stack knob wiring on a P/J - passive but active buffered

[bigjohn]

I've been thinking about stack knob controls a la '62 Jazz basses on my P/J.

Reading around the subject there's the issue that the controls are dependent on each other. ie, The tone control on one pickup is only independent from the other if the volume of the other pickup is completely off. 

Surely there's a way of actively buffering this so the controls are truly independent? Hasn't someone already done this? I watched a vid of someone from Overwater saying how they have a preamp that's passive, but with active buffering to do this and that it's John East made, but none of the straight John East Pre's have normal stack knob controls.

Anyone have any ideas?

 

 

[itu]

Noll, East, EMG.

- EMG has the buffers in the pickups already.

- Noll has an active balance pot, approx. £50.

- East is the whole preamp, around £200.

Then there are a few studio grade preamps from certain manufacturers like Wal but usually they are available only with the instrument.

Nearly all other preamps available are just tone controlling circuits after plain pots without active blend. Here is a list:

https://www.thomann.de/gb/electronics_for_basses.html

Only EMG BQ and BT have active blends.

To make the Noll part of a concentric pot needs some extra work and parts. It might be easier to keep the pots as they are and put simple buffers after the pickups. Buffer parts cost just few pounds. You may try an op-amp like TL072, NE5532, OPA-series or similar. This is very simple and very functional buffer:

https://www.electrosmash.com/klon-centaur-analysis#input_buffer

Edited June 19, 2019 by itu

[bigjohn]

None of these use the concentric VTVT config though do they?

Sorry if I wasn't clear in my OP. 

 

 

[Chienmortbb]

You will need to have a buffer for each pickup and then a mixer stage. That requires either two small or one large opamp packages. 

[itu]

Mixer stage may be a blend pot (or two volumes), as the buffers take care of the pickup outputs. The pot has no more effect on the pickup frequency response as it can not load the pickup. So a dual opamp (one side for each pickup) like the basic TL072 is enough.

If a blend is in order, there are pots that function as a blend. The dual resistor track is cut at noon. Try to find a Bourns 250k MN or 500k MN. They have center detents, too.

[Chienmortbb]

4 hours ago, itu said:

Mixer stage may be a blend pot (or two volumes), as the buffers take care of the pickup outputs. The pot has no more effect on the pickup frequency response as it can not load the pickup. So a dual opamp (one side for each pickup) like the basic TL072 is enough.

If a blend is in order, there are pots that function as a blend. The dual resistor track is cut at noon. Try to find a Bourns 250k MN or 500k MN. They have center detents, too.

True but I like driving the cable from an opamp directly. However yours is a good way. I may have a spare Bourns 250K Mn if it is useful. 

[itu]

On 20/06/2019 at 17:34, Chienmortbb said:

True but I like driving the cable from an opamp directly.

I am on your side, Sir. I just figured the simplest way there is. But if you start to use buffers, I want all stages to be active. My current Modulus Quantum has that Noll blend and a bartolini tone stack. Noll made a difference in sound.

I am amazed, how few possibilities there are if you want a complete lo-Z signal chain. There are many retrofit tone capsules but only few (East, EMG) that include active blends and volumes.

[Chienmortbb]

Agreed. I think pickups should be buffered  before the volume and/or blend pots then there is no interaction. 

[bigjohn]

Thanks for your all your help. 

I've gone with a passive Kiogon loom in the end. 

 

[NikNik]

Why don't you just use the modern stack-pot circuit? 

[itu]

That modern stack-pot circuit has not an active blend nor volume. They have hi-Z ("passive") first stages. The only ones that have active blend and vol are East and EMG, maybe some MEC is.

signal route of a bass:

pickups - blend (or vol) - vol - tone stack - output

If there are no buffers right after the pickups, the hi-Z pots affect (load) pickups and change their response. I think that I tried to say this earlier.

[Woodinblack]

Yes, it would be easy with a dual input preamp. Something designed that way would be good but you could take any old  preamp, put 2 large input resistors in, increase the preamp gain to compensate, and bobs your auntie, you would have totally independent circuits. Most of the old fender (the man not the company) circuits pull be like that, grab one from a g&l or something