Denon PMA 757 advice and opinions

[strandtentje]

I have acquired a Denon PMA 757 by means of exchanging it with a fellow audio nut for my Musical Fidelity David. We both seemed very pleased with the deal. The David seems to sit in a slightly higher price category, but the Denon unit (picture attached) was looking a lot better than the David, so I can't complain.

The unit sounds mostly charming, but it's only starting to hold up in brilliance (ssh, hi-hat, etc.) against the 5570 when it's been playing for over an hour. The previous owner did mention he has no knowledge of it ever being serviced, beyond him blowing a whacktonne of dust out of it a while back. What are your experiences with the sound of this unit, particularly detaily bits above say, 6k?

I'll be diving in to check if the dust hasn't found its way into the bias pots- only one side is getting mildly warm too, other side remains cold. It could explain the warm-up time for brilliance. I'll report back with the results and the board revision this unit contains (apparently there's 757 board revs with clockwise bias pots, and different board revs with counterclockwise bias pots. scary.)

While I am in there, are there particular components that are known to go bad in this unit? Any semiconductors that go noisy and cause a ruckus and/or short I should be wary of? Can I expect the electrolytics Denon employed to hold up in 2017, or am I likely to find a couple that have drifted?

Thanks!

 

[Powertech]

Well designed and built units. Note the clever use of flexible mechanical linkages between the selector switches on the front panel to the actual selector switches close to the input connectors at the rear. This is put in for sonic reasons. Input board is separate from main board carrying the PSU and power amps. All 80s Denon kit I have had over the years has been well designed using good quality components. The heatsink runs across the centre of the amp with the power transistors mounted at the right hand area, so it probably would be warmer on that side.

 

[ivandezande]

Gonna half to check the schematic for the possible bad transistors, but probably will be ok. At 31 years old a recap would help.

 

[Fomoco1649]

I have acquired a Denon PMA 757 by means of exchanging it with a fellow audio nut for my Musical Fidelity David. We both seemed very pleased with the deal. The David seems to sit in a slightly higher price category, but the Denon unit (picture attached) was looking a lot better than the David, so I can't complain.

The unit sounds mostly charming, but it's only starting to hold up in brilliance (ssh, hi-hat, etc.) against the 5570 when it's been playing for over an hour. The previous owner did mention he has no knowledge of it ever being serviced, beyond him blowing a whacktonne of dust out of it a while back. What are your experiences with the sound of this unit, particularly detaily bits above say, 6k?

I'll be diving in to check if the dust hasn't found its way into the bias pots- only one side is getting mildly warm too, other side remains cold. It could explain the warm-up time for brilliance. I'll report back with the results and the board revision this unit contains (apparently there's 757 board revs with clockwise bias pots, and different board revs with counterclockwise bias pots. scary.)

While I am in there, are there particular components that are known to go bad in this unit? Any semiconductors that go noisy and cause a ruckus and/or short I should be wary of? Can I expect the electrolytics Denon employed to hold up in 2017, or am I likely to find a couple that have drifted?

Thanks!

Yes…love mine , running it with quality vintage JBL speakers