Ernie Ball as a AB panning pedal

[PhiloB]

I have a guy who wants to split his guitar signal coming off his board.  He wants to be able to direct his signal either to his acoustic amp or electric amp.  He also wants to be able to blend the two. 
I've never done this but I am concerned about volume when at the 50/50 mark on the pan.  Each amp would only receive 50% of the signal.  Wouldn't the perceived volume in the audience be significantly less with only 1/2 signal to each amp.  Not to mention changes in tone from the amps themselves.
Is there a better approach than just a simple Pan from one amp to another?


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[Rockhorst]

EDIT 2: I still think I've misinterpreted what your trying to do. Sorry for the clusterf***. If you could sketch it up quickly in a diagram what you want to do, that'd be great.

EDIT: in my response below I started typing and forgot about the volume pedal you mentioned. Still, I think the information still applies. Use a buffer to split the signals and then use a clean blend type of circuit. You should do a quick and dirty test without the buffer to see if there's any noise problems. Then transformer isolation would come in handy. I can help you out with both clean blend and transformer circuits if needed (PM me if you need it).

A buffer will solve all your problems. From your description it seems your mentally modelling a guitar signal as a current of electrons that splits in two. It's more useful to think of it as a voltage source. What amps are concerned with is the voltage drop over their input to ground. If the signal is a low impedance buffered signal into the high input impedance of the amps, losses should be negligible. It's comparable to splitting a signal in two: one for the amp and one for a tuner. Searching for 'buffered tuner out schematic' or similar should help you out.

[PhiloB]

My concern is in the "in between" positions on the pot.   He wants the option to have signal going to both amps in various proportions.  I.e.
60% of signal going to amp A and 40% going to Amp B.

What will be the experience of the listener or sound man as this guy selects combination of both amps.  Will there be significant drops in volume?

I wrote "volume" on the sketch above but it really will serve only to pan.


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[midwayfair]

Your concern is warranted. The entire point of a panning effect is to pan between two things. A good setup could get the same raw volume at 50/50 but he can't get 100/100.

You can do it with a dual gang such that the center is 100% on both but you probably can't get that into the EB working properly. Also, how would he find the exact center on the pedal on the fly?

The real solution here is the one he probably won't want to hear: he uses a splitter and runs the two paths through two separate volume pedals to control their volume separately. He could plug them in backwards so that toe down on one is silence. It takes up space on the board but it does what he needs and doesn't compromise the pedal or the pot.

[PhiloB]

Thanks Jon for the input.  I had a similar thought about dual gang pot.  It really is helpful to have an outside opinion. Thanks also to Rockhorst.  I really appreciate it guys.


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[Rockhorst]

The solutions I was proposing were indeed more along the lines of what Jon is suggesting (splitting and having two separate levels). I agree with him that with your diagram 100/100 is not going to work. On the other hand, I don't think 100/100 would be what I would be aiming for?  I would want the total perceived level of the mixed signal to match the total perceived level of the single amp and anything in between. There's some panning options to be found on Google, combined with a buffer it may work well enough in practice.

[Mikro93]

Hey,

What pots are used in mixing consoles for the Pan knobs? Do they have an effect (i.e. an attenuation) on L and R signals when in center position? Shouldn't a quick modification with a log/antilog (not sure of the terms here) do the trick?

Also, if the electric amp is not clean, the pedal should go in the effect loop, so that it decreases the volume and not the gain. Just for the record

[Rockhorst]

I keep thinking about it. I'd get a buffer, split the signal and indeed use a dual gang with one side wired in reverse to just control both levels going to the amps. I think that should work well in practice. Possibly a second buffer after the output of each pot for some improved impedance ratios. It could work well enough for the guy?

[mrclean77]

I feel like this should be required reading for people considering "getting into" pedal making.

Why? Because...

The questions you THINK/HOPE you're gonna get
-----I think I want to try a Big Muff, can you make me a (insert BMP variety)? Make sure it has huge knobs!!!!

The questions you ACTUALLY get
-----I need a clean/dirty/fuzz compressor pedal for my Wednesday gigs at Larry's coffee house where the sound guy is horrible. It'd be cool if it would clean up if you rolled back on the guitar volume, but an absolutely MUST-HAVE feature is dotted 8th-octave up-glitch-reverb swells. I'm gonna need it to run in stereo (would prefer three sets of stereo outs, more on that later) and I'm SOL on board space, so can you make it into one of those little mini boxes? If you're gonna use a bigger box, let's go ahead and include a rotating knobs that choose between modes...you know, like (insert commercial unit with SMD components or any bit of NASA equipment) does...that thing is so cool, man. This WILL be the same price as that boost you made me, right?

[EBK]

Not necessarily the solution you want, but it will answer some technical questions:
http://www.thatcorp.com/datashts/dn120.pdf

The simple solution is given early on in that doc:

The pan potentiometer (pan pot) allows users to steer an audio signal between two channels and, unlike standard potentiometers which have a linear taper, or audio potentiometers which have something like a log taper, the elements in a pan pot will have something approximating a sin vs. cos taper.  The intent is to yield a constant power  sum of the two output channels as the pan control is swept.

The common method of implementing a pan pot, using a single linear potentiometer with the wiper grounded, and resistors of approximately equal value to the pan pot connected appropriately, approximates the sin vs. cos taper described earlier.

[PhiloB]

I feel like this should be required reading for people considering "getting into" pedal making.

Why? Because...

The questions you THINK/HOPE you're gonna get
-----I think I want to try a Big Muff, can you make me a (insert BMP variety)? Make sure it has huge knobs!!!!

The questions you ACTUALLY get
-----I need a clean/dirty/fuzz compressor pedal for my Wednesday gigs at Larry's coffee house where the sound guy is horrible. It'd be cool if it would clean up if you rolled back on the guitar volume, but an absolutely MUST-HAVE feature is dotted 8th-octave up-glitch-reverb swells. I'm gonna need it to run in stereo (would prefer three sets of stereo outs, more on that later) and I'm SOL on board space, so can you make it into one of those little mini boxes? If you're gonna use a bigger box, let's go ahead and include a rotating knobs that choose between modes...you know, like (insert commercial unit with SMD components or any bit of NASA equipment) does...that thing is so cool, man. This WILL be the same price as that boost you made me, right?

Lol.  This is what I like about the whole thing.  I like solving problems for people and don't hesitate to say "I'm not your man for that" at the type of request above. 
Thanks for all the feedback ya'll.  I plan to have a conversation with the guy this evening.  Based on our previous conversation I think his response will be "I think I'll use my ABY pedal".
Fun to think through these things:) thanks for joining in the conversation and providing ideas and sounding board!


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[PhiloB]

Not necessarily the solution you want, but it will answer some technical questions:
http://www.thatcorp.com/datashts/dn120.pdf

The simple solution is given early on in that doc:

The pan potentiometer (pan pot) allows users to steer an audio signal between two channels and, unlike standard potentiometers which have a linear taper, or audio potentiometers which have something like a log taper, the elements in a pan pot will have something approximating a sin vs. cos taper.  The intent is to yield a constant power  sum of the two output channels as the pan control is swept.

The common method of implementing a pan pot, using a single linear potentiometer with the wiper grounded, and resistors of approximately equal value to the pan pot connected appropriately, approximates the sin vs. cos taper described earlier.

Thanks EBK.  I've bookmarked that and will check it out at lunch.


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[EBK]

More reading material for you:
http://www.geofex.com/Article_Folders/panner.pdf

[Rockhorst]

More reading material for you:
http://www.geofex.com/Article_Folders/panner.pdf

I must stick a post-it note on my monitor: check Geofex
The last past of that document shows what I had in mind. The hum issues can be solved with a transformer for one output channel. I once designed a 3 way splitter with transformers, worked like a charm. That was basically also taken Geofex by the way.

[PhiloB]

More reading material for you:
http://www.geofex.com/Article_Folders/panner.pdf

I must stick a post-it note on my monitor: check Geofex
The last past of that document shows what I had in mind. The hum issues can be solved with a transformer for one output channel. I once designed a 3 way splitter with transformers, worked like a charm. That was basically also taken Geofex by the way.

I offered to build him this.  Even have a transformer that'd work.  He just wants me to add dc jack to his AB pedal.  I asked him if he was sure it was an active box and not just a battery to power an led.  He is certain he wants a jack put in:)
I learned something along the way...thanks to everyone who contributed.


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