my wet/dry mix control

[birt]

This is nothing fancy, i just took some little parts from here and there and made one schem out of it. (mostly Jack Orman stuff)

The jFet on top has a 10K trimpot to adjust the gain. the 100K lin is the mixpot and the 100K log the overall volume.

i hope it works the way i think it will :p




greets,
Bert

[birt]

i forgot a 10K resistor between 9V and drain of the top  jFet.

edit: and the top part doesn't work
it blends from wet to nothing

[birt]

the top jFet was a bad one so i replaced it. checked the wiring again, put in a new one (tested to make sure it works) and again, nothing. it is such a simple booster circuit. i don't get it. the mix control acts as a volume control. the effect part works, the clean part doesn't.

[birt]

ok so now i got it to work if i used the top jFet as a buffer like the bottom one. but i need the top one as a boost and i just can't get it to boost. i've tried drain and source resistor values from other jFet boosters but it just doens't work here.

i really need some help with this

[John Lyons]

In the Drawing the ToP (and bottom) FET(s) are set up as buffers or Source followers.
With the variable resistance of the Source I don't think that will work will it? ]
In order to get any gain you would have to take the signal off the Drain no?

How about adding a typical FET boost and then the buffer second (in the top half of the schematic).

John

[birt]

ok there's my stupid mistake. i've spend hours trying to figure out why i couldn't get a boost and you just tell me i need to take the signal off the drain. thanks for that. but the signal gets inverted that way right?

[nordine]

how about with opamps?

[birt]

i didn't want to use opamps because that's more circuit board real estate :p

and thanks to Johns comment i got it to work!

[John Lyons]

With a FET as a bipolar transistor you can hook them up as buffers (Emiter/source followers) or as an amplifier.
The Drain or Collector output is the amplifing pin. This is the way most boosts or amplifing circuits are set up, no inversion there as far as I know.
So it works now? How are you using it...what did you put in the loop?
The Good thing about an op amp it that it is a lot more stable and predictable.
Plus you get more possible amplification and really it is a tighter/smaller device once you consider that it's two stages for a (dual op amp)
Take a look at the "splitter blend" and possibly others at runoffgroove.com


John

[birt]

i have a modded version of the random number generator in the loop. right now i have about maximum gain from the jfet and i'm going to tame the rng a bit to get to the same audio level. then when the signal is mixed it is the same volume the whole travel of the pot. then comes the volumepot.

[birt]

this is what it looks like right now. the gain of the jfet is not enough (if i attenuate the RNG to have the same level as the clean signal i mix it with it loses a lot of bass response) so i might have to redo this with opamps.

there lies my new problem. i'm using this for bass. so i need to design an opamp circuit that has high input impedance, wide frequency response (some compression or even a bit of overdrive is OK) and quite a bit of boost. i have no idea about how to start designing this, for a start i'm puzzled about what input of the opamp i have to use to have the signal in fase with the signal from the RNG like it is now. 2 cascaded inverting gain stages maybe?

[Phorhas]

If you intend to keep the amplification here below clipping threshold (i.e. power supply limits) and want to keep the signal liner - then I recommend working with OAs. Good ones are quite, have high input Z, need less external parts to work and are more consistent. Also they are more convenient when you need to non-inverting gain.

Cheers

[Phorhas]

My English here was rather messy... I need more coffee