pan pedal

[liddokun]

I know I posted something up a long time ago, but I can't seem to find it. 
I want to build a pan pedal, to pan between two different amps.  I'd mount it in a rocker pedal enclosure, so basically I'd like to have heel down means one amp, toe down means other amp.  But I want to have some kind of volume in between, so it's a smooth transition, otherwise I'd just build an A/B box. 
Could I just wire up two jacks to a 100k audio pot, one wired backwards, one wired forwards (eg. one with normal connection, then one with ccw and cw reversed). 

Any ideas?  I'd like to keep this passive, but if need be, I can add a battery.

EDIT: Silly me, I managed to find it.  http://www.diystompboxes.com/smfforum/index.php?topic=65510.0
But if anyone still wants to contribute, any ideas would be great.

[F.V]

Would this not be best done with a dual gang pot rather than a single? so that the input goes to both "halves" of the dual gang pot, and each half is for a separate output, one wired in reverse, and both acting as a volume pot.
So the lugs would be like this,

1-out one     1-ground
2-in             2- in
3-ground     3- out two

[Ben N]

Would this not be best done with a dual gang pot rather than a single?

Yes, and with the added advantage that the pedal can be used after a stereo pedal.

[ambulancevoice]

single gang pot
some resistors
done
Dann Green from 4ms uses this, he gave it to me

http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=36452&g2_serialNumber=1

it does drop the volume a little bit cause of the resistors
if it does it to much for you, change the 47k to 10k
no less than 10k

[kurtlives]

^whats the point of the resistors?

[frequencycentral]

single gang pot
some resistors
done
Dann Green from 4ms uses this, he gave it to me

http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=36452&g2_serialNumber=1

it does drop the volume a little bit cause of the resistors
if it does it to much for you, change the 47k to 10k
no less than 10k

^whats the point of the resistors?

Tonesucking? All that serial resistance..........................

[liddokun]

The problem with using a dual gang is that I'd have to find one with a longer shaft and find a gear to fit it to mount it in a Crybaby enclosure I have.  Might be hard for me to find one.  

[frequencycentral]

If you want to do it with a single gang pot, you should maybe consider two VCAs fed by a single pot hooked up the provide a control voltage. Invert the control voltage to one of the VCAs. A LM13700 dual transconductance opamp would do the job with a minimum of other components. Have a look at the data sheet.

[liddokun]

I will take a look at the datasheets, but please excuse my ignorance.  What is a VCA?  I'm not familiar with that.  Hey Rick, I didn't recognize it was you until I actually read your user name.  I don't often read user names in posts, but your old display picture was changed to this radar one. 

[Jimmy-H]

If passive isn't satisfying, maybe you could leave the two out resistors and replace it with two buffers.
And maybe a third as input buffer.

there are plenty of buffer schema's around.

[frequencycentral]

What is a VCA?  I'm not familiar with that.   

Voltage Controlled Amplifier.

Think of it like an opamp with another 'control' input that defines the volume.

0 volts at the control input = no output.

+ve voltage at the control input = output.

The volume of the output is proportional to the amount of +ve voltage at the control input.

[R.G.]

Go read "Panning for fun" at GEO, http://www.geofex.com, where it shows how to pan between two channels either on the input or output, with one pot. The trick is to ground the wiper, and let the remaining resistances on both sides set the gain on that side.

[ambulancevoice]

^whats the point of the resistors?

stops the signal shunting to ground
if i remember correctly what Dann said

[Paul Perry (Frostwave)]

Yes, stops direct shunt to ground, also when the sig on one side is shunted it cuts the sig down further (think of a voltagte divider formed by the 47K from the source, and the end resistance of the pot).
And you don't want a "volume control" taper, you want the B "linear" taper.

[ambulancevoice]

And you don't want a "volume control" taper, you want the B "linear" taper.

yeah forgot to mention that

[liddokun]

I read "panning for fun" over at Geofex, and one of the applications seems to be the same as what Alex put up, with opamp's tacked on.  R.G., the one I want to use is the one on the right of the one in the box on the first page.  From what alex put up, I'm assuming the first 4 resistors can be 10k, and the pot can be 100k.  What opamps are recommended, and what values for the resistors connected to each opamp? 

Lastly, in a crybaby enclosure, I probably won't be able to get full rotation on the pot, and thus not have a complete pan from each amp right? Anyone know where to get a 100kb pot with long shaft and gear?  Or will  wah pot do?

[R.G.]

I've updated "Panning for Fun" at GEO with a circuit that does what I think you want.

Note the warning - it will neither make hum caused by connecting to two amps better or worse. I did not (yet) add a hum-immunity section to it from the hum-free A/B/Y project.

[liddokun]

Alright, thanks a lot R.G.

Bias voltage is 4.5v, correct? Wherever I see a Vb in the schematic, can I use a 10k trimpot?  Or should it be less?  1k?

[R.G.]

Yes the bias voltage is intended to be 4.5V.

No, you cannot in general use a 10K trimpot for a bias voltage. Many of them, yes, it's OK, but by no means all of them.

The point of a fixed bias generator is that it is fixed. Making it out of a trimpot is both more expensive and prone to maladjustment.

Or possibly I don't understand your intentions?

[liddokun]

Sorry, ignore my post about the trimpot.  I didn't see the 2 10k's going to +9v and the voltage divider.  My bad.  So the arrow pointing to Vb is already 4.5v, because the 10k resistor going to 9v, and then the 10k going to ground?  Thanks for all the help.