A while back, I described some problems with trying to use treble bleed on this guitar with three volume pots and a 3-way switch. When turning down one volume pot, that pickup retains brightness, but the other pickups get duller. In this diagram, with middle and neck pickups in a blended switch position, the middle volume is up full and the neck volume is turned down. The middle pickup high frequencies have a path to ground through the neck treble bleed cap.
This problem can be avoided on a typical two pickup 3-way switch guitar (Les Paul, ES-335, Sheraton, etc) because on those, with only two pickups, the 3-way switch has two non-blending positions which completely isolate a pickup. So instead of using the independent-volume (decoupled) wiring (pickup signal wired to center volume pot lug), you can use non-independent-volume (coupled) wiring (pickup signal wiring to side pot lug). In that configuration, there is no treble loss when turning down the volume, but if you turn down the volume all the way, it also kills the volume for the other pickup. (Hence the “non-independent” in the name). But this isn’t a problem because with only two pickups, if you want to turn off one of the pickups, you can just use the 3-way switch – you’ll never need to turn a volume pot all the way down.
But with three volume pots and a three way switch like my Epiphone Riviera P93, there is no way to isolate one pickup. The middle pickup is always on in all three switch positions, so there will always be bad interactions with the treble bleed. The stock Epiphone G-400 Custom exhibits this problem, with treble bleed caps on all three pickups.
I punted on a solution for my Epiphone Riviera P93, and just left it without treble bleed. However, I’m finding that the way I use this guitar would really benefit from some treble bleed.
So, here are some possibilities to consider:
- Update Feb 9, 2011: Another option occurred to me. This is a variation on #1,2 and 7 below. Replace the middle volume pot with a push/pull pot. Make this a master volume control with treble bleed, and make the push/pull enable/disable the middle pickup. Additionally, move this pot to be the closest to the player position. I’m liking this idea a lot, and may give it a try.
- Update 10/24/2017: That idea worked out well! I finally wrote up the new circuit here.
- Put treble bleed capacitors on just the neck and bridge volume pots. The bleed caps will work well in the up and down switch positions, if the middle pickup is turned down. In the middle switch position, there’d be the same interaction problem between neck and bridge, just as with any two-pickup guitar.
- Same as the previous idea but additionally put a push/pull pot on the middle volume to turn off the middle pickup. This makes it easier to isolate the neck or bridge, without having to turn down the middle volume knob. But with middle pickup on, or in the middle switch position, you’ll still hear the problem.
- Replace the three way switch with a five way switch, wired like a Strat. This provides three switch positions which completely isolate a pickup. In positions two and four, the middle pickup is blended with a neck and bridge. There’s no way to play with all three pickups simultaneously, nor bridge+neck. Requires drilling two new holes and routing a slot.
- Replace the three way switch with a five way four pole super switch. This switch is pretty amazing, allowing you to enable the treble bleed caps only in the non-blended positions. E.g. Neck with treble bleed, neck + middle no treble bleed, middle with treble bleed, middle + bridge no treble bleed, and bridge with treble bleed. Unfortunately, it requires a two new holes and a slot to be routed. Fairly pricey too.
- Same as the previous idea but make it a 5 or 6 position four pole rotary switch. The 6th position would allow all three pickups together or neck+bridge. Doesn’t require slot-routing or drilling. Cool, but a rotary switch is a bit more fiddly to adjust when playing live.
- Replace the three-way switch with a Free-Way 6-position switch. Doesn’t require slot-routing or drilling. Provides fast switching. Allows pickup isolation for all three pickups, as well as the same blended choices as the 6-way rotary. Doesn’t allow the treble-bleed to be selectively enabled for the non-blended positions. Quite pricey.
- Add a master volume knob with treble bleed. This would require drilling another hole in the guitar, and I think five knobs is just too many.
- Instead of three volume pots and one tone, have three tone pots and one master volume, and a 5 or 6 way switch. Hey, it’s a 4 knob Strat!
- Replace all three volume pots with push/pull pots, pull to individually disengage treble bleed. Too tweaky to use!
- Replace the three volume pots with volume controls which open-circuit when turned down to a 0 detent. Do these even exist?
- Something else I missed?
A number of people suggested trying to use diodes to make a one-way valve for the signal, but this won’t work. A guitar’s audio signal is alternating current (A/C), so a diode would act as a half-wave rectifier, clipping the signal and resulting in distortion. In fact, you can make a simple passive distortion circuit by using a pair of diodes to symmetrically clip the signal. That’s just how the little Black Ice device works.
So many choices, hmmm. I’m leaning towards #2 (bleed only on neck/bridge, with push/pull on middle), #6 (free-way switch), or possibly #5 (rotary 4-pole). Update Feb 9, 2011: see the first item on the list for my new preferred idea.