Wow, it's been a while since i've posted(due to school)...these new forums are pretty cool.
I've got an old guitar that a friend has asked me to repair, a premier single pickup archtop hollowbody.
The electronics are kinda strange. There is one big single-coil pickup mounted at the neck with a switch that implements a capacitor and bypasses the tone control(for playing jazz i'm sure). However, without the switch engaged, the electronics are essentially this:
The capacitor value is .02microfarad. I THINK the pots are 1meg impedance.
The guitar has an amazing feel and sound, and the pickup is actually bright enough to play most styles of music, even at the neck. The problem is that as soon as the volume control is turned down from 100%, the brigtness of the tone is lost almost completely. The volume also experiences a substantial drop. I've tried, bypassing the tone pot, and swapping out the volume pot, but the problem persists.
Does anyone have any idea how to fix this? I'm dying to play this guitar, but need a working volume control on it.
Thanks!
a switch that implements a capacitor and bypasses the tone control
Does it keep the highs when the switch is engaged?
Because it's not uncommon to see a treble bypass cap that is switchable in the way you describe. (Sometimes the volume pot sits on a push/pull switch which accomplishes the same thing in a less invasive way.)
Higher value pots may be quite bright, but as you've noticed the highs can drop off dramatically as soon as you roll off the volume a touch. A treble bypass cap should let you roll back volume without losing the highs.
In other words, what you say is happening with the volume pot may be normal, and that switch is probably there to compensate.
The other possibility is that it's a "no load" volume pot, which basically passes the full signal when the pot is at "10" and attenuates it at all other levels; but for practical purposes the bypass switch would achieve the same result (keeping highs when the volume is rolled off.)
"Everybody got to elevate from the norm."
Well the switch takes the tone control out of the circut. instead, It puts a capacitor in the line that is connected in parallel to the hot from the pickup (before the master volume) and the ground. I can find the value of the cap when I get home. When that cap is activated, the tone control of course doesn't work, but the switch also makes the tone super-dull sounding.
I did try taking out the volume pot and substituting a 250k pot from a Fender Jazz Bass. I'm sure that this pot was completely normal, and the same thing occured.
I also tried wiring the pickup directly to the output jack, and it sounded exactly like it does with full volume and tone with the tone control on.
Don't forget, when the volume brought down even a tiny bit, there is the severe loss of highs, but also a large volume drop.
Something else interesting, and i'm not sure if this is helpful, but all of the wiring is done with a regular hot inside of regulator insulating, and then the ground is braided sheilding around this. If that is significant, I can take pictures to clarify.
Thanks for the help!
Ah, okay, when you wrote in the original post that the switch bypasses the tone pot, I assumed the sound was then bright. But now that you say the sound is "super dull" it makes more sense.
I think you've got two things going on: (1) the switch, which is apparently a low-pass filter of some sort (opposite of what I thought), and (2) the problem with the volume pot cutting the highs in an unwanted manner (which again is fairly normal.)
With regard to the switch, I've read that Gretsch uses (or previously used) something like that on some of their models. Their version has two settings, one described as "muddy" and the other described as "muddier." :lol: In your project, you can disengage that switch entirely, or you can leave it in case your friend decides he wants to muddy up his sound. ;) But I think it's largely unrelated to your volume issue.
Now, on to the volume pot. What I described above - a treble bypass circuit, sometimes called a treble bleed circuit - is what I mistakenly thought you had with the switch, but you don't, and it's what you want! It will keep the highs as you roll off the volume pot.
Fortunately this is a very simple mod. Unfortunately, there are several ways to get it done, so you'll need to experiment and see what works best for you. The simplest is to just run a small value capacitor across the volume pot lugs. A second method is to run the capacitor in parallel with a resistor. A third method, espoused by Kinman, is to run the resistor in series with the cap.
These three methods of adding a treble bleed circuit are described in good detail here:
http://www.bothner.co.za/articles/volumepot2.shtml
and here (about 3/4ths of the way down the page):
http://www.projectguitar.com/tut/potm.htm
Since you've got a single coil, I'd suggest trying one of the versions that use a resistor, either in series or parallel, and experimenting with different values for both the cap and resistor.
Hopefully that helps! 8)
"Everybody got to elevate from the norm."
