JLM AUDIO

Hi

I recently purchased a couple of 1272 to 1290 module kits to use with my 1271s that had been converted to 1272.

Got everything up and working with one problem - everything works fine until the gain knob gets to position 8 (8th clockwise click), after which the preamp produces a loud whining/humming sound.

This happens on both modules, has anyone encountered this before, any clues on where to look?

I've also installed go between kits on each of the 2 channels, both modules are running off the JLM power plant.

Thanks!

method1 wrote:Hi

I recently purchased a couple of 1272 to 1290 module kits to use with my 1271s that had been converted to 1272.

Got everything up and working with one problem - everything works fine until the gain knob gets to position 8 (8th clockwise click), after which the preamp produces a loud whining/humming sound.

This happens on both modules, has anyone encountered this before, any clues on where to look?

I've also installed go between kits on each of the 2 channels, both modules are running off the JLM power plant.

Thanks!

The first 8 positions are passive attenuator so will work without power. The 9 position switches in the extra preamp module which needs the 24v power on the 1272 to 1290 module.

Do you get 24vdc between the red and black wire going to the 1272 to 1290 module?

It is fairly complex to convert 1271 to 1272 so I would definitely be checking the 1272 conversion was a 100% with no boosting parts fitted to the modules rear terminal block.

Definitely worth emailing me some large in focus well lit photos of the 1271's insides and the internal and rear connector wiring etc so I can check them over.

Thanks Joe - I"ll dismantle the thing and post some pics, thanks for the response!

Hi Joe

I mailed you these pics, just adding them here too. Hopefully they can help with the diagnosis!

There appears to be 24v DC over red and black.

Bump.. any ideas?

I can get more pics if that would help, would really appreciate some input on this!

bump…..

method1 wrote:bump…..

HI Sorry for the delay as I have been away working on a iPhone only so could not check the photos properly.

I did notice there doesn't seem to be a 0v on the rear connector to hold the intermediate level pot wiring to 0v and also no K-L link to get the audio from the preamp stage to the output stage without a level pot????

So not sure how audio would get to the output?

But looking at the photo's now the wiring looks so different to a normal 1272 I cannot tell what else maybe wrong.

If you do not have a good tech to work on this it maybe best to send them to us as I am sure we could work it out quickly on the bench.

Thanks Joe - we got them working at last, here's a pic of the results!



Added a pair of P&G faders (on the outputs) from an old neve console too.

method1 wrote:Thanks Joe - we got them working at last, here's a pic of the results!

Added a pair of P&G faders (on the outputs) from an old neve console too.

Cool great to hear you got it all working.

Nice work. Really like the cube idea with the faders