Panning with a foot pedal?

[MarkDonMel]

Hey all.

I was wondering if anyone knew of a project for a stereo balance L/R pedal with a wah-pedal type rocker thing. If I didn't explain that enough I'll try again haha.

I'm looking to sweep a guitar signal from a left to right, and back, stereo speaker set up, from a guitar amp using a wah pedal shell so I can control the position of a stereo amplified guitar.  So I can sort of change the speaker that the sound will come from, either change it from left to right, or sweep it back and forth quickly in kind of a tremolo effect, without the sound level decreasing, just back and forth... if that makes any sense.

Or maybe any ideas on how to accomplish this?

Thanks, Matt.

[Alpha579]

You could use two amps, and have a wah pot controling how much of the signal goes to each one:


           -------Amp 1
          |  
          /  
In----> /    
          /      
          |
           -------Amp 2      

Very simpy done. You might want to try putting a little booster infront 0f the pot for less signal loss through the pot.

[Mark Hammer]

Take a look at the schematic for the MXR Bluebox (Caja Azul over at Tonepad).  You will note that it has a "Blend" control that is essentially a pot with the outside lugs going to each of two signal sources, and the wiper going to ground.  Rotate it in one direction and one signal gets attenuated (i.e., more shunted to ground) while the other gets unattenuated.  When rotated fully to one side, one of the signals goes directly to ground, while the other gets a large resistance (full pot value) placed between it and ground.

These two signals are mixed down into a mono output, but they don't need to be.  In fact, this approach to channel-to-channel balance is exactly what stereo amps have been using for decades.

So, here is a suggested approach:

1) You'll need a linear pot, say 500k, *OR* a dual-ganged 100k linear pot.

2) You'll need some sort of active input-buffer/gain stage.  Could be a FET-based or op-amp or bipolar-based one.

3) You'll need two additional output buffers to isolate two copies of the signal.

Your instrument feeds the input stage (a small amont of gain, like 2-3, is probably a good idea) which sends copies to the two output-buffer stages.  Each of the output buffer stages is a standard unity-gain buffer. and feeds a 10uf utput cap and a 47k series resistor.  The Foot-controlled pot is tied to the free end of these resistors.  Push the treadle one way and you reduce the resistance to ground for one output channel while increasing resistance for the other.

This suggested circuit accomplishes "panning" by having complementary attenuation/boosting for each of two outputs.

The smoothest panning will likely be achieved by something other than a true linear pot sweep.  In which case, it may be wise to include a trimpot in parallel with each leg of the panpot (or each pot in the dual-ganged version) that can be used to customize taper of sweep.  You may need to offset any passive loss due to sweep adjustments by turning up the gain on the input stage.

Should work as suggested, though.

[R.G.]

Have you read "Panning for Fun" at GEO?

You get constant-power panning with one pot; suitable for insertion into a scavenged Wah-pedal rocker assembly.

[RedHouse]

There's also a nice circuit in the National Semiconductor data sheet for the LM833 on page 8.
(which is a nice, very low-noise op-amp BTW)

[MarkDonMel]

I am going to read that article, I never noticed it before, but those geo articles are great.

Being new to this, some of that is confusing, but I am going through what you wrote Mark.  I thought it seemed like a simple thing, but I am going to have to do some reading and actually figure this out versus using the easier step-by-step projects like on ggg.

I guess I saw the circuit as a simple thing, almost like I could yank a balance pot and circuit out of something and slap a gear on the knob and align it in my pedal.  haha... naive of me I guess.

Thanks much as always for all of the help... wish I had two amps, but I am trying to figure out how to do this with one amp and an extension cab.

Thanks again, Matt.

[Paul Perry (Frostwave)]

Thanks much as always for all of the help... wish I had two amps, but I am trying to figure out how to do this with one amp and an extension cab.
Thanks again, Matt.

I was in a thrift the otehr day & saw a box that allows you to adjust volume of speakers in sdifferent rooms, by using wire wound (that is, high power and low resistance) pots.
You could build 2 of these pots into a pedal and use them, but 1. you would have to be very careful wityh values & wiring not to overload the amp and 2. you would lose some power.