Dahon Electro Acoustic Help Please

[Keithb]

Thanks for taking the time to read this.
I have a Dahon electro acoustic that has been sitting at home for the past two years with the intention of eventually getting it up and running. I have begun working on it and although I thought the wiring had become detached and was lying around in the guitar this has not proved to be the case. The wiring has been cut all around the circuit board and as I have a extremely limited knowledge of electrics I am not sure which wires should be connected to the transducer and which should go to the output jack. I have uploaded 2 pics


Although this is a request for help I would really like to be able to figure this out for myself in the future and have decided to bite the bullet and really try and get to grips with some basic electronic skills and understanding. If it was at all possible I would be really grateful if someone could explain in idiots language how they know which connections to make and how to test - trace a circuit of this sort. I have sourced some info from another group re general electronics and I am waiting for a bread board to arrive to begin to develop my understanding. At the age of 60 it feels a bit like going back to school and learning to read but some understanding of electronics has always been something that has frustrated and eluded me - it feels a bit like maths - inexplicable and scary and leaving me feeling like a idiot.

Anyway, sorry about the ramble but I did not want anyone to think I was joining the group solely to take your expertise and disappear.

Thanks Keith

[Steve Conner]

Never mind all this complicated electronic theory, I'd start by matching up the wire colours

If the transducer and output jack wires are the same colours, then we have to get a bit more advanced. The 4558 is a standard dual op-amp, so pull up the datasheet (type "4558 datasheet pdf" into Google) and check which pins are the outputs. (1 and 7, IIRC.) The output jack wire should trace back to one of the output pins, maybe with a low value resistor in series.

If you don't like the sound of that, why not just try both combinations: getting the output and input mixed up won't damage anything.

[Keithb]

Thanks Steve - sorry if you have two of these the other one disappeared.

I have down loaded the pdf document and will have a look at it in a minute. I will try all variations of the wiring as suggested - I would normally do this but my aim is to understand how this all works. I am not sure what this sophisticated set up offers over two pots and a capacitor ? - I will find out I guess.

Thanks again Keith

[52 Bill]

- I would normally do this but my aim is to understand how this all works. I am not sure what this sophisticated set up offers over two pots and a capacitor ? - I will find out I guess.

Steve is right, once you look at the pinout for the ic, you can then figure out the circuit by reverse engineering. It would help us here if you were to give us a bit more information to work with. I'm not at all familiar with the name Dahon. What sort of transducers does it have and what kind of output jack(s), etc.

I did a really quick circuit analysis and I will guess that the output is a balanced 3 pin xlr. Each of the controls is a basic volume control, so are there two pickups on the guitar?

The op amp uses one stage as a gain stage/mixer, the second stage is wired as an unity gain inverter for the other side of the balanced output.

The inputs go to the two pot clockwise terminals. The outputs go to the two terminals on the left edge of the board (top view yellow and plain wires). The black wire is the ground and the red wire at the center of the board is for the positive battery terminal.

[Keithb]

Thank you old timer for your help. I will try to answer some of the questions. Dahon was a Japanese guitar manufacturer during the 70s / 80s from memory. They made some very respectable guitars. I have two, one a budget dreadnought and this one - electro acoustic. The transducer is set in the bridge, this is the only pick up on the guitar and the output jack has been removed. I have purchased a 1/4 inch barrel output jack as a replacement. The size of the cavity is not large enough for an XLR fitting, unless you can get mini ones that have passed me by.
I judged that the guitar had a passive transducer set up as there is nowhere for a battery to be located on the guitar - no cavity around the controls where I would expect to find it. I wondered why it was so complicated as it is a passive set up.

Have I got this generally right or generally wrong - a op amp as you describe it first stage - increases the gain - increases the signal. If you have two signals it will mix them as desired. The second stage it turns them upside down or inverts them - why is that necessary.

Thanks for your help and patience

Keith

[J M Fahey]

Sorry but it's not passive at all !!!
That 4558 Op Amp runs on 9V.
Maybe there are not obvious doors or clips to hold a battery, but definitely one was used there.
A couple makers used a small pouch for it, held by Velcro inside.
If you lose it, or if verlcro unglues, it looks like it never had one.

[52 Bill]

Are you certain that this preamp board came with this guitar? The circuit is as I had described it, it will take two inputs each with its' own volume control and then amplify it and send it out as a balanced signal.

A balanced signal is what is normally used by PA board inputs. It normally uses an xlr connector, but it could also be used with a 1/4" TRS stereo type jack as well. If the guitar doesn't have the space for an xlr, maybe it used a 1/4" stereo jack, but then it would need a switch to turn on and off the battery.

Do the two controls fit the holes that are in the guitar? Do the wires in the guitar match the ones still attached to the pc board?

[Keithb]

Thank you again for your help. I am delighted with the help given and tonight I will search all the darkest corners of the guitar for confirmation of where the battery compartment used to be.

Without your help I would have gone on believing that it was passive. My ignorance is obvious so all the light that is shown on it will be great. Electronics for me is like magic but somehow based in obscure (to me) science Why I thought it was passive was the absence of a battery compartment, coupled with the limited knowledge that passive pic ups work somehow through magic and science and this must be the same.

I will let you know how I get on later in the day

Thanks again Keith

[warunasanjaya55]

I 52 Bill is an expert. He/she solved keithb's problem.

[Keithb]

Hi - I had a quick look and feel around of the guitar cavity and sure enough two strips of self adhesive tape tucked away. I will now digest all the guidance and look towards trying to get it working this coming weekend. I will let you know the outcome

Thanks Keith

[Keithb]

Hi again - I didn't get the chance to study the information over the weekend but have begun today - as well as charge up the batteries for my new Interain Lab with 300 projects. It is only suitable for the over 12s so I am very well qualified !

I have tried to trace the tracks to the wires but I am struggling - at points they seem to go nowhere. I keep turning the board this way and that way but I am not clear but will press on. I was hoping they would lead me to the wires directly but they seem to go into a dead end. I will do some research on the difference between unbalanced and balanced - I put myself in the former category. Any ideas on where the other red wire should go, if the one in the center of the board goes to one side of the battery?

Thanks again for your patience and help

Keith

[J M Fahey]

So far you have shown us *only* the board (of which we are not even too sure it belongs to your guitar) but we know nothing about your guitar.
How many pickups does it have?
What wires does it have? Etc.
Draw it and show, say, "this black wire goes to the pickup, the green one to the jack", etc.
Plus a couple guitar pics.
Does it still have a jack?

[Keithb]

Hi Old timer -thanks for your help. I will answer your questions in order.

The board I am sure belongs to the guitar. The two pots sit within a decorative unit that has the maker name repeated upon it.

It has just one pick up that is housed in the bridge of the guitar the lead passing through into the hollow body
It has only the one wire attached to the transducer - which carries carries the hot wire and the ground - the wires - one white and the other bare
The jack has been removed

I wrote the above and went off to take some pics which hopefully will accompany this - the white wire is not white at all - its yellow. Oh dear I will have to change my glasses. Having taken the pics and made this error it occurred to me that I could zoom in and get a much better view of the board and components, something I will be able to use in the future.

I am not sure if I have added all the pics if not I will have another go in a minute

Thanks for you help

Keith

[J M Fahey]

Weeeeellll, don't know why you didn't start by following this advice:

Steve Conner said:
Never mind all this complicated electronic theory, I'd start by matching up the wire colours

You have yellow and "bare" pickup wires .... the board shows a couple inches of ... yellow and "bare" wires ..... any idea pops up?.
The black wire is soldered to circuit ground .... so it also goes to output jack ground.
We don't know where the red one goes in the board, because it can't be seen from below and from above it's hidden by a grey electrolytic.
Post a better picture showing it.
The best would be to post 2 pictures, taken straight perpendicular, both board sides, same distance and orientation, so they practically be superimposed to leave no doubts.
I *guess* it goes to +9V but would love confirmation before proceeding.
The 5th and last wire, by logic must be the "hot" output wire.

As a side note, I must slap your wrist (ok, lightly ): you keep referring to the guitar as Dahon, which does not exist, while it's a quite well known brand: "Daion".
Daion Guitars
No, Mr Google does not know that and does not provide useful answers ... until now

[Keithb]

Thanks - a few mistakes on my part along the way - sorry about that. It must be the ageing process or stupidity , probably a combination or it could be the weather - yep thats what it is I will take some more pics tomorrow and post them.

The help is much appreciated

Keith