Passive tone after a buffer--best way to avoid loading?

[bongomania]

Edited for clarity:

I am building a dual buffer; each pickup's output goes directly into each buffer input. The buffer outputs will connect in parallel, and proceed as one signal to any tone-shaping stage and the output. The reason for having two buffers there is an experiment in active blending.

For a simple and minimalistic tone stage between the buffers and the output jack, I was thinking of adding a classic passive tone pot, but I'd like to minimize the amount it loads down the buffered signal. Seems like a varitone (multi-position switch with caps but no resistor) would work, and of course there are no-load pots which would help at least when the tone knob is all the way open, or I could make an active treble cut EQ. What do you suggest?

pickup --> buffer --> tone stage --> output

 

[HogieWan]

if it's buffered - it's not passive

 

[bongomania]

A passive tone pot is still passive even if you feed a buffered signal into it. And it will normally load down that buffered signal.

 

[Bootzilla]

Loading is an essential part of the sound of a pickup so loading it might actually be beneficial to your sound. Some good info on loading is found here: http://buildyourguitar.com/resources/lemme/

Edit: I now realize that the circuit will only load the buffered signal and not the pickup so just ignore what I said.

A varitone could work but maybe only in the bypass position.

 

[PilbaraBass]

i'm not following you "loading the buffered signal" do you mean that you're installing a tone control after the buffer?

actually, if you're buffering, do a dual-buffer, then a single-pole low pass followed by a final buffer stage...

 

[HogieWan]

A passive tone pot is still passive even if you feed a buffered signal into it. And it will normally load down that buffered signal.

We normally hear people talk about passive tone - I'm just saying that if you buffer the pups, you won't have passive tone.

 

[bongomania]

i'm not following you "loading the buffered signal" do you mean that you're installing a tone control after the buffer?

Yeah that was the thought, just asking if that's a good idea, and the best way to go about it.

actually, if you're buffering, do a dual-buffer, then a single-pole low pass followed by a final buffer stage...

Yeah, certainly adding an active EQ and an output buffer would drop the z out back down, but I guess ideally I was trying to keep the circuit "minimalistic" if possible.

I'll edit the OP so it's more clear what I'm after.

Keep the input coming folks, I appreciate it!

 

[gyancey]

You'll still need a resistor network to connect the outputs of the two buffers as you can't just tie the outputs of two amplifiers together directly even if they are unity-gain buffers.

 

[bongomania]

Ah hah, good to know. Seems like something I should have known already, but I didn't.

 

[walterw]

You'll still need a resistor network to connect the outputs of the two buffers as you can't just tie the outputs of two amplifiers together directly even if they are unity-gain buffers.

that's true, but with EMGs, it happens all the time. i've always wondered about that.

 

[bassbenj]

Edited for clarity:

I am building a dual buffer; each pickup's output goes directly into each buffer input. The buffer outputs will connect in parallel, and proceed as one signal to any tone-shaping stage and the output. The reason for having two buffers there is an experiment in active blending.

For a simple and minimalistic tone stage between the buffers and the output jack, I was thinking of adding a classic passive tone pot, but I'd like to minimize the amount it loads down the buffered signal. Seems like a varitone (multi-position switch with caps but no resistor) would work, and of course there are no-load pots which would help at least when the tone knob is all the way open, or I could make an active treble cut EQ. What do you suggest?

pickup --> buffer --> tone stage --> output

This is not quite as simple as you think. Buffers do provide for mixing of pickups without knob interactions but a normal passive tone control (or the varitone) works differently than you think! The deal is that the pickups are inductance and resistance and the tone pot is adding resistance and capacitance. The varitone just adds capacitance. It all works together to create the tone you hear from the bass.

But if you insert buffers you now isolate the tone cap from the pickups and the interaction does not occur! You can create a high frequency roll-off using a standard tone control but you have to have a resistor in series with the output line to get it to work right. This then reduces the advantage of buffers driving the cable. But it could work. But the tone would not sound the same as if say you had two passive tone controls attached to EACH pickup ahead of the buffer(s).

There are reasons why this is all good ideas (I'm trying to do the same thing with my OLP stingray to eliminate all the nasty knob interactions) but the devil es certainly in the details.