Potentiometer Load

[Elias Graves]

My Epi Alleykat suffers from Dark Tone Syndrome, which is likely related to the master volume Gretsch style wiring scheme.
I've read that running two 500k pots yeilds a load of 250k. Is that right?
If you add a third 500k pot into that chain, what's the load? I haven't been able to locate the actual formula for calculating that.
I swapped the master volume 500k for a 1 meg, hoping to brighten things up a bit but I didn't really hear much difference. The pot I removed was a CTS that measured 499k and the new CTS measured 980k. That should have made an audible difference, no?
Am I doomed to removing the master volume or is there a workaround? Maybe a tone switch like a gretsch of something?
Thanks,

EG

[Mark Hammer]

The loading effects of different pot values have their greatest impact when the pots are up full. So, if the guitar is plugged direct into the amp, and you have a guitar with a volume pot turned up full and a pickup, the amp "sees" what is essentially two parallel paths to ground, provided by a pickup of around 6-8k, and whatever the volume pot value is. If we have an 8k pickup and a 500k pot, the amp "sees" more of the full range of that pickup than it might when the contrast between pot and pickup is reduced by use of a 250k pot.

But here is where it gets wonky.

Turn that pot down a bit, and now some of the resistance of the pot is effectively added in series with the pickup. So, turn the volume on a 500k pot down to maybe 7-8 or so, and perhaps 100k of the pot on the input side of the wiper is added to the pickup load, such that the amp now sees two paths: 400k to ground via the remainder of the pot, and 108k to ground via the PU+pot. Even less contrast than in the case of a 250k pot turned up full.

What's the punchline here? What pot values do when they are turned up full can be different than what they do even turning down a little bit. And if there are more pots involved, turned down a bit, you start to run into serious loading issues.

One solution is to stick with the pots you have, and use compensation caps across the volume pots, Fender style, to retain some of the sparkle should you turn down.

[Elias Graves]

Thanks. That helps some.
I'm finding that I don't like the taper on the 1 meg pot much at all. Having so much range, I suppose, makes it extremely touchy and it gets dark in a big hurry when I turn it down. Much more noticeably than with the 500k that was there.

For pickups, I'm presently using a Rose Day Breaker bridge. This is a PAF/filtertron style with a4 magnets. It's fairly jangly for a humbucker and reads about 7.5k resistance. That may get yanked in favor of the ole Seth Lover. The neck is a Duncan SM3-N that reats about 6.7k. So, both are fairly low output pickups.
Current pot setup is 980k master, 500k neck and bridge volume and 500k tone with a .015 tone cap. I've swapped a bunch of pots and caps in and out with higher and lower values to see what I got. Have used several caps as well, including some orange drops (.015 and .022) and an .022 russian PIO. There is an old vitamin q in there now.
I've done all kinds of fooling around with this thing trying to get a good sound for it without a complete rewire. I do like the master volume feature, but if it's going to remain this problematic, I may go with a Gibson style wiring.
Before I do that, I may build some sort of 3 or 5 position tone switch for it and see if that lightens the load somewhat.

EG

[Mark Hammer]

Thanks. That helps some.
I'm finding that I don't like the taper on the 1 meg pot much at all. Having so much range, I suppose, makes it extremely touchy and it gets dark in a big hurry when I turn it down. Much more noticeably than with the 500k that was there.

Well that's just it. If the volume is always up full, a higher value pot does some nice things for retaining sparkle (just as a lower-value pot does nice things for mellowing out). But once you move the knob from 10 in a downward direction, everything changes.

Some folks are going to leave the volume up full all the time, unless they turn down to go "What? I didn't hear you.". For them, I say "Believe everything people say about pot value". Other folks will be diddling the volume constantly, simply because what they play demands it. In those cases, a higher value is no panacea, since turning down will end up loading the pickups like crazy.

I think you need to seriously consider going with a 500k volume pot and a compensation cap across the pot (i.e., small value bypass cap between input and wiper) to retain highs when you turn down. With such a cap in place, it is as if the portion of the volume pot that might otherwise be added in series with the pickup does not even exist for high frequencies.

[Elias Graves]

That makes sense.
I'm kind of an old school player...class A amps and constantly riding volume and tone for sound varieties.
This third pot just may not work out for me. I'm going to build a 5 position tone switch, I believe and try that out. I've used a treble bleed a time or two and found them rather "artificial" sounding...not to my liking. If the tone switch setup doesn't help things out, I'll either have to rewire the whole thing or sell it and move on to something else.

EG

[pdf64]

Do you normally leave the tone control at max?
If so, consider replacing it with a 'no-load' type. On max, a regular one is effectively yet another 500k load to damp pick resonance.
Have you tried different cables? Low capacitence types such as George L make a difference.

[Elias Graves]

On my other guitars, I rarely have the tone full open. On this one, however,it's dark on 10. Roll it back any at all and it's just awful.
Have not tried other cables. I think my main one is a Planet Waves 10 footer. Worth a shot, you think?

EG

[pdf64]

It's worth a shot but don't expect a magical transformation - have you got a capacitence meter? (maybe a function on a digital multimeter) to check your cable with.
The no-load tone pot has more impact.
How about you temporarily link one of your pickups to the output jack socket, eliminate all pots etc?
If it's still dark then, it's time to move on.

[Elias Graves]

Yes, I have a meter. What kind of values should I be seeing?

I've had these same pickups in other guitars with traditional Gibson style harnesses and didn't find them dark at all. The mini, especially. It sounds more like a single coil than a bucker.

The no load pot idea would probably work, but then I'm still with no tone control. I'd be back to dark city when I turned it out of the "off" position.
This may be a fruitless chase.

EG

[pdf64]

Cable capacitance; from memory, 1nF would be bad, a woolly sounding cable, 100pF would be really good for 10', 250-500pF is about average. Much more than 250pF and I'd be looking for a better cable.
A premium 20' Planet Waves cable that a buddy recently bought was worse than expected, about 700pF as I remember.

[Mark Hammer]

What I frequently recommend to folks is the following experiment. Take the shortest cable you can manage that will physically allow you to plug directly into the amp and still play the guitar...albeit awkwardly. Listen closely. Now take the longest cable you have and use that instead. The difference you hear in tone is the effect of cable capacitance.

Although certainly 1nf per line foot would be simply awful, lower capacitance (e.g., 18pf/ft, vs 22pf/ft) isn't always best. There are many different properties of shielded cable and capacitance is only one of them.

I think a multiposition tone switch is an excellent idea.

You might want to look at this thread for some info: Update on Alley Kats?

[Elias Graves]

I think that thread is the most discussion I've ever seen on Alley Kats. Thanks.
NOT moving the pickup, however.

I did notice from the Gibson wiring scheme that the master volume is the last in the chain. A tone switch might work well in that slot without having to rewire the whol thing.
I have noticed the individual volumes don't behave quite the same as on a regular Gibson setup. Now I know why.
Still thinking I may just go with a regular Gibson wiring scheme, though. They do work well.
Before I do that, though, I'm going to try one more bridge pickup. It's the other half of my Rose Day Breaker set and is actually the designated bridge pickup. It's A4 and wound to about 12ish, but the screw side is hotter and works very well split. In split mode, it has a very Dynasonic flavor. That may brighten things up enough.

EG