I've just been given an old SS amplifier by another mate.
He says it was loosing power and "definition" and had an intermittent fault where volume rose and fell.
Anybody here with any experience with this model?
I paid for postage [ $38-] but I don't want to muck about too much and a contact would be doing the work not myself. Been listening to it play in the background for a while and I think it's a little "boomy and muddy" in the bass and I had to use the tone controls on the bass all the way down.
Was it made and sold to go with tiny& bass shy speakers back in the 90's?
Not the same quality as other Denon amps I've hefted in the past
He says it was loosing power and "definition" and had an intermittent fault where volume rose and fell.
Anybody here with any experience with this model?
I paid for postage [ $38-] but I don't want to muck about too much and a contact would be doing the work not myself. Been listening to it play in the background for a while and I think it's a little "boomy and muddy" in the bass and I had to use the tone controls on the bass all the way down.
Was it made and sold to go with tiny& bass shy speakers back in the 90's?
Not the same quality as other Denon amps I've hefted in the past
Check its on source direct (ie cutting out the tone controls completely), loudness off before judging the frequency response. That should be flat, and the same as using the tone controls set to 12 o'clock - if not the tone circuit is probably the issue.
Its a perfectly normal amp as far as I can see from the schematic (the service manual is easy to find at least).
It may indeed be failing due to its age, may need some new caps, but the fact its sort of working OK makes it harder to diagnose whether its off-specification.
I'd check the output DC offset (ideally < 0.1V), and that the channels are behaving the same, and that all the controls adjust smoothly (often a clean is needed for switches and pots). Is the heatsink getting hot after idling for a long time (warm is normal, hot might indicate biasing issue)
Can you check the response (ie have an AC voltmeter and signal generator at least)?
Its a perfectly normal amp as far as I can see from the schematic (the service manual is easy to find at least).
It may indeed be failing due to its age, may need some new caps, but the fact its sort of working OK makes it harder to diagnose whether its off-specification.
I'd check the output DC offset (ideally < 0.1V), and that the channels are behaving the same, and that all the controls adjust smoothly (often a clean is needed for switches and pots). Is the heatsink getting hot after idling for a long time (warm is normal, hot might indicate biasing issue)
Can you check the response (ie have an AC voltmeter and signal generator at least)?
Thanx guys.
So far none of the issues my mate reported have surfaced, but I've been driving small 8R speakers and his are Krix Lyrix which are nominally 4R and probably a bit lower.
That boominess may well be a stuck "Loudness" switch but it is one of the amps reported issues in on-line critiques.
Said mate doesn't want the amp back as he now has a new Rotel A-14.
I'll leave it powered up for a while today and see if it gets hot and if one side gets hotter than the other. The rest I'll leave to feller that does repairs because I don't have the tools. However on a quick glance inside; the main smoothing caps don't look the same, one is darker than the other and is loose on the board although neither are bulged
So far none of the issues my mate reported have surfaced, but I've been driving small 8R speakers and his are Krix Lyrix which are nominally 4R and probably a bit lower.
That boominess may well be a stuck "Loudness" switch but it is one of the amps reported issues in on-line critiques.
Said mate doesn't want the amp back as he now has a new Rotel A-14.
I'll leave it powered up for a while today and see if it gets hot and if one side gets hotter than the other. The rest I'll leave to feller that does repairs because I don't have the tools. However on a quick glance inside; the main smoothing caps don't look the same, one is darker than the other and is loose on the board although neither are bulged
Assuming the "darker" appearance of one of the power supply caps means that they are dissimilar types, grades or brands etc. then it means the amplifier has likely been fiddled with by a "cheapie" repairer - perhaps even the previous owner or one of his pals.
When we find one side of a balanced dual power supply has a faulty cap, surely logic suggests we should replace the pair, even if the good cap seems to be OK, since they're likely both to have deteriorated due to age (probably ~25years). That isn't necessarily too old for good quality electrolytic caps but this isn't a premium grade product, so they may only be short lifetime (1-2,000 hr rated caps), as you find in budget amplifier models.
A bona fide repairer would ensure that there was at least a balanced waveform response, if not an ideal one, at full rated power. I think that's unlikely with one ailing smoothing cap.
When we find one side of a balanced dual power supply has a faulty cap, surely logic suggests we should replace the pair, even if the good cap seems to be OK, since they're likely both to have deteriorated due to age (probably ~25years). That isn't necessarily too old for good quality electrolytic caps but this isn't a premium grade product, so they may only be short lifetime (1-2,000 hr rated caps), as you find in budget amplifier models.
A bona fide repairer would ensure that there was at least a balanced waveform response, if not an ideal one, at full rated power. I think that's unlikely with one ailing smoothing cap.
I also go along with the comment by MikePP on the source/direct switch. I've seen many amps including my own Technics model, that have miniature, alternate action switches with silver plated contacts there. Silver tarnishes and the resulting film is non-conductive, so you have occasional contact and sound or no sound at all, depending on the state of the surfaces that happen to be in contact at the time. Unless completely sealed, any type of silver contact is a bad idea at signal voltages.
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Ian I was going to have my mate replace both smoothing caps and also go up a voltage and temperature rating but I don't think there is anything else wrong with the amp.
I think the caps are original
Something tells me that the previous owner had insufficient clearance above and around the unit and it simply got too hot
I think the caps are original
Something tells me that the previous owner had insufficient clearance above and around the unit and it simply got too hot
That actually looks like a nice one.
I recently got a free Onkyo from the same era, was the 180wpc top of the line with proprietary cables. It had something wrong in the multitude of circuits that fed the amp, and all of them had power. Not wanting to spend any more time on it, I gutted the front end entirely, just left a pair of rca jacks jumpered to the amp input.
It sits in our shop at work now with a $2 Bluetooth board.
Also have had three free Denons, all have been given a new home. One I attempted to adjust the bias and it went poof, hadn’t seen that before, may have been a bad pot, and likely would’ve helped if I had cycled it a few times before that.
I recently got a free Onkyo from the same era, was the 180wpc top of the line with proprietary cables. It had something wrong in the multitude of circuits that fed the amp, and all of them had power. Not wanting to spend any more time on it, I gutted the front end entirely, just left a pair of rca jacks jumpered to the amp input.
It sits in our shop at work now with a $2 Bluetooth board.
Also have had three free Denons, all have been given a new home. One I attempted to adjust the bias and it went poof, hadn’t seen that before, may have been a bad pot, and likely would’ve helped if I had cycled it a few times before that.
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Yes, the silver oxide I posted before deleting it, was an error of judgement. The process of tarnishing is called oxidation because that's the general class of reaction but it's actually sulphur that gets into the act. In heavy industrial cities and environs, you wind up with a largely silver sulphide film. Yeah, it sounds confusing but a lot of traditional terms and classifications that go back centuries in the Chemistry field, are still in common use today.
I also recall a few threads here where guys were comparing their cat's behaviour near their amplifier when it was somewhere accessible. One guy thought his cat was relieving itself into the amp because of the stench but it turned out to be the Urea-Formaldehyde resin used to bind the old brown "phenolic" type PCBs together. As the amp. warmed up, the smell became more obvious and objectionable.
So strike a match or turn your oven's hotplate up to cherry red then char, don't burn, a bit of an old PCB or a very old, off-white coloured and brittle type electrical fitting and you'll get what I mean
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I also recall a few threads here where guys were comparing their cat's behaviour near their amplifier when it was somewhere accessible. One guy thought his cat was relieving itself into the amp because of the stench but it turned out to be the Urea-Formaldehyde resin used to bind the old brown "phenolic" type PCBs together. As the amp. warmed up, the smell became more obvious and objectionable.
So strike a match or turn your oven's hotplate up to cherry red then char, don't burn, a bit of an old PCB or a very old, off-white coloured and brittle type electrical fitting and you'll get what I mean
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