dirtbag impedance

[gitaar0]

When turning down the volume on my guitar I am experiencing quite a drop in volume and duller tone.
Gone with a buffer in front.

There is quite a bit written on the low impedance of the DMM and changing that by enlarging the input 100k resistor (with a 1m trimpot eg). If I want to make up for the then changed  gain can I do that by just putting a trimpot after the level pot?

I was also wondering if it was a deliberate choice to use 47uf and 22 uf at the blend pot instead of the 22uf and 10uf in other DMM schematics. Any experience with this?

[madbean]

The factory schematic specified the 47/22uF combination listed in the BOM, so that is what I used. There are many schematics out there for the DMM so I don't find it surprising that you might find some variations.

As far as the input impedance, you can try doubling that 100k at the input. I believe this is what Analogman does on his impedance mod, which is probably similar to what Howard Davis does. Or, just remove it temporarily, put in a variable resistor of 500k and dial it in to where you like...then replace with a fixed resistor. You should still have plenty of gain on tap after making that adjustment, but if you feel you need more, then increase the value of R3....say 100k. Haven't tried any of these mods myself, but based on the 10 minutes of reading I just did it seems like a good idea

[gitaar0]

Well that was my conclusion as well, that's why I asked.

Thanks and I will follow up on your suggestion

[madbean]

Cool, yeah let us know what you find. Interestingly, the input of the Zero Point is similar (without the Gain pot) so I might try larger values for the two resistors on that to see what difference it produces.

[gitaar0]

Ok.

220k for R2 gives a better input impedance. Less tone loss.
I could have left it like that but tried changing R3 as well.
With R3 150k i had the level control at around the same  level control as before, but i can not go back to a low level now. Not really necessary but not as nice... So I switched to 100k and left it there, it just means that i have to turn up the level control higher, but there is still enouh gain left.
Also what happens is that the delay signal has become  a bit louder so I am getting feedback oscillation earlier in the FB pots turn. I can of course adjust the gain in the bbd line, and that is what i ended up doing.

Changed the input and output caps to 22uf and 10 uf also, as per some of the older dmm schematics.
Sounds better to me.

Swapped IC 1 for a BB2604. Sounds very good if you want a clearer sound.

[gitaar0]

Brian,

Did you try this out for the Zeropoint as you wrote and what did you find?

Marc

[madbean]

I have not yet but it is on my list of things to do. I'm going to try a 470k input and either 470k or 1M in the feedback loop. I will definitely report back once I've done this.