Tonemender gain pot or very simple overdrive to add

[JackSkellington]

Hi guys!
This is the thing. I have to put together the Tonemender with an high gain distortion. But I would like to have just a bit of overdrive, too. I wanted add a gain pot to the Tonemender. I replaced the resistor 4.7k with lower value, but the sound is still clean.
I hoped there was an easy way to get a bit of overdrive.


If that is impossible I could add a little overdrive board, but what?
- It has to be little, simple, with just few components.
- Verified stripboard or protoboard.
- it can work at 12v.
- Just a gain pot which doesn't drop the volume at minimum setting.
- Transparent sound at minimum setting gain, as if it there's no.
- I can get a fix value for the volume with a trimmer.

I'm not saying that exist a pedal like that! Just I wanna know if I can find it.

Thank you!

[WormBoy]

If you just want to get a bit of overdrive from the tonemender, you could easily put in some diodes in the feedback loop of the last opamp stage (TubeScreamer style). However, the overdrive would be generated post eq, which will be different from most pedals (but could be interesting). You can experiment with the values of the two caps to get a nice sound out of it.

[JackSkellington]

I tried something.


On an external board I have included:
C4, D1 and D2 (red led), R6 (47k), P1 (1M Linear).
R4 and C3.
I got sound, loud, clean at the minimum setting, overdriven at higher, and that's ok. But, at any setting, the bass is completely cut off.
I changed C4 until 300pF and C3 until 100nF, them don't change anything.

Did I miss something? Or I can change something else?

[Ralfg]

Try increasing c3 until you get the sound you are looking for. Your current setup is cutting bass. You could try 100n, but you should experiment to see what works for you. You can use AMZ's RC filter calculator to dial in the corner frequency. Anything below the corner frequency will get cut.

http://www.muzique.com/schem/filter.htm

[WormBoy]

I would simply start from the tonemender schematic and only add some diodes in the feedback loop. If you use diodes that don't clip too hard in this particular setting, your eq will not change much. As Ralfg said: C3 is the likely culprit in th screamer scheme (this cap is 470nf in the tonemender). C4 only cuts treble, so increasing it will make your sound duller at higher gain settings.

[JackSkellington]

[...]
I changed C4 until 300pF and C3 until 100nF, them don't change anything.
[...]

I would simply start from the tonemender schematic and only add some diodes in the feedback loop.
[...]

I tried to add in the feedback loop of the IC just two red leds with the R6 and the pot. No distortion at all, but a clean sound at any setting. Maybe just a bit compressed at higher setting.

I guess I have start to think about which circuit I have to put (before or after) the Tonemender.
Nothing more complicated of DOD250* or Son of Screamer. But I remind all this:

- It has to be little, simple, with just few components.
- Verified stripboard or protoboard.
- it can work at 12v.
- Just a gain pot which doesn't drop the volume at minimum setting.
- Transparent sound at minimum setting gain, as if it there's no.
- I can get a fix value for the volume with a trimmer.

I add also:
- No adding noise.
- It should have a way to set the max amount of gain with a mod in case it has too much.
- It should have a way to set the tone with a fix value.

* I put my modded DOD250 in front of the stock circuit of the Tonemender and it doesn't sound right for me. Nor with 1n924s, nor with leds, nor without diodes.

Thanks again!

[WormBoy]

I tried to add in the feedback loop of the IC just two red leds with the R6 and the pot. No distortion at all, but a clean sound at any setting. Maybe just a bit compressed at higher setting.

Likely not enough voltage gain for LEDs to clip (they have a very high threshold). The circuit starts with a unity gain buffer, followed by a lossy tone stack. So, after the tone stack, volume will be really low. The second opamp stage has to make up for all that. That one has gain 100 so I guess it will gives some volume boost as a net result, which might be enough to get some clipping and still keep a good volume output. You could try silicon diodes (or something with even lower thresholds such as some Schottky's or Ge's), that should give some audible crunch. Or increase the gain pot, decrease the 4k7 to ground ... many options to explore  .

[Max]

Well, I don't know if it's my circuit only, but the output of the second op amp is pretty loud, I have unity more or less with the volume between 9 and 10 o'clock.

[JackSkellington]

My Tonemender circuit has a lot of volume. If you try higher values to replace the 4.7k resistor you can get  less volume. But seems to me not change the min volume. It is never mute.

Meanwhile, I'm making some tests with the whole clipping section changing several values. The things are going better.
See soon.