Fault issue - please help

sossages

Novice Member
AMPLIFIER / SPEAKER FAULT
Anyone technical able to diagnose fault?

My amplifier keeps blowing up. Just 6 months old and working fine one day I turn it on at low volume. It worked perfectly (as always) but only for 2 mins before cutting out.
Sent away and repaired. Got back and worked perfectly at low volume for two minutes before cutting out.
New replacement amplifier sent out. Worked perfectly at low volume for a minute before cutting out.

Denon Amplifier fault history in detail;-
Works fine from new for nearly 6 months. No glitches. Used daily.
Connections;-
SACD player both analogue RCA and Digital Co-ax
Turntable to Phono input
Mac via USB
AV receiver to HT Bypass (EXT.PRE)

Fault 1
For no reason, having been used without issue the previous day and for the previous few months, a minute or two after turning on and working fine it cuts out and blinks red. Volume only at 9 o’clock. Source digital co-ax 1 in from SACD player. All other supplies in either turned off or on standby. Amplifier circuit has failed.

Fault 2
Back from repair connect only digital co-ax 1 and speakers and play SACD player, volume at 9 o’clock
Works fine for one or two minutes and then cuts out and blinks red. Amplifier circuit has failed.

Fault 3
Brand new replacement amplifier using existing power lead.
Connect everything up including HT Bypass (EXT.PRE) but everything either off or on standby. Turn it on with volume at zero. Fine. Scroll through input selector and notice hum on HT Bypass which there had never been on the first amplifier before there had been any faults. Seconds later it cuts out and blinks red. Amplifier circuit has failed. The AV Receiver was in standby. Note the AV receiver was not connected to HT Bypass when fault 2 occurred. I did not scroll through to HT Bypass immediately before fault 1 or 2 so don’t know if there was a hum.

I have checked connections to speakers. All good. They are factory Airlock terminations with banana one end and spades the other. No cuts in the cable.
The Monitor Audio speakers are spec. wise compatible and are currently away for fault test. So far no fault has been found but will be tested again.
The SACD player is connected to the same double socket and continues to work fine.
All the other inputs other than the Mac are on the same ring main and continue to work fine.
Other than these and a TV left in standby and Sub switched off nothing else is on the ring main.
I have had an electrician test the voltage etc of the mains and it is fine. He also states that a high voltage would have affected all on the circuit, which it hasn’t.
 

John7

Well-known Member
To my mind, it HAS to be a speaker/wiring problem or ventilation (overheating) issue.

I'd start by buying/borrowing some cheapo speaker cable and running that temporarily for a while - see what happens. Also put an ohm meter across each speaker and see if within spec.

Check air space around amp and make sure no obstructions an airflow is sufficient.

That's all I can think of at the moment......
 

sossages

Novice Member
Thank's John7
Definitely not an overheating issue. ~Plenty of ventilation and happens just after being on a minute i.e. when still cold
Unfortunately I can't test it as a) the amp is currently not working and b) the speakers are with AVonline being tested, albeit so far they can't find anything wrong.
Cables have been inspected and no issues and were working fine until this happened.
My current guess is it's a fault within the speaker as two different amps have blown the same way but don't understand if this could cause such a fault in the amp and why it's not showing up with AVonlie with a different amp (Monitor Audio are unable to examine due to Covid)
 

sossages

Novice Member
Would a fault in the speaker cause a hum in HT Bypass (Power amp only) but not on other settings going through preamp. Note that 2nd time this happened no connection to HT Bypass so can't be a fault with the AV receiver
 

dobrykamil

Well-known Member
May I ask, what is the mode of your Denon amp?
 

dobrykamil

Well-known Member
Does the amp still power up?
 

sossages

Novice Member
Unfortunately not. As stated above manual states "amplifier circuit has failed"
That is to say when powered on the green light flashes as normal then goes straight to rapid red flashing
This is the same for both amps
 
Last edited:

dobrykamil

Well-known Member
I don't think there is a problem with the speakers, because even if there was an issue, with volume at 9 o'clock, over current protection would switch amp off without causing any damage to the output transistors. Outer bit of Coax's socket is internally connected to ground. Your SACD was connected to that socket every single time, right? Many points in the amplifier circuit have predefined, safe voltage values compared to the ground=0V. If that gound has a positive value (+1,2,3V..ect), voltage of those safe points will change. Unfortunately, rapid red flashing means high DC voltage on the speaker outputs aka shorted power transistors. Obviously this is just my theory, but I would take a closer look at SACD player.
 

gibbsy

Moderator
What is the model of the SACD player?
 

sossages

Novice Member
UPDATE
Finally got my speakers back from being tested by AVOnline (Monitor Audio were closed and unable to test) after they took two weeks to get round to sending them back out and then demanded a ransom of £49 before they would (not good PR considering I am a repeat customer...)
Anyhows there's nothing wrong with the speakers.
I now have them connected to an old amp, CD player and speaker cable and they are playing fine from the same wall socket which rules out the supply being the problem.
I have spoken to HIFI Corner re the SACD player potentially being faulty as dobrymakil suggests. Their opinion is that this (as well as every other possibility) is very unlikely and they are stumped. They are seeking advice from the official Denon repairers who are also currently closed so that's not going very far at the mo. Unfortunately I don't have a voltage meter to read if there is a fault and I wouldn't really ken what I was doing either.
If not the SACD player then that, to me, leaves the amp power cord or the speaker cable.
I will over the coming days reconnect the turntable and AV input (the old amp I am currently using does not have HT Bypass so I was thinking of just sticking into an input and slowly turning up the volume from zero until it sounds about right as a temp solution - is this safe to do?)
I do not want to connect the SACD player incase it blows my old amp.
Anyone any more thoughts?
 

noiseboy72

Distinguished Member
So 3 potential issues come to mind...

SACD is outputting high frequency signal - well above the threshold of hearing but low enough to be amplified. The speakers could be presenting a very low impedance at this frequency, causing the fault.

SACD is outputting very low frequency - same issues as above.

Powerful RF source nearby is causing instability in the amplifier, causing it to fail.

Unlikely to be power chord or speaker cable, but either could become antennae for RF signals

The only other suggestion would be incorrectly wired mains, so that the earth cable is carrying current for some reason and this is damaging the amplifier. This is highly unlikely in the UK unless some cowboy has been busy with the electrics and has tried to compensate for an error in the wiring elsewhere.
 

sossages

Novice Member
Thank's noiseboy72 for the reply.

All was working perfectly for 6 months.
Nothing changed to cause the issue.
The disk being played each of the 3 times was just a standard CD and, whilst new, had been played the previous day to the 1st time at louder volume no probs.
This, to my unknowledgeable mind rules out high / low frequency output albeit I am happy to stand corrected.
What would be a powerful RF source?
None of the sources had changed in the 6 months
Mains has been checked by an electrician and is good and everything else on it is working fine. Furthermore both the amp and the SACD player factory supplied leads have plastic earth pins in the mains plug and only live and neutral into them. I don't know how they are earthed.
 

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