bass guitar piezo preamp suggestions?

[FUZZZZzzzz]

I found a beat up Dean Pace bass that needs some fixing. It needs a new topnut, machine head. backcover. battery door etc. The preamp thats inside (theres a piezo under the bridge) is pretty crap with only a volumecontrol. I'd like to build a new preamp with volume, tone and maybe even more controls. I found a lot of stuff on google but nothing that ticks all those boxes. There are two 9volt battery compartment on the back so i can easily go to 18v.

Any suggestions?

[FUZZZZzzzz]

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

[Seljer]

For piezo stuff you want high input impedance. The 250kiloohm volume pots at the start there are kind of to the low side. The tone control and all that part is alright.

So yeah, if you've only got one pickup so ditch one of the input sections, ditch the volume pot at the start and replace it with a fixed big resistor (I recently used a homemade active DI box on a upright a piezo pickup attached and it didn't seem to mind it's 1megaohm input impedance :shrug:....might want to go even higher to play it safe). Put the volume control at the end (a 50kiloohm pot instead of R13 would probably work)


edit: yep, on that page mr kreuzer himself mentions he upped the volume potentiometers up to 2.5megaohms when he used it with piezo pickups...
With multiple pickups I'd have gone for a topology with a blend control on a bass buts thats just what I'm used to (so you can ride the overall volume with just one knob)

You could also easily rebias it to work with a higher voltage supply and/or different FETs. Its just a case of changing the 2k2 and 6k8 resistors around the FETs.

[FUZZZZzzzz]

useful reply: thanks a lot!!

[Gus]

With bass you might have an high output voltage

You might want to search for piezo threads at this site I posted a few one with a pad for the piezo

You might want to build a piezo buffer then add the control section you want

I googled dean pace bass, is it a upright?
If so a first stage with gain might not be what you want a buffer and maybe a capacitive pad might be the best first stage

Can you tell us or take a picture of what the preamp has on the PCB JFET(s)? IC(s) or a combination of parts?
You might be able to adjust the stock circuit a little more to your liking.

Here is a thread look at the pad section
http://www.diystompboxes.com/smfforum/index.php?topic=92274.0
Is the preamp +-9VDC powered or +18VDC powered?

[FUZZZZzzzz]

this is the one (but thats not me ). It's actually a 35" scale bassguitar played upright. it is powered by two 9v batteries. there are 4 piezos. one under each string in the bridge
the preamp is very simple with only a volume and the pcb is poorly made. i will post some pictures tonight.