hi,
I have the following setup:
preamp: nakamichi CA5
amp: nakamichi PA5
speakers: infinity modulus (1990)
recently one of the infinitys burned down, and I had it recoiled by a local guy who has been doing this for 30 years.
after 2 minutes of playing... it burned down again.
now, I'm suspicious that there might be a problem with my amp, or preamp. and I want to make sure it will work, as the guy who recoiled it was more sad about it than me (the guy takes pride in his work)
I tried hooking a different speaker to the amp, and it produces sound as it should, but I only had it hooked up for a few seconds to make sure that it still produces sound.
I tried measuring DC voltage on Amp Output and its about 25-30 mV on idle, but it goes up to 100mV when I play some music, but I need to double check that, since the measurement was done while the whole thing is still in rack, and wasn't accessible as it should, so there might be a measurement fckup on my part.
DC voltage on Preamp output is below 10mV, but also, I'd like to have another go at measurement (Get a new multimeter, and measure the amps, as attm, I'm getting 0.00 mA on both amp and preamp)
I'm not sure what else I can do to make sure that the Amp/Preamp are in working order.
the amp and preamp are 100% original and mint... and don't want to tamper it unless I'm sure it needs tampering.
please refrain from: have it serviced comments. Comment only if you actually know something about servicing and electronics.
I have the following setup:
preamp: nakamichi CA5
amp: nakamichi PA5
speakers: infinity modulus (1990)
recently one of the infinitys burned down, and I had it recoiled by a local guy who has been doing this for 30 years.
after 2 minutes of playing... it burned down again.
now, I'm suspicious that there might be a problem with my amp, or preamp. and I want to make sure it will work, as the guy who recoiled it was more sad about it than me (the guy takes pride in his work)
I tried hooking a different speaker to the amp, and it produces sound as it should, but I only had it hooked up for a few seconds to make sure that it still produces sound.
I tried measuring DC voltage on Amp Output and its about 25-30 mV on idle, but it goes up to 100mV when I play some music, but I need to double check that, since the measurement was done while the whole thing is still in rack, and wasn't accessible as it should, so there might be a measurement fckup on my part.
DC voltage on Preamp output is below 10mV, but also, I'd like to have another go at measurement (Get a new multimeter, and measure the amps, as attm, I'm getting 0.00 mA on both amp and preamp)
I'm not sure what else I can do to make sure that the Amp/Preamp are in working order.
the amp and preamp are 100% original and mint... and don't want to tamper it unless I'm sure it needs tampering.
please refrain from: have it serviced comments. Comment only if you actually know something about servicing and electronics.
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I'm hoping for a rule of thumb diagnostics, at least so I know what to have serviced. Amp or preamp.
I know my way around the electronics for basic diagnostics... but since the amp is "technically working" as it produces sound, its a bit harder to diagnose the cause than if it was an obvious "dead channel", as the fault might not be showing symptoms continuously, but occasionally.
I know enough that I should check the Power Capacitors (but I think they are fine), and the Bridge rectifier... but I guess that's fine as well, or it would not work at all.
but I'd like to know more of the "usual suspects" before going around with a 15-20 kg amp that might not be faulty to begin with.
also, is the Nac pa5 equipped with some sort of "DC filter" cap? and which one it is?
I know my way around the electronics for basic diagnostics... but since the amp is "technically working" as it produces sound, its a bit harder to diagnose the cause than if it was an obvious "dead channel", as the fault might not be showing symptoms continuously, but occasionally.
I know enough that I should check the Power Capacitors (but I think they are fine), and the Bridge rectifier... but I guess that's fine as well, or it would not work at all.
but I'd like to know more of the "usual suspects" before going around with a 15-20 kg amp that might not be faulty to begin with.
also, is the Nac pa5 equipped with some sort of "DC filter" cap? and which one it is?
If only one channel is out, you can compare, and find the defective parts.
However, get the schematics and service manuals first, and they were not sold in large volumes, parts may not be easy to obtain.
After the faulty part is found, I would change them on both sides, after a burn in to check faulty channel is OK, doing the working channel later.
Insurance, as the other channel may fail later.
However, get the schematics and service manuals first, and they were not sold in large volumes, parts may not be easy to obtain.
After the faulty part is found, I would change them on both sides, after a burn in to check faulty channel is OK, doing the working channel later.
Insurance, as the other channel may fail later.
the thing is... on output... it all looks the same.
25 mV - 30mV DC current on idle (rises a bit with warmup).
and I wanna be sure its not a "occasional fault"... that happens on high frequencies... low frequencies,... or only when Madonna sings.
suspect oscillations of power amp
most likely from amp itself but, then, less likely resulting from preamp
signal generator, dummy load, Scope time
if you have those, go for it
if not, have it serviced
most likely from amp itself but, then, less likely resulting from preamp
signal generator, dummy load, Scope time
if you have those, go for it
if not, have it serviced
Did you get a sound from the speakers when they burned?
Bang or loud buzzing?
If you did, could be DC on the output caused by an intermittent connection, dry joint, faulty pot etc.
Could be worth fitting a sacrificial resistor * in series with the speakers and tapping the board, pots etc. with a plastic pen or screwdriver handle to see if you can find it
* 47 ohm would still allow you to hear any problem without damaging the speaker, though I would use a sacrificial speaker too if you have one
Brian
Bang or loud buzzing?
If you did, could be DC on the output caused by an intermittent connection, dry joint, faulty pot etc.
Could be worth fitting a sacrificial resistor * in series with the speakers and tapping the board, pots etc. with a plastic pen or screwdriver handle to see if you can find it
* 47 ohm would still allow you to hear any problem without damaging the speaker, though I would use a sacrificial speaker too if you have one
Brian
Hook a DC coupled scope to output and leave it there.
Play music while watching screen all the time.
Whatever is killing your speaker WILL be visible there, we are dealing with physical/material stuff, not ghosts.
Intermittent DC? Oscillation? Any and all will be visible in that screen.
As a side note: impolite comments such as:
Play music while watching screen all the time.
Whatever is killing your speaker WILL be visible there, we are dealing with physical/material stuff, not ghosts.
Intermittent DC? Oscillation? Any and all will be visible in that screen.
As a side note: impolite comments such as:
will quickly drain any goodwill initially assigned to beginners.
Sadly not such a thing, it´s only wishful thinking, you need actual troubleshooting ... as in scoping output.
I apologize. It was not meant to be an insult, or merely for my benefit.
I wouldn't have bothered editing that in, had the first comment not had been "you need a technician for that - use cheap headphones" from a guy with 18k posts.
Its like going to a racing forum, and someone tells you you need a 4 wheels and a driving license for that.
I don't mind reading such comments, but I'm somewhat of a forum geek (not just here) and I have high appreciation for people who contribute quality content. when reading 10 year old posts, its nice to see structure and condensed knowledge (and who knows, in 10 years someone might find this thread)... and on the matter of electronics, many of threads such as these I find educational... and posts for the sake of posting are disrespectful not as much to the OP, but to the people who actually know and contribute in educational and quality way like you your self just did... you taught me that I actually need to get an oscilloscope and learn to use it, to learn about intermittent current as cause, Oscilations,... as you took time to elaborate on your recommendations.
Maybe not for the case at question... but for the sake of curiosity, as in the long run, I'd like to be able to learn something about electronics, and every time something breaks down... I like to take the opportunity to understand something new.
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Glad to hear that. 🙂
In a nutshell, nobody can guess what´s the perticular broken/bad component, specially not having an schematic to begin with.
Not dissing car mechanics by any means, a whole World on their own, but there some generic questions often bring useful "universal/generic" answers; say you ask "my engine coughs and rattles at low speed" and somebody could answer "check gasoline filter or fuel injectors" or depending on where you live "you might have some water condensation in your tank" or something to that effect.
And the problem is sometimes visible to the naked eye.
But in Electronics, we usually have dozens or even 100 components interacting, and we "see" nothing without instruments, so guessing an answer is difficult.
IF you can scope output, better, because anything which can damage your speakers will appear there, from DC to subsonics to Audio to ultrasounds to RF.
And STILL somebody must troubleshoot it .
What did actually happen to your speaker?
"Forensics" and all that, I use it all the time.
Evenly burnt and destroyed VC: plain excess power:
Half lightly toasted half burnt: DC pushed it fully 1 way, what stayed inside the gap was somewhat cooler:
In a nutshell, nobody can guess what´s the perticular broken/bad component, specially not having an schematic to begin with.
Not dissing car mechanics by any means, a whole World on their own, but there some generic questions often bring useful "universal/generic" answers; say you ask "my engine coughs and rattles at low speed" and somebody could answer "check gasoline filter or fuel injectors" or depending on where you live "you might have some water condensation in your tank" or something to that effect.
And the problem is sometimes visible to the naked eye.
But in Electronics, we usually have dozens or even 100 components interacting, and we "see" nothing without instruments, so guessing an answer is difficult.
IF you can scope output, better, because anything which can damage your speakers will appear there, from DC to subsonics to Audio to ultrasounds to RF.
And STILL somebody must troubleshoot it .
What did actually happen to your speaker?
- Blown woofer?
- What about the tweeter?
"Forensics" and all that, I use it all the time.
Evenly burnt and destroyed VC: plain excess power:
Half lightly toasted half burnt: DC pushed it fully 1 way, what stayed inside the gap was somewhat cooler:
Oh, thank JBL who published a "forensic gallery" showing all the damage causes you could "read" by looking at a damaged voice coil.
Also showing foreign matter in the gap, scratching because of misalignment, bumping against the back plate and other horrors.
Rodd Elliott also has a page on it.
Both worth reading.
Also showing foreign matter in the gap, scratching because of misalignment, bumping against the back plate and other horrors.
Rodd Elliott also has a page on it.
Both worth reading.
Or a big electrolytic cap in series from output to speaker + and then speaker - to negative rail.
As I do a lot of design and testing I use a stand alone speaker DC protect unit, it must have saved me a fortune over the years.
Hi, I have repaired many speakers, but never seen a voice coil like that! Looks very odd, with the wire all loose, while not appearing overheated (in this pic at least). But the paper former does look burnt.
I wonder if the coil was properly epoxied/laquered?..
I don't see how that can "just happen" - you should have been able to hear something was not quite right - before complete destruction.
Oscillation in amplifier was suggested above somewhere, but that should not (normally) affect a woofer - as it is more or less immune to high frequency signals.
It might have been more interesting to see the original voicecoil, and what the failure mode on that was.
Also, in my experience it rarely makes sense to try and replace a voice coil on a small (relatively cheap) woofer. Usually better to replace both woofers with new suitable units - and adjust the crossover if need be.
I wonder if the coil was properly epoxied/laquered?..
I don't see how that can "just happen" - you should have been able to hear something was not quite right - before complete destruction.
Oscillation in amplifier was suggested above somewhere, but that should not (normally) affect a woofer - as it is more or less immune to high frequency signals.
It might have been more interesting to see the original voicecoil, and what the failure mode on that was.
Also, in my experience it rarely makes sense to try and replace a voice coil on a small (relatively cheap) woofer. Usually better to replace both woofers with new suitable units - and adjust the crossover if need be.
As above... a plethora of Substandard bits. Been doing this Audio Nonsense since 1966.
NEVER had a failure and certainly not even seen anything like yours!
Bin all the crap /timed out pieces you have ..and Start over.
I certainly would
NEVER had a failure and certainly not even seen anything like yours!
Bin all the crap /timed out pieces you have ..and Start over.
I certainly would
I am by no means an amp technician but I think if the amp had gone DC it would have fried the tweeter as well. I can see burnt wire in the voice coil and what looks to be damage to the voice coil former. I suspect what happened was the voice coil came unraveled due to lack of epoxy and got jammed up in the magnetic gap and fried. Doubt it has anything to do with the amp. Hook up a sacrificial speaker and play it for a while and see if you have any problems. Make sure it has the same impedance though so it drives the amp the same.
'recently one of the infinitys burned down, and I had it recoiled by a local guy who has been doing this for 30 years.
after 2 minutes of playing... it burned down again.'
Tweeters have crossover caps, that would have saved them from DC.
It is an amp fault, not what the above poster thinks...
after 2 minutes of playing... it burned down again.'
Tweeters have crossover caps, that would have saved them from DC.
It is an amp fault, not what the above poster thinks...
Like I said, hook up a sacrificial speaker and play it for a while. If it is the amp it should reveal it's self. Judging by the way the voice coil failed I think there was a mechanical failure. I see vary little charring of the wire and almost no epoxy.
To the OP I have a couple of questions. Does the destroyed voice coil smell like it was cooked? Has the whole voice coil come unwound? Is there any glue left?