Boss CE2 dry blend

[Dimitree]

hello
I'd like to add a potentiometer to my Boss CE2 (clone, with true bypass) that let me set the amount of dry in the mix.
What I want is:
- full counter clockwise = no dry, only wet (vibrato)
- full clockwise = 50% dry, 50% wet.
or even the opposite direction is fine.

I'm aware of the CE2B, that let you set the amount of wet signal. I could just copy that on the dry, but I don't like this approach because it won't totally kill the dry signal, it would only reduce the gain to something like 15% dry and 85% wet.

So, can I just put a potentiometer wired as voltage divider before (or after) R21?
do I need some other parts?

[MrStab]

i can't see why a voltage divider wouldn't work. maybe the CE-2B limits the minimum wet level to avoid a handful of users being confused when they hear no effect. or maybe there's some other reason. if i were you, i'd try it and expect it to work (assuming it's executed in the same part of the path as the 2B version). just make sure you tie Lug 1 of the pot to Vb and not Ground.

[Dimitree]

thank you,
for VB you mean virtual ground at 4.5V?
why there and not to ground? maybe because after IC1 there is no bypass cap so the signal there is biased to the voltage at IC1 pin 5?

[antonis]

Mainly because the clean signal is going to pin 2 and is compared with the Vcc/2 which bias the pin 3.

[duck_arse]

R21 carries the dry, and R22 carries the wet. when the effect is "bypassed", Q8 goes high resistance and closes off the wet feed to the mixer opamp following. you can add another fet to the dry line, same config as the Q8, to cut all the dry (when the fx is on). I have a circuit laying around, but would need to 'eagle it up' some. give me a hoy if interested.

[Dimitree]

thanks but my clone doesn't have any fet (it's true bypass), and furthermore a fet would only give on-off status, not the blend that I want

[antonis]

a fet would only give on-off status, not the blend that I want

Not if you use the FET as voltage dependable variable resistor..

[Dimitree]

ok, but since I have to vary the voltage for the FET with a potentiometer, wouldn't it be easier to directly use the potentiometer?

[MrStab]

wouldn't it be easier to directly use the potentiometer?

very much so, from my limited experience. you can get something that kinda works easily, but there are a lot of caveats with FET VCAs such as distortion above 50mV and control voltage feedthrough. it's all a balance of compromises, and IMO it'd be overkill. the reason i dabbled was to control 2 channels with 1 pot, which isn't the case here.

for complete "wet OR dry" as opposed to "how much wet", maybe you could go with the basic pan arrangment you sometimes find on guitars, with a dual pot being used as 2 voltage dividers in opposing directions.

[Dimitree]

I will use a simple potentiometer wired as voltage divider, just before R21.
What value is recommended here?