My NAD 2200PE amp put out a really weird sound when I turned it on a while back. It was hooked up to my passive sub.
I've hooked up my Mp3 as a source later on, and some times it puts out this awful sound, and sometimes it does not. And, it will play music just fine.
I tried it a few nights ago, and it still plays music, no nasty noise. I don't understand what could cause this noise.
If it helps, a few years ago, I turned on the amp for my my sub and discovered the sub was blown. Weeks b/f the sub worked just fine. I replaced the driver, and all was fine for 2 years. That's when, one day, I turn on the amp and that awful noise was coming from the sub.
That's when I put the amp on my workbench where it's been sittin' lonely w/ nothing to do.
Could this be a DC offset thing or a bias adjustment out of whack? This is a class G amp, btw.
I've hooked up my Mp3 as a source later on, and some times it puts out this awful sound, and sometimes it does not. And, it will play music just fine.
I tried it a few nights ago, and it still plays music, no nasty noise. I don't understand what could cause this noise.
If it helps, a few years ago, I turned on the amp for my my sub and discovered the sub was blown. Weeks b/f the sub worked just fine. I replaced the driver, and all was fine for 2 years. That's when, one day, I turn on the amp and that awful noise was coming from the sub.
That's when I put the amp on my workbench where it's been sittin' lonely w/ nothing to do.
Could this be a DC offset thing or a bias adjustment out of whack? This is a class G amp, btw.
Perhaps time contants in the amp are long and it yakes more time to stabilize, whilst the nfb tryes to correct it. An easy solution may be a delayed relay that connect the amp to the lousdpeaker once it is stable. There are many of them available.
This amp has speaker output relays that don't switch on for a few seconds after the power switch has been switched on. That's not it.
The relays are controlled by a TA7317 chip which does appear to monitor the output for 0V. It is conservatively rated at 100W/8R per channel but much more in short bursts. In other words, a big amp. with a small power supply. NAD 2200 SERVICE MANUAL Pdf Download | ManualsLib
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Could it really be the relays? I don't understand how that could be. I even replaced them 3 years ago, as they were known to have a problem w/ their contacts.
Please note: If it helps, a few years ago, I turned on the amp for my my sub and discovered the sub was blown. Weeks b/f the sub worked just fine. I replaced the driver, and all was fine for 2 years. That's when, one day, I turn on the amp and that awful noise was coming from the sub.
That's when I put the amp on my workbench where it's been sittin' lonely w/ nothing to do.
Could this be a DC offset thing or a bias adjustment out of whack? This is a class G amp, btw.
I have the service manual.
Please note: If it helps, a few years ago, I turned on the amp for my my sub and discovered the sub was blown. Weeks b/f the sub worked just fine. I replaced the driver, and all was fine for 2 years. That's when, one day, I turn on the amp and that awful noise was coming from the sub.
That's when I put the amp on my workbench where it's been sittin' lonely w/ nothing to do.
Could this be a DC offset thing or a bias adjustment out of whack? This is a class G amp, btw.
I have the service manual.
I doubt it has much to do with speaker relays, other than if they are switching on and off at the appropriate time and aren't chattering, sparking etc. You need to diagnose the fault properly and using an oscilloscope to see what's happening at the output with a dummy load connected, is the best and simplest way to do it - assuming you know what to look for. If that's all too difficult or expensive, take it to a repairer who knows what they're doing. i.e. they should know a lot more than just how simple class B amplifiers work and they indeed repair audio equipment successfully and professionally.
While thinking about the options, you could verify the marked DC voltages that should be present and check them off on a print of the schematic. That may help to identify if there is a DC fault there and make a start on identifying the area. Note that the supply voltages only switch to the higher levels when the input signal is large enough to require it. It also seems that there were issues in the past and perhaps this problem is just a further step towards failure so I would make sure that the supplies are correct before going further or attempting any sort of change.
While thinking about the options, you could verify the marked DC voltages that should be present and check them off on a print of the schematic. That may help to identify if there is a DC fault there and make a start on identifying the area. Note that the supply voltages only switch to the higher levels when the input signal is large enough to require it. It also seems that there were issues in the past and perhaps this problem is just a further step towards failure so I would make sure that the supplies are correct before going further or attempting any sort of change.
It is a classic aproach to have a large amp with a poor psu. Here is where PMPO ratings was created. Silicon is cheap, iron and copper aren't.
I never had a class G amp at my eyes, but perhaps a bad switching between voltages of the final stage are a bit crazy because bad design, bad caps or the like. So no clear point to indicate from me.
I never had a class G amp at my eyes, but perhaps a bad switching between voltages of the final stage are a bit crazy because bad design, bad caps or the like. So no clear point to indicate from me.
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Like Ian said, do not guess, scope it.
Scope set to DC so you capture both oscillation and DC problems.
See it this way: ONLY way to blow your Subs is by something applied to them.
You need energy and time to damage voice coils, so by actually checking what is being delivered to them, you are in the right path.
Amp class by itself does not mean much, voice coils only know voltage - current- frequency at speaker terminals.
And I guess you *assume* oscillation, yet to be confirmed, "really weird sound" means nothing without further clarification.
Scope set to DC so you capture both oscillation and DC problems.
See it this way: ONLY way to blow your Subs is by something applied to them.
You need energy and time to damage voice coils, so by actually checking what is being delivered to them, you are in the right path.
Amp class by itself does not mean much, voice coils only know voltage - current- frequency at speaker terminals.
And I guess you *assume* oscillation, yet to be confirmed, "really weird sound" means nothing without further clarification.
What type of specs do I need a scope to have to measure wave-forms and what not?
Is it OK if to save money, I buy a scope that can only measure/test one channel at a time?
Take a look at this scope sold on Amazon. Could it do the things I might have to test/measure?
https://www.amazon.com/dp/B013QQDTF...colid=8BKBTNDQA2SK&psc=1&ref_=lv_ov_lig_dp_it
Is it OK if to save money, I buy a scope that can only measure/test one channel at a time?
Take a look at this scope sold on Amazon. Could it do the things I might have to test/measure?
https://www.amazon.com/dp/B013QQDTF...colid=8BKBTNDQA2SK&psc=1&ref_=lv_ov_lig_dp_it
One of the most important specs to check is the max sample rate the scope can handle - the one you linked from Amazon goes up to 25MHz, I don't know what switching rate your power supply/amp runs at.
I got an old analogue Tektronix scope off ebay for about half that price, handles up to 60MHz but being ancient it does take up a lot more bench/cupboard space!
I got an old analogue Tektronix scope off ebay for about half that price, handles up to 60MHz but being ancient it does take up a lot more bench/cupboard space!
All this
You're on a hiding to nothing trying to locate a fault yourself, take it to an engineer who sees them daily,, he'll spot it faster than you ever will (no insult intended), simply because he'll have heard it before, or seen your amp (model) before and know it's weak points.
Speaking as one myself.
The symptoms description doesn't give much away at all by the way.
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Given that subwoofers tend to have rather high inductance wouldn't oscillation be an unlikely cause for it's destruction?
If the amplifier was oscillating at a very high frequency the inductance would cause the impedance to be very high at such a frequency. Very little current would be passed and the voice coils would remain cool.
If the amplifier has DC offset protection then it's unlikely that DC destroyed the sub. Of course the DC offset protection will have its own time constant and the subwoofer voice coil would take time to heat up and die from thermal failure. The time constant should be short enough so that wouldn't happen especially as subwoofers tend to have fairly chunky voice coils. Unless it's really a woofer masquerading as a subwoofer.
The awful noise might be more instructive than you think. It's possible that the amplifier is perfectly stable and that the DC offset protection is functioning normally. The awful noise was low enough in frequency that you could hear it. For a subwoofer this means it's quite low in frequency, as they tend to roll off quickly above ~1kHz or so, so whatever it is isn't the typical high frequency oscillation that amplifiers are prone to - you wouldn't hear this.
It's possible that this is something as simple as a bad solder joint. Something that is fine for 99.9% of the time but occasionally has a problem. Depending on where this is it could cause parts of the circuit to become unstable in ways you wouldn't expect. Maybe one time it would emit a horrible noise, maybe another time the amplifier would send out a burst of DC. Not large enough to melt the voice coils of the subwoofer, before the DC offset protection kicked in, but large enough for it to hit its excursion limits and fail before it does.
The trouble with such a connection is that the DC operating points could measure absolutely fine most of the time making it difficult to fix.
Impact therapy can sometimes help in these cases. You'd want to connect an old speaker to the amplifier, turn it on, and then start tapping components inside the amplifier with something like a wooden chopstick. The idea is that if a component is poorly soldered a tap will upset its connection briefly and make a noise through the speaker. Obviously this could destroy the speaker or blow fuses inside the amp if something really goes wrong, like something falling apart.
If the amplifier was oscillating at a very high frequency the inductance would cause the impedance to be very high at such a frequency. Very little current would be passed and the voice coils would remain cool.
If the amplifier has DC offset protection then it's unlikely that DC destroyed the sub. Of course the DC offset protection will have its own time constant and the subwoofer voice coil would take time to heat up and die from thermal failure. The time constant should be short enough so that wouldn't happen especially as subwoofers tend to have fairly chunky voice coils. Unless it's really a woofer masquerading as a subwoofer.
The awful noise might be more instructive than you think. It's possible that the amplifier is perfectly stable and that the DC offset protection is functioning normally. The awful noise was low enough in frequency that you could hear it. For a subwoofer this means it's quite low in frequency, as they tend to roll off quickly above ~1kHz or so, so whatever it is isn't the typical high frequency oscillation that amplifiers are prone to - you wouldn't hear this.
It's possible that this is something as simple as a bad solder joint. Something that is fine for 99.9% of the time but occasionally has a problem. Depending on where this is it could cause parts of the circuit to become unstable in ways you wouldn't expect. Maybe one time it would emit a horrible noise, maybe another time the amplifier would send out a burst of DC. Not large enough to melt the voice coils of the subwoofer, before the DC offset protection kicked in, but large enough for it to hit its excursion limits and fail before it does.
The trouble with such a connection is that the DC operating points could measure absolutely fine most of the time making it difficult to fix.
Impact therapy can sometimes help in these cases. You'd want to connect an old speaker to the amplifier, turn it on, and then start tapping components inside the amplifier with something like a wooden chopstick. The idea is that if a component is poorly soldered a tap will upset its connection briefly and make a noise through the speaker. Obviously this could destroy the speaker or blow fuses inside the amp if something really goes wrong, like something falling apart.