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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

transformer coupled output= dc block?
transformer coupled output= dc block?
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Old 27th July 2011, 06:03 PM   #1
PreSapian is offline PreSapian
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Default transformer coupled output= dc block?

hello, i got a silvaweld swc1000 that has transformer coupled output. does this mean i can run a dc coupled amp with it without fear of blowing up my speakers?
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Old 27th July 2011, 06:13 PM   #2
DF96 is offline DF96  England
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If the amp can cope with a DC near short circuit at its input. It is just about possible (but unlikely) that this could cause an excessive DC offset at the output.
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Old 27th July 2011, 06:24 PM   #3
revintage is offline revintage
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With a transformercoupled output pre-amp there is no possibility whatsoever to get DC-offset at the output. A transformer can only transfer AC.

So relax and run your DC-input power-amp without fear.
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Old 27th July 2011, 07:48 PM   #4
AndrewT is offline AndrewT  Scotland
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A DC coupled amplifier is sensitive to source resistance (Rs) and the output offset will change for the worse if the incorrect combination of resistances are used.

If the NFB route is also DC coupled then the low impedance of the lower leg of the NFB loop can be matched by a similar value for total Rs seen by the amp input. This total Rs includes the RF filter.
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Old 2nd August 2011, 05:31 AM   #5
Pano is offline Pano  United States
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transformer coupled output= dc block?
The answer to the original question is YES. If you use a volume pot at the input, then the concerns in posts #2&4 are far less.
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Old 17th August 2011, 12:24 AM   #6
PreSapian is offline PreSapian
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i should add that the preamp thumps at the power up. isn't it a symptom of dc leak?
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Old 17th August 2011, 07:39 PM   #7
Speedskater is offline Speedskater  United States
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Not necessarily a DC leak.

Some circuit designs turn ON or OFF asymmetrically. That is the components on the positive supply have a different start-up rate than the negative supply this off-set generates the thump.

My DBX active cross-over has a nasty turn-off thump.
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Old 29th August 2011, 06:04 AM   #8
PreSapian is offline PreSapian
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hi gents, another one for the book

if my dac has a coupling cap at the output, will it be ok to use a passive volume pot pre to the dc coupled amp? thanks for your help once more.
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