Tone Quest, PIO caps & Pots,

[96tbird]

Please humor me. I like sifting through the discussions on which cap is better, what pot to use, etc. The problem is you get all these opinions and it muddies the waters of what's true and what's anecdotal. So I have ordered some cheap Russian PIO caps of different values to play with. I do have some questions and would like opinions.

1) PIO caps dry out over time, no good for amps, but any effect on the millivolt bass circuits? Why, Why not?
2)What are caps actually doing to the signal? I really don't understand how they "bleed off" highs.
2) Higher the value cap = more highs cut... correct?
3)Same goes for pots whether used for volume or tone? If this is correct, wouldn't it be simple to sharpen up mudbuckers cheaply by lowering pot and cap values instead of dropping a wad on pups? (Bill Lawrence seems to think that's the case and he's got lots of years mucking with electronics).
4) My Gibson G-3 original wiring is an unusual selection of parts, 300K volume audio taper, 100k audio tone pot, .1uF cap (ceramic). What was the reasoning behind the odd setup?
5) Where are the poor suckers that pay $500+ on EBay for original 1958 wiring harness' with 53 year old pots and how can I help them from making this horrible error in judgement OR if you are interested, I have a 1976 Gibson 300k pot and would you like to buy it for $75.

Seriously though, I would like some straight answers from people that really understand electronics, like techs or engineers. Please remember though that I am looking for simple explanations: I don't understand much tech-speak. Thanks

 

[line6man]

1) PIO caps dry out over time, no good for amps, but any effect on the millivolt bass circuits? Why, Why not?

I really wouldn't worry too much about it. By the time a cap dries out, it will cost you a couple of bucks and a few minutes with the soldering iron to replace it.

2)What are caps actually doing to the signal? I really don't understand how they "bleed off" highs.

The capacitor works by passing high frequencies and blocking low frequencies. Since the capacitor is parallel to the signal path, the highs are grounded while the lows remain unaffected.

2) Higher the value cap = more highs cut... correct?

The higher the value, the lower the frequency cutoff point.

3)Same goes for pots whether used for volume or tone? If this is correct, wouldn't it be simple to sharpen up mudbuckers cheaply by lowering pot and cap values instead of dropping a wad on pups? (Bill Lawrence seems to think that's the case and he's got lots of years mucking with electronics).

A higher pot value will place less resistance between the signal and ground, (Whether directly, or through the cap, with a tone control.) so thus, will sound a bit brighter.

4) My Gibson G-3 original wiring is an unusual selection of parts, 300K volume audio taper, 100k audio tone pot, .1uF cap (ceramic). What was the reasoning behind the odd setup?

There is no reasoning. That's probably the combo that Gibson felt sounded best, and/or was most usable.

5) Where are the poor suckers that pay $500+ on EBay for original 1958 wiring harness' with 53 year old pots and how can I help them from making this horrible error in judgement OR if you are interested, I have a 1976 Gibson 300k pot and would you like to buy it for $75.

No idea.

 

[bassbenj]

Please humor me. I like sifting through the discussions on which cap is better, what pot to use, etc. The problem is you get all these opinions and it muddies the waters of what's true and what's anecdotal. So I have ordered some cheap Russian PIO caps of different values to play with. I do have some questions and would like opinions.

1) PIO caps dry out over time, no good for amps, but any effect on the millivolt bass circuits? Why, Why not?
2)What are caps actually doing to the signal? I really don't understand how they "bleed off" highs.
2) Higher the value cap = more highs cut... correct?
3)Same goes for pots whether used for volume or tone? If this is correct, wouldn't it be simple to sharpen up mudbuckers cheaply by lowering pot and cap values instead of dropping a wad on pups? (Bill Lawrence seems to think that's the case and he's got lots of years mucking with electronics).
4) My Gibson G-3 original wiring is an unusual selection of parts, 300K volume audio taper, 100k audio tone pot, .1uF cap (ceramic). What was the reasoning behind the odd setup?
5) Where are the poor suckers that pay $500+ on EBay for original 1958 wiring harness' with 53 year old pots and how can I help them from making this horrible error in judgement OR if you are interested, I have a 1976 Gibson 300k pot and would you like to buy it for $75.

Seriously though, I would like some straight answers from people that really understand electronics, like techs or engineers. Please remember though that I am looking for simple explanations: I don't understand much tech-speak. Thanks

Ok, we'll humor you!

1. PIO (paper in oil, also called 'vitamin Q') do not "dry out" over time, You are thinking electrolytic capacitors. PIO are hermetically sealed in glass and metal. They are excellent caps for any purpose including tone circuits and amps. In fact are probably overkill as any plastic film capacitor will work just fine.

2. If you feed an audio (AC) signal through a cap it will have a certain "resistance" to that signal just like a resistor. Only people use the term "impedance" to distinguish between resistors. They do that because the resistance of a resistor does not change with frequency. The "resistance" of a cap does. The value not only depends on the capacitance of the cap but also on the frequency. The "resistance" gets lower and lower as you go higher and higher in frequency. Hence for a "tone" cap that is connected though a reistor (pot) to ground. As the frequency is higher and higher or the value bigger and bigger, the cap "bleeds" more and more signal. OK?

The "other" number 2. Yes. We just said that the impedance of a cap depends on it's value and the frequency. (actually "inversely" which means as 1/(freq x C).

3. Not quite. first off the reason humbuckers are "muddy" is they sense the strings at two different spots. That mixes up the harmonics and gives the classic sound. Playing with caps and Rs won't change that. However ONE reason pickups sound different from each other is that they have diferent capacitance, inductance and resistance. This filters the signal to change the tone. And yes, one CAN play with external components to change the tone. Varitone does this.

4. They chose those values because it gave the tone they wanted. 300k isn't all that different from the usual 250k. The tone pot is probably low to roll off some of the brightness plus keep the pot from having little or no action in the upper range. The .1 ceramic was used to move the frequencies rolling off higher than the usual .047 and they picked a ceramic because even though they suck as tone caps, Gibson could care less because it was cheap as dirt.

5. Nope 50 year old pot (of any kind) is not what you want.

6. Note that you still don't quite get it, because in a passive bass there are more than just caps. The inductance (which also has frequency-dependent impedance, but goes the opposite way from a capacitor) of the pickup(s) is also important as well as the resistance of the parts in the circuit. These all interact in very complex ways to shape the tone an create "resonances" that "peak up" certain frequencies. These effects interact in many ways and can't be easily "explained" without resorting to tech-speak.

 

[96tbird]

Guys, that is exactly what I was hoping for, you have cleared this up for me. Now when I look at a circuit I will not be mystified. Oh and thanks for adding the difference of resistor vs. a cap, I knew that a pot is just a variable resistor. Thanks a bunch. Sweet!