Tonemender with Hiwatt dr-103 tonestack

[traktop]

I´ve just build the runoffgroove tonemender and it´s great, but it don´t work properly for what I have in mind.
I´m playing my hiwatt dr103 cranked and tried the tonemender as a "volume pedal with tonestack" similar to the homebrew detox/mad professor underdrive, (to clean up the amp and tweak the eq a little bit), but I´m having a similar experience to what I got  with the wampler ´65 with gain at zero and using just the tonestack for this matter: unnatural eq response.

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I was wondering if someone could adapt that strange tonestack to the tomender layout.
Cheers, Gilberto.

[Neil mcNasty]

Have a look and see if you spot any mistakes...
Only things I've changed, are two of the pot values  so that they match modern part values (250K instead of 220K, and 500K instead of 470K).

Updated and Verified Layout:

[traktop]

Thanks so much for taking your time Neil, appreciate it!!!
Everything seems correct.
I will verified as soon as possible.
Cheers, Gilberto.

[traktop]

I´ve just tried the layout.
Everything seemed correct, but the bass control is not working. Master volume worked as it should and the rest of tonestack worked perfect, but the moment I plug bass lug 1 to ground the pot gradually make the signal dissapear when turned counterclockwise, (to lugs 2/3), and grainy and distorted when turned clockwise, (to lug1/ground).
Looking at the schematics and the layout, I´m kind of lost with the behaviour of bass lug 1 to ground cause the rest of the tonestack, (treble and mids), worked like a charm going to ground via both 47n caps.
I checked and rechecked the whole build, (components placement, solder bridges, and pots), and I´m confident that everything´s in order.
Anyway, could anyone tell me which is the bass cap/s involved on this intrincate tonestack?
Cheers, Gilberto.

[traktop]

This is a picture of my build:
Still puzzled with the behaviour of bass 1 to ground. As soon as the violet wire is connected to any ground point I gradually lose all the signal when turned counterclockwise and the sound becomes grainy when turned clockwise, (at any volume).
The rest of the tonestack and master volume worked beautifully though.
I checked all capacitors/resistors values and possible unwanted solder bridges, but everything is correct.
Checked the layout again and I can´t find any mistake in the translation.
Any Idea?
Cheers, Gilberto.

[Neil mcNasty]

Could it be a bad pot?
Have you tried replacing the Bass pot?

Bass pot's lug 1 connecting to ground is standard for tone stacks, so that should not be the problem.

[traktop]

Didn´t replace it, but I ckecked it with the multimeter and everything seemed correct.
Will try with a new one tonight.
Could you locate the bass cap here?
Cheers, Gilberto.

[traktop]

Changed the bass pot and the problem still persists. Changed the mid knob as well just in case, but more of the same: The bass pot sends the whole signal to ground as the wiper points to lug 1.

[Neil mcNasty]

Try connecting the Bass Lug 1 wire to the vRef point between Input and Treble 1...

[traktop]

Bingo!
You can tag it as verified.
I really didn´t compare it with the original tonemender circuit, where tonestack ground points go to vref instead. I was wondering what difference it does make... (I guess just circuit design).
Anyway, it really does its job nicely: cleaned my cranked hiwatt amp, (just like a guitar volume knob), compensating any possible lack of the remaining sound with its natural eq response.
The only thing is that this thing has massive output level. I guess that a 1M level pot will do the trick.
Thanks so much for the layout!

[Neil mcNasty]

Cool. I'll update the layout!

After looking at both the schematics, it suddenly dawned on me that the tonemender had the "lowest" lug on the tone-stack connected to Vref instead of the regular ground, and that this might be essential for the circuit.

Regarding high volume output:
Yes it is very loud!
Increasing the Level pot puts more resistance in the feedback loop, making it louder.
You want to go the other way around: a lower value pot (try a 250K).
That should give you about half the volume output, and more precision at lower volumes.

Thanks for verifying!

Cheers!

[traktop]

You´re so welcome.

[Frank_NH]

"After looking at both the schematics, it suddenly dawned on me that the tonemender had the "lowest" lug on the tone-stack connected to Vref instead of the regular ground, and that this might be essential for the circuit."

Vref in the tone stack is needed in this case unless you had a coupling cap between the tone stack and pin 5 of the op amp.  Note that pin 5 has to see Vref for correct bias, which it gets from the 1M resistor connected to Vref.

[Neil mcNasty]

Ahha.... Now I get what is going on here.
Thanks for sharing the knowledge!