I've found in surplus shops, first in Sacramento then through a friend at a Singapore shop.

This build doesn't target any particular recorded tone or artist's signature style. It's just meant to be a good balance of articulation (the small 200pf filter cap in the input stage along with the polyester film input cap and treble bleed on the sustain pot help with this) and power.

Thanks. Fixed it and attached the schem. They just look a lot like some vintage Fairchild's I've got at a quick glance, didn't even look at the logo.

culturejam · Post by **culturejam** » 08 Dec 2011, 01:39

Moved the caps talk to Member's Corner

Skreddy · Post by **Skreddy** » 08 Dec 2011, 21:08

mmolteratx wrote: Thanks. Fixed it and attached the schem. They just look a lot like some vintage Fairchild's I've got at a quick glance, didn't even look at the logo.

Oops; sorry I missed this the first time, but the emitter resistors at Q2 and Q3 are 180R, not 150R. No big, though.

mmolteratx · Post by **mmolteratx** » 08 Dec 2011, 22:36

Skreddy wrote:
mmolteratx wrote: Thanks. Fixed it and attached the schem. They just look a lot like some vintage Fairchild's I've got at a quick glance, didn't even look at the logo.
Oops; sorry I missed this the first time, but the emitter resistors at Q2 and Q3 are 180R, not 150R. No big, though.

Crap. I caught that in the pictures right after I posted the initial schem but forgot to change it. Color codes and me aren't friends.

EDIT: Forgot to say anything about its sound. This is probably my favorite Muff variant that I've owned and I've owned a lot. I had a Pig Mine for a long while before this that I really loved but the CDMKIII is just flat out awesome. It's really smooth but has a ton of clarity. Sounds huge for rhythms too. No mush, no flab. Just a big wall of sound. Highly recommended.

gilmour_pugliese · Post by **gilmour_pugliese** » 29 Mar 2012, 09:07

Skreddy, what are the main differences between the Cognitive Dissonance Mk2 and Mk3?

Skreddy · Post by **Skreddy** » 30 Mar 2012, 05:29

gilmour_pugliese wrote:Skreddy, what are the main differences between the Cognitive Dissonance Mk2 and Mk3?

The main difference is the transistors. In both cases, the transistors were very high gain; so the tweaks (variations from the typical BMP schematic) were mainly to compensate for that. I don't recall the specifics of the Mk2 offhand, but they're pretty similar values throughout.

gilmour_pugliese · Post by **gilmour_pugliese** » 30 Mar 2012, 08:07

Skreddy wrote:
gilmour_pugliese wrote:Skreddy, what are the main differences between the Cognitive Dissonance Mk2 and Mk3?
The main difference is the transistors. In both cases, the transistors were very high gain; so the tweaks (variations from the typical BMP schematic) were mainly to compensate for that. I don't recall the specifics of the Mk2 offhand, but they're pretty similar values throughout.

Thank you man for your reply... A Mk2 of my friend has 3 693G (maybe 2SC693G?) and 1 BC184...

Skreddy · Post by **Skreddy** » 30 Mar 2012, 08:50

gilmour_pugliese wrote:
Skreddy wrote:
gilmour_pugliese wrote:Skreddy, what are the main differences between the Cognitive Dissonance Mk2 and Mk3?
The main difference is the transistors. In both cases, the transistors were very high gain; so the tweaks (variations from the typical BMP schematic) were mainly to compensate for that. I don't recall the specifics of the Mk2 offhand, but they're pretty similar values throughout.
Thank you man for your reply... A Mk2 of my friend has 3 693G (maybe 2SC693G?) and 1 BC184...

Yeah; those are some obscure Japanese transistors.

gilmour_pugliese · Post by **gilmour_pugliese** » 30 Mar 2012, 12:56

Skreddy wrote:
gilmour_pugliese wrote:
Skreddy wrote:
gilmour_pugliese wrote:Skreddy, what are the main differences between the Cognitive Dissonance Mk2 and Mk3?
The main difference is the transistors. In both cases, the transistors were very high gain; so the tweaks (variations from the typical BMP schematic) were mainly to compensate for that. I don't recall the specifics of the Mk2 offhand, but they're pretty similar values throughout.
Thank you man for your reply... A Mk2 of my friend has 3 693G (maybe 2SC693G?) and 1 BC184...
Yeah; those are some obscure Japanese transistors.

I've picked up just one 693G from an old Toshiba radio receiver... But it's very hard to find another two radios for doing the same operation

Skreddy Cognitive Dissonance MKIII [traced]