Denon PMA720AE amplifier right speaker channel not working

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Hi everyone,

First post here and hope it is in the right place? I couldn't find a technical part of the forum so here goes.

I have a Denon PMA720AE amplifier that is coming up to 5 years old. Due to financial issues I was using PC speakers through the headphone socket until able to buy some "proper" speakers.

I bought some secondhand speakers and hooked them up. For a couple of days the sound was amazing. Then one day I noticed the volume in the right speaker had diminished quite severely and become incredibly distorted. As they were old 2nd hand speakers I naively assumed it was a speaker fault and ordered some Wharfedale speakers I had been saving up for as a replacement.

Well, it seems it is not the speaker at fault, I'm experiencing the same issue with the new Wharfedales. I have swapped over the cable from the speaker that was working fine and tried it in both channel A and B of the amp and still the same quiet, distorted issue.

What else could be causing the issue? Is it likely that a 5 yr old amp is already on its way out? Is it simply a channel blown that can easily be repaired?

Many thanks in advance.
 
Have you popped the lid off and looked for any damage on the circuit boards?
 
No, I've been too scared of messing something up to take the lid off! Does that void warranty (although I'd imagine after 5 years there is no warranty)?
 
Sorry, forgot to say thanks for your reply! Also, if there's a problem with the left channel and it's not fixable, would the addition of a power amp bypass the problem? Thinking the Denon amp line out to power amp line in and speakers plugged in to the power amp?
 
Curious, does the sound to the speaker automatically cut off when you plug the Headphones in? I notice it has Speaker-A and Speaker-B switches, so probably not but I would like to know for sure.

What is the Source of your sound, and by that I mean CD, Turntable, other?

Try swapping the cables for the Source, and see if the problem stays the same or if it switches with the wires.

With no music playing, try rotating each of the knobs (Bass, Treble, Balance, Volume) and see if you hear any noise. That would indicate that the noisy control has become dirty. Frequently simply rotating the control knob over the noisy area repeatedly can wipe it clean.

The same could be true of the various switches. Try rotating or toggling the various switches repeatedly and see if that makes a difference.

It sounds like in the process of checking things out, you have reconnected the speaker wire on both the amp and the speaker, but you want to make doubly sure that the connections are clean and tight, and that no stray strands of wire risk shorting the terminals.

If you are using Banana Plugs, and if possible, open the plugs up and inspect the wire. It is possible that the Plug to Wire contact area has become corroded. Or perhaps the wire has become frayed.

Is there any chance that there is any way that a small piece of metal has fallen into the Amp? Perhaps when trimming the speaker wire, a snipped bit of copper fell into the amp?

How dirty is the amp inside? If it has a thin film of dust that is not so bad, but occasionally a very substantial amount of dust can accumulate, and that could effect the cooling of the amp.

It is probably reasonably safe to open the amp, though you have to make an assessment of you abilities in this area. DISCONNECT THE ELECTRICAL POWER AT THE WALL. There is only one area that is potentially dangerous and that would be the Power Supply Capacitors as even with the power off, they still retain voltage.

However, judging from this photo, the contacts on the capacitors are not exposed so the likelihood of accidentally touching them is slim.


In the middle of the amp you will see two large plastic covered can-shaped objects, these are the capacitors. You should see several of these inside the amp in a wide variety of sizes. These are one of the things you want to inspect.

Inside the amp look for anything that look charred, burnt, or discolored. Look for capacitors that look like they are bulging, or partly melted, in some case capacitors that have literally exploded, or that are leaking a thick dark brown fluid. If you see any of these things, that is an indication that there is a problem with the amp itself.

It is possible to add a Power Amp to the system, but I think you will find that a Power Amp is equal to more more expensive than replacing the Amp itself. Generally Power Amp, unless they are used, are not cheap.

Just a few thoughts.

Steve/bluewizard
 
Hi Blue Wizard,

Many thanks for your detailed and in-depth reply.

Initially this problem had been detected while playing cd's. I have tested using a different cable to connect the cd player and also tested playing records.

I had noticed the distorted noise and low volume of the right speaker when using the PC speakers connected to the headphone socket (I know, I know), I assumed it was the speaker not being able to cope with the volume and a tear appearing in the cone. With PC speakers its a bit more difficult to assess whether this is the case or not. It did, however, give me the impetus to purchase a pair of second hand speakers. A pair of KEF Coda 7's. Both wired in to the speaker B Left and Right and B speaker selected on the front of the amp (both A and B switched off for using headphones, which I had previously done).

This was the first time I had actually used the Denon amp with wired speakers. The sound was amazing and there was no distortion or loss of signal or noise. The speaker wires, however, are just the bare copper threads twisted and inserted in to the holes presented when unscrewing the plastic caps on the back of the amp. Is this a no no?

A week or so ago my wife bought a new shelving unit and I had to move everything. In doing so I initially wired one of the speakers incorrectly and noticed no sound at all. I switched everything off and swapped the cables around. This time we had perfect sound again. I reset the hifi up on the new shelves and all was good, everything working properly.

I came back from work on Monday to find my wife telling me one of the speakers had blown. It didn't twig at the time that this was the same channel that had been affected with the PC speakers.

Also rather naively, I didn't think to swap speakers over to make sure that wasn't it, such is impulsiveness crossed with some anxiety, and ordered a set of Wharfedale Diamond 9.1s to replace the "faulty" speakers.

They arrived yesterday, I set them up and .... yep, the problem is still there on the right channel. I used the old right speaker on the left channel and, would you believe it, it worked ok. So, no new speakers were needed :(

I also unplugged all speaker wires and tried using headphones to see if it was just the speaker channel. Again, the right channel seems to be faulty. It's quiet, muffled and when the volume is raised it distorts.

I've done some research online and found that AV repair places close to me are likely to be upwards of £35 just to inspect.

I had seen a power amp for about £65 inc VAT, thinking it "might" be cheaper to just bypass the channels of my Denon amp rather than sending it to get fixed.

I shall take the lid off tomorrow and have a good look inside. I shan't prod anything but I shall look out for dust or anything that looks damaged. It just seems such a shame as it's still fairly "new" at 5 years old, perhaps again that's my naivety thinking amps will still last 10 - 20 years.
 
If you try switching the speakers left for right, that should verify that it is not the speakers.

If you switch the CD Cables left for right, that should verify that it is not the CD Player or CD Cables.

So, if we can verify that the problem is consistently in the Right Channel, then that very strongly indicates the problem is the Amp. Especially since it is in both the Headphones and Speakers.

But we have to wonder where in the Amp. If it is in the Pre-Amp stage then adding a Power Amp will not fix it. If it is in the Power Amp stage, then a Power Amp might fix it.

My inclination would be to play a Stereo Test Tone through that Amp and measure the outputs of the Pre-Amp with a AC Volt Meter. If the Left and Right are roughly the same voltage, then likely the Pre-Amp section is OK.

Most AC Volt Meters are only accurate in the 50hz/60hz range, but that doesn't matter much, we don't need an accurate reading, we just need to know that each channel is the same. Typically you can buy a basic Digital Volt/Ohm/Multi-Meter Meter for very little money, frequently in the £10 range. Most building supply and hardware store will have them, and of course, electronic shops.




I would suggest you plug in some RCA cables to the Pre-Out, then connect the Multimeter to the ends of the RCA Cable. That should make connecting the Multimeter Probes relatively easy.

As to where you can get test tones, there are several places. You can find them on YouTube, so if you can connect your computer to the system, then simply find some tones on and play them. You can also download them.

YouTube - Audio Test Tones

YouTube - Sonic Electronix - Test Tone Play List

Real Traps has a slow sweep from about 10hz up to about 350hz. That should be enough to determine if the outputs are the same. I've burn the sweeps onto a CD to make it easier to use. Best to have the speaker OFF when running these test tones to protect the speakers.


There are several place on the Internet that will play test tone, you just need to search them out.

Once you verify that the Pre-Amp section is working properly, then you can consider a Power Amp.

If not, sadly, you will have to scrape the Amp and start again.

Steve/bluewizard
 
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If you are interested, there are several Audio Test CDs on Amazon to consider. Though that is going to drive the price up.






Just a thought.

Steve/bluewizard
 
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You can find some more Test Tone information here for those interested -


Steve/bluewizard
 
Hi Blue Wizard.

Many thanks for all your replies.

I have had the chance to test the output through the pre amp outs and am getting the same result. So it's an amp problem.

Now to decide whether it's worth getting repaired or replaced???
 
If it is in the Pre-Amp stage then adding a Power Amp will not fix it.

I have had the chance to test the output through the pre amp outs and am getting the same result.

So it does appear that the pre-amp section of this integrated amp is where the problem lies. As BlueWizard has said, adding a power amp won't sort the problem.

This Denon is supposed to be a half-decent 50W/channel amp. To replace it with a modern equivalent, in terms of sound quality and power output, would cost around £200 - £250 (I'm thinking of the budget Yamaha and Onkyo amps).

To repair or replace - it's a close call. If you can find a reputable local repairer, I'd be tempted to go for a repair because a well-built amp, like the Denon allegedly is, should give you at least ten years of service - if not abused. Also, a repair is probably more environmentally friendly. But get a repair quote (after the repairer has investigated), before agreeing to go ahead with repair. All-in, I wouldn't spend more than around £100 on it.

Just my opinion.
 

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