# Complex OD (Friedman Small Box)



## Chuck D. Bones (Dec 30, 2020)

A couple questions for the PedalPCB Man or anyone who has built one of these...

That STRUCTURE switch, all it does is cut the gain?  Seems semi-useless since the GAIN pot does that already.  I'm building the Thermionic Deluxe, and rather than build channel B as a Brown Betty (which I already have), I'm going to build it as a Complex OD.  Looks like I can leave that switch out and maybe use an A500K in place of the A1M for GAIN. Should work because channel B is intended for lower gain operation.

C14-R20 on the Complex OD adds a 6dB boost that starts at 7KHz and tops out at 14KHz.  Who the Hell is gonna hear that?  Not me, that's for sure.  I might try increasing C14 to move the treble bump down 2 or 3 octaves.  The TREBLE and PRESENCE controls are cut only, so I think a 6dB boost starting at 3.5KHz or so will work.

I might mess with D1-D4 on Channel B also.

Your thoughts?


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## jubal81 (Dec 30, 2020)

Switch is pretty redundant unless someone wanted to put it on a footswitch. Even then it really only seems to make a noticeable difference at higher gain anyway. Might as well use another boost pedal, IMHO.

To my ears, it doesn't really need any more treble. Nicely smooth but articulate for me even at max gain with EQs at noon. Overall it's scoopy, but that's pretty much what I expected. That 470pF might be a late addition where it just needed 'that little bit on top' and it was a first solution that worked well enough. I dunno. 7Khz is way the hell up there, though.

Shorting one of those feedback diodes pairs might be a better use of the switch - might be an amp sim/distortion control.


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## Chuck D. Bones (Dec 30, 2020)

Thanks for the feedback.  My baseline plan is A500K for GAINB and shorting out D4 for some mild asymmetry.  Still on the fence on what to do with C14, but I can figure that out by ear when it's built.


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## cooder (Dec 30, 2020)

The good ol' Boneyard deluxe treatment is descending on the Smallbox... nice move.


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## Chuck D. Bones (Dec 30, 2020)

It's just a Thermionic Deluxe with a few component value changes.  Not such a "Small Box" since it requires a 1590xx.  Ha ha ha ha.


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## mjh36 (Dec 30, 2020)

I'm gonna give a go at this mod too. Between you and @Bucksears and comparing schematics I think I got it. Noob mod questions sorry:

For the Thermionic Deluxe C20 (100u changed to 47u), I don't have a 47u, can I leave it 100u? Or put another in parallel for "50u" right?

Also I don't have a 10R Ohm resistor that I see in the power section, do I really need it?


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## Chuck D. Bones (Dec 30, 2020)

47uF or 100uF, either one is ok for C100.  

A zero Ohm resistor will suffice for R100.


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## mjh36 (Dec 31, 2020)

Well I don't have a Complex yet, but these mods sound dang good. I socketed the C8 (220pf) and the R18 (47k/470pf). Ya I couldn't hear anything with that combo. So I used a 4n7, also a 47n, both sound cool, but I don't know the math of what Hz they change though.


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## Chuck D. Bones (Dec 31, 2020)

Treble boost starts at:

f = 1 / (2 * pi * 47K * C)

Treble boost peaks out at:

f = 1 / (2 * pi * 24K * C)

With 4.7nF, the freq response starts rising at 720Hz and flattens out at 1.4KHz.

With 47nF, the freq response starts rising at 72Hz and flattens out at 140Hz.  Might as well be a jumper with that much capacitance.


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## mjh36 (Jan 1, 2021)

This is great thanks I legit learned something. I had a couple "ah-ha" moments working on this last night. I would take that formula and double check my bad math with a reactance calculator I found online. With that I narrowed down what capacitors to use. Always wondered about stuff like that. I wish I had a more options but so far 1n, 2n2, and 4n7 were good sounding. I see now how it shifts to the lower frequencies.


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