Panpot Considerations

[fieldwrangler]

Folks -

So, I went out and bought the cheapest Epiphone Les Paul Junior kindof thing to use as a test mule for a pair of pickups I just finished ($129 American). Decided that I was just gonna send them through a master volume w/panpot (a 250K that was lying around) this time.

When I was done I started thinking about what kindof load the parallel combination of all them peskey pots was gonna present to the poor pickups (which are running at 12K and 15K dcr.)

Y'know, they really don't sound too great looking into 100K; surprise, surprise. (Not to mention that the pickup's outputs go to the wipers of the panpot, and therefore the load is varying with knob position.) I s'ppose I could buffer them individually, but I'm kindof a passive-harness-onboard-only kindof guy.

Anyhow, anyone else who might think at some point about doing this (and might not have thought it through beforehand, like I didn't); you might wanna reconsider and learn from my mistake... Or at the very least use a 500K panpot and maybe a 1 meg volume control with a liberal sprinkling of compensating caps & resistors hanging off their lugs.

Bob Palmieri

[David Schwab]

500K pan pots sound fine. You have to watch how you wire them up though. If thy are N/M or A/C taper, where the ground is connected matters, since they will have less resistance between the wiper to one of the outside lugs. The higher resistance side goes to ground.

If you wire the pan pot up backwards you will have dull sounding pickups.

[fieldwrangler]

Thanks, David.

I just ordered a 500k from StewMac (as well as a plain old 3-way just in case.)

When it arrives I'll look into the issue you've raised and report back.

Bob Palmieri

[David Schwab]

Stew-Mac now list their post as linear taper. Their older ones were audio, but the taper ran in the same direction, so they were really stereo volume controls.

The new ones seem to work fine.

AllParts and GuitarJonesUSA also sell good pan pots.

[Rick Turner]

The really trick pan pots have both sections full up in the middle with one having no resistance change from mid to full clockwise and the other on resistance change from mid to full anti-clockwise. So using them adds no more load than a master volume control would.

[fieldwrangler]

The really trick pan pots have both sections full up in the middle with one having no resistance change from mid to full clockwise and the other on resistance change from mid to full anti-clockwise. So using them adds no more load than a master volume control would.

Rick -

Certainly true regarding the series resistance. Unfortunately (in the most common wiring scheme) it's the shunt load that took me by surprise.

With the usual cross-wiring-to-opposite-lug setup (as is, in fact, so common as to be pre-wired into the supplied ganged pots) the two pots are always in parallel.
Therefore, even with one pickup full on and the other shorted across its output (as it is when wire to the wiper) the working pickup sees the parallel sum of the pots' resistances (125K in the case of a 2-gang 250K unit.) Then you gotta have a volume control, right? So, with a 500K volume your pickups are now seeing 100K. Yuk.

So, last night I threw in a 2-gang 500K "blend" pot from StewMac. With the new load around 165K things are much improved. And they might be even better if someone made a 1 meg pair (and a good compensation scheme was worked out.

By the way, I also discovered yet more surprises when I tried to throw some compensation caps across the pots...

Bob Palmieri

[David Schwab]

By the way, I also discovered yet more surprises when I tried to throw some compensation caps across the pots...

I do that sometimes with resistors to get the taper the way I want.

[Rick Turner]

Yes on the shunt loading issue. Understood, and yes, if those pots were available at 1 meg, it would be a good thing. This is one of the limitations of passive electronics, of course. Only by buffering and going active, whether you want to add gain or EQ or not, can you get away from the pesky loading issues. And it's this varying load that makes it even weirder. It's a bunch of compromises wrapped in mysteries, and sure, there's science to it, but it's also an arcane art.

[David Schwab]

Yes on the shunt loading issue. Understood, and yes, if those pots were available at 1 meg, it would be a good thing. This is one of the limitations of passive electronics, of course. Only by buffering and going active, whether you want to add gain or EQ or not, can you get away from the pesky loading issues. And it's this varying load that makes it even weirder. It's a bunch of compromises wrapped in mysteries, and sure, there's science to it, but it's also an arcane art.

I agree 100% about the the active passive blending issue. I prefer to buffer the pickups first and then blend them. That works so much better.

[RedHouse]

...I went out and bought the cheapest Epiphone Les Paul Junior kindof thing to use as a test mule ...

Just an FYI, be real careful if you start doing critical listening tests on that test mule, keeping in mind that the wood (guitar) is most of the equation when you start evaluating pickups critically for tone.
(say PAFs etc)

[fieldwrangler]

Pretty much true, although the hardware, scale length & string gauge are other physical factors I can't fake from one setup to another.

The wood on the Epiphone is some kindof mahogany-like substance; with 11's (and a pickup I already know pretty well) I have a pretty good idea of what's going on. I weight a few of these and this was by far the lightest.

Other current Beasts of Burden are a '62 Melody Maker with heavy flats, a '65 Melody Maker with 11 gauge roundwounds, a Yamaha Weddington with 10's and a light relic Tele with 11's.

The wood on the Yamaha is really quite nice, the Magical Mid-60's Mahog on the MM's is really just great and the Epiphone is in the back of the pack, but not bad by any measure.

Bob Palmieri

[Rick Turner]

I do both depending on the end results I'm trying to achieve.

With my Electroline basses, I have no problem with blending the two magnetics passively, as what I'm trying to get from those pickups is a more "normal and classic" set of tones...yes, more P bass/Jazz bass kind of thing. I then actively blend the mag pickups with a piezo to go more "full range modern". I'm looking for a kind of best of both worlds result, fully understanding the issues with passively paralleling two mag pickups. Call it an artistic choice. On those basses, my favorite sound is with all pickups up all the way. The mags give a kind of mid focus while the piezo speaks to whales and bats...