Pots And Reverse Polarity Humbuckers?!

[jay_ashcroft]

Hi everyone!

I'm new to this forum and you will have to pardon my ignorance and general lack of knowledge about guitar electronics!

Basically i have a crappy Ibanez RG250 which is to become a project guitar. I will shortly be stripping and repainting it to a custom design. I have already had 3 new pickups put in, Bareknuckle pickups to be exact. Now for their value they are pretty decent pickups but they still lack that lil bit of power i was hoping for.

So my question is...

If i change my pots to 1000K will this help the situation?

I'm not the best with electronics but as i understand the higher the value the more power that gets through producing a heavier tone (more powerful tone?!).

Also i've always been interested about reverse polarity humbuckers. What does this do to the sound and is it easily done?

Thanks in advance for putting up with my electronics studipity!!!!!

Jay

[MerlinTheWizard]

If i change my pots to 1000K will this help the situation?

I'm not the best with electronics but as i understand the higher the value the more power that gets through producing a heavier tone (more powerful tone?!).

Not really.

Actually, with very high resistance volume pots, you will have output impedance problems when the pot is not cranked up to full volume. So it will be counter productive.

There is nothing much you can do to make your output level higher, except from changing the pickups - or installing an on-board preamp.

[lovekraft]

Actually, with very high resistance volume pots, you will have output impedance problems when the pot is not cranked up to full volume.

OK, that's going to require an explanation - what possible output impedance problems could result from using 1Meg pots that weren't equally problematic at 500K or 250K?

[MerlinTheWizard]

OK, that's going to require an explanation - what possible output impedance problems could result from using 1Meg pots that weren't equally problematic at 500K or 250K?

The higher the total resistance of the pot, the higher the output impedance for any given wiper position that's not on full volume. Which in turn creates more loss over the cable. That's why more often than not, on passive gutars, the lower the volume pot, the less highs in the frequency response.

That's why we don't use arbitrarily high resistance pots in guitars. It must be high enough so as not to load the pickups too much, but not too high so as to keep the output impedance to an acceptable value. This is all a trade-off.

Of course, this is much less of a concern when using active pickups/preamps.

[JohnH]

Theres one thing you could do to get higher output, which is to do a mod which gives you options for putting the pickups in series instead of parallel - ie they are connected end to end. This results in their signals adding up, instead of averaging. There are lots of modifications along these lines on websites, such as guitarnuts.com. I have a design where theres a toggle for each of three pups to turn it on or off, and another for overall series/parallel - ill post it if interested.

JohnH

[MerlinTheWizard]

Theres one thing you could do to get higher output, which is to do a mod which gives you options for putting the pickups in series instead of parallel - ie they are connected end to end.

Right, but you have to make sure they are wired in phase, not out of phase. You have to know their respective polarity and such...

You are likely to get more output (although not as much as you would expect, since the two pickups are not close enough for that, so some harmonics will cancel out), but the sound will get less clear.

One thing to seriously think about is a simple preamp. Here is something to try, for instance: http://www.muzique.com/schem/mosfet.htm

[lovekraft]

The higher the total resistance of the pot, the higher the output impedance for any given wiper position that's not on full volume. Which in turn creates more loss over the cable. That's why more often than not, on passive gutars, the lower the volume pot, the less highs in the frequency response.

But hasn't that been addressed (as far back as the 50s, IINM) with a treble bleed cap, as in the Telecaster? And if a 500K pot is acceptable without any compensation (as in a Les Paul, for instance), why wouldn't a 1Meg pot be work as well, or even better, at least in the useful range of the volume control? Besides, if one uses quality low capacitance cable, doesn't most of the treble rolloff occur above the range that a guitar amplifier can be reasonably expected to reproduce (ie, above 6KHz or thereabouts)?At any rate, for any given level of attenuation, the lower resistance pot is going to have a lower corner frequency, just as it does when the pot is wide open. Take a look at this simple simulation (note that some values have been somewhat exaggerated to make the changes more obvious - there probably isn't a pickup in the world that measures both 10H and 10K, and a guitar cable with 150pF of stray capacitance is probably not going to be considered acceptable either, but they still illustrate the point):

The 500K/500K voltage divider represents a 1Meg pot set at the 50% point - if you decrease both halves of that divider by half (to represent a 500K pot), the -3dB frequency is decreased, and if you lower both again to 125K each (to represent a 250K pot), the corner frequency drops even further. But don't take my word for it -do the math.

Edited August 2, 2005 by lovekraft

[thegarehanman]

And that...is why I'm a mechanical engineering major and not an electrical engineering major.

[frank falbo]

Claiming that a higher value pot will actually incur more treble loss/capacitance from the cable is like saying if you use too much salt in the stew, it will taste less salty. There is more high end to be attenuated, and more is attenuated, but there was more to begin with.

The only thing it would affect is the taper. The capacitance during travel is irrelevant. If you're trying to say that a 500k pot at 50% will have less treble loss than a 1Meg pot at 50% because the 1K pot allows a higher impedance at 50%, I'll still disagree with it's relevance, even if it can be proven scientifically. The payoff of a 1Meg pot is at the top, when it's wide open. Any slight change one way or the other in the tone during travel is not worth factoring in.

This whole post is "IMO" by the way. I don't have the degree in electrical engineering either. But sometimes that education makes you miss the forest for the trees.

[MerlinTheWizard]

This whole post is "IMO" by the way.

Just try it. I was explaining that it was certainly not a way of gaining more volume, and that it was more likely to be counter-productive.

But if you think you'll gain something by using 1Meg volume pots, by all means, do it.