Design Challenge #2.1 - The CMOS Overdrive Deluxe

HamishR

Well-known member
Where I live I have three different electronics chains and a few different actual stores. But two of them sell only generic stuff for about a zillion dollars more per item than Tayda, and the other one has a better range but is ridiculously expensive. And none of them has much in the way of stuff I actually want.

Amazing build, Cooder. Way above my level!
 

Chuck D. Bones

Circuit Wizard
It's done! Beautiful hand-painted case by Dan commemorates William Shatner getting blasted into space on Bezos' rocket.

CMOS OD Deluxe front 02.jpg

Primo circuit board by Stephan. It was a snug fit getting seven pots into a 125B case, but he did it. I managed to solder the SMD TL072s without screwing it up. Parts from Small Bear, Mouser, Tayda, Stomp Box Parts & Electronic Goldmine.

CMOS OD Deluxe innards 02.jpg

CMOS OD Deluxe solder side 02.jpg

Checking the pot clearances.

CMOS OD Deluxe pots 02.jpg
 

Chuck D. Bones

Circuit Wizard
One last design update:
The MID BOOST control has too much range (like that's even possible?) and is prone to feedback and howling at zero and 10 when GAIN is dimed. I have changed C6 from 33nF to 22nF. It lowers the max boost/cut and filter Q just enough to make the entire control range useful. I verified this fix on the breadboard and the Shot The Shat box.
 

jjjimi84

Well-known member
How did I miss this post? Man I really love this box and painting. There is something really fun about a silly ass idea coming to life like shooting the shat.
 

cooder

Well-known member
@Gordo my laser printer has died so I'm off the film decal faceplates for now and I'm glad that I got the Tayda UV print as option, which is what I have been going for lately. If I need to do the faceplate thing I need to hassle someone or pay for a laser print out... sigh... I might get me a printer again though.
 

Chuck D. Bones

Circuit Wizard
One last update...
I felt that at low DRIVE (AKA MASTER) settings, this pedal was too dark. I tried fiddling C9 & C11, but couldn't find values that sounded good across the full DRIVE range. The discussion on amps & bright caps that Mike started got me thinking about putting a bright cap (C18) on the DRIVE control. I tried 470pF... it was a eureka! moment. 470pF was maybe a bit too bright, so I ended up dialing it back to 330pF. That was the ticket, to my ears anyway. While I was in there futzing around, I reduced R5 to 680Ω to get a little more tightness when BASS was dialed all the way down and reduced R10 to 270K to pick up 3dB more gain without running out of headroom. Final schematic, including the C6 change noted above:

CMOS Overdrive Deluxe sch rev 1.1.png
 
Last edited:
Top