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Carlsbro Glx documentation - pre amp problem

Started by tedsorvino, March 16, 2018, 10:19:12 PM

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tedsorvino

Hi. I'm using an old Carlsbro Glx 80 for about 20 years now.
It's well maintained but suddenly the preamp section on both channels went really weak (I checked the other sections - power amp in, effect send- and they work fine) .
I can't figure out what could have gone wrong since all the mechanical parts work ok....Leads, pots, etc. .
I 'm not sure how it is constructed so I'm looking for any relevant or specific documentation (service maual, schematics etc.) of any model of the Carlsbro GLX series- especially something close to this one.
Thanks in advance

phatt

Before you open it up,,,Try bridging the FX Send and Power amp in with a lead.
If that fixes the issue then the switch inside the socket is likely dirty.
Options;
1/ You can spray electrical cleaner into the socket and insert/remove a plug a few times might fix it.
2/ Replace the socket,, which is likely fiddly if you are not familiar with working on electrical gear.
Or 3/ (my favorite) Get a short jumper lead and leave it connected to the loop.
Phil.

tedsorvino

Thanks for the advice Phatt. I m quite familiar with electronic projects and i ve already opened the box. Done it several times actually. I ve tried the patch trick...but to no good results.

phatt

Check the supply voltages all the way through to the preamp,, see if you are getting voltage at pins of opamps.
Phil.

tedsorvino

Will do Phatt. The thing is I ve got no idea what the optimum voltages are in general. Usually op amps have half of the supply on most pins. Am i right?

phatt

Most common is dual opamps which have pin 4 and 8 for supply.
Phil.

g1

Half of supply on ins and outs with single ended supply.
With +/- split supply there will be zero volts on ins and outs (unless a DC application).