The hum may be a characteristic of the amp... yes it should be silent but many amps aren't. If its a deep pure 50hz tone then it could be induced hum from the field of the transformer, if there is any harshness to it (so a buzz and not a pure tone) then it could be many things, poor PCB layout and grounding internally, or it could be a dried up cap somewhere. Hard to say. It may well be "normal" for that amp.
I see,well it's not a pure tone it's definitely a buzz, so I guess it could be many of the things you've suggested .I'll just see if I can live with it,if not I'll investigate further.My main concern was,is it a dangerous?but I guess that's difficult to answer unless you hear it yourself?.Maybe I'll pop it into a repair shop to see what they think.
Is there test I could do to identify a faulty/dried-up capacitor .
thanks
dean
Is there test I could do to identify a faulty/dried-up capacitor .
thanks
dean
A scope is the best tool for fault-finding, including looking at any ripple voltage across caps. Many just change all the electroylitics as a matter of course but its nice to find the fault properly.
Its almost certainly not dangerous unless there is some unknown history to it (ebay special that's been modded and worked on etc).
Ultimately, and without figures to work to, its impossible to say whether its actually faulty or not, but hum shouldn't be noticeable at more than a couple feet or so from the speakers.
Its almost certainly not dangerous unless there is some unknown history to it (ebay special that's been modded and worked on etc).
Ultimately, and without figures to work to, its impossible to say whether its actually faulty or not, but hum shouldn't be noticeable at more than a couple feet or so from the speakers.
I'm guessing, but is your NVA A20 from these people? NVA Index Frame
I'm also guessing that this NVA amplifier is a lot younger than the AU101, <15 years and as such, with a small power supply and amplifiers, I wouldn't expect it to run even warm. So, with the usual suspects for a buzzing hum in both channels being the main power supply electrolytics, I'm thinking it's a bit soon for that fault to show up. If it is in fact the same manufacturer, the assembly of these products is pretty radical - nothing like conventional amplifiers and more like DIY "valve style wiring, if the product blurb is anything to go by.
Usually, amplifier buzzes develop over time. All is fine for many years then slowly over weeks or months, or after extended storage, a buzz develops and increases to a heavy buzzing din that destroys speakers, if not the fuses or output semis first. That developing noise is consistent with the way electrolyte vaporizes and escapes slowly at first from the caps. but as more escapes, the temperature rises and the process accelerates as more of the electrolyte passes through the unavoidable, even molecular size gaps in the casing and seal.
One never knows what quality components are used in domestic audio products. There are many small operations in the UK that don't show up on the radar here but probably enjoy a lot of local and european popularity. Some UK products I have come across are well enough constructed - perhaps too well to be competitive, but others have been really strange with very disappointing economy cuts made into the key areas of what most would call good power amplifier design. Can't say about this one - I know little about it and a schematic is unlikely but an inside pic would be nice.
I'm also guessing that this NVA amplifier is a lot younger than the AU101, <15 years and as such, with a small power supply and amplifiers, I wouldn't expect it to run even warm. So, with the usual suspects for a buzzing hum in both channels being the main power supply electrolytics, I'm thinking it's a bit soon for that fault to show up. If it is in fact the same manufacturer, the assembly of these products is pretty radical - nothing like conventional amplifiers and more like DIY "valve style wiring, if the product blurb is anything to go by.
Usually, amplifier buzzes develop over time. All is fine for many years then slowly over weeks or months, or after extended storage, a buzz develops and increases to a heavy buzzing din that destroys speakers, if not the fuses or output semis first. That developing noise is consistent with the way electrolyte vaporizes and escapes slowly at first from the caps. but as more escapes, the temperature rises and the process accelerates as more of the electrolyte passes through the unavoidable, even molecular size gaps in the casing and seal.
One never knows what quality components are used in domestic audio products. There are many small operations in the UK that don't show up on the radar here but probably enjoy a lot of local and european popularity. Some UK products I have come across are well enough constructed - perhaps too well to be competitive, but others have been really strange with very disappointing economy cuts made into the key areas of what most would call good power amplifier design. Can't say about this one - I know little about it and a schematic is unlikely but an inside pic would be nice.
ICan't say about this one - I know little about it and a schematic is unlikely but an inside pic would be nice.
Inside pics: Recapping and tweaking a Sansui AU-101 - DIY Audio Projects - StereoNET Australia
Schematic: http://i.imgur.com/fQZGvVI.jpg
Thanks for the links but the OP has changed to the NVA A20 model (or is that AP20?) and he's looking for help with buzzing sound from it. I've seen a schematic of a much larger model but if you've seen pics of the earlier AP10 model, you'll know that repairs won't be fun. These have no coil, relay protection, limiters - nothing and they are glued together, even the the BDV66/67 darlington transistors (onto the baseplate)
I guess that's out of my limits,I don't even know what a "scope" is let alone "ripple voltage"
and it's probably an expensive tool too!I think I'm wading in to deep and need to get back to shallows
The chap told me that it had gone back to NVA to have a volume pot fitted about 2yrs ago.I should imagine the manufacture would have tested it then
I can easily hear it from anywhere in my 5 metre length room !
Took it to my friends house,can hear it there as well
Hi Ian,yeah that's the company.Apparently the amp is about 20yrs old and it runs as cool as a cucumber. The amp doesn't have any screws so I can't get the lid-off but here's a picture of a smaller AP10 integrated of similar age.
Redirect Notice
Uh oh ! what have I bought,I know £25 may not seem like a lot of money for an amp but if it's useless then I've lost £25
Actually ,that's a great linkQuote:
Originally Posted by Ian Finch
ICan't say about this one - I know little about it and a schematic is unlikely but an inside pic would be nice.
Inside pics: Recapping and tweaking a Sansui AU-101 - DIY Audio Projects - StereoNET Australia
Schematic: http://i.imgur.com/fQZGvVI.jpg
because I've still got to recap the Sansui AU-101 for my friend.cheers guys
Dean
'scope = oscilloscope. The single most useful piece of test equipment you can own imo. It shows voltage with respect to time in a screen so allowing you to "see" voltages that are dynamic and changing.If you can hear the buzz at 5m then that's not acceptable... and its hard to say that kind of level would be normal for the amp to. I can't really suggest anything easy for you try on this. Replacing caps in the hope it might fix it isn't really the way to go.
I've no easy answers on that one I'm afraid.
From what I have been dredging up, the schematic is not quite as simple as it looks; There is a very fancy, enhanced, 9 transistor voltage amp. there, which appears to be the same on the smallest to the larger models too, like the A70 schematic posted in this thread by Duncan F: http://www.diyaudio.com/forums/solid-state/212450-beefing-up-nva-ap10p-amp.html
Note , there are no adjustments or protection circuits on these DC coupled amps either,
so like Naim amplifiers, they rely on suitable speaker leads for stability, or so the story goes.
The output transitors, smoothing capacitors and transformer are all glued to the aluminium baseplate too, and being close, they will all be sharing whatever heat there is to go around. This is sure radical construction .
Note , there are no adjustments or protection circuits on these DC coupled amps either,
so like Naim amplifiers, they rely on suitable speaker leads for stability, or so the story goes.
The output transitors, smoothing capacitors and transformer are all glued to the aluminium baseplate too, and being close, they will all be sharing whatever heat there is to go around. This is sure radical construction .
I'm speechless. Its like the best of the worst efforts of an enthusiastic diyer. In some ways it reminds me of the "all glue and sellotape" construction of the ubiquitous 1980's / 1990's cheapo music centres.
and I thoought my 1970's Keletron KSA1500 was cheap, it was built like a tank compared to that NVA P.O.S. Got me thinking about 1970's budget amps, Remember the AMS 8000 MkII ? That was about the cheapest I new of. The AU101 was the entry level proper amp as I remember it. I'm talking impoverished student / paper boy budgets here!
Thank you once again for your interest guys.
So,I guess you think that due to it’s design there was an inevitability that it was going cause future problems ie buzzing
I guess this designer sees “metal” as an enemy with all the glue used. I don’t know diddly-squat about amplifier design but I do question if such “radical application” can really make that much of a difference in terms of sound quality ,but on the other hand, I must admit, to me the amplifier sounds good, it manages to dig deeper into the recording than most amplifiers I’ve heard, easily presenting you the differences in recording quality, be it CD or Vinyl and sounds smooth from top to bottom.
The question is, is it “safe” to keep it and is it worth having it repaired? That’s if I can find anyone, because at the moment no-one seems to want to touch it .Can anyone recommend a repairist in the UK
I’ve taken the plunge and managed to open it up, here’s what it looks like inside.
So,I guess you think that due to it’s design there was an inevitability that it was going cause future problems ie buzzing
I guess this designer sees “metal” as an enemy with all the glue used. I don’t know diddly-squat about amplifier design but I do question if such “radical application” can really make that much of a difference in terms of sound quality ,but on the other hand, I must admit, to me the amplifier sounds good, it manages to dig deeper into the recording than most amplifiers I’ve heard, easily presenting you the differences in recording quality, be it CD or Vinyl and sounds smooth from top to bottom.
The question is, is it “safe” to keep it and is it worth having it repaired? That’s if I can find anyone, because at the moment no-one seems to want to touch it .Can anyone recommend a repairist in the UK
I’ve taken the plunge and managed to open it up, here’s what it looks like inside.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
I'm even more speechless now
If the buzzing is down to a component fault then it can only realistically be a cap or remotely, the bridge rectifier, and you could replace them all for a few pounds. Looking at the build quality (or lack of it... I'm sorry but its truly dreadful tbh) then the buzzing may well be normal. The grounding looks to be all over the place.
Is it safe... well I don't think it would pass any modern safety tests. Its probably safe as long as there are no faults... which is a contradiction in terms but you know what I mean. If the switch came apart or a wire came loose... zap Its unshielded and unprotected. Is the case earthed via the mains lead ? I can't see a third core.
If the unit has value (because of what it is) then I would sell it and move on tbh.
If the buzzing is down to a component fault then it can only realistically be a cap or remotely, the bridge rectifier, and you could replace them all for a few pounds. Looking at the build quality (or lack of it... I'm sorry but its truly dreadful tbh) then the buzzing may well be normal. The grounding looks to be all over the place.
Is it safe... well I don't think it would pass any modern safety tests. Its probably safe as long as there are no faults... which is a contradiction in terms but you know what I mean. If the switch came apart or a wire came loose... zap
Its unshielded and unprotected. Is the case earthed via the mains lead ? I can't see a third core.If the unit has value (because of what it is) then I would sell it and move on tbh.
You're going to love this and Mooly will probably be struck completely dumb this time.....
The cable is 3-core but the earth wire (I'm fairly certain) is snipped off flush with the PVC outer sheath.
I don't know the rules for the UK but ours have slavishly followed them for the best part of a century and those wiring practices would just not be permitted for a retail domestic appliance. To be fair, DIYs around the world have been building worse and having it last for decades without incident but a customer should not receive something in that condition after money changes hands. Considering his background, its not like the manufacturer isn't aware of how it should be done so this is flagrant disregard, however wonderful the concept and sound quality.
The cable is 3-core but the earth wire (I'm fairly certain) is snipped off flush with the PVC outer sheath.
I don't know the rules for the UK but ours have slavishly followed them for the best part of a century and those wiring practices would just not be permitted for a retail domestic appliance. To be fair, DIYs around the world have been building worse and having it last for decades without incident but a customer should not receive something in that condition after money changes hands. Considering his background, its not like the manufacturer isn't aware of how it should be done so this is flagrant disregard, however wonderful the concept and sound quality.
Appalling, ugh.. Don't even know where to start, but that thing should be tossed in the nearest trash can..
Transistors and rectifier not bolted to chassis, no fuse, no safety ground, no strain relief on the cord, uninsulated flimsy bus wire carrying power all over the place.
Rectifier is not located electrically in the right place - should be connected directly to filter caps with no intervening common wiring unless you want excessive ripple on the rails.
The fact that this thing has not self-immolated and perhaps burned down the residence where it was used is a miracle. Total rebuild required just to address the safety issues...
Transistors and rectifier not bolted to chassis, no fuse, no safety ground, no strain relief on the cord, uninsulated flimsy bus wire carrying power all over the place.
Rectifier is not located electrically in the right place - should be connected directly to filter caps with no intervening common wiring unless you want excessive ripple on the rails.
The fact that this thing has not self-immolated and perhaps burned down the residence where it was used is a miracle. Total rebuild required just to address the safety issues...
You're going to love this and Mooly will probably be struck completely dumb this time.....
The cable is 3-core but the earth wire (I'm fairly certain) is snipped off flush with the PVC outer sheath.
What can one say
Answer... not a lot !I think Kevin summed it rather well
I hope their build quality has improved because NVA is still active and selling on ebay:
NVA Index Frame
Read that bit about 'special casework' - still glueing then.
NVA Index Frame
Read that bit about 'special casework' - still glueing then.
Thinking about that buzzing noise and the 'special casework' I am reminded of odd situations where I've had buzzing from an amplifier or other audio gadget on the bench.
When there is no earthed shield, noise from around the area is often higher and the circuit has to be earth referenced somewhere but modern input sources like players are floating by design too - the expectation being that the amplifier provides a single point, safety earth reference for the whole audio system electronics. Often a system can be earthed at the wrong end and noisy - like via an old record player, where hum increases dramatically due to earth loops too, even when the phono option is not selected. Player earthing was via a flimsy chassis interconnection wire between the player and the amplifier, a dicey arrangement that would not function here at all.
You need to be wary of fitting older design equipment to new or oddball equipment and this may be a case where a problem shows up in external noise. So what have you got to lose by checking around the vicinity, like within a room's distance all round for possible noise sources? Check electronic power supplies used in PCs, low voltage lighting power, TVs, equipment on standby even and many modern appliances. Don't forget light dimmers, aquarium pumps, kitchen appliances, battery chargers and so on and if your neighbours are close by, they may have something noisy too.
My bench lighting for many years, was an unshielded 4' fluorescent light and this caught me out many times with buzzing sounds, noise like hash with tuners, communications gear etc. The audio system is an aerial when it is completely ungrounded so maybe the time spent turning off a few nearby gadgets, one after the other, could be a simple and worthwhile check.
With all input leads removed and the system cut back to just the amplifier and speakers, many other possibilities are removed. An electrolytic capacitor (the big ones) then becomes one of the remaining and more likely faults as suggested. Why not try some more simple things first, as it costs nothing.
Nice pics again, BTW
When there is no earthed shield, noise from around the area is often higher and the circuit has to be earth referenced somewhere but modern input sources like players are floating by design too - the expectation being that the amplifier provides a single point, safety earth reference for the whole audio system electronics. Often a system can be earthed at the wrong end and noisy - like via an old record player, where hum increases dramatically due to earth loops too, even when the phono option is not selected. Player earthing was via a flimsy chassis interconnection wire between the player and the amplifier, a dicey arrangement that would not function here at all.
You need to be wary of fitting older design equipment to new or oddball equipment and this may be a case where a problem shows up in external noise. So what have you got to lose by checking around the vicinity, like within a room's distance all round for possible noise sources? Check electronic power supplies used in PCs, low voltage lighting power, TVs, equipment on standby even and many modern appliances. Don't forget light dimmers, aquarium pumps, kitchen appliances, battery chargers and so on and if your neighbours are close by, they may have something noisy too.
My bench lighting for many years, was an unshielded 4' fluorescent light and this caught me out many times with buzzing sounds, noise like hash with tuners, communications gear etc. The audio system is an aerial when it is completely ungrounded so maybe the time spent turning off a few nearby gadgets, one after the other, could be a simple and worthwhile check.
With all input leads removed and the system cut back to just the amplifier and speakers, many other possibilities are removed. An electrolytic capacitor (the big ones) then becomes one of the remaining and more likely faults as suggested. Why not try some more simple things first, as it costs nothing.
Nice pics again, BTW
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