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I was given an acoustic electric guitar, but I've never used one before. After changing the battery I tried plugging it into a portable speaker and a consumer stereo/receiver just to see if it gave any output. Nothing — the frequency histogram on the display of the external amplifier doesn't even twitch when playing. I don't have the proper equipment or cables, just what's at hand at home, i.e. consumer electronics and cables.

I've tried all combinations on the dials, and although I don't know what half of them do, I think I can rule them out as the problem at this point. It's by a manufacturer that no longer exists, and I've not found any instruction manuals online.

controls

There's no power switch, so I've worked under the assumption that it conserves power by only being active when there's a plug in the jack. I don't know know whether that's true, but the low battery LED blinks momentarily when plugging it in/out, so I guess that's right.

I've disassembled the preamp (if that's what it's called) and reseated all connectors (7 in total — 3 pin headers and 4 cables) but apparently bad connections weren't the problem either. Visual inspection didn't reveal any defects in the components.

Still, I can't say at this point whether it's working or broken. Did I misunderstand something about this thing?

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    Plugging in to a receiver may well not give the guitar signal a good impedance match. Needs trying with a proper guitar amp, using a proper jack-jack lead. Any music shop should oblige. The pickup system is well thought of, so persevere!
    – Tim
    Dec 7, 2020 at 15:33
  • @Tim Thank you for your suggestion! I am not interested in "good" though — any quality will do as long as it gives a life sign. If opportunity arises I will try to seek out a music shop, but it might be a while.
    – Andreas
    Dec 7, 2020 at 15:57
  • What cable did you plug into the guitar? A ¼" stereo one probably won't work, it must be mono.
    – leftaroundabout
    Dec 7, 2020 at 21:23
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    Because many guitars use exactly this short between the shaft and ring as the “power switch”. When you plug in a stereo plug then it would only briefly power the circuit as the tip slides across the contacts (which could explain the blinking of the LED at the start) but then simply biases the right stereo channel to -9V without any significant current flowing to keep the power on.
    – leftaroundabout
    Dec 8, 2020 at 11:07
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    @leftaroundabout Thank you for the explanation, that's good news to me. I was hoping you'd say that, which means I might not have any repairs to do. I'll test this with a manual short later. Now that you mention it, I should have figured this out when reseating the three wire connector for the jack... 🤦‍♀️🤦‍♂️
    – Andreas
    Dec 8, 2020 at 12:48

4 Answers 4

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[Turning my earlier comment into an answer]

As you've correctly assumed, active guitars generally switch on their power whenever a cable is plugged in. But though there are jacks that have a proper, isolated auto-switch built in for this purpose, many guitars don't have such sockets but instead use a simple hack to get the power switch functionality out of an ordinary stereo jack: if you plug a mono plug into a stereo socket, the shaft will connect to both the “ring” and ”shaft” contacts. Thus, if the battery's + pole is fixed but the − pole connected to the ring contact, having a mono plug plugged in will cause − to be connected to ground, thus closing the power circuit.

That however does not work when using a stereo plug instead: then the ring will simply dangle at -9V, and not enough current flows to power the preamp.

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If you can find a plug in guitar tuner - not the sort that clips on - that may show signs that the guitar output is o.k.

Obviously the volume needs to be turned up. The AST and UST are the two 'pickups'. AST stand for acoustic soundboard transducer, and UST is under saddle transducer. If they're not switched on, no signal is forthcoming. So check they're on, and the balance is central.

Other than that, trying it through an amp designed for the purpose is the best test. Good luck.

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  • Thanks for explaining the labels. How would I check that AST and UST are switched on? Judging by the picture, I can't see a state in which they're not. Except maybe using the two holes in the bottom left, which expose two trimpots to a screwdriver.
    – Andreas
    Dec 8, 2020 at 4:55
  • Basically, there's a 50:50 with the pups! Put the switches in opposite states, and one is bound to be on.
    – Tim
    Dec 8, 2020 at 8:12
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A portable speaker won't work if it is passive. But if you have (or can easily borrow) one of those external speakers for PC, anything with an external power supply, then you should be able to hear it. In that case the only other thing you'll need is an adapter from 1/2" plug (guitar) to 3.5mm (typical speakers/headphones jacks).

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  • Thanks for confirming that it should produce some sound. The speaker has an amp — it's a Bluetooth speaker. The stereo receiver also does, naturally. I have loads of those adapters (stereo) as well but haven't had any luck so far.
    – Andreas
    Dec 8, 2020 at 1:59
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Here's how I ended up testing it, based on the missing piece provided in the comments of how these things turn on:

enter image description here

A simple short of the right channel with some random RCA adapter.

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  • What an, erm, beautiful piece of precision engineering...
    – leftaroundabout
    Dec 9, 2020 at 8:49
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    @leftaroundabout An adaption of a larger piece in alu minor
    – Andreas
    Dec 9, 2020 at 8:52
  • So how did the test results go?
    – Dekkadeci
    Dec 9, 2020 at 12:52
  • @Dekkadeci I got audible/visible static out of it for one thing, which is enough to know it actually turns on. It also picked up the strings and played it back, so there seem to be no problems. Time to put it back together and make myself a cable.
    – Andreas
    Dec 9, 2020 at 12:58

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