Wiring two independent volume knobs - How do you do it?

[BuddyPrince]

Thanks to some more experienced folks I got one piece of my puzzle worked out.  I've got a nice sounding clean boost to add into my OD pedal.  Independently each circuit behaves as it should and I'm quite happy with them.  What I can't seem to figure out (I've read some of the threads on this forum) is how to wire two volume knobs so that they don't interact with each other.  I'm not looking for a single blend knob, but rather two independent volume controls.

I've got two individual circuits on separate boards.  The input to each circuit is coming straight from the input jack tip.

How do you do this?  I've tried a variety of wiring options at the pots (e.g. effect out to lug 2, lug 3 to output jack and vice versa).  I've placed RC decouplers between the power source and +9V on each board.

Can I do this with a 3PDT switch?  Would a 4PDT switch work?

Thanks in advance!

[GibsonGM]

To clarify, do you want an input jack >>> switch to Effect 1's volume >> Effect 1......and then switch over to Effect 2 volume >>> Effect 2?

I'm a little confused.     In your description, it sounds kind of like you have the input going in parallel to each of them  right now (not the best thing to do, they interact...), and you want a volume knob for the input signal going to each?

OR - do you want  to go  Boost (switchable in/out or what have you) >>> OD pedal, with 2 output volumes you can switch between?

If it's not clear what I'm asking, maybe you could do a quick sketch of what you're looking for, just a black-box kind of thing.

This is a standard way of 'turning one volume pot into 2 separate ones' so to speak, using a 3PDT, maybe it's helpful.

[ElectricDruid]

Two independent volume controls sounds like a mixer circuit to me.

You can try a "passive mixer", which will have some interaction, or an "active mixer" which won't have any much.

There's a ton of examples on here and elsewhere.

HTH,
Tom

[BuddyPrince]

Sorry for not being clear.  Hopefully the attached sketch will help clarify things...

GibsonGM, I think you're right that I currently have them in parallel right now.  I want a volume knob for each that controls the output level, as opposed to input gain.  I don't want to switch between the two effects.  I want them either both on or both off.  Really, how all of this came about (and there's a good chance I'm going about it all wrong) is that I built a bass overdrive that I like a lot, but wanted to be able to add in some clean signal and preferred to set up the clean signal as a boost/cut sort of thing.  With your help and the help of others, I got the boost portion working.  Now, it's on to being able to control the output levels of each effect independently.

Tom, I'll look into active mixers...thanks!

If more clarification is needed, let me know.  I'll do my best!

[BuddyPrince]

If I'm looking at an active mixer, specifically, I'm looking for a 2-channel active mixer, correct?  One channel for the clean/boost channel and one for the OD channel?

OK, so after a little searching, I found these two things, a JFET Parallel Looper http://tagboardeffects.blogspot.com/2010/11/jfet-parallel-looper.html

and

the AMZ Buffered Splitter http://www.muzique.com/lab/splitter.htm

Are either of these what I'm looking for with regards to an active mixer?

Looking at the AMZ buffered splitter, could I take the output from each channel and run it to it's own volume pot then to the output jack?  Would that give me independent volume control? 

Output 1 ---> Vol 1 -- \
                                  \______ Output jack
                                 /
Output 2 ---> Vol 2 --/

If these aren't the right direction, can someone point me in the right direction?  I'm not exactly sure what it is I'm looking for...

Thanks!

[MaxPower]

The jfet parallel looper should do the trick. Do a search for "op amp mixer" for another option.

[ElectricDruid]

Yep, that first link with the JFET parallel looper looks good. You only need the mixer part on the RHS, and you only need two channels not three (or leave yourself room for expansion?!).

The op-amp active mixer looks very much the same, but replaces the Jfet with an op-amp:



I'd go with the Jfet mixer. Looks easier.

HTH,
Tom

[GibsonGM]

Yes, that looks like a "splitter blend" kind of thing to me, but not complex.   Your 3pdt flips you between bypass and the combined Boost / OD (B/OD).   

At the B/OD input, you need to split so the inputs don't interact.  The FET splitter would work, or use 1 side of a dual opamp if you like.  You could just use resistors, but there are benefits to the opamp (buffering, less noise and so on).  Just went over this on another post last week - due to the ready availability of opamps, that was sort of favored.   An opamp can drive MANY outputs as long as each has a resistor of like 1k, I believe, to keep them separate.

Then you have the B/OD output, which again need to be mixed.   The other 1/2 of an opamp, thru a couple of resistors after a volume pot for each effect, will do that fine, I would imagine, as Tom posted.

I like the clean mix with dirty for bass idea, I think it will serve you well. 

[duck_arse]

The op-amp active mixer looks very much the same, but replaces the Jfet with an op-amp:



HTH,
Tom

E.B. - are not all those 10uF caps on the LHS backwards?

[samhay]

>E.B. - are not all those 10uF caps on the LHS backwards?

Op-amp (+) input biased to ground, so (-) input is probably supposed to be there too. Circuit is likely running on bipolar supply.
The caps should be at ground on both sides, so you can flip a coin as to their orientation.

[BuddyPrince]

Cool. It's coming together...

To be sure I'm understanding correctly, Tom, when you say I only need the RHS (right hand side), mixer portion, of the parallel looper, I would attach effect 1 out to return 1 and effect 2 out to return 2 and take it from there? I'm guessing this also means that I don't have the volume knobs wired to the circuit board of each effect, but rather wired in to the parallel Looper.


In thinking about wiring this whole thing up, is this looking on target?

[ElectricDruid]

To be sure I'm understanding correctly, Tom, when you say I only need the RHS (right hand side), mixer portion, of the parallel looper, I would attach effect 1 out to return 1 and effect 2 out to return 2 and take it from there? I'm guessing this also means that I don't have the volume knobs wired to the circuit board of each effect, but rather wired in to the parallel Looper.

Yes, that's what I meant. others have mentioned that you could split the signal properly too, so that you don't have any trouble with the *inputs* interacting, but your original question was about the outputs, so I sort-of glossed that over. I guess for bonus points you can implement the split part as well to feed the input of each pedal.

In thinking about wiring this whole thing up, is this looking on target?

Yep, looks good to me.

T.

[GibsonGM]

I think you should split the inputs, even if you just run thru 2 resistors.  1k each maybe.

[BuddyPrince]

Awesome! Thanks guys.  :-)

I like the idea of splitting the input too. It makes sense to me. I'm gathering that I can either go with the JFET splitter (LHS of that circuit) or simply use a couple of resistors? If I just use resistors, is it as simple as placing a single resistor in line from the input jack to each of the effect's input?

I've some parts coming in in the next few days. I look forward to building this next component!

[BuddyPrince]

UPDATE:  After some trial and error and MOSFETs and JFETs I got my pedal working!  I'm excited!

A 2-channel version of the Parallel Looper as an active mixer did the trick.  I've got the overdrive and a clean boost both working with independent volume controls.

I'll give it a run at rehearsals this week and hopefully it'll be all good to go...

Thanks for the help fellas!