I have re-capped a Harman Kardon PM655VXi and it is putting a ton of clean power. When I try to adjust the DC offset, it is going up and down by about 20mv on each channel. Is that a sign of a problem? Everything looks good on the scope. The amp heats up when idling but they're known to do that and it isn't a bad heat. Thanks for any help or advise.
The cover is off. So that isn't a sign of a problem if the DC offset is moving that much? I can generally get it centered somewhere between -8 and +8 MV and it then swings another 10mv in each direction so it goes from say -5mv to +15mv
Bolt on that cover and wait an hour for it to stabilize. This is a direct coupled circuit, no servo,
so that's actually pretty good.
so that's actually pretty good.
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Cool. Thanks. It seems to be in great shape and it certainly puts out a lot of clean power. I really like how it sounds.
I know this integrated amplifier. According the schematic from HiFi Engine - go to
Harman Kardon PM655VXi - Manual - Stereo Integrated Amplifier - HiFi Engine
there isn't different voltage gain factor between AC and DC (approximately 50 times), because there is no capacitor in series to the NFB resistor R425/426.
This means, that the claim to equality of LTP (Q403/405 resp. Q404/406) is very high.
Also of importance is the input capacitor C401/402 of the power amp. It should be replace by a foil version.
If offset voltage below ∓1mV wanted, additional offset servo unit is necessary.
Harman Kardon PM655VXi - Manual - Stereo Integrated Amplifier - HiFi Engine
there isn't different voltage gain factor between AC and DC (approximately 50 times), because there is no capacitor in series to the NFB resistor R425/426.
This means, that the claim to equality of LTP (Q403/405 resp. Q404/406) is very high.
Also of importance is the input capacitor C401/402 of the power amp. It should be replace by a foil version.
If offset voltage below ∓1mV wanted, additional offset servo unit is necessary.