Wiring help for 9v Pre-Amp

[robin]

To all the wiring gurus out there (Weirdy, I’m looking at you) I could do with some advice please.

I am still researching my next build but (if I go ahead) it will include a pre-amp that I already have laying around that has volume, eq, etc as part of a unit that is meant for external mounting on an acoustic guitar. My plan is to locate this pre-amp INSIDE the body of the guitar thus making access to the volume knob rather problematic.


I was wondering if I could set the volume on the pre-amp to max and then insert another pot on the wiring that goes from the pre-amp unit to the output jack thus giving me an external volume knob. Would this second pot interfere/degrade the signal and if not would I need a special pot for this or would one of the run of the mill 250/500k pots do the job. Once the guitar is complete I could experiment with pots to see which gives me the sound I am after.

As I am a complete numpty when it comes to wiring any help would be appreciated.

Cheers
rob

[wokkaboy]

good stuff Westie07, is this an acoustic guitar or bass ?

better wait for the guru to respond. I'd guess a standard A type pot should be fine for the volume and shouldn't affect the signal.

[WeirdBits]

Do you have any details for the pre-amp, make/model, images etc? I take it you want to keep the pre-amp intact, not disassembled/modified etc?

[robin]

Hey there Warren. Acoustic? I wish.

It will be another solid body pine scratchie. I have not made any decisions as yet just thowing up a lot of ideas for now.

Researching the build is part of the fun. I need to boot The Black Dog out, so I will probably take some time with this one.

Hopefully I will make a decision soon and get started.

[wokkaboy]

Hey Westie, I didn't read your 1st post correctly, I see the unit is off an acoustic !!

sounds good bro

wiring guru chimed in needs more info

who the hell is Warren ? bwhahahah

[robin]

Thanks Scott for your help.

Its a Fishman, but I have no idea of model or specs. I know it was originally for a piezo pickup.

As long as it's not too technical, pulling it apart is no problem. I have already taken the back off as I will have to remotely locate the battery box as it is too big to fit in a regular size solid body electric. I'll post some pics tomorrow.

Thanks again for any help.

[robin]

D'oh. Double post

[WeirdBits]

You're planning on embedding this in the guitar to use with a piezo pickup, right, rather than trying to use it to amplify a standard magnetic pup? If it is the latter then it probably won't work well due to the low impedance of magnetic pups vs the high impedance of piezos.

[Brendan]

You could use something like this with a peizo - and no pickup?
http://www.ebay.com.au/itm/Piezo-Tune-O-Matic-Bridge-Kit-UK-SELLER-STOCK-/111799392391?var=&hash=item1a07c35887:m:mQUquCDT-a3UdjYLdsgy9UQ

[robin]

who the hell is Warren ? bwhahahah

I'm still trying to figure out who Westie is. :p

[robin]

Thanks for the link Brendan. I like the look of that bridge. Opens up all sorts of possibilities.

Unfortunately I have to use what I've got for this build. But maybe next time. :)

[robin]

You're planning on embedding this in the guitar to use with a piezo pickup, right, rather than trying to use it to amplify a standard magnetic pup? If it is the latter then it probably won't work well due to the low impedance of magnetic pups vs the high impedance of piezos.

Thanks for the info Scott.

Yes I was planning to embed the pre-amp and not use any of the controls on the unit, and just have an external volume pot. I was undecided as to what pickups to use, but it appears that magnetics are out of the question. So if I want to use this pre-amp it will have to be with a piezo. Hmmm.

I need to rethink a few things now. If I did use this pre-amp with the piezo do you think that a second volume pot would work OK?

And one more question, there are 3 wires going from the pre-amp unit to the output jack. What do you reckon, stereo or something else going on?

Cheers mate
rob

[kimball492]

If you have the right bridge that takes a piezo mic you could then use this Robin. But may be costly

[WeirdBits]

it's a stereo socket with used to power on the system. Insert a standard mono plug and it completes the battery's negative connection by shorting the ring to the sleeve, turning the power on. You will be able to use a stereo version of our standard open guitar jacks to do the same thing, rather than having to use the endpin jack.

You could run another volume, it probably uses a 50K pot, how you connect it would depend on how the original is wired. Are you going to make the preamp's controls accessible on the back of the guitar or hidden under a cover? If possible I'd leave them accessible (along with the 2nd volume) and do a combined piezo and magnetic pickup build. If you google 'piezo preamp with magnetic pickup' and similar terms you should find a lot of layouts where people have combined their piezo circuit with a passive magnetic pup circuit etc. so you can have both in the one guitar.

[robin]

If you have the right bridge that takes a piezo mic you could then use this Robin. But may be costly
Thanks KB. I was hoping for a easy (AKA cheap) solution, but it looks like I may have to rethink things. But thanks anyway.

[robin]

You could run another volume, it probably uses a 50K pot, how you connect it would depend on how the original is wired. Are you going to make the preamp's controls accessible on the back of the guitar or hidden under a cover? If possible I'd leave them accessible (along with the 2nd volume) and do a combined piezo and magnetic pickup build. If you google 'piezo preamp with magnetic pickup' and similar terms you should find a lot of layouts where people have combined their piezo circuit with a passive magnetic pup circuit etc. so you can have both in the one guitar.

Thanks again Scott. The original plan was to max everything out on the pre-amp, "set and forget" and hide the it under a cover. I would control volume with the second volume pot and save a few presets in my fx pedal to take care of tone settings.

Thanks for your time mate, I think I need to do some more research. I think you have just saved me a massive headache.

Back to the drawing board.

Cheers
rob

[WeirdBits]

Is there a specific reason you wanted an onboard preamp to use with magnetic pickups?

If so, you can easily make your own small preamp for around $10. I'm looking at an onboard circuit now that will give 2x-10x amplification. It has 1 switch, 1 gain pot and 1 IC and you can build it on a small piece of Veroboard. Very easy to build.

[robin]

Is there a specific reason you wanted an onboard preamp to use with magnetic pickups?

If so, you can easily make your own small preamp for around $10. I'm looking at an onboard circuit now that will give 2x-10x amplification. It has 1 switch, 1 gain pot and 1 IC and you can build it on a small piece of Veroboard. Very easy to build.

No logical reason Scott. Just had it and some PBG original magnetic pickups laying around and thought, what the heck, I might as well put them to use. I really need to keep myself busy and although I could easily spend the time doing some much needed house reno's the only thing that really works for me at present is to throw my energy into guitars.

Based on what you have already told me my thinking has changed somewhat and I might use the Piezo in another guitar. As I said, more research needed.

That DIY pre-amp sounds very tempting and although a complete novice at electrocutions, I would be eager to try this for a future build.

Ta mate
rob