Vintage Tone Controls

[jzucker]

Can the sadowsky style vintage tone control be added to a bartolini 9v preamp?

[PilbaraBass]

a vintage tone control is nothing more than a potentiometer with one end lug tied to the signal and the wiper connected to a capacitor with the other end shunted to ground

Signal ---> Preamp

Also, SIGNAL ---> POT Left Lug

Pot Wiper (centre lug) ----> Capacitor lead

other capacitor lead ---> ground


if you have a one pickup bass, it's simple...you connect it on the signal between the pickup and the preamp...

if you have a two pickup bass with a passive blend to a single-input preamp, again, it's simple...you connect on the signal between the blend and the preamp...

if you have a two pickup bass with an active blend on a preamp with two inputs...that may not be easily done...what you COULD do in this case, however, is use a ganged pot and two tone controls simultaneously, and again connect them between the pickups and the preamp inputs.

[jzucker]

but isn't it dependent on the impedance of the active circuit? So, if the circuit outputs low impedance, you can't switch between active and passive and have the tone control work properly...Or am I confused?

[PilbaraBass]

Originally Posted by jzucker

but isn't it dependent on the impedance of the active circuit? So, if the circuit outputs low impedance, you can't switch between active and passive and have the tone control work properly...Or am I confused?

you're confusing me, even...

remember, a passive tone control is an RC shunt circuit and must connect to the signal line BEFORE the preamp.


the preamp has a high input impedance, like your amp would...

so the passive tone control will work in passive OR active mode.

[A9X]

Originally Posted by PilbaraBass

you're confusing me, even...

remember, a passive tone control is an RC shunt circuit and must connect to the signal line BEFORE the preamp.


the preamp has a high input impedance, like your amp would...

so the passive tone control will work in passive OR active mode.

You can easily do it after the preamp. Just use a (say) 20k pot and scale the cap to the appropriate value. Won't work in passive this way though.

[PilbaraBass]

Originally Posted by A9X

You can easily do it after the preamp. Just use a (say) 20k pot and scale the cap to the appropriate value. Won't work in passive this way though.

yeah, that's why I'd prefer to do it before the preamp...

cap value for 250k pot is usually 0.05 or 0.1 uF...to get the same roll-off frequency for a 20k pot it would have to be 12.5 times that or 6.3uF or 13uF

[A9X]

Originally Posted by PilbaraBass

yeah, that's why I'd prefer to do it before the preamp...

cap value for 250k pot is usually 0.05 or 0.1 uF...to get the same roll-off frequency for a 20k pot it would have to be 12.5 times that or 6.3uF or 13uF

0.05u x 12.5 = 0.625u
0.1u x 12.5 = 1.25u
Not hard to get, but a bit bigger physically than a ceramic disc in the usual passive bass values..
I just don't see the point* of an active pre without individual buffered inputs (whether it has active cut/boost or not) so tend to be either passive (from the factory) or active. The 'vintage' style tone control at the output can give a useful effect and only means an increased output Z, but still in the range of a passive bass.

* I know why it's done, but it's bad engineering and compromises the active.

[jzucker]

Originally Posted by A9X

0.05u x 12.5 = 0.625u
0.1u x 12.5 = 1.25u
Not hard to get, but a bit bigger physically than a ceramic disc in the usual passive bass values..
I just don't see the point* of an active pre without individual buffered inputs (whether it has active cut/boost or not) so tend to be either passive (from the factory) or active. The 'vintage' style tone control at the output can give a useful effect and only means an increased output Z, but still in the range of a passive bass.

* I know why it's done, but it's bad engineering and compromises the active.

So...I assume there's no issue putting it before the preamp then?

[A9X]

Originally Posted by jzucker

So...I assume there's no issue putting it before the preamp then?

No, if that's what you want to do. Use the higher impedance pots as Pilbara describes or check Aguilar's OBP1 wiring diagram

[jzucker]

thanks!

[PilbaraBass]

Originally Posted by A9X

I know why it's done, but it's bad engineering and compromises the active.

I agree with your point...what you're effectively doing is adding an unnecessary load to the pickups before they even have a chance of being buffered by a nice high-Z input...and yes, 'tis bad engineering...

a better solution, is to build an active high-Z in/low-Z out circuit that simulates the response of a passive treble roll-off...I don't know, does anyone do this or has anyone done this???

[luknfur]

Originally Posted by PilbaraBass

I agree with your point...what you're effectively doing is adding an unnecessary load to the pickups before they even have a chance of being buffered by a nice high-Z input...and yes, 'tis bad engineering...

a better solution, is to build an active high-Z in/low-Z out circuit that simulates the response of a passive treble roll-off...I don't know, does anyone do this or has anyone done this???

FWIW:

never looked into it but if the Sad VTC is no more than a tone pot, that's amusing.

Also never really looked into it but I get the impression the Audere has the Hi-LoZ thing going in some of his pre’s (mid Z too it seemed). Seems like the LoZ aspect of it is not a fav though. The LP 2x1ac pre has a LoZ option diagram but it looked like the setup A9X was talking about.