Onboard 9V bass preamp projects: suggestions?

[zjokka]

hi all,

I'm playing bass nowadays for a friends recording project and currently have a Jazz bass on loan that I'm playing there. I have had a Cort bass lying around for some time for homerecording that I would like to upgrade and use.

The point is the Cort as an onboard Mighty Mite preamp . There is something wrong with one of the four pots and I never really figured out what that broken one is supposed to do. I was first planning to just rip it out and use it passive, but the pickups have a bad rep so I might want to preamp it.

The current board is based on a TL063 and though I did find the diagram explaining how to wire up the preamp board to the pickups etc, there is no schematic of the preamp itself. Anyway it never really impressed me. As the cavity is rather big, there's room for whole framily of boards if I would want to go crazy.

I was very impressed with the Flipster, but as I am not going count on playing this bass passive, the noise level is an important factor. The existing preamp is dead quiet, so I don't want to take it a step back. In the stock setup you cannot play it without battery. Does this mean you cannot play it passive? No passive switch or pushpull either?

Should I focus on opamp based designs for a new preamp? Any experiences with similar project would be great.
thanks for reading.

here are some pictures:

[Gilles C]

This could be an option

http://www.albertkreuzer.com/preamp_onboard.htm

Gilles

[zjokka]

This could be an option

http://www.albertkreuzer.com/preamp_onboard.htm

Gilles

I know that one, was promising, but it's a preamp with seperate channels for the two pickups. He writes that he wants to retain to volume controls, which I really want to get rid off. Also I was put back a bit by the noise level of the Flipsters and was wondering whether an opamp based circuit might be better in this respect.

Also no real consensus on that one
http://www.diystompboxes.com/smfforum/index.php?topic=39522.0

Then I found this very intersting thread:

http://www.bassworld.co.uk/pn/index.php?name=PNphpBB2&file=printview&t=889&start=15


ZJ

[Meanderthal]

 Measure the impedance of the pickups. If it's in the 5 to 15k ohm range they should work fine passive, but if they're way low impedance then an onboard(or other) preamp is needed. If they're high impedance, you might have the option of hearing the raw pickup sound, which might surprise you.
The only active bass I ever personally owned (besides this crazy roland g-77 bass synth thing, but even that takes its power thru the cord) was a Gibson RD Artist with Moog/Alembic compressor/expander preamp. Sounded pretty good in its own way, but I really hated having to open it up over and over to change batteries. I haven't really liked the sound of any of the other active basses I tried out, compared to a good passive. They all color the sound a little, or seem to be trying to make up for having a dull, lifeless sound to begin with, or like the gibson just sound sterile. And then you need batteries.

If you eliminate volume pots you'll be wanting a pickup selector switch...

That looks like a very nice bass you got there!

[George Giblet]

The Mighty Might (which I've traced) is the same as the Tobias Preamp,

http://www.musicyo.com/planet/graphics/tbyactvcrct.gif

Why not fix it?    It won't be too hard and it's got to be easier than building a new one.  If you suspect a pot replace it.

I suggest measuring the voltage at the opamp outputs they should be at half the supply voltage 4.5V.    A faulty bass pot will cause funny DC voltages.

If you want to change to tone of the preamp tweak the tone control cap values - *many* bass preamps use this basic circuit.

[zjokka]

Indeed, have read the thread now and instead of the two opamps in the Tobias schematic, the Mighty Mite setup uses a dual opamp instead of two separate ones. the basswork.co.uk thread is truely interesting as the tone circuit is being retuned to more musical values.

Unfortunately the final schematic has dissapeared, because it was hosted on a personal photobucket site that's probably delete now. the disavantages of fora.

Of course, George I could and will fix, but had given up beforehand after googling in vain for the details of this bass. Let alone the preamp... Just because I had been playing around with jfet simulations like the Flipster, which sounded killer to me and have no comparison to the controls on the bass now, but much will depend on how the pickups sound by themselves. If they're really weak the jfet preamp I figure might be too noisy... don't know.

Was fishing for experiences with onboard jfet bass preamps. I hear the Kreuzer's kinda noisy...

ZJ