Befuddled by a Blend Knob

[00Stevens]

Okay, i made a fuzz pedal with a "split n' blend" circuit built in, and it works well, but i'm trying to get 100% dry throughout the blend knob sweep- like it is in my Bass Big Muff- and i can't figure out how. As it is the more wet you dial in, the less dry you have, and i'm losing too much bass for the pedal to work in my rig. I've tried bypassing the blend knob and running the buffered clean signal straight to the output (grounding the blend pot to make it a volume control for the fuzz) but that doesn't work. It causes the blend knob to sound like mostly dry signal until the last 1/4 turn, where it begins to cut the dry and let the fuzz signal in.

I've tried a lot of things with alligator clips, and nothing really works. The closest i got was when i ran the dry signal to an external pot and the wet signal to a separate external pot and connected both of those to separate lugs on a stereo jack. When i tried a mono jack, they both worked by themselves, but joined together the pots interact with one another. I'm completely lost and burnt out for now. Needless to say i don't know what i'm doing, and any insight will be appreciated.

Thanks

[samhay]

To clarify, you want the blend to keep the dry signal at a constant volume and to blend in the wet signal from 0 to full?

If so, that's not what the Split n Blend* does, as you've discovered.
However, you can make it do that by connecting another cap (100n will work) to the source of the second JFET, with the other end connected to out. (i.e. in parallel to C3, but connected to the wiper of the pot rather than one end).
I would make this switchable if you have built the the blender as a separate effect.

*Assuming this is what you have:

https://s.webry.info/sp/kjc-guitar-betta-taro.at.webry.info/201408/article_2.html

[00Stevens]

I just gave that a try and i couldn't get it to work. I connected a 100n capacitor from the middle pin of the second transistor to the middle lug of the blend pot- so that the blend pot has: fuzz connected to lug 3, the capacitor and output wire on the 2nd lug, and on lug 1, i tried both grounding it and running the original out from the split n' blend board to it. It seemed to do the same thing- where the first three quarters of the turn are mostly dry, then the last quarter makes it all wet signal. By the way, do you know any blend circuits that would do what i'm looking for?

[PRR]

You need more than two JFETs. Opamps are a friend.

[00Stevens]

Well, i've tried everything i can think of and i still cant get it to maintain 100% dry signal, and dial in the wet over top of that. I'm sick of it. Let me know if anyone knows a blend or mix circuit that can do it- 'cause i haven't been able to find one.

[anotherjim]

That kind of blend really needs low impedance sources so the signals at the pot ends can't fight each other -  hence Paul mentions op-amps. With op-amps, when the pot wiper is all to one source, the other has no chance of wiggling it in the slightest. Even then, the coupling caps must be large enough that they have small impedance at the lowest signal frequency.
At low E around 80Hz, 100nF is worth 20k ohm which is a bit too much with a 100k blend pot. 470nF would be better.

When the 2 sources don't match, sometimes you can get lucky with a log taper pot to get an apparently equal mix with the pot at mid swing.

[slacker]

Try this, it will give you a constant amount of dry signal and the pot will blend in what ever is in the send/return loop. If the pedal in the loop already has a volume pot on the end you can leave out the pot. If you want to boost the dry signal then you can make the 10k resistor between the opamps smaller. The 10k resistor on the end could be replaced with a pot to give an overall volume control.

[PRR]

> You need more than two JFETs.

Surprised I have not got flamed for this.

My mind had "two FET followers", but my fingers were on another track.

Here's two JFETs. There's more to it than the original. It could be simpler but I don't want to argue about dime capacitors. Ian's op-amp implementation will perform better.

[marcelomd]

Hi,
I'm not at my computer right now, but Google "Darkglass b3k schematic". It uses two knobs. A volume for the wet signal and a blend between wet and dry. Dry stays at unity gain.
Maybe it is what you are looking for.

[00Stevens]

Thank you lads; that opamp circuit seems like just the thing. Unfortunately, i can barely read schematics and i've never touched an op-amp, lol. So i've got a little learning to do. I just did a stripboard layout of Paul's version though, and i think i'm starting to get my head around the stuff. As soon as i learn how to hook up an op-amp, and they arrive in the mail (and i'm sure my stripboard layout is right), i'll try it out in the pedal. I just want to play the thing really- it sounds great- but i need that low end.