Some "beginner" questions about volume pot mods

[draelyc]

Hi, folks,

I have a Hamer USA Mirage I koa top, which I've had modified with a full sized humbucker (a Duncan Custom Custom) in the bridge position in place of the stock Hot Rails. The guitar also has a pair of Duncan Cool Rails in the neck & mid slots.

Recently, I've been messing with the wiring to try to get the guitar to clean up better when I roll back the volume knob. When I got the guitar (used), it had some sort of resistor wired to the volume knob, and the taper of the pot was odd ... rolling the volume up from nothing resulted in an abrupt change from silence to LOUD, and it didn't clean up all that well. However, the tone was fairly full & chimey when rolling back from "10"...

Now, I know nothing about electronics, so a buddy of mine who's great with a soldering iron has been helping me out. First, we removed the resistor that was in there (it has since disappeared, sadly, so I have on idea what value it was!), and the pot's taper improved DRASTICALLY. However, rolling back from 10 now meant complete loss of all high end frequencies.

So I tried changing from the stock pot to a 500K one. Some slight improvement, but the treble loss was still too much, especially on the single coil pickups.

On some folks' advice, I then tried a .001mF cap on the volume pot ~ the "treble bleed mod." Well, the treble came back like gangbusters, but now rolling the volume back meant dialing out all the lows & mids...

So I asked around online again, and folks recommended I try a 150K 1/4 Ohm resistor. Well, we just put that in on Monday, and it *is* an improvement ~ the bridge pickup works great, now. But the single coils still lose entirely too much treble when the volume is rolled back.

Now, I'm hesitant to try the cap *with* the resistor, because the cap by itself was so bad. Is that just my ignorance talking, though? Will the resistor balance out the cap better than I expect?

Moreover, I've read that for single coils, 250K pots work best for keeping them warm, but that 500K are best for 'buckers. What about guitars with combinations, like mine?

I did a search on here, before I posted this, and saw an interesting thread about the "50s mod" ... Would that be a better option for this particular guitar?

Any help at all will be very greatly appreciated ~ thanks, y'all!

[cugel]

Originally Posted by draelyc

Hi, folks,

I have a Hamer USA Mirage I koa top, which I've had modified with a full sized humbucker (a Duncan Custom Custom) in the bridge position in place of the stock Hot Rails. The guitar also has a pair of Duncan Cool Rails in the neck & mid slots.

Recently, I've been messing with the wiring to try to get the guitar to clean up better when I roll back the volume knob. When I got the guitar (used), it had some sort of resistor wired to the volume knob, and the taper of the pot was odd ... rolling the volume up from nothing resulted in an abrupt change from silence to LOUD, and it didn't clean up all that well. However, the tone was fairly full & chimey when rolling back from "10"...

Now, I know nothing about electronics, so a buddy of mine who's great with a soldering iron has been helping me out. First, we removed the resistor that was in there (it has since disappeared, sadly, so I have on idea what value it was!), and the pot's taper improved DRASTICALLY. However, rolling back from 10 now meant complete loss of all high end frequencies.

So I tried changing from the stock pot to a 500K one. Some slight improvement, but the treble loss was still too much, especially on the single coil pickups.

On some folks' advice, I then tried a .001mF cap on the volume pot ~ the "treble bleed mod." Well, the treble came back like gangbusters, but now rolling the volume back meant dialing out all the lows & mids...

So I asked around online again, and folks recommended I try a 150K 1/4 Ohm resistor. Well, we just put that in on Monday, and it *is* an improvement ~ the bridge pickup works great, now. But the single coils still lose entirely too much treble when the volume is rolled back.

Now, I'm hesitant to try the cap *with* the resistor, because the cap by itself was so bad. Is that just my ignorance talking, though? Will the resistor balance out the cap better than I expect?

Moreover, I've read that for single coils, 250K pots work best for keeping them warm, but that 500K are best for 'buckers. What about guitars with combinations, like mine?

I did a search on here, before I posted this, and saw an interesting thread about the "50s mod" ... Would that be a better option for this particular guitar?

Any help at all will be very greatly appreciated ~ thanks, y'all!

you may want audio taper pots. sounds like you may have linear pots in there now. you can leave the 250s in and have a resistor for the hb so its sees 500k. but i think you may want to take an hour and play around with pickup height to help with the brightness you are talking about. really makes a huge difference and its fast easy and reversible.

now i dont know duncans but if those are rails then they aint single coils. they maybe the same size but i bet the are humbuckers. if thats the case i would put 500k cts pots from rs guitar works innit with 0.022 caps between vol and tone, 50s style is optional, and take time with finding the correct height for the treble side of those pickups.

btw those ARE definitly humbuckers, so you dont have a single coil pup in the guitar

[draelyc]

Thanks, cugel -- that's a lot of very helpful info!

Sorry I got sloppy with my terminology... I know the Cool Rails aren't true single coils. I was just trying to make a quick distinction between them & the Custom Custom, since their tone & output are so different, and since they seem to be *much* more sensitive to treble loss that the CC in the bridge.

I'll try the different cap value & maybe the different pot, too. And I'll play with the pickup height a bit more, too. Already worked with that a bit, but that was before the 150K resistor -- probably need to readjust before trying anything else.

Thanks!
Chris

[walterw]

you're on your way, just keep experimenting. i would try a much smaller capacitor, like .0005uF. this will not make things so brittle when turning down. (the bigger the cap number, the more treble stays up when you turn down.)

[draelyc]

Thanks, Walter! I went by Radio Shack, but their selection of caps was pretty sparse... Only thing smaller than .001uF I could find was 100pF. I'll try another electronic supply place in town next week, though.

I'm very curious to hear what the difference is between running resistor + cap, & just running either one alone.

C

[Bob V]

You might be chasing your tail with the treble-bleed mod - I've found, like you did, that it cures one problem and causes another.

So yes, I would recommend you try the 50's mod. Simple - just locate whatever lead was running from the volume pot over to the tone pot (sometimes its a wire, sometimes its one leg of the cap). Instead of attaching that wire on the outer lug of the volume pot (or earlier on the circuit like from the pickup selector on a Strat) together with the pickup, you move the tone control so it runs off of the center lug of the volume pot. Now, technically, it comes "after the voltage divider" and the volume and tone controls will be more interactive. The plus side is that you retain trebles as you roll off the volume (important if you like to keep your amp pegged and your guitar turned down for clean tones). The finicky thing is that the taper of the volume control seems more abrupt with the 50's mod (something that came about with the changes in the Les Paul circuit over the years), so in that case you probably want to experiment with audio vs. linear taper volume pots. RS Guitarworks sells a special taper volume pot.

If it's a guitar with a rear-access control panel it should be easy to move things around and try different combinations until you get what you like. You can even leave the pickup leads hanging out of the back and twist wires until you like what you hear in terms of coil splitting and phase, etc.

[draelyc]

Thanks, Bob! Now, with this 50's mod, would I leave in that resistor I had installed in the circuit, or do I need to take it out first?

[RvChevron]

Originally Posted by draelyc

Thanks, Walter! I went by Radio Shack, but their selection of caps was pretty sparse... Only thing smaller than .001uF I could find was 100pF. I'll try another electronic supply place in town next week, though.

I'm very curious to hear what the difference is between running resistor + cap, & just running either one alone.

C

If you like the tapering of the stock 500K pot without any resistor, then leave it as is with no resistor.

For retaining high end when turning down the pot, try smaller value than .001uf.

You can buy a few of those 100pf ones from RS, twist two or more together and increase the value of the capacitance.

For instance, twist two 100pf caps together (in series), you get 200pf value and so forth.

You do it buy twisting each side of the wires of each cap with the same sides of the other one.

Like this:

cap A:

1 ----------O----------- 2

Cap B:

3 ----------O------------ 4

Twist 1 and 3 together and 2 and 4 together. Make sure you insulate the exposed portions of the wire.

[walterw]

Originally Posted by RvChevron

For instance, twist two 100pf caps together (in series), you get 200pf value and so forth.

+1 to all that, but of course you meant "parallel".

[draelyc]

Thanks, fellas. Well, the first round of experimenting was a bit frustrating. We tried the 50's mod; we tried the resistor by itself (actually, that was the starting point); we tried the .001uF cap again; we tried the 100 pF cap; we tried a couple other caps my friend had lying around the shop whose values I can't remember now, both alone and with the resistor...

It seemed like we could either achieve A) a nice, smooth taper on the volume pot, or B) a good, consistent tone no matter where the vol. pot was set ... but we could not manage to achieve both at the same time. With A), we lost the high end when dialing back the volume; with B), the volume didn't really have a taper, but was pretty much completely on, until it went completely off, when rolling it back.

Next time around, we'll try a high end, audio taper pot that's on order right now, and we'll keep experimenting with various cap values.

I did ask Hamer about it, and apparently when the Mirage first came out, there was nothing on the volume pot stock, but at some point during the run, a resistor and a .001uF cap were added to the volume at the factory ... but nobody there could remember the value of that resistor. Natch.

Chris

[RvChevron]

Originally Posted by walterw

+1 to all that, but of course you meant "parallel".

Sorry if I confused anyone...

Yes Walt, they should be wired in parallel, physically speaking.

I said "in-series" cuz you get the sum of the values of the combined caps.

[draelyc]

What I don't understand (and this really highlights my ignorance regarding electronics) is why a volume pot doesn't just alter the *volume*, but also changes the tone/frequency response as well...

My other Hamer, for example, a USA Studio, has nothing wired to its volume pots, and while there is a slight reduction in treble with the volume dialed back, it's not so HUGE a drop-off as to render the tones unusable. If I could get that sort of subtle difference going on the Mirage, I'd be in bidness, but the Mirage's Cool Rails seem to be much more prone to the high end rolloff...

Well, we'll see how that audio taper pot does when it comes in...

[draelyc]

Well, I'm still waiting for that new pot to come in ...

Meanwhile, I find myself wondering if I might be better served with some different pickups than the Cool Rails. The Custom Custom in the bridge doesn't suffer nearly as much as the Cool Rails, in terms of getting muddy & losing treble when the volume is rolled back...

I like having at least an approximation of single-coil tones out of the neck & mid position pups, but maybe there's something out there that would be a better match with the Custom Custom? Any suggestions there?

Thanks!
Chris

[earthtonesaudio]

First, a bit of advice: slow down! From your description it seems like you've been changing several things at once and never getting a chance to compare apples to apples.

Some general info: the "system" you're listening to consists of several parts: string, pickup, volume/tone controls, cable, amp input. Making changes in different parts of this system may have effects primarily "upstream" or primarily "downstream" or may affect both simultaneously.

An example: assuming you have a single pickup and a single volume control, the value of the volume control when set to maximum volume will have an effect on the pickup. A large value loads the pickup less, which means more volume and a higher resonant peak (brighter). A small value loads the pickup more, reducing volume and damping the resonant peak (duller). Note that so far I've only been talking about the volume pot up full, basically acting only as a simple resistor.
As you turn the volume down (assuming you have it wired as a standard voltage divider, i.e. pickup connects to lug 3, signal out from lug 2 and ground on lug 1), you start to introduce series resistance between the pickup and the cable. This has very little effect on the pickup, but now there is a big effect on what happens in the cable. The cable's dominant characteristic is its capacitance to ground, and adding resistance in series before the cable forms a low-pass filter and causes highs to be cut.

Adding the "treble bleed" capacitor provides an alternative path for the signal from the pickup when the volume knob is turned down (with the volume at max this capacitor is short-circuited and effectively removed from the circuit). Since it's a capacitor, its impedance goes down as frequency goes up, so turning down this volume pot (with treble bleed mod) reduces treble less than before. It bypasses that portion of the volume pot between the pickup and the output, and in so doing, bypasses the low-pass filter of the cable.


So to attempt to drive the point home, a large value volume pot will make your pickups sound brighter when you have it set to maximum volume. However, that same pot will cut more highs when you turn it down. Thus for a larger value pot you'll probably be more likely to want that treble bleed mod.


Now when it comes time to do that mod, there are several approaches. You've tried some, but not all of the ways of connecting a cap and resistor here. What I would suggest that you haven't yet tried is a cap and resistor in series between lug 3 and 2.
Not only that, but to spare you the tedium of trying resistor after resistor in search of the magic value, I would suggest experimenting with a variable resistor in the circuit. You can adjust to your heart's content and then measure that value, find the nearest value fixed resistor and use that. (The temporary variable resistor would work equally well if you wanted to do cap+resistor in parallel.)
Anyway there's still a chance that a certain cap value will work best, but testing in this manner is a lot more efficient than swapping both parts at once, and you get a better "feel" for what works and what doesn't.


[edit]
One more bit: Bob V is incorrect about the "50s mod" not reducing treble. I have a guitar with volume pots wired this way and it indeed cuts treble when you turn the volume down. Based on the electronics, it should actually cut treble more than the standard configuration, because as you turn it down, the pickup gets loaded down more and the resonant peak shifts down in frequency. You could test this out yourself by wiring up the 50s mod with a treble bleed cap. Even with the cap the pickup should become duller sounding as you reduce the volume.

[Jef Bardsley]

Originally Posted by earthtonesaudio

One more bit: Bob V is incorrect about the "50s mod" not reducing treble. I have a guitar with volume pots wired this way and it indeed cuts treble when you turn the volume down. Based on the electronics, it should actually cut treble more than the standard configuration, because as you turn it down, the pickup gets loaded down more and the resonant peak shifts down in frequency. You could test this out yourself by wiring up the 50s mod with a treble bleed cap. Even with the cap the pickup should become duller sounding as you reduce the volume.

Uh, no. With standard wiring, when you turn the volume down 50%, you have a 500K volume pot and a 500K tone pot in parallel loading the circuit. With '50s wiring you have a 500K volume pot, and a 750K tone pot in parallel. There are several problems with the '50s wiring, and one of them is at low volume settings the resonant peak is way too high.