# Design Challenge #2.1 - The CMOS Overdrive Deluxe



## Chuck D. Bones (Jun 29, 2021)

A few weeks ago, MattG asked if it would be possible to replace the CD4007 OD's JFET front-end with an opamp.  That sent me down the proverbial rabbit hole and this is what (eventually) popped out.  First stage is an opamp 18dB clean boost.  Second stage is a variable-gain CMOS amplifier.  Third stage is a Catalinbread VariOboost, with slighty-altered component values.  Fourth and fifth stages are the same variable gain stages used in the original design, with a few component value changes.  At the end is a BMP-style tone control followed by a volume control.

Seven knobs  
PREAMP sets the 2nd stage gain.
BASS is a variable freq bass rolloff based on the Friedman TIGHT control.  It's located near the front of the signal chain, ahead of the distortion stages.
MID & MID FREQ are the familiar VariOboost controls.  VR5 is a dual-gang C100K.
TREBLE is a passive high freq cut / boost, using the familiar BMP tone circuit.  It's located at the end of the signal chain, after all of the distortion stages.
MASTER sets the 4th & 5th stage gains.
LEVEL is the usual volume control.

With PREAMP & MASTER dialed-down, it's a clean boost.  Turning PREAMP up gradually adds dirt before the Mid controls.  Turning MASTER up adds dirt after the Mid controls.

So far, it only exists as a Breadboard.  I'm pretty happy with it as-is.  The most I'd change at this point, if anything, would be a couple of component values.  Total gain at the output of the 5th stage is a healthy 72dB with the MID controls set to noon and everything else dimed.


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## cooder (Jun 29, 2021)

Super cool and great to see the varioboost incorporated in it, now let me wrap my brains around that... looking very interesting.


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## Chuck D. Bones (Jul 10, 2021)

I came up with a name for this one...

The _Harmonic Overdrive Experience_, "HOE" for short.  I thought about using a different word that started with "O."

_*Brothers & Sisters!  Pimp your pedal board with a top-notch HOE!
Everybody needs a HOE!*_


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## cooder (Jul 10, 2021)

I take that as a "yes stick your fork into it"... cheers!


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## Chuck D. Bones (Jul 10, 2021)

You are correct sir!


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## cooder (Sep 13, 2021)

With Chuck's blessings I put a board together for this, he helped me comb over the schematic and all, so big shout out to the man, Sir Chuck!
When I put it in the box I had it going but it didn't quite qo right, the mid pot had an off range and mid freq was off too. I must have had a solder bridge somewhere and after some poking arond and redoing the smd chips, re flowing some joints it's all go now and a rippa! 
Very versatile and unique, I really dig the gainier side of things with pre and gain halfway or higher, and of course the ability to shape the sound big time with the vario boost snippet in there. I really like the Varioboost as a stand alone circuit already, having it in here is just sweet.
Having four pots in the lower row meant of course using 9mm pots there to get it in to the 125B. 

I present you the 'Mirage' aka Harmonic Overdrive Experience #2.1.


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## Chuck D. Bones (Sep 13, 2021)

Beautiful artwork and board layout!

The CD4007 is nice and quiet, yes?


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## cooder (Sep 13, 2021)

Thanks man! Where would we be without the boneyard and this forum!
With both pre and gain dimed there is some noise but considering the gain amount it's not not out of line I would say. My neighbours might disagree, but I think they mainly are concerned about my playing as such... 
This CD4007 is from Tayda, I might get myself one from Mouser next order and compare, maybe? Any hints what to shoot for as sources and specs?


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## temol (Sep 13, 2021)

Samples, please...


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## Chuck D. Bones (Sep 14, 2021)

cooder said:


> This CD4007 is from Tayda, I might get myself one from Mouser next order and compare, maybe? Any hints what to shoot for as sources and specs?


AFAIK they're all made by Texas Instruments.  Specs?  We don't need no steenking specs!


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## Sturdag Lagernathy (Sep 14, 2021)

Chuck D. Bones said:


> AFAIK they're all made by Texas Instruments.  Specs?  We don't need no steenking specs!


I used a Motorola MC14007UB, an equivalent. Sounds great!


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## Chuck D. Bones (Sep 14, 2021)

If it's new, it's not from Motorola, it's from ON Semiconductor.  Still, good to have an alternate source.


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## cooder (Sep 14, 2021)

Sturdag Lagernathy said:


> I used a Motorola MC14007UB, an equivalent. Sounds great!


Where did you get that? I checked Mouser and they only seem to have it as smd footprint.


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## fig (Sep 14, 2021)

That's a stunning build @cooder .


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## MattG (Sep 14, 2021)

@cooder - that looks absolutely fantastic!  Thanks for posting the pics.  At first I thought it was a bigger enclosure than 125B, all the more impressive how you made it all fit without looking congested.

Looks like you're using a soft-switch instead of the mechanical type?  And presumably you integrated the soft-switch circuitry on the PCB along with the overdrive circuit?  Is that soft-switch circuit your own design?


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## cooder (Sep 14, 2021)

Thanks guys! All Chucks brain power in there, I'm just putti ng it together.


MattG said:


> @cooder - that looks absolutely fantastic!  Thanks for posting the pics.  At first I thought it was a bigger enclosure than 125B, all the more impressive how you made it all fit without looking congested.
> 
> Looks like you're using a soft-switch instead of the mechanical type?  And presumably you integrated the soft-switch circuitry on the PCB along with the overdrive circuit?  Is that soft-switch circuit your own design?


The soft touch switch is based on the coda effects one (I have a slightly changed code, but pretty much similar), you can find it here:
https://www.coda-effects.com/2016/04/relay-bypass-conception-and-relay.html


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## Sturdag Lagernathy (Sep 15, 2021)

cooder said:


> Where did you get that? I checked Mouser and they only seem to have it as smd footprint.


Local electro shop. Good for some things, but their glory days are past..


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## Chuck D. Bones (Sep 16, 2021)

cooder said:


> Thanks guys! All Chucks brain power in there, I'm just putti ng it together.
> 
> The soft touch switch is based on the coda effects one (I have a slightly changed code, but pretty much similar), you can find it here:
> https://www.coda-effects.com/2016/04/relay-bypass-conception-and-relay.html


You are too modest.  It's a beautiful board layout and integrated relay switching is top shelf.


cooder said:


> Where did you get that? I checked Mouser and they only seem to have it as smd footprint.


The thru-hole MC14007UB is no longer in production.  On Semi is only making them in the SOIC-14 package.


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## Sturdag Lagernathy (Sep 19, 2021)

Chuck D. Bones said:


> The thru-hole MC14007UB is no longer in production.  On Semi is only making them in the SOIC-14 package.


Yeah, my local shop doesn't get much new stock. It was always kind of a pull-a-part type place. Years ago, it had all kinds of radio equipment, industrial machines of all kinds, bought out electronics manufacturing raw parts. It was really incredible. 1.00$ grab bags were an especially fun time. I made a movie accurate proton pack after many long hours digging. It's a shell of itself now. Couldn't get a B100k pot of any kind yesterday.


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## Chuck D. Bones (Sep 21, 2021)

Around here, there is only one brick & mortar electronics shop left.


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## HamishR (Oct 3, 2021)

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!


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## Chuck D. Bones (Nov 7, 2021)

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





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.









Checking the pot clearances.


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## cooder (Nov 7, 2021)

Awesome! Great to see Sir @Chuck D. Bones thanks for creatig all that circuit magic and the boneyard and your generous sharing!
Top notch enclosure by Dan there as well, don't we love some teamwork!


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## Chuck D. Bones (Nov 28, 2021)

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.


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## jjjimi84 (Mar 18, 2022)

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.


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## JamieJ (Mar 18, 2022)

I missed this build too! Amazing work guys!


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## Gordo (Mar 19, 2022)

Me too.  Cooder it's unusual to see you forgo your normal faceplate style.  Great graphics.  Well done Chuck,  as the owner of a Dan painted enclosure on one of my projects it ups the level of coolness about 500%


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## cooder (Mar 19, 2022)

@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.


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## Chuck D. Bones (Apr 21, 2022)

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:


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## cooder (Apr 21, 2022)

Thanks for the update! Seems easy enough to install on pot.


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## Chuck D. Bones (Apr 21, 2022)

Yeah, I wouldn't rev the board routing just for that.


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