Tube Amps / Music Electronics
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|8/8/1999 10:30 PM|
||Volume Pot Question|
Am I reading these messages correctly? Are you saying that pickups in series require a *higher* value volume pot than regular single coil pickups?
I have a guitar with 3 single coil pickups in series. My thinking was that since all the coils were in series, they would give me the ohmmage I need to limit the current. So I used a 250k pot just as I would've with a regular single coil wiring setup. Am I loading down my pickups this way?
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|8/9/1999 6:02 PM|
Classic fender-type single coil pickups have a clear, bright, open sound. To keep them from sounding overly bright, they are usually paralleled with a 250k volume control. This results in a slight loading down of the pickup, and takes the high edge off. It also seems to allow for a decent adjustability range as a volume control.
Pickups with a large number of total turns of wire, whether they be extra hot single coils or series wound humbuckers, are a bit darker sounding than classic single coils. These higher inductance pickups are usually paralleled with a 500k volume control (or sometimes a 1-megohm control) so as to not darken the sound any farther.
It's a matter of convention, and what usually works best all-around. Although these general guidelines are followed by most manufacturers and guitar modifiers, you have the option to go with whatever combination of coils and pots sounds best to you.
|8/10/1999 3:51 AM|
So, the deal is that a 250k pot shouldn't do anything much when only ONE pickup is engaged, but you might lose an undesirable amount of high end if two or more coils are placed in series, and used with a 250k pot. Conversely, a 500k pot may be desirable to minimize pickup loading when two or more coils are in use in series, but give brittle headaches when only one pickup is at work.
I offer the following compromise:
1) Use a 500k volume pot.
2) Use a 1meg audio/log taper tone control, with a .02uf cap and a 1800pf cap (or something in that range...season to taste), each soldered to the chassis and one of the outside lugs of the pot. The centre lug would be wired to the input of the volume pot. Ideally, the 1800pf cap should be soldered to the lug at the "short" side of the pot (i.e., the side where only a few degreees of rotation gets you from the half-resistance to full resistance point).
3) When a single pickup is used, rotating the tone control towards the end with the 1800pf cap will roll off only the highest highs and remove the brittleness that comes with single-coils and a 500k pot, in effect mimicking a 250k pot. A few degrees rotation the other way will mimic having two 500k tone pots in parallel; one going to a cap with a largely inaudible cap value (500k in series with 1800pf won't lose much treble), and the other going to a .02uf cap (a standard tone control value, which also doesn't lose much trble when in series with 500k).
4) When two or more pickups are used in series, setting the tone pot to its electronic midpoint (whichwill not be its PHYSICAL midpoint if you are using a log taper pot). will provide the natural rounding of edges that occurs when using a high impedance coil with a 500k volume pot. Given that the pot is log taper, there will still be plenty of pot rotation to dial in the desired flavour.
On my guitar, I have a 500k volume pot and a 3-way toggle tone switch with the small value cap on one side, and the larger value cap on the other. The centre "tone-out" position, does indeed give a brittle sound in combination with the 500k volume control. The slight tone rolloff rounds out the edges, while keeping the bite. The lower rolloff (bigger cap value) gives a more traditional muting sound. The tone pot wiring scheme I suggested achieves the same thing in a different way, with intermediate sounds available.
|8/10/1999 6:10 PM|
That's a great idea about the tone pot with 2 different caps but I'd probably have a hard time finding and keeping the #2 neutral setting. A 1MB pot with a center detent would make it easier for me (but your suggestion would allow for better control over the "regular" tone section). Or just wire up the tone control on a p-p pot to add in the 1800pF cap to ground.
If there are certain linkages that really need that 1800pF cap they could be hard-wired to a 4 pole/5 position "mega" switch. (The possibilities for those switches are mind-boggling- it seems like every week I hear of another great use for them!)
|8/10/1999 12:55 PM|
Thanks Doc & Mark. Let me describe what's happening and maybe someone out there can give me some advice.
I've got 2 guitars, both with the same wiring scheme. Same size pots, same pickups, same schematic, pickups set at same height relative to strings, different output voltages. The sound is similar, but one signal has to be boosted to get it to the correct level. The pickups are all functioning properly.
What am I looking at here? I'm trying to think of differences between the two guitars: the "normal" guitar has a fixed bridge, the one with the weaker signal has a floating Wilkinson tremolo.
Could the material that the strings were manufactured from play a significant difference? The guitar with the weaker signal has Nickel strings, don't know what's on the normal guitar. Possibly the gauge? (although if the gauge is different, it's not by much.)
Any ideas appreciated.
|8/10/1999 7:05 PM|
The floating bridge guitar has two pivots and the spring claw to put energy into the guitar body. The fixed bridge one has a larger area to tranfer energy into the body. As it has been said many times everthing on a guitar affects its tone and output, the pickguard, the route under the pickguard etc. I think it is the bridges.
|8/10/1999 11:14 PM|
I thought that the output voltage was produced by the interaction between the ferromagnetic strings and the coils? Where does the body come into it?
One piece of info I didn't include: The guitar with the Wilkinson tremolo is louder unplugged than the fixed bridge guitar, but that's probably due in part to the hole used to mount the tremolo. Although, now that I think about it, the Wilkinson guitar does have a lighter-weight body that the fixed bridge guitar...
Fun guitar, by the way. I've never had a guitar with a tremolo before. Once you get used to it, it's great.
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