Hi all ,
I recently sold my NC400 amp to a buyer who doesn't know much about it and bought first... then asked questions later. And now it's cutting out after an hour's use at high volume.
Could I run my theory past people on what is going on and get opinion on whether this would cause the problem?
1) He's running from a pre-amp with single ended outputs and using a cable to connect to the XLR inputs. I don't know what pre-amp this is (am waiting for a reply) but I'm going to say that whatever it is, the NC400s are at most only getting half their required input voltage from the single-ended pre-amp and so the result will be the output to the speakers will be quiet - so he'll be turning the volume way up to compensate.
2) He bought some Magnepan 3.5rs *afterwards* to match with the NC400s. These are 84db sensitivity and a difficult load. So at the best of times, they're going to again play quietly due to the low sensitivity and the 26dB gain of the NC400s (the Magnepans probably need a much high gain amp).
So, given 1) and 2), he's having to wack the volume all the way up to play at loud volumes, pushing NC400s to their limits into a difficult load and so at their extremes for thermal dissipation/load.
The DIY build for my NC400 was for average use and only uses the aluminium casing for cooling, with vents only above the power supplies. The NC400 modules themselves are in seperate sections of the case.
Essentially, the amp build doesn't have cooling for extreme use and on top, this guy's partnering equipment is a worse-case scenario and he's pushing it to the limits with bad matching , mostly with the pre-amp.
Could anyone say if my thoughts sound correct?
I recently sold my NC400 amp to a buyer who doesn't know much about it and bought first... then asked questions later. And now it's cutting out after an hour's use at high volume.
Could I run my theory past people on what is going on and get opinion on whether this would cause the problem?
1) He's running from a pre-amp with single ended outputs and using a cable to connect to the XLR inputs. I don't know what pre-amp this is (am waiting for a reply) but I'm going to say that whatever it is, the NC400s are at most only getting half their required input voltage from the single-ended pre-amp and so the result will be the output to the speakers will be quiet - so he'll be turning the volume way up to compensate.
2) He bought some Magnepan 3.5rs *afterwards* to match with the NC400s. These are 84db sensitivity and a difficult load. So at the best of times, they're going to again play quietly due to the low sensitivity and the 26dB gain of the NC400s (the Magnepans probably need a much high gain amp).
So, given 1) and 2), he's having to wack the volume all the way up to play at loud volumes, pushing NC400s to their limits into a difficult load and so at their extremes for thermal dissipation/load.
The DIY build for my NC400 was for average use and only uses the aluminium casing for cooling, with vents only above the power supplies. The NC400 modules themselves are in seperate sections of the case.
Essentially, the amp build doesn't have cooling for extreme use and on top, this guy's partnering equipment is a worse-case scenario and he's pushing it to the limits with bad matching , mostly with the pre-amp.
Could anyone say if my thoughts sound correct?
Sounds like it's shutting down from overheating. Maybe a small fan placed in the right location
would help enough. Probably not a preamp problem, though.
Take the amp back and refund money, you both made a mistake and the only solution is to make it "never happened".
You made a "barely heatsinked" amplifier so it will handle many situations but not all by any means and he has a difficult load which not many amplifiers will handle.
Since you will NOT fit larger heatsinking and a fan and he will NOT stop using his magneplanars, only solution is to backtrack on the deal, both of you.
Then you can happily sell your amp to a more "normal" user and he can pursue a beefier than normal amp.
Keeping everything as it´s today will make both of you unhappy, not worth it.
You made a "barely heatsinked" amplifier so it will handle many situations but not all by any means and he has a difficult load which not many amplifiers will handle.
Since you will NOT fit larger heatsinking and a fan and he will NOT stop using his magneplanars, only solution is to backtrack on the deal, both of you.
Then you can happily sell your amp to a more "normal" user and he can pursue a beefier than normal amp.
Keeping everything as it´s today will make both of you unhappy, not worth it.
Those are wise words JM !
I bought the amp myself from a fellow DIYAudio-er , but yes it's ok for most situations but not his.
I think I am wrong about the pre-amp part - it would explain why he complained it was quieter than the Quad 909 he bought instead (because he can't get enough output from the pre-amp), but the NC400s will only work as hard as the input signal its actually getting I guess.
The annoying thing is that I will be forced to pay for return postage by ebay. I didn't want to sell my amp but I needed some money after a slow few months of work - to pay rent etc.. So now I have to find the money again AND loose money on the postage.
All the more annoying because he didnt ask me any questions about the amp, and then bought the Magnepans *after* he'd bought the amp anyway...
I bought the amp myself from a fellow DIYAudio-er , but yes it's ok for most situations but not his.
I think I am wrong about the pre-amp part - it would explain why he complained it was quieter than the Quad 909 he bought instead (because he can't get enough output from the pre-amp), but the NC400s will only work as hard as the input signal its actually getting I guess.
The annoying thing is that I will be forced to pay for return postage by ebay. I didn't want to sell my amp but I needed some money after a slow few months of work - to pay rent etc.. So now I have to find the money again AND loose money on the postage.
All the more annoying because he didnt ask me any questions about the amp, and then bought the Magnepans *after* he'd bought the amp anyway...
I have a set of Mono NC400 amps. They have no additional cooling, and I live in Sydney so they get reasonably hot. I also leave them on 24x7 and run Scanspeak 32w 13" subwoofers with them.
I did have an issue with one of them cutting out occasionally, and then a few months later it started cycling on startup (click,click...). I swapped the power supplies between the 2, and found it was the PS that was causing the issue. I contacted Hypex and they were extremely helpful and responded to emails almost instantly. They said it was a fault (random failure), and unlikely to be related to the heat. I sent the PS to them and they fixed for around 40 euros. Have not had a problem since. Might be worth contacting Hypex for advice
I did have an issue with one of them cutting out occasionally, and then a few months later it started cycling on startup (click,click...). I swapped the power supplies between the 2, and found it was the PS that was causing the issue. I contacted Hypex and they were extremely helpful and responded to emails almost instantly. They said it was a fault (random failure), and unlikely to be related to the heat. I sent the PS to them and they fixed for around 40 euros. Have not had a problem since. Might be worth contacting Hypex for advice
Why not just tell the buyer to put on a larger heatsink and be done?? There's nothing wrong with the amp!
Jan
More than likely the PSU is not running at full power and causing the issue.
NC400s are quite robust.
Just as an aside, under EU law, if it is "random failure" and less than 7 years old, (a reasonable amount of time the amplifier should last with no issues), it should have been repaired for free as components do not fail at random unless they are sub standard.
NC400s are quite robust.
Just as an aside, under EU law, if it is "random failure" and less than 7 years old, (a reasonable amount of time the amplifier should last with no issues), it should have been repaired for free as components do not fail at random unless they are sub standard.
It's e-bay plus the OP has outgoings.
Random rich HI-FI DONG buys expensive stuff off e-bay then says MEH having bought replacement expensive amp to match his expensive MagnaWanks.
Random rich DONG uses paypal protection to stiff the original seller.
If it were not for the amount of cash involved and the sellers circumstances then, depending on the clarity of the advert, I would advise the seller to tell the buyer "You bought it. You own it." but in nicer terms.
I regularly suck my £50 mistakes on e-bay.
https://www.diyaudio.com/forums/members/natdberg.html
PM your paypal address and I'll drop you £50 to politely tell Mr DONG to get lost and explain why he should do so. If you lose you keep my money. If you win you pay me back.
Assuming £900 you only need another 17 supporters. Ask someone more rational to help you with the process and words.
Anyone else up?
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