Dahon Electro Acoustic Help Please

[olddawg]

It seems to me this is probably a standard piezo acoustic pickup under the bridge bone and it's preamp. If you can't figure it out, the pickup will probably work direct. 4558 opamps were the most common opamp there was for years. If you look at the pin out first identify your power supply B+/-. Then the input and output. You will need a stereo jack to work as a power switch by opening the ground when the guitar is unplugged. I would guess that the red wire would go to the positive terminal of a 9v battery but verify that. One of the black ground wires probably goes to the jack jack sleeve terminal then from it's adjacent terminal to the negative terminal of the battery. Then connect the input to the two pickup wires. Btw, if you still have problems after dissing it out, suspect those 30 year old Asian electrolytic capacitors.

[52 Bill]

If you look at the pin out first identify your power supply B+/-. Then the input and output. You will need a stereo jack to work as a power switch by opening the ground when the guitar is unplugged. I would guess that the red wire would go to the positive terminal of a 9v battery but verify that. One of the black ground wires probably goes to the jack jack sleeve terminal then from it's adjacent terminal to the negative terminal of the battery. Then connect the input to the two pickup wires. Btw, if you still have problems after dissing it out, suspect those 30 year old Asian electrolytic capacitors.

I guess I should have done this in the first post, but here is a quick reverse engineered schematic.

Each pot is a volume control. There are two balanced outputs.

Please forgive the crude drawing.

[Keithb]

Thank you very much - Olddawg and 52Bill - thats very kind of you to go to such lengths. I will study the information you sent - I did take two more pics a minute ago and I will upload these although I appreciate they may not be needed now. They were taken on my bread board which arrived today !

Keith

[J M Fahey]

Well. quite a few things do not add up here. Strange.
1) The longer red wire is *not* a power one (as in the expected +9V) *but* goes to the hot pin of a volume pot, so it looks like the hot wire from one (unknown) pickup.
2) the black wire does go to ground.
Pin4 of IC1 also goes to ground. Fine.
3) the short red wire (which in an earlier pictured looked as joining the long red one) now is seen to be independent and goes to IC1 Pin8 , confirming it's +9V .
4) there is incompatibility between what's shown and the intended use:
a) it looks like a mixer for 2 conventional (magnetic) pickups ... but we have only one .....
b) it does *not* provide Tone and Volume functions as written on the guitar control panel but, as I said, 2 volumes.
c) the input impedance is quite low, barely acceptable for magnetic pickups, absolutely unusable for Piezo ones.
d) the "mystery" pickup, still unseen, is assumed to be a bridge Piezo.
Quite incompatible with using 2 unshielded wires to carry its signal !!!!!!!
e) the schematic shows 2 balanced outputs. Cool but usually meant for an XLR output.
Using a stereo output jack balanced out is possible, but it makes it impossible to be used as an automatic 9V power switch like in most pedals and active guitars.

Just on a hunch:
1) measure resistance across yellow and bare wires coming from the pickup area, on different scales, until you get a reading (or surpass 1 Megohm, whichever comes first) .
Wouldn't be too surprised to find a hidden magnetic pickup.
2) connect those wires to a jack (yellow hot, bare ground) and connect it to a regular guitar amp. Play some chords.
Do we have sound?
Describe it (or post an MP3 )
Full/muddy/shrill/hummy/buzzy?
We might be chasing a phantom here.

Note: 52 bill's schematic looks ***very*** reasonable. Thanks.

[olddawg]

At this point I would find out what kind of pickup is in it. If it is a magnetic or a microphone pickup, I would wire it to a pin jack and run straight into an amp. If it is piezo, I would do the same thing but plug into a $12 preamp available on eBay. Who knows? The thing may be apart because it never worked. Quick, easy, and will probably work better. The eBay preamps even have a built in tuner. They also come with a piezo under the bridge pickup. I just ordered 2 myself to put in some cheap acoustics. Nothing says the preamp has to be in the guitar.

[J M Fahey]

Stupid me, only now I notice the brown wire which goes to the other pot, thus being the hot *also unshielded* wire from a second (unseen) pickup.
Mystery upon mystery.
I can be almost 100% sure that that small board does not belong in that guitar, simple as that.
Piezo or magnetic, that pales to the fact that those are *not* a tone and volume controls. Period.
Just letting my fertile imagination fly, I might guess that somebody (quite unexperienced) pulled that guitar apart, let it sit for a long time, maybe did the same with a couple others, and when he had to put it together to sell it or give it back to the original owner and grabbed a PCB and pots that fitted the holes ... and nothing else.
It's happened to me personally (it's not am Internet tale) to receive an amp for repair accompanied by a small bag of parts and the owner saying "Joe/the soundman/a tech/whatever tried to repair it"
This might be a beginner/pawnshop/music shop job.
Forget that PCB which even if it works is incompatible and follow the new preamp and pickup solution posted above.

[Keithb]

I am sorry I did not respond earlier but I have only just discovered that I am not receiving any further notifications. I will print off the past two posts and study them - a quick look tells me to give up on the board.

Thanks again for your help as before it is very much appreciated. I think I will spend a bit of time with my bread board and then post my next headache

Best wishes Keith