Mad Professor Evolution Underdrive (with photos)

[zosotone]

I have this new baby. In theory it's similar to the Home Brew Electronics - Detox EQ. Cleans very well the sound of the overdrive amp.

[zosotone]

Photos:

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[Neil mcNasty]

FYI: A so-called "Underdrive" is simply an EQ pedal that is set below unity level.
You can use any EQ pedal to accomplish this:
Filter away some highs and lows and leave the mids up + turn the volume below unity...
"Underdrive" is simply a new snake-oil marketing buzzword/hype in order to sell you something you (probably) already have.

Do not get me wrong!
I do not doubt that it is a great pedal.
But just think about it for a second...
How do you clean up a dirty/distorted amp?
- You simply turn down the input volume of the amp, or your guitar volume, and it gets cleaner!
But this often gets muddy, we need to add the EQ.
And since EQ pedals are really horrible sellers on the market, we rebrand it "Underdrive"...
You know... To clean up dirty amps...
And God forbid... DO NOT tell anyone that this can be accomplished with something you already have lying around unused since the 90's.
You need a NEW pedal to do this!!!

Sorry for that rant... I just had to get  it out! I Feel much better now!

So what am I actually trying to say here, besides letting out some steam about the "Underdrives"?
For those of you that desperately want this (or the Detox pedal), I would recommend building the ROG Tonemender first, and see if this suits your purpose, before ordering these new magical pedals that cleans up so well.
If you upgrade the opamp to a high quality one (like a OP275 or similar...) you pretty much got the Detox pedal.

Of course there is a slight chance that I got this all wrong, and that there is actually some new break-trough in circuitry design that works wonder on overdriven amps.
So I hope that we can manage to trace these pedals so see what is actually hiding under the hood...
There better be some Mojo to it!!!

[zosotone]

Well, I tried some options to clean the amp, treble bleeds, Xotic RC clone, parametric eq with volume pot... and this pedal works well on my rig.

I intend to share this PCB because there is no information available from these two pedals.

I'm not the best drawing layouts but it is possible that there is someone out there who can help.

Cheers.

[Frank_NH]

Here's a good explanation of the detox EQ (and similar pedals) from the gear page:

    
The detox is essentially a guitar volume pot with bass and treble EQ added on.

It'll clean up your amp or pedal exactly the same way your volume pot on your guitar cleans it up except you will be able to dial in EQ to make up for the typically muddy treble and thin bass when the volume is rolled back. So if you amp or pedal responds very well to the guitar volume then the Detox will be very useful. If they don't respond well to the guitar volume then the Detox won't make it any better.

The detox works best with single channel non master volume amps as these are the kind that tend to go from clean to mean with just a twist of the guitar volume.

http://www.thegearpage.net/board/index.php?threads/hbe-detox-eq-yay-or-nay.1013202/

Having a volume knob as a switchable pedal sounds like a reasonable idea, although using a two channel amp may be a better solution IMHO.
     

[traktop]

This is great. I tried a detox eq long ago,in order to "clean" my cranked Hiwatt. I´m not gonna say this is a "magical" device, but you can feel that this was designed to do what it prays to do, and in a nice way. I´ve got a danelectro eq, which is great, but it simply didn´t work for this task; not even close the detox did. I think is because the way the the eq bands are designed, (very natural). It was supersilent as well.
We want it!!!

[zosotone]

A preliminary trace without resistors and some caps:

[zosotone]

Does anyone want to help me with the scheme?

[Sphere80]

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[zosotone]

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[zosotone]

Layout update. Some caps and resistors with right values. I added the brand colors to these resistors too.




Multilayer caps:

C5 it's marked with "331"
C4 with "105"
C11 with "105"
C14 with "105"

105 = 15nf?
331 = 330pf?

[BuGG]

The caps marked 105 are 1uF,  331 is 330pF.

[zosotone]

Updated. I added the link between C3-R6, and the two pins IC. Thanks to Sphere80 and BuGG.

[Greedy_Fly]

Verified???

[zosotone]

Not yet. I need help with the vero.

[Greedy_Fly]

Hmmm.... Communication of all components are true on your pic???...

[zosotone]

The drawing it’s in progress. If you can help, there are some pics at the beginning.

[Greedy_Fly]

Hi... I can't understand... Where is the resistor for LED? Whats the zener diode on small pcb?

[zosotone]

Diode it's for the power protection. The drawing only shows the essential parts.

[joolsa]

It's rainy, so I turned the trace into some schematics. Probably some errors in there. I'm not sure if the trace is right between the final op-amp and the output. There's lots of caps and resistors in there!