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Strings Wiring Prob?

jeremyjuicewah

jeremyjuicewah

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Costa Blanca Spain
Its not really a guitar question, just about a guitar circuit. I changed the pre amp on my hollow guitar a couple of years ago. Recently I changed the wiring so that it has an xlr and quarter jack output, both balanced. Whereas the battery in the preamp used to last about two months with light but regular use, now it lasts about a week. So, there is obviously a draw on it when its not in use. It works just fine, very slight hum at high volume, but I am not sure thats not the poor earth in most Spanish domestic/bar and cafe circuits.

Is it possible that the balanced output wiring is draining the battery and if so why would it? I repeat, I have not found any other fault with it.
Cheers
Mike
 
Guessing, but sounds like it's got an active system - these are switched on/off by the jack plug. You've probably bypassed the switching mechanism, mayabe you need to add an on/off switch - or take the batteries out when you're not using it.
 
Hi
If you use a double pole switch, that is one that will break both positive and negative when operated, it will provide complete isolation when in the off position.
Hope this helps
Regards
 
What was the original configuration - XLR or quarter inch jack? If it was the jack then Kev may well be right that you have by-passed some switching, perhaps by auxilliary contacts in the jack socket. In that case, how have you wired the XLR? If you've wired it in parallel with the jack then you won't have a balanced output because the jack is not itself a balanced output device; the sleeve will be earthed somewhere. If it was originally XLR then unplugging may have broken the circuit and something different is happening now in the jack. Even if taking the battery out between uses means it still drains quickly indicates that there is current flowing directly to earth somewhere where it wasn't before. The hum at high volume indicates there may be an earth loop somewhere - fitting a jack across a balanced XLR could well do that (if that's what you've done).
 
Hi. The original wiring was a quarter jack, balanced. I did not realise it was balanced till I decided to add the xlr. Then I was surprised and disbelieving to find it was indeed a balanced jack output so I just wired to an xlr from the balanced jack. What you are saying there is what I was thinking but did not really know why. Yes, taking the battery out but it still is running down much more quickly. Both jack and xlr are balanced, wired to the jack then on to the xlr.

What exaclty is a ground loop? Actually, I will google it. But if the wiring to the stereo jack is correct, and I am sure it is from the Fishman diagram, I cant see how the wiring to the xlr can be wrong.

Cheers to all
Mike
 
No, I dont think its ground loop. I have the three connections to the jack, then I have just jumped them on to the xlr. Only one positive so from what I can read up quickly on what seems to be a fairly difficult concept it cant be a ground loop. But, there must be a current draw, else why the faster draining of the battery?

Cheers
Mike
 
Mike, yes it occurred to me after writing the post that of course a stereo jack can be used in a balanced configuration. In that kind of jack, often called TRS - tip, ring, sleeve - the balanced signal is carried on the tip and ring connections with the cable shielding on the sleeve (working from the tip end of the jack plug to towards the body, obviously) . With the discovery that this was being done in the pre-amp, I wonder why you needed to put an XLR connector in parallel with it ? They just do the same thing in a different plug format. Unless, as I said earlier, there is some switching in the TRS socket via auxilliary contacts thenI can't see either why the addition of an XLR connector should give greater battery drain.

I only commented on the hum in case a ground lop had been set up because of changes you had made. Ground loops are often set up due to mains hum being induced into a circuit formed by chassis connections (through equipment mounting in a common rack) or mains earths along with signal cable grounds, the hum being fed into the amp. If it's not a major problem then perhaps don't worry. Otherwise you need to look at the whole system to see what's happening. As you saw, there is plenty of info on the web (and I'm not an audio engineer so it starts to stretch my knowledge!).
 
Hi Col. To keep it short the original preamp had jack and xlr, but I suspect now, neither balanced. I had to renew the preamp and then the plate that held the jack and the then defunct xlr which was had been on the old preamp broke and when i had to make a new plate I decided to include the xlr and decided I would try to wire up the xlr for the security of the connection and so it could go straight to the desk without a di box. I didnt even know at that stage that the quarter jack was a stereo jack. So now I have the two balanced connectors, but for some %$£!!!!!!!!!!!!!!!! reason I have this problem. I think I may take it to a tech and have it checked out for all its problems. Trouble is I now play the thing near enough every week on two or three numbers. Still, If I have a breakthrough on this I will post the outcome.

Cheers all
Mike
 
Did some work today. New xlr and stereo jacks, just in case. All soldered nice and neat and everything cleaned. Whatever manufacturers say, hollow body guitars I dont think are rigid enough for xlr. I found even the new one was prone to crackle due to movement. So, wont use the xlr.

The new stereo jack has a safety retainer on it so dont really need xlr anyway. Into my Fender 100w amp with a balanced jack there is the most horrific racket. Into it with unbalanced jack I can put vol up to max and max on guitar, no hum. But I am certain its not delivering anything like 100w. In my music room you would know about it.

Via a di box that has two 20db cut outs on it into my 100w Bose L1 which has xlr connection and quarter jack, I can get hum to a decent level by using one of the cut outs. Without that the noise is bad. But to get throught the di box into the Bose uses such a mish mash of connectors I am not keen on it.

So I can go into the mixer direct via stereo jack or into the Fender amp via mono jacks.

Whether or not the battery use will revert to reasonable I will find out I am sure.

I will take it to a tech for a once over after Saturdays gig. Like saxs they can do with it now and then.

Maybe I will have a good excuse to buy a new one. Gas is just as bad on strings as woodwind.

I will update when it gets back from the tech.

Meanwhile, thanks
Mike
 

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