Denon PMA 1060 cuts out at quarter volume - diyAudio
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Old 1st December 2015, 12:07 PM   #1
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Default Denon PMA 1060 cuts out at quarter volume

Hi all,

First time poster here. I just recently bought a Denon PMA 1060 stereo amplifier which has an issue. The audio will cut out at about quarter volume. The actual volume varies slightly with different music (louder music will cut out at a lower volume, quieter music will cut out at slightly higher volume). I have to power cycle the amp to restore audio but if I go too loud again, it will cut out.

I'm guessing the protection circuit has kicked in but don't know why.

I've checked for stray strands of speaker wire, but I use banana plugs and don't see any stray wires.
I have tried left and right channels connected by themselves, with no change.
I have tried the second (B) set of speaker terminals, no difference.

The speakers connected are Aaron ATS4, rated at 160W at 6 ohm so should be able to handle the power. The amplifier I replaced but is still working doesn't cut out with these speakers at quite loud volume.

I do have a multimeter, but am not strong with amplifiers or analog electronics. I've measured the voltage across the speaker terminals and there does not appear to be a big DC offset voltage on the terminals. I've found a service manual online and there is a procedure to adjust the idle current, but I don't think that would cause this issue, would it? From what I've read, too high idle current makes the amp run hot, and too low affects sound quality. I don't think either of this is happening in this case.

I'm wondering if anyone knows what the issue might be? I can take it to a repair shop who seem confident on what the problem is, but wondering if it's a cheap and/or common fix, or more complex!

Thanks in advance.
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Old 1st December 2015, 01:27 PM   #2
Mooly is offline Mooly  United Kingdom
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How loud is loud ?

I'd be very very surprised if you were driving the amp hard enough for it to trip... however faults like this need quantifying with basic measurements. It is possible to provoke some protection circuits by driving an adverse or reactive load hard.

This thread allows you get a good idea of the voltage and power you are delivering to your speakers. It might be worth trying this... drive the amp to the point you find it trips and then leave the volume control where it is and try this. Instructions and files are in post #2

A Test. How much Voltage (power) do your speakers need?
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Old 1st December 2015, 01:35 PM   #3
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Something like this is often indicative of a resistor that's gone high somewhere near the output of the power amp (emitter resistors of outputs or drivers and other things in the vicinity). Fortunately a resistor in-circuit may read lower than what it is, but will newer read higher unless it really is out of spec. A good look at solder joints tends not to be a bad idea either.
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Old 1st December 2015, 11:45 PM   #4
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Thanks for your responses guys.

@Mooly - Quite loud (yes I know, subjective). To be honest, I'd only want to drive the amp slightly more and even then I think the neighbours would have something to say if it was late at night. I might do as you suggest and see how much power is delivered at the point of shutting off, I'd be interested in how much power the amp is outputting at that volume level.

@sgrossklass - Thanks, I have a schematic which I'll look over. Given that this problem also occurs with independent channels (left connected only, right connected only, and both connected), is it likely to be the power amp output? The power amp would separated into left/right channel correct? So if the problem was a resistor, it would have to be the same resistor on both, or a component which is common to both.

Since I have the service manual, I am going to try and measure/adjust the idle current. But I don't think this will fix the problem unless it's high and running hot? (I haven't touched the heatsinks but with the casing on, the air being vented is warm, not hot.
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Old 2nd December 2015, 01:25 AM   #5
anatech is offline anatech  Canada
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Hi lordsnipe,
You might want to check the capacitors in the protection circuit. For this kind of fault it is the most likely. They are probably not dead, esr measurements might not tell you much. For this you want the effective capacitance and dissipation reading as a measure of quality. If you don't have a capacitance checker (LCR meter), then just replace those capacitors in that section.

I don't have the manual for this model or I could have given you the part location codes. Another thing to check will be the speaker protection relay. It may need replacing due to burned contacts by now.

-Chris
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Old 2nd December 2015, 01:44 AM   #6
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Thanks anatech, I would attach the PDF service manual I found online but it's over 3Mb.

Found a link to the schematic, not the same PDF that I found which had the service manual and parts list, but can still be useful:

http://support.karat-service.net/Uns...20PMA-1060.pdf

Last edited by lordsnipe; 2nd December 2015 at 01:49 AM.
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Old 2nd December 2015, 01:52 AM   #7
anatech is offline anatech  Canada
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Hi lordsnipe,
Many thanks.

-Chris
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Old 2nd December 2015, 02:00 AM   #8
anatech is offline anatech  Canada
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Hi lordsnipe,
That link is incomplete for the protection circuit. Check capacitors C603, C604 and C605, and there are probably others off the page.

-Chris
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Old 2nd December 2015, 02:47 AM   #9
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Thanks Chris.
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Old 2nd December 2015, 10:10 AM   #10
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So I pulled off the cover this evening to take a look at the protection circuit, I was going to replace the caps because I don't have an ESR meter (and to use an ESR meter, the cap has to be removed anyway).

I've disassembled my fair share of PCs, game consoles and even CRT arcade monitors/CRT TVs, and never have I seen the board interconnections like this before.

It looks like wire wrapped around a long header pin? Surely this wasn't the pinnacle of Japanese electronic engineering in the early 90s? The amp has quite a few of these connections, so I don't think it was a home job...?

It looks to be a pain to remove this speaker terminal/protection circuit board. It has a number of these connections, the screw holding it to the back panel has a cap soldered to the end of it .. this is all odd looking to me!
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