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Thinking of switching to stacked vol/tone knobs

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darthbatman

Feb 2, 2009
102
0
#1
My bass (a Birdsong) has two volumes and a Vari-tone.

I've been thinking it might be really cool to install individual tone controls stacked on the volumes.
That way I could have the neck pickup on a real low dubby sound and the bridge pickup more trebly,
and I could switch between the two or perhaps blend the two tones? Although in my searching on the subject,
it seems the general wisdom is not to have two tone knobs, as it puts them parallel to each other? Whatever that means.

I really don't know, could someone walk me through why this would or wouldn't work? :confused:
 
#3
Hm, that's a pretty cool idea. Are you talking active or passive? The clicks kinda lends itself to the varitone concept but is smooth in between positions as well.. Kooky.

I was thinking doing this would free me up to do something really crazy with the varitone but i'm not sure what. Has to be passive so no crazy effects. I was thinking though that it would be really cool to have something like a timbre knob that shifts the frequency response on amps, but right on the bass. Don't know if i could do something like that, you know like turn it left and you've cut highs and boosted lows, vice versa for twisting right.. Boost from what i understand is hard to do with passive.

Just rambling here. But, so, in your set up do you get two diff tone settings blended together? Is it like two distinct tones or more of a combined singular sound? Is there some treble loss by having two tone controls like I've reard in some other threads here?

Thanks for your input here btw
 
#5
if you're talking about a passive circuit, I am curious how you could keep the individual tone circuits from affecting the other pickup, especially when one or both volumes are fully open and the pickups are directly parallel. In other words, I think that the capacitance would combine variously when tied to the pickup side of the volume pots.

Your pickup volume/tone sections would need to be isolated using buffers.
 
#6
So, a volume and tone on each pickup, and a varitone overall? That sure sounds like a Gibson ES-series guitar. There was also a stereo version with two separate varitones. I don't know what the birdsong circuit looks like, but I'm attaching the Gibson schematics for you to examine & maybe get some ideas from.

Note the pickup selector switch - that's how they get around the problem of the parallel controls. If you select both pickups, the controls do interact, but that can produce some useful tones too, at least in the guitar world. I haven't tried this on bass.

Interestingly, the mono schem shows one pickup wired with the tone control tied to the volume wiper, and the other with the tone tied to the pickup output. I'm not sure why. I do know that earlier Les Pauls used the former scheme for both pickups, and later ones used the latter for both. There's a LOT of discussion on the web about that change and what the effects are. You can take a look here if you want.

Reid
 

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#7
aphexafx said:
if you're talking about a passive circuit, I am curious how you could keep the individual tone circuits from affecting the other pickup, especially when one or both volumes are fully open and the pickups are directly parallel. In other words, I think that the capacitance would combine variously when tied to the pickup side of the volume pots.

Your pickup volume/tone sections would need to be isolated using buffers.
Click to expand...

The circuits must be isolated with resistors. The same way Fender did it in the '60s. Of course, there is a reason that never caught on. You lose too much for it to be worth it, for most people.
 
#8
darthbatman said:
Boost from what i understand is hard to do with passive.
Click to expand...

Just about impossible, in general. I say "just about" because there actually is a bass boost of sorts in any passive bass (or guitar). We tend to think of the tone control as a simple low-pass filter (tech-speak for "it removes highs") but it's actually a bit more complex than that. Because the pickups are inductive (they are coils), and the tone control is capacitive, there is a phenomenon called "resonance" that comes into play, and resonance does indeed produce a small (but often audible) peak ("boost") in the frequency response. When you turn down the tone control to remove the highs, you're also making the resonant peak bigger and lowering its frequency, so you get a bit of bass boost as well. (In fact, Fender's "Greasebucket" tone control is specifically designed to flatten the resonant peak, IIRC.)

Other than that, you can't get boost in a passive circuit.

Reid
 
#13
The volume loss using the resistors being noticeable depends on your ears, how you like things to sound, and what else is going on around you. However, it's patently wrong to assume that the tone control wired to the bridge PUP affects only the bridge PUP and does nothing to the neck PUP if you do not use the resistors. It may be a useful sound for you, but it's certainly not working in the manner way too many people assume it does.

John
 
#14
A bit OT, but for a long time, I've had the thought that fender used the resistors to isolate the volumes, not the tones. They simply hadn't thought to wire the vol pots the other way. I'm as big a fan of Leo as anyone, so I don't want to put 60's fender fan's noses out of joint, but I don't think there were many, if any, two p'up guitars or basses that had independant volumes in the 60's. Fender were the first to think that without a pickup switch, bass players might want to blend and the resistors were a natural idea as this is how mixing boards work.

If you don't use an MN blend pot, you get a resistive mix of the two signals due to the resistance in the remainder of the pot's sweep. If you use a DG linear pot however, there's too much resistance and you get a volume (and tonal) drop in the middle of its rotation. You can add resistors across the pot's terminals to change the sweep of the pot to improve the situation (this is not the way fender used resistors, BTW), however you need to start with a pot larger than 1Meg and this would be pretty hard to find. The best solution is to use a log/antilog pot, but these are hard to find as well (I make my own from two pots). The other option is simply to buffer the p'ups individually, prior to the blend control, but this of course means adding a battery and a circuit.
 
#18
Will the controls remain passive, as in no boost (cut only). Is this this a good option to cure the above stated problem of frequency/output loss? Or is there a way to use the 2 stacked knobs with full EQ controls? I guess this would mean routing in a battery compartment. I'm guessing the preamps should fit in the existing cavety?
 
#20
6stringvince said:
This bass is P/J, no pezio
Click to expand...

Sorry, I'm mixing this thread up with another thread on piezos. I've deleted my previous posts.

If you want isolated tone controls on a bass with two or more magnetic pickups, without the use of resistors, you will need buffering on each signal path. This buffering can come from a circuit as simple as a discrete FET transistor or an opamp, and a few resistors and capacitors; or from traditional onboard preamps with equalization. Whether or not you want active equalization in addition to the passive tone controls is up to you. That's a wiring choice.
 

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