Tone Bender MK I - tone control/tone pot

[Arangonix]

Hey guys,

is there a way to put a tone regulation pot in MK I circuit? I finally finished and fine tuned my MK I clone (with your help, thx ) and now I'm playin' with some mods and tweaks to see how it works.

I've tried to implement tone conrtol from MK II, but it didn't work properly



Maybe some thin/fat switch?

I built my MK I using Sola Sound circuit:

[antonis]

Replace R9 with a 50k pot (wired as variable resistor) + 1k resistor..
You'll form a HPF of  31 - 1590 Hz..

For 25k pot, range is 61 - 1590 Hz, and so on..

[Halkbi]

I'm guessing that you're referring to the tone control found in the MKIII/MKIV, since the MKII doesn't have one. If wired properly, it's bound to work in place of an output cap in any circuit.

For a simple thin/fat-switch just make C4 switchable. You could probably go as low as 2.2nF for a thin sound, but I would start off around 10nF. The downside of such an arrangement is that the fat position is going to be a whole lot louder than the thin position due to the fact that it has more frequency content.

A better and whole lot more flexible way of doing it is to utilize an output cap blend pot (which is basically what the MKIII tone control is) instead of a switch. Wire a 1n-10n cap between the collector of Q3 and lug 1 of the cap blend pot (100k should be fine), as well as an 18k resistor in series with a 100n between the collector of Q3 and lug 3 of the pot. The output then comes from lug 2 of the pot. This lets you pan between the small and the big output cap instead of a hard switch, and the 18k is a limiter resistor that attenuates the level of the bass side of the pot so that it matches the bright side. The 18k value is a mere starting point that I pulled from the MKIII and you will probably have to increase it in order to keep the volume uniform across the sweep.

The downside of such a blend pot arrangement is that it will suck some output level. I have no experience with the MKI but looking at the schematic, I would simply lower R10 until I got the volume needed. If I were to build one from scratch I would probably ditch both R9 and R10 and wire a 50k volume pot straight from the output cap blend pot to give an approximation of the original 100n/47k output filter, but that could end up making the pedal too loud.

[Arangonix]

antonis, will check it today. Linear pot, right?

Halkbi, I was reffering to this particular modified Si MK II circuit from my first post, not to whole MK II family of effects. I found it in the internet accidentally and just check this idea of tone control in my MK I. This idea works fine in MK II circuit, as I bread-boarded it for fun. Will try your ideas too and drop u a line how it worked out.

[iainpunk]

i suggest cutting off everything after the .1uF cap that connects to the last transistor on both circuits, and just graft it over onto the other.

cheers

[Arangonix]

antonis, repaceing R9 resistor with 50k lin pot didn't work good for me. The difference was really subtle between min and max.

halkbi, 100k pot blend was kinda nice but when the pot was fully on 100nF side, it attenuated the sound by a lot + it gave blanket-over-amp sound.

iainpunk, I did it and use MK II vol/tone wiring (as in schematic from my first post). It works but overall sound is fizzier.

Every idea had changed the original sound of my circuit. What should I do to maintait it's vibe and have a tone control?

[antonis]

antonis, repaceing R9 resistor with 50k lin pot didn't work good for me. The difference was really subtle between min and max.

If you realize as "subtle" the 31Hz  - 1590Hz HPF corner frequency margin, I believe we're talking about totally different tone control meaning..

[iainpunk]

Every idea had changed the original sound of my circuit. What should I do to maintait it's vibe and have a tone control?

buy a boss GE-7
or add a buffer to the last stage, and put the tone control after the buffer.


cheers, Iain

[Halkbi]

halkbi, 100k pot blend was kinda nice but when the pot was fully on 100nF side, it attenuated the sound by a lot + it gave blanket-over-amp sound.

What value did you use for the limiter resistor? Sounds like 18k is too high for this circuit. Try lowering it until you get the same output level across the pot sweep. Also make sure to put the resistor before the cap. The 100n side should be pretty much identical to the stock setup and my guess is that the blanket effect that you're talking about is all about the loss in volume due to the fact that lower volume means less perceived highs (look up the fletcher munson effect). You could always try raising the pot value, but I doubt that that's the issue here (a bigger pot value would mean more rejection of the non-dominant side of the cap blend pot = bassier bass side/treblier treble side). I suggest you wire up a stock version for an objective comparison. Ears are easily fooled.