oep transformer removal? (from BA)

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greenmanhumming
Posts: 117
Joined: Tue Apr 10, 2007 1:19 am

oep transformer removal? (from BA)

Post by greenmanhumming »

I've got a couple of channels of BA with oep transformers, but I'm thinking after using them for a bit that the oep transformers are not to my taste, they are good, but maybe just not what i'm after, i find myself using the JLM14 channels more.

so i'm wondering about changing them - so i have questions.

* has anyone taken these off a BA board before and did you have difficulty with unsoldering them? (several pins quite a distance apart!)

* anyone want to buy a pair of OEP transformers for BA in the UK?

* would I be better to make 2 whole new channels and sell the ones with the OEP transformers on? (if they are hard to unsolder)

I would describe the OEP sound as stable, neutral and solid with a focused midrange emphasis. the JLM14 seems a bit more coloured but also a bit more sparkly and more air and more bass.

is this others experience? should i tweak something in the circuit with the OEP's before finally deciding to change them?

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Joe Malone
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Post by Joe Malone »

I've got a couple of channels of BA with oep transformers, but I'm thinking after using them for a bit that the oep transformers are not to my taste, they are good, but maybe just not what i'm after, i find myself using the JLM14 channels more.
We have removed OEP before and you will need a good solder sucker and add some new solder just before you use the sucker. It isn't for the faint hearted. Once all the solder is removed the OEP will usually be held by very fine bits of solder which can be broken loose by gently using a flat screw driver between the OEP and PCB. Or use the soldering iron and small flat screw driver to release each pin into the centre of the unsoldered Pad hole until all pins are free.

Below is the general info we give out for desoldering but obviously because you want to keep the OEP as a working unit you would not cut the legs of it. :D

How to desolder double sided PCB's

To desolder from double sided PCB always cut the components legs off and pull softly on each leg with pointy pliers while heating the solder joint. Each leg will come out easily. To desolder electro caps heat each solder pad while rocking the cap back and forth slowing walking the legs out of the PCB. Apply new solder to each solder pad and then and only then use the desoldering tool to suck the solder filled holes clean for the new part. If you use the desolder tool to desolder the legs of a full component and then pull it out you have a good chance of a small bit of solder on the top layer still being attached to the component and pulling the track off the PCB. Also good desolder wick works better than a desolder tool as it helps remove the heat once the iron is removed and doesn't pull on the pad being desoldered. Also keep the heat of your soldering iron down closer to 300 degrees mark not the 450 degrees that most soldering iron stations can do. Usually the glue holding the copper down will debond if higher than 350 degrees is kept on the pad for long times. If you follow this you should be able to repair our PCB's over and over without the PCB showing any distress.
Joe :-)
JLM Audio
Capturing Audio without Injury

greenmanhumming
Posts: 117
Joined: Tue Apr 10, 2007 1:19 am

Post by greenmanhumming »

I changed the transformer, but now the preamp is noisier than it should be.

theres about 20dB more hiss with no mic plugged in and the gain down than another channel the same configuration.

the hiss turns up when i turn the gain up.

what have I messed up? I can't see anything

i did slightly damage a pad on the top of the board getting the OEP off, but it was one that is only used by the OEP, and in any case still seems to be correctly connected.

what could cause the extra hiss?

greenmanhumming
Posts: 117
Joined: Tue Apr 10, 2007 1:19 am

Post by greenmanhumming »

It took me ages to realise it, but it seems to have been a dodgy OPA2604

i guess i shouldnt have left it in while removing the transformer!

i would have thought it was far enough away that stray heat wasn't an issue though.

how could i have damaged it so it became noisy?

anyway i replaced it and now the channels match with much lower noise on the newly modified one.

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