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Author Topic: Carlsbro Glx documentation - pre amp problem  (Read 1015 times)

tedsorvino

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Carlsbro Glx documentation - pre amp problem
« on: March 16, 2018, 10:19:12 PM »
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

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Re: Carlsbro Glx documentation - pre amp problem
« Reply #1 on: March 16, 2018, 11:26:34 PM »
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

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Re: Carlsbro Glx documentation - pre amp problem
« Reply #2 on: March 17, 2018, 12:03:42 AM »
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

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Re: Carlsbro Glx documentation - pre amp problem
« Reply #3 on: March 17, 2018, 08:55:48 AM »
Check the supply voltages all the way through to the preamp,, see if you are getting voltage at pins of opamps.
Phil.

tedsorvino

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Re: Carlsbro Glx documentation - pre amp problem
« Reply #4 on: March 17, 2018, 03:55:13 PM »
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

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Re: Carlsbro Glx documentation - pre amp problem
« Reply #5 on: March 18, 2018, 04:40:44 AM »
Most common is dual opamps which have pin 4 and 8 for supply.
Phil.

g1

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Re: Carlsbro Glx documentation - pre amp problem
« Reply #6 on: March 19, 2018, 02:27:10 PM »
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).

 

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