H.B.E. Detox EQ

[JoeyBloggs]

As I've been using this website for a number of years now, seemed only fair to post some new stuff as I got the vero-diction. Looking to make this more regular. A while back fell a bit skint, so had to sell my precious Detox EQ, but not before reverse engineering it. See design below, apologies for my amateur layout skills. I originally tried to make it as small as possible to fit in a 1590B with a battery also. Technically this is verified, as I have built it more than once...

[purity]

Are my eyes deceiving me or is the input hooked up via two jumpers straight to the opamps ground pin 4? And pin 4 isnt otherwise hooked up to ground? Trying to work out the schematic of this gem over a beer or two ^^

[GrooveChampion]

Kinda reminds me of the Tonemender

[JoeyBloggs]

whoops, good spot purity. Should probably checked the design against my own builds.. I'll clean this up later, also realised some cuts aren't relevant. I believe the immediate fix is just extending that second jumper down by one row, so it is actually going to GND. But I will double check also...

[storyboardist]

Is there another cap that spans between Mid 1 and 3? Most EQ stacks like this I've seen have one there...

[purity]

I have a preliminary schematic drawn up at work, I'll post it tomorrow. Maybe the OP can chip in aswell?

I expected the design to be different, more like a parallel blended filter, but this is a series filter of sorts. Its quite simple, but rather unrecognizable to me. The signal is fed to the first opamp, output is hooked up to one end of a quite symmetrical 'tonestack' of which the other end goes to the second opamp input. Then a slightly odd highpass filter (2.2u/100k) to the level pot, which i guess is variable high pass.

I will have to wait on the OP to verify my schematic though, see if the half supply stuff is hooked up ok.

[traktop]

Yes!!!
So, is the layout updated?
I want to build this so bad...

[zosotone]

This is the schematic from PedalPCB:

[purity]

I noticed there are differences between the schem I drew up from the vero and the schem from pedalpcb. Not just polarity protection and filtering, e.g. the cap across the volume pot is not present.

I still don't have my schem copy, only a rough printout.  
https://imgur.com/a/3mFzgOh

[purity]

Here are the differences I can spot. First is the vero, then the pedalpcb change.

Main circuit:
Input pulldown res: 1M to 10M
Output of first opamp / bass pot: 1uF cap in different position
Bass pot 1-3: 33n to 100n,
Bass wiper 4k7 to 6k8
Mid pot 1-3: no cap to 33n
Mid wiper: 6k4 / 22n to 22n
Output of 2nd opamp: 47R to 27R
Level pot 2-3: 100n to none

On the power supply:
Series 10R is omitted in pedalpcb schem
Parallel 1N4001 to series 1N5817
Vref decoupling cap: 47n to 4u7

[zosotone]

A lot of differences, I suppose that these changes are made to market the PCB. So, it's your layout verified? I can compare your Detox with my original Mad Professor Underdrive, that it's very similar.

[Sphere80]

Zosotone, could you take a look at this? The copy used to claim it inspired the Underdrive:
http://guitar-fx-layouts.42897.x6.nabble.com/Guitar-PCB-Tone-Tweq-td41663.html

Updated link to schem:
https://guitarpcb.com/wp-content/uploads/2018/07/BD_Tone-TwEQ.pdf

Like the Detox, it's a clean 3 band Baxandall, but I see a few component differences.

[zosotone]

Well, my Underdrive it's not traced yet (I don't have a lot of time). This is my post about it:

http://guitar-fx-layouts.42897.x6.nabble.com/Mad-Professor-Evolution-Underdrive-with-photos-td30670.html#a30754

I don't know if the Tone Tweq has a similar structure to the Underdrive...

If someone wants to help to trace it, I would appreciate it.

Anyway, I can make the Tone Tweq or the Detox and compare it with my Underdrive, but I think that the Tone Tweq it's not verified.

[Sphere80]

The Underdrive has a quad op amp, so I guess not. Thanks for sharing.  

[zosotone]

A lot of work today with the Underdrive. It's a preliminary trace without resistors and some caps:

[zosotone]

Does anyone want to help me with the scheme? face to face with the Detox.

[BuGG]

There are apparently multiple versions of the Detox.

https://www.thegearpage.net/board/index.php?threads/detox-dupe.1985585/
https://www.thegearpage.net/board/index.php?threads/help-with-detox-eq-pedal-need-only-one-photo.1436776/

Between these two threads (and the schematic posted above) you'll see three different opamps.
NE5532, RC4558, RC4559, and OPA2134.

In one version you'll see that the cap across the volume pot appears to be 1nF, in another it isn't present at all, and here it is listed as 100nF.

In this photo you can see that the input pulldown resistor is 10M.  (Brown Black Blue)
http://sia1.subirimagenes.net/img/2014/05/26/140526063817737345.jpg

Not to mention a few obvious errors have been pointed out in the vero posted above, so until the OP posts an updated/corrected layout I wouldn't call it verified.    

I'm just speculating without seeing the unit that was traced by the OP, but I've never seen a 47nF Vref filter cap on any pedal...   The original that I've seen had a 4u7 tantalum.  Looking at the pics in the threads above you'll see 4 tantalum capacitors, which suggests that is likely what they are using as well.

As far as the polarity protection, I will almost always use a series diode as opposed to parallel to ground..... A shorted protection diode is still a broken pedal to the average user.


As soon as I get some free time I'll draw up a schematic based on your trace of the Underdrive and we'll take a look.

[Sphere80]

zosotone is updating his trace here:

http://guitar-fx-layouts.42897.x6.nabble.com/Mad-Professor-Evolution-Underdrive-with-photos-td30670.html

[zosotone]

Corrected. Not verified yet.

[zosotone]

Verified by squirrels. Thanks!