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Old 12th December 2006, 10:10 PM   #1
packer is offline packer  United Kingdom
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Default Galien Krueger 800RB DC Offset!!

Just finished replacing all shorted O/P trans on this amp.
With a lamp in series with ac line all is ok both amps run perfectly.
But if you plug amp directly into ac supply with bass spkr connected O/P stages Blow.

All - + supplies ok in tolerence no ac ripple.

On the the 300w side there is a large voltage swing at turn on at the Spkr terminals to the -VE rail
Also with no spkrs connected and amp turned on the off 300W amp o/p terminal goes to -ve rail. This does not occur on on the 100W section .

If you run the amp with the ac supply in series with a lamp and the bass spkr is connected before you turn the amp draws massive current.

However if you connect the spkr after you turn on all is ok. Inject 1k sine at input stage no distrtion waveform is symetrical on o/p all voltages at each stage are correct!!!

SO what is causing this large neg voltage swing at turn on and turn off??

Interestingly in the S/manual GK mentions bringing up the amp on a variac at approx 50v the amp O/P will swing negitive and snap back to 0v which it does.
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Old 12th December 2006, 11:16 PM   #2
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HMMM maybe look at the input section. neg feedback side...maybe
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Old 13th December 2006, 01:03 AM   #3
Leolabs is offline Leolabs  Malaysia
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Check the driver stages too.
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