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Plausible ideas for powering acoustic guitar active pickups other than 9v batteries

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Re: Plausible ideas for powering acoustic guitar active pickups other than 9v batteries

PostPosted: Tue Dec 18, 2018 1:26 pm
by BillB
Wonks wrote:Fixed link (for long URLs you need to manually put the [ url ] boxes around the link or it doesn't work).

Thanks Wonks - I should have checked the link.

Re: Plausible ideas for powering acoustic guitar active pickups other than 9v batteries

PostPosted: Tue Dec 18, 2018 1:38 pm
by Wonks
Yes you can provisionally do it with a TRS jack and an external power supply, but the wiring within the guitar needs to be suitable. Most pre-amps are wired with the battery +ve permanently connected to the pre-amp board, with the -ve going to the R of the TRS socket, and the pre-amp 0v connection wired to the S of the TRS socket, so that the barrel of a TS jack plug bridges the R and S to complete the battery 0v connection, which is also connected to the signal ground.

So you'd need to modify the guitar wiring so that the T still carried the guitar signal, the R had the +9v supply (or whatever voltage the pre-amp ran at) and the S has both the 0v and signal ground connections. You should be able to break out the wiring from most pre-amps to work with an external supply, but you'd probably be unable to then run it from a battery without adding an extra switch on the guitar, as it won't easily be able to tell if it's got a TS or TRS jack inserted. You could probably get the external power supply to drive a relay to cut out the battery supply , but it really makes things very complicated. And end-pin barrel jack sockets are pretty much limited to basic TRS connections, so anything more complicated would mean a side-mounted jack socket, and if you are going to do that, then you might as well fit a side-mount battery compartment.

Re: Plausible ideas for powering acoustic guitar active pickups other than 9v batteries

PostPosted: Tue Dec 18, 2018 1:43 pm
by Wonks
zenguitar wrote:In a lot of guitars with pre-amps the power is 'switched on' when the jack plug is inserted. The guitar has a TRS socket with the power circuit connected to the ring connection. But the 'trick' is that the guitarist uses a TS jack plug so the ring connection is connected to ground which completes the circuit.

The AG stomp takes advantage of this connection to inject power into the circuit.

First para is of course correct, but I'm struggling to understand how the AG stomp sends power without having to modify the guitar?

Re: Plausible ideas for powering acoustic guitar active pickups other than 9v batteries

PostPosted: Tue Dec 18, 2018 1:48 pm
by Sam Spoons
A battery box in the side would be my suggestion too (as I said up-thread) but Andy's ref to the AG Stomp using a battery clip with the wires shorted to replace the real one would work fine on 95% of acoustic guitars (and avoid any rewiring of the guitar). Then you just need to supply 9VDC across the ring and sleeve of the guitar jack socket via a TRS lead. The only possible down side is that, bizarrely, screened twin mic cable can be microphonic used with passive guitar pickups, but maybe not with actives.

Re: Plausible ideas for powering acoustic guitar active pickups other than 9v batteries

PostPosted: Tue Dec 18, 2018 2:16 pm
by Wonks
OK, I see it now. Took a bit of head-scratching before the penny dropped.

Re: Plausible ideas for powering acoustic guitar active pickups other than 9v batteries

PostPosted: Tue Dec 18, 2018 5:03 pm
by blinddrew
BillB wrote:Not sure how adaptable / appropriate this is, but just a thought:

https://www.andertons.co.uk/guitar-dept ... s-with-jtv)
These are actually very complicated boxes inside, I think you'd need to be very hot on your electronics to make adapting one of these viable.

Re: Plausible ideas for powering acoustic guitar active pickups other than 9v batteries

PostPosted: Tue Dec 18, 2018 6:02 pm
by BillB
I wasn't so much thinking of adapting the Line 6 box as adapting the socket/system at the guitar end. The box results in a TRS cable with signal (in) on tip, 9vDC on ring and earth on sleeve.

I haven't really followed what is happening at the guitar end though. I just thought that a robust pre-made (as opposed to home-made) solution for delivering 9v to a guitar might be an option - but appreciate that it may not :thumbup: :thumbdown:

Re: Plausible ideas for powering acoustic guitar active pickups other than 9v batteries

PostPosted: Tue Dec 18, 2018 6:13 pm
by blinddrew
Ah right, got you. For some reason I'd got it into my head that the line6 box wasn't kicking out at 9v. I don't know why I thought that. I didn't measure mine when I was fiddling around with things a while ago. Given that it will also run from a 9v battery that would make it a logical assumption.
I've not slept a lot recently, probably best to regard all of my comments with even more disdain than usual... ;)

Re: Plausible ideas for powering acoustic guitar active pickups other than 9v batteries

PostPosted: Tue Dec 18, 2018 6:15 pm
by Wonks
Yes, it's normally possible, though not all pre-amps use 9v or use a 9v PP3, (where it's generally easy to provide a shorting clip for the battery connections), and on some where they use a jack socket with an independent switch for the battery, then it may not work.

But it should be possible to get at least 90% of electro-acoustic pre-amps remotely powered.

Re: Plausible ideas for powering acoustic guitar active pickups other than 9v batteries

PostPosted: Tue Dec 18, 2018 6:46 pm
by ef37a
Bought 3 batts (still found nothing for SWMBO!) and they come apart very easily, knife blade and the top pings off bish-bosh. Big blue cell reads 1.7V off load after 1/2 hour on charge and there is a sub postage stamp PCB with USB ports and an MP3401A SM chip and inductor on it. Some form of "swinging choke chopper" converter.
Red and black wires from cell to PCB are ~25mm and could easily be extended.

I have found sites that PROMISE a .pdf of the chip but none so far deliver (Brexit FX) but I bet better eyes and steadier hands than mine could kludge the feedback circuit to get 10volts?

I have modified a pedal converter that normally produces 300V to give 48V of very stable and clean phantom power from 20V DC.

Dave.