Merging Pedal

[Frankyfox]

Hey!

I'm looking to build a pedal to merge two signals from two separate 1/4 ins into one 1/4 out. Not sure if something like this exists already or not. It's basically for mixing the dry and effect outputs of a pedal into one out so I wouldn't need any control on the levels. Thanks!

[Phoenix]

Here's something I knocked up quickly.
It has high input impedance for both inputs (~1Meg). There's a phase switch on one of the inputs in case one of your sources has inverted phase. There are independent volume controls for each channel. If you want just a single blend control, you can use an MN taper pot like those available from Bourns, just flip one of the pots end-for-end to reverse its action. It uses an active mixer to blend the signals.

Hope this helps.

[Jdansti]

Welcome!  What you need is called a passive mixer. See this website: http://www.all-electric.com/schematic/simp_mix.htm. The schematic on the upper left is what you want. You'll only need two inputs and one output. Ignore the text. It's difficult to read over the crazy background.

[Chrisfromiowa]

I feel kind of weird replying on a post thats not at least 5 years old. Kind of a new thing for me... anyways, Has anyone actually made a mixing pedal? Something to take two inputs and combine them into one with either an expression pedal jack or using a foot treadle? The couple of stereo volume pedals I've taken apart use these double pots instead of two separate ones. Thanks CFI

[blackieNYC]

Lots of pedal mixer circuits. You could go with J's passive linked above, or you can look at the right half of the runoffgroove splitter blender. Or AMZ herehttp://www.muzique.com/schem/mixer.gif
Or read up at geofex and really get inside the thing. You could go passive, just be aware of the polarity reverser (geofex)
You can get carried away with features (see nightmare at left) or go thru a passive volume pedal. This would turn one audio path up or down. If you want to turn one up while the other goes down, that might be hard to do passively. A stereo balance pot might do this very well but you might not get one into a volume pedal assembly. How about a little box with two stomps and two volume knobs each with a 10k/100k pot as a voltage dividing attenuators to ground (standard pot implementation. If you are blending two pedals with volume controls, maybe just two resistors is enough of a mixer. If this will be used live, think about how much knob twiddle you want to get into.
Simple, complicated, or anywhere between.

[R.G.]

Read "panning for fun" at geofex.com

[Chrisfromiowa]

Hey Blackie, R.G.,
The whole knob twiddling thing is why I'm trying to figure out a foot pedal. Like the Ernie Ball stereo panning pedal, but backwards, 2 in 1 out. I don't have the skills to do anything but passive. Im thinking maybe a cheaper Ernie Ball mono pedal and cram an extra one of their $15 pots, but backwards facing the installed one, then use the tuner out as my input and maybe switch the mono output jack for a stereo one. Really I'm just more surprised no one has ever really done this before with a foot treadle, there seem to be pedals for everything else... thanks for the input, it's apreaciated. Regards C

[R.G.]

The whole knob twiddling thing is why I'm trying to figure out a foot pedal. Like the Ernie Ball stereo panning pedal, but backwards, 2 in 1 out.

Well, nothing says the single pot needed for a panner has to be on a panel with a knob. What I actually had in mind was converting a wah pedal into your panner by using the wah pot as the single pot in the panner circuit. The electrons in the pot don't know the pot is in a rocker pedal.

I don't have the skills to do anything but passive.

Ah. That's a problem all right. If that's true, you're tied to using only mechanically coupled pots. Again, the rocker mechanism is a trivial item to the circuit, but of paramount importance to your use.

Im thinking maybe a cheaper Ernie Ball mono pedal and cram an extra one of their $15 pots, but backwards facing the installed one, then use the tuner out as my input and maybe switch the mono output jack for a stereo one. Really I'm just more surprised no one has ever really done this before with a foot treadle, there seem to be pedals for everything else.

Actually, I'm pretty sure someone has. But it is a real problem to get this to all work passively. Not the least of the problem is that you have to load both pots with any passive mixer, and you're going to see a sizeable signal drop in that.

It's the nature of the beast that directly driving a pot loads down a guitar signal. For no audible treble loss, you're going to need 250K or up. 1M is the place most people agree has almost no treble loss. Your passive mixer is going to need to be about a factor of five to ten bigger than the pot value to keep its loading on the pot from being a problem with the pot's apparent ratio and avoiding interaction between the two pots. By the time you get through that, you've picked up an exposure to resistor noise and about a 10:1 signal level drop. All resistor panners used to be used in old mixing consoles, but when better active mixing circuits became available, they replaced the old passive ones pretty quickly, for the reasons above.

It's possible to make a passive mixer pot from an ordinary dual pot (for easier mounting; the mechanics on the two-pots-facing is going to need a lot of tinkering) by using a dual linear pot and tapering resistors on opposite ends. That still leaves you with the problem of passive mixing.

I strongly encourage you to raise your skill set or acquire a friend who already has the skills. You might well find that the time is better spent on skills than building something and then finding out it's disappointing enough not to use when you get it done.

[antonis]

Here's something I knocked up quickly.

Greg, correct me if I'm wrong but in case of SW1 is set to Vr possition, U1C non-inverting input is effectively AC grounded..
(hence U1B out via R9..)

Did you forget some 1M2 bias resistor or do I need an extra cup of coffee..?? 

[Phoenix]

Greg, correct me if I'm wrong but in case of SW1 is set to Vr possition, U1C non-inverting input is effectively AC grounded..
(hence U1B out via R9..)

Did you forget some 1M2 bias resistor or do I need an extra cup of coffee..?? 

No, that's exactly as I meant it. The "polarity reverser" is shamelessly stolen from RG's article over at Geofex: Standard - and Strange... - uses of the Polarity Reversing Circuit.

If SW1 is open, then we are getting gain through BOTH the inverting and non-inverting inputs. The gain through the non-inverting input is (R8/R7)+1 or (10k/10k)+1 which is +2. However, we also have to consider the gain of the inverting input, which is -(R8/R7) or -(10k/10k) which is -1. If we add +2 and -1, we get +1.

If we close SW1 though, the non-inverting input is grounded, so we get no gain, and only have the gain from the inverting input, which is the same as before, -1. Nice and simple way to switch back-and-fourth between inverted and non-inverted.

[antonis]

If we close SW1 though, the non-inverting input is grounded, so we get no gain, and only have the gain from the inverting input, which is the same as before, -1.

I thought it wasn't wise to ground the non-inverting input of a single supply inverting op-amp...
(unless you are fond of fully asymmetrical clipping or half-wave rectifying...)

P.S.
Anyway, I'll drink that @#$% cup of coffee...

[Phoenix]

I thought it wasn't wise to ground the non-inverting input of a single supply inverting op-amp...
(unless you are fond of fully asymmetrical clipping or half-wave rectifying...)

P.S.
Anyway, I'll drink that @#$% cup of coffee...

*AC ground* - switch it to VR, not to the negative rail

[antonis]

*AC ground* - switch it to VR, not to the negative rail

Thanx Greg...!!!!
(although you drive me to dipsomania...) 

[Chrisfromiowa]

Damn, teach me to bring a crayon to a slide rule fight... ok, here's another idea that I'd like run past the brain trust. Optical volume pedals use a photoelectric cell as the potentiometer, and it looks like the stereo version uses two of them, if I could find a negative cell of equal value could I just replace one of them with it, then wire the two outputs into one stereo jack so when I plug a TR cable in, I get both signals?
Please feel free to tell me why this won't work.
I know it's no where near as elegant as the panning circuit provided, but it fits my lack of technical abilities perfectly.
Thank you all for your time and ideas, regards CfI...


Well, looking through Morley schematics, they actually kind of already did this and then discontinued it. It's for blending an effects loop with the dry signal, but it has the foot treadle to vary the percentages. On the plus side it was discontinued recently enough that I found one for cheaper than the parts to build it. Thank you inefficient supply chains... and all of you as well.