Problem with Big Muff +Blend

[Coolhat]

Hi,

a newb bassist/guitarist from Finland here!

I am building a Green Russian Big Muff with clean blend. Both The Muff and the blend circuit (JFET Mini Blend) seem to be operating properly, but I have trouble combining the two, because the BMP output is waaaay louder than the clean signal. I can only get usable blend functionality when the BMP volume is near zero. If I rise the volume even slightly, the big muff signal starts to "leak" to the clean side of the blend pot.

I have checked the blend circuit over and over again and I can not find fault with it - after all, it is just 6 components. The BMP does sound very good, so I assume it is OK. It is very loud, but then again, isn´t that how a BMP is supposed to be?

Any help is greatly appreciated. Fortunately the whole thing is still on a breadboard, so any fixes and mods are easy to do.

[anotherjim]

See this...
http://www.diystompboxes.com/smfforum/index.php?topic=107103.0

[Coolhat]

See this...
http://www.diystompboxes.com/smfforum/index.php?topic=107103.0

Thanks,

tried it, unfortunately it didn´t work very well either. The clean signal was still too weak, so the difference between dry and wet was almost inaudible. Also, there was quite severe oscillation in the output when I cranked up the BMP sustain pot and set the blend to dry.

[Bill Mountain]

You best bet is going to be to boost the clean side and then mix the two.

[stonerbox]

If you go with an active blend be sure so the signal does not get inverted.

[Coolhat]

You best bet is going to be to boost the clean side and then mix the two.

I´ve been thinking about that. The thing is, I´d rather keep things simple and the reason I decided to use the JFET mini blend was because I found many reports of people getting good results using it with the BMP. That makes me think there is something fundamentally wrong with my setup, but I just can not figure out what.

[stonerbox]

You best bet is going to be to boost the clean side and then mix the two.

I´ve been thinking about that. The thing is, I´d rather keep things simple and the reason I decided to use the JFET mini blend was because I found many reports of people getting good results using it with the BMP. That makes me think there is something fundamentally wrong with my setup, but I just can not figure out what.

Perhaps you should modify the JFET blender for more gain or have you all ready tried this?

[anotherjim]

JFET blender I've just looked at is near unity gain. Put a bypass cap across its source resistor for some gain. At least 1uF if Rs is 4k7. Then it will be inverting (output from drain), so it will have to be mixed at the output (assuming fed from 1st BMP stage).

Oscillation might be layout issues, a breadboard can be a dangerous place. BMP circuits can squeal anyway if the input is too close to the output.

[Coolhat]

JFET blender I've just looked at is near unity gain. Put a bypass cap across its source resistor for some gain. At least 1uF if Rs is 4k7. Then it will be inverting (output from drain), so it will have to be mixed at the output (assuming fed from 1st BMP stage).

Oscillation might be layout issues, a breadboard can be a dangerous place. BMP circuits can squeal anyway if the input is too close to the output.

D´oh! It was so obvious, I had taken my dry feed straight from the input so of course it was very weak! Now its coming from the 1st gain stage and everything is working perfectly. Thank you very much, another lesson learned.