Can anyone verify this onboard preamp?

[scottyd]

I found this schematic online and I am really interested in building this type of preamp. Im just wondering if anyone has had success with this one before I order all the stuff. If not do you have any to suggest? Im more or less interested in 2 and 3 bands Thanks alot!

[teemuk]

Looks plausible: A pretty basic Baxandall circuit with added middle control. I would remove that 1uF capacitor from the input and drive the circuit with a directly coupled buffer that is made out of unused half of that opamp though.

[scottyd]

Interesting how would you go about doing that?

[Nigel Goodwin]

Originally posted by scottyd
Interesting how would you go about doing that?

I wouldn't worry about it, if you add a buffer to the front you still need the capacitor at the front of that. The Baxandall tone control really needs feeding from a low impedance source, so it depends what it's going to be fed from? - which is why he suggested the buffer.

This ISN'T a preamp by the way, its the tone control section from one!.

[scottyd]

Thanks for pointing that out. I could still use this setup with an active set of pickups though correct?

[Nigel Goodwin]

The output from the jack should be low impedance, so would be OK - essentially it's already got a buffer IC on the output.

[turbolx5oh]

Check this web site out: http://www.till.com/articles/GuitarPreamp/

[scottyd]

Yeah Ive seen that, Im going to build that one for sure, it should be fairly easy and straight foward. One question though, the author says if that thing is connected directly to a pickup it does not need R1. Does that mean that a jumper is put in its place or that particular wire from source to ground is left out all together?

[Nigel Goodwin]

Originally posted by scottyd
Yeah Ive seen that, Im going to build that one for sure, it should be fairly easy and straight foward. One question though, the author says if that thing is connected directly to a pickup it does not need R1. Does that mean that a jumper is put in its place or that particular wire from source to ground is left out all together?

Just left out - but I would advise leaving it in, it wouldn't give any benefit leaving it out, except for the saving of a resistor!.

[teemuk]

Originally posted by Nigel Goodwin

...it wouldn't give any benefit leaving it out, except for the saving of a resistor!.

Actually in the concerned application it would. Magnetic guitar pickups benefit from very large input impedances - even more so do piezoelectric pickups. Rather replace that 1 Meg resistor with 10 megaohm one.

Edit: And by the way, if you really want this circuit to perform use something else than J201, i.e. 2N5045, 2N5434, 2N5452, 2N5457 or U309 (change source resistor to 3K3 with last one). Donald Tillman (the author of the circuit) substituted original FET (2N5457) with J201 just for better noise performance. In this circuit J201 has pretty poor headroom and it will take only about 500mVpeak input signal to overdrive it.