wiring help needed

[ubertar]

I've made a guitar pickup with a separate output for each string. I want to output to two jacks, for stereo, with each string having its own stereo pan control. I set it up with 500k audio pots wired so that the "hot" lead from each coil goes to the wiper of its pot, and the outer lugs connect to the "hot" of each jack. The colds all go to ground on the jacks, which are connected together. It ended up acting more like a switch... I get signal in one amp with the pot all the way to the left, and signal in the other with the pot all the way to the right, with nothing in-between.

It would seem the pot value would be too high, but experimenting with a single coil with one outer lug connected to ground, and the other as output, I get the opposite effect: starting from full volume and going down, there is strong signal until near the end, where there is a sharp drop-off, so it seems the pot value is too low. With higher values, there is a more gradual change. A 5meg audio pot was the best I tried.

My guess is I'd be better off using dual pots (two pots, one shaft (not to be confused with two girls, one cup)), 5 megs each, with the right of one and the left of the other connected to ground, and the opposite ones going to their respective outputs. But before I search for dual mini 5meg audio pots, I thought I'd ask you guys what you think.

 

[shabtek]

i think you need to go active---maybe 2 tl074 quad opamps. assuming a 6string;each string into an opamp feeding a 'pan' pot like you've suggested, with remaining 2 opamp sections performing left and right summing.
check figure 7here for pan idea http://sound.westhost.com/project30a.htm

 

[Harpo]

did you almost try to flip your coils hot to pot outer lug, wiper to series resistor, leading to your out jack?
Something like NYDave's panpot
Don't think you'll get lucky with your dual audio taper pot. Most come with about 10% of its total resistance at center, leading to a ~-20dB loss when centered. I'd go linear taper with a resistor in parallel between pots' outer lug and wiper to bend its law to taste. YMMV

 

[ubertar]

I'd really like to stay passive with this, if possible. NY Dave's scheme looks interesting. What would you suggest for the value of the dual linear pot?

 

[ubertar]

So I decided to switch to switches, figuring that would be easier. I got some dpdt on-on-on switches, to do left-middle-right. The signal goes to the two centers, and one out is the top right and the other the bottom left. All the top rights are attached together in series and go to one jack, and the bottom lefts are attached together in series and go to the other. I ran into two problems:

1. Left and right work great. But since all the left outs go together, and the right outs go together, if any one pickup is switched to middle, they all become middle.

2. If the signal from any of the pickups goes to the original jack (the one the regular single coils are connected to-- it's a strat with a 5 way switch... the hexaphonic pickup is in middle position) it shorts out either regular single coil when in "blend" position. I've tested them outside of the guitar, without the switches, and have found a single string pickup and a regular pickup cannot be connected at the same time. I think what's going on is the resistance from the little coil is meaningless to the regular pickup, and it's as though a wire were connected from signal to ground, shorting it out.

My guess at a solution for both problems is to use diodes-- for #1, a diode between each positive lead and the positive jack terminal should keep each middle position individual. I'm not so sure if they'd work for problem #2, but I'm hoping that would achieve some kind of separation that would keep the pickups from interfering with each other.

My questions are:

1. Does this make sense?

2. I suppose I need diodes with very low voltage rating... less than a volt. Do you know of anything common I could try? I've never used diodes before, except in following someone else's schematic.

3. Any other suggestions? Did I screw up something obvious?

Thanks!

 

[ubertar]

After a little research, I'm thinking 1N4148... I'll have to go get some and try it out. I tested with something else, I forget the # but it's rated 50v... it'll pass a regular pickup, but not one of the little coils.

 

[PRR]

> use diodes

No. You are not visualizing how AC (audio) signals happen.

> wiring help needed

No, this is not a wiring problem. It is a Mixer Design problem. All mixer troubles can be changed (perhaps made "better") if you stick amplifiers here and there to isolate things (what you may be thinking the diodes do). However you rejected this plan, and for gitar, I agree you should keep the instrument pure (until you prove that you can't get what you want).

Mixing is a tricky problem. There are ways to do it losslessly, but not with resistors.

Pan-pots are a very sticky problem. There is perhaps a way to do it losslessly, but not with resistors.

Loss increases with number of channels, and you have 6 to 12 to 2.

Resistive mixers tend to shift impedances. But guitar pickups are sensitive to loading. A 5K pot will suck some of the level and all the highs off the signal. We generally like to load with much more than 100K. The guitar amp input is not infinite, and the guitar cable can have a lot of effect.

This is the best I see. Needs a dual linear pot (per pickup), fortunately a standard part, wired with an "X" as shown. For same vibration at all strings, all pots set full L (or full R), it is nearly unity gain. But you don't have same-vibration, and you didn't want all to one output. You may have just one string singing. If mixed full L it is -16dB, if mixed Center it is -22dB.

Huh. The "standard wiring", six pickups in parallel (electrically or magnetically) actually gives -15.5dB. The individual pickup has higher output than the instrument. So -16.2 full-L and -22.4 centered is not a lot less than a normal axe.

Please don't say "individual level controls".

 

[ubertar]

Hey, thanks. I figured out pretty quickly that diodes wouldn't work... I had forgotten I was dealing with AC. These pickups are on the quiet side to begin with, and I'd really like to avoid going active with them, so I'm going to stick with the switches for now, and just do left/right for each, since the switches are already in there, wired up. But I'll definitely revisit this at some point, perhaps in another guitar, so your work won't go to waste. It's very much appreciated.