burnt amplifier

[asbril]

 I have Chromecast devices that I use to cast music throughout my home and that are controlled by the AVRemote nodeserver (*).

This setup has been in place for a few years.

Two weeks ago the amplifier that is connected to one of the Chromecast suddenly stopped working and was super hot, clearly burnt.  I blamed the amplifier  being several years old and replaced it with a new amplifier (I use cheap Pyle amplifiers).

Unfortunately after 2 days the new amplifier also blew up.  I then put a new power strip with surge protector and again replaced the amplifier............ and a day later that amplifier also blew up.

I am at a loss what causes this as  a TV, a Comcast box, a sound bar and a Alexa Echo are also connected to the same power strip, and have no problems with these.

Does anyone here have any idea what could be the cause ?

(*) great nodeserver

[mwester]

Speaker wiring or speakers themselves.  Quality amps will have protection built-in, but that's might be a possible cost-cutting area for low-priced amps.

[DaveStLou]

1 minute ago, mwester said:

Speaker wiring or speakers themselves.  Quality amps will have protection built-in, but that's might be a possible cost-cutting area for low-priced amps.

That's what I'm thinking too. @asbril, which model Pyle are you using?

[asbril]

2 hours ago, DaveStLou said:

That's what I'm thinking too. @asbril, which model Pyle are you using?

They are thrown away. Can you  or @mwester recommend a decently priced amp with built-in protection ?

[KSchex]

@asbril I am not very well versed in this particular equipment but I do have some suggestions that may or not apply.  Just changing the amp out to a high dollar unit may not solve your problem.  What ever caused the amp to fail is still there.  First I would determine what failed in the amp; output, power supply, input.  Obviously something has changed in your system;  adding speakers, new TV, grounding, etc.  The output of this amp is probably a bridge arrangement that is designed to source an 8 or 4 ohm load that is UN Grounded.  Lower cost amps sometimes have little protection from speaker faults or miss connection.  It is possible for one of your other devices to be providing a path to ground or "amp power common" within the amp.

I had a similar problem connecting the output of an MP3 player to an amp.  The player output was expecting a 4 ohm speaker.  The amp input common was grounding the output of the player and cooked the amp in the player.  Best of luck..

[asbril]

4 minutes ago, KSchex said:

@asbril I am not very well versed in this particular equipment but I do have some suggestions that may or not apply.  Just changing the amp out to a high dollar unit may not solve your problem.  What ever caused the amp to fail is still there.  First I would determine what failed in the amp; output, power supply, input.  Obviously something has changed in your system;  adding speakers, new TV, grounding, etc.  The output of this amp is probably a bridge arrangement that is designed to source an 8 or 4 ohm load that is UN Grounded.  Lower cost amps sometimes have little protection from speaker faults or miss connection.  It is possible for one of your other devices to be providing a path to ground or "amp power common" within the amp.

I had a similar problem connecting the output of an MP3 player to an amp.  The player output was expecting a 4 ohm speaker.  The amp input common was grounding the output of the player and cooked the amp in the player.  Best of luck..

Many thanks for your input.  I will test the outlet as well as the speaker wires, but what puzzles me is that it all worked  for several years and I am not aware of having made any changes. The speakers and their wiring are exactly the same as always. A real puzzle.

[mwester]

First thing to test is if there's been a short between the wires and ground -- either the sheild of the speaker wires, if your wiring is sheilded or to the house's idea of ground (water pipe or electrical ground conductor).  That can be easily checked with a multimeter -- should be near-infinite resistance from either positive or negative speaker conductor to the sheild and to ground.

A shorted speaker can do a lot of damage -- four ohms versus a dead short is a killer for an unprotected solid-state amp.  You might be able to detect this with a multimeter by ohm'ing out each speaker and comparing to the others in the house (they may not measure 4 ohms, since that's impedance, not resistance, but they shouldn't be zero either).  The problem is that a short may not be apparent until the voice coil starts to move, meaning you won't know for sure until the music starts (and stops when the short happens!).  You can dodge this problem by installing a 4 ohm, high-wattage resistor in series between the amp's positive and the postive to the speaker.  Do this for each speaker of the pair.  This will ensure that if there's a short, the amp will still see at least four ohms, which it should be able to survive.  A damaged speaker will be apparent, as it won't make any sound, or it will crackle audibly when the short circuit happens as the voice coil moves.

 

When my house was insulated with expanding foam insulation, nobody had thought to mention that to the electrician - so some of the low-voltage wiring was damaged as the hot foam softened the insulation and pushed the wires against the edges of the holes in the studs.  So, my patio speaker wires worked, but I do not trust them -- I kept the four-ohm resistors inline for those speakers, and just set the volume higher on that Sonos amp to compensate; the Sonos amp is an extraordinarily expensive device to risk (even though I'd expect it to be internally protected, I'm not taking any chances!)

For the curious, most of the ethernet cables to the second floor had the conductors shorted together, and I had to pull a new set.  On the first floor, things seemed to fare better, but one of the drops works only with 100mbit, but can't provide the full gigabit networking.  Had the electrician known, he would have routed the wires through conduit whereever they passed through a hole in the plates or studs, but neither I nor the contractor thought about it at the time.

[DaveStLou]

3 hours ago, asbril said:

They are thrown away. Can you  or @mwester recommend a decently priced amp with built-in protection ?

@mwester has given you the best advice: find the short before you buy new. I've had good results with Onkyo. People either love them or hate them. However most of their units are probably overkill for your application.

[larryllix]

Years ago, I bought  Heathkit amp, with fabulous specs (at that time), assembled it,  and a year later had a problem with speaker output transistors burning out. After about 3-4 shop repairs under warranty, replacing the output transistors each time, one tech finally found the problem. To fix it permanently, he drilled out the rear chassis where the speaker screw terminals had gone right through the bakelite Jones block terminals  and shorted to the metal chassis.

About a month later I remembered having trouble making speaker wire connections under the tiny Jones block terminals and installed longer copper metal screws....ooooops.  The Jones Block terminals had no bottom barriers in their design.

With those very fine wire strands used in speaker cables, make sure your stripped wires are not allowing fine strands to stick out and touch each other.

Edited January 27, 2022 by larryllix

[apostolakisl]

I assume prior to burning out the amp made, appropriate sound came out of the speakers.  If that is the case, you couldn't have had a short, it would have been silent.

I suspect that the speaker impedance is too low.  Perhaps you have 2 ohm speakers?  Or maybe you have multiple higher impedance speakers wired in parallel?  Electronic amps can not handle the current draw of low impedance and it burns them up (conversely, tube amps will tend to blow with too high of impedance. .. like if you turn it up with no speaker connected at all).  In summary, don't run speakers in parallel, if you have multiples on the same channel, run them in series.  And make sure you have higher impedance speakers.  It is unusual to see low impedance speakers anymore, but I don't know what you have.  For cheaper amps, you typically want 8 ohms or more.

Edited January 27, 2022 by apostolakisl

[asbril]

2 hours ago, DaveStLou said:

@mwester has given you the best advice: find the short before you buy new. I've had good results with Onkyo. People either love them or hate them. However most of their units are probably overkill for your application.

I need to find the short. Even more than price, I also need a relative small size.

Reading the comments of you all, the short might be in the speaker wires and it will not be easy to find this, as the wires are behind a wall unit and then going from the bedroom to the bathroom behind the wall (which I had requested when the condo was built).

[larryllix]

18 minutes ago, asbril said:

I need to find the short. Even more than price, I also need a relative small size.

Reading the comments of you all, the short might be in the speaker wires and it will not be easy to find this, as the wires are behind a wall unit and then going from the bedroom to the bathroom behind the wall (which I had requested when the condo was built).

To find the short you will need to deisconnect the amp and speakers (Both ends of the cables). The speakers are typically 3.2 or 4 ohms (usual standard). The impedance of same is usually rated at 8 ohms (think signal resistance).

These low resistances/impedances make the short hard to find with an ohmmeter, so you will need to disconnect the cables first. I mark the speaker and amp polarities on the conductors with black markers so they go back into the same place / speaker polarities when you are done.

Check with a high scaled ohmmeter from wire to wire and each wire to a ground place. If you can get some alligator clips on for each test, making a firm connection, wiggle and pull each cable end into the wall. Look for any sporadic readings that make the meter jump around or even show a resistance reading at all. Many times shorts are intermittent around sharp bends and ends.

If no weird readings are found you may consider opening up each speaker and having a look at wiring for pinched conductors inside.

Best of luck.

Edited January 28, 2022 by larryllix

[asbril]

2 hours ago, larryllix said:

To find the short you will need to deisconnect the amp and speakers (Both ends of the cables). The speakers are typically 3.2 or 4 ohms (usual standard). The impedance of same is usually rated at 8 ohms (think signal resistance).

These low resistances/impedances make the short hard to find with an ohmmeter, so you will need to disconnect the cables first. I mark the speaker and amp polarities on the conductors with black markers so they go back into the same place / speaker polarities when you are done.

Check with a high scaled ohmmeter from wire to wire and each wire to a ground place. If you can get some alligator clips on for each test, making a firm connection, wiggle and pull each cable end into the wall. Look for any sporadic readings that make the meter jump around or even show a resistance reading at all. Many times shorts are intermittent around sharp bends and ends.

If no weird readings are found you may consider opening up each speaker and having a look at wiring for pinched conductors inside.

Best of luck.

Wow..... that is not something that I am familiar with, so I may need want to look for someone to help me.

Furthermore, the speakers are built in the ceiling and have been there for 20 years, with the cables mostly running inside the wall. I am going on a trip in 2 days and when I come back I will first check where it may more likely  "hurt", which is between  the amp and the wall. That part of the cabling is not original and I would not be surprised if something happend when I moved around the cable box.

Thanks to you all for your suggestions. Just for info, in the meantime I put 2 Google Nest Minis in the bathroom, paired these to operate in stereo. They sound pretty good but it does not look as good as the ceiling speakers.

[stillwater]

As a replacement amp, consider the rather small  Class D Aiyima A07.  In the user manual it says it has overload protection, though it says this only indirectly in a FAQ.  It is marketed as a 300 W amp but of course this depends on power supply voltage and current capability and I don't think the box has enough cooling for anything like that on a sustained basis.  (You probably won't need more than 20 watts for a bathroom anyway)  The amp is rated down to 4 ohms (which some amps today aren't).   $80 on amazon (+ power brick) or cheaper on the Aiyima site if you can wait for delivery from China.  From China you can also choose LM4562 op amps which have better specs than the standard NE5532 though if the circuit is properly designed I  doubt anyone could  hear the difference.  

[asbril]

21 minutes ago, stillwater said:

As a replacement amp, consider the rather small  Class D Aiyima A07.  In the user manual it says it has overload protection, though it says this only indirectly in a FAQ.  It is marketed as a 300 W amp but of course this depends on power supply voltage and current capability and I don't think the box has enough cooling for anything like that on a sustained basis.  (You probably won't need more than 20 watts for a bathroom anyway)  The amp is rated down to 4 ohms (which some amps today aren't).   $80 on amazon (+ power brick) or cheaper on the Aiyima site if you can wait for delivery from China.  From China you can also choose LM4562 op amps which have better specs than the standard NE5532 though if the circuit is properly designed I  doubt anyone could  hear the difference.  

Thanks. At least from the outside, it looks like the Fosi amplifier, which also blew up. I really should identify the cause before getting another amplifier. This will not be easy.

[stillwater]

Yes, finding the short is necessary.   As someone else suggested, putting a  4 ohm high wattage resistor in series with each channel seems sensible until you are sure you have found the short.   You could probably get by with 2  8.2 ohm 5w resistors in parallel with each other or extremely conservatively 6 22 ohm 5 w resistors in parallel.  You could also (or instead, if you think you've found the short) put  a fuse in an in-line holder  in series with each speaker channel output.   It sounds like maybe you have similar speakers with an amplifier that works.  You could measure the typical current with an ammeter and use a fuse with some margin for louder music or transients    Or, based on 4 ohm speakers and maybe at most 40 watts, you could estimate a current of 3.2 amps.  If the speakers are 8 ohms, then 2.2 amps.  But I think 40 watts per channel is way high for a bathroom.   I think once I got past seeing that the speakers make sound with the resistors I'd consider putting a  1.5 amp slow blow fuse in series with the speaker output instead of the resistors. If the fuse blows while normal music is playing I'd go to 2 and then 3 amps.   This would likely protect the amplifier though I can't guarantee it. 

There is one other possibility, at least theoretically.  I am not familiar with the Pyle amps.  In the unlikely event that they are DC coupled, it's possible that whatever you are using as an input source has failed in a way that is  putting a DC voltage into the amp and the amp is failing by trying to amplify that and drawing lots of power.   But a DC -coupled amp would be very unusual.    You could measure the output of your chromecast device (if that is the signal source with a multimeter set to DC volts -- there shouldn't be any or at most a few millivolts.  But even if there is in a typical amplifier it is blocked by a capacitor at the input  and between stages.  (again unless it is DC-coupled, which would be unusual).     You could also put a blocking capacitor (Ideally something like a 1  microfarad film capacitor) in series with the center terminal  of the RCA connector  between the output  of each channel of the chromecast device (assuming that is your signal source)  and the amplifier.   But again I doubt this is the problem.  Also if the chromecast device has a digital connection to your amplifier (coax or toslink) then it certainly isn't the problem.  (Also, depending on the amplifier rail voltage and the input, if DC were appearing at the speaker output it might well blow your speakers.)

 

[asbril]

7 hours ago, stillwater said:

Yes, finding the short is necessary.   As someone else suggested, putting a  4 ohm high wattage resistor in series with each channel seems sensible until you are sure you have found the short.   You could probably get by with 2  8.2 ohm 5w resistors in parallel with each other or extremely conservatively 6 22 ohm 5 w resistors in parallel.  You could also (or instead, if you think you've found the short) put  a fuse in an in-line holder  in series with each speaker channel output.   It sounds like maybe you have similar speakers with an amplifier that works.  You could measure the typical current with an ammeter and use a fuse with some margin for louder music or transients    Or, based on 4 ohm speakers and maybe at most 40 watts, you could estimate a current of 3.2 amps.  If the speakers are 8 ohms, then 2.2 amps.  But I think 40 watts per channel is way high for a bathroom.   I think once I got past seeing that the speakers make sound with the resistors I'd consider putting a  1.5 amp slow blow fuse in series with the speaker output instead of the resistors. If the fuse blows while normal music is playing I'd go to 2 and then 3 amps.   This would likely protect the amplifier though I can't guarantee it. 

There is one other possibility, at least theoretically.  I am not familiar with the Pyle amps.  In the unlikely event that they are DC coupled, it's possible that whatever you are using as an input source has failed in a way that is  putting a DC voltage into the amp and the amp is failing by trying to amplify that and drawing lots of power.   But a DC -coupled amp would be very unusual.    You could measure the output of your chromecast device (if that is the signal source with a multimeter set to DC volts -- there shouldn't be any or at most a few millivolts.  But even if there is in a typical amplifier it is blocked by a capacitor at the input  and between stages.  (again unless it is DC-coupled, which would be unusual).     You could also put a blocking capacitor (Ideally something like a 1  microfarad film capacitor) in series with the center terminal  of the RCA connector  between the output  of each channel of the chromecast device (assuming that is your signal source)  and the amplifier.   But again I doubt this is the problem.  Also if the chromecast device has a digital connection to your amplifier (coax or toslink) then it certainly isn't the problem.  (Also, depending on the amplifier rail voltage and the input, if DC were appearing at the speaker output it might well blow your speakers.)

 

This is very helpful, except that it goes way beyond my technical understanding. When I am back from my trip I'm getting help from a professional install who maintains the C4 setup of a friend.

But thanks for your extensive response. Very much appreciated.

[larryllix]

1 hour ago, asbril said:

This is very helpful, except that it goes way beyond my technical understanding. When I am back from my trip I'm getting help from a professional install who maintains the C4 setup of a friend.

But thanks for your extensive response. Very much appreciated.

I would believe that if you had a partial short in your wiring you should hear some crackling in your music / sounds coming out of a speaker at some point. When you are playing some music you could try wiggling, pulling and shaking your wiring going into the wall. If you can locate a problem it would indicate which one, perhaps, and a bit of vinyl tape on the split conductors to insulate them from each other and the metal parts in the wall may fix the problem.

[asbril]

2 minutes ago, larryllix said:

I would believe that if you had a partial short in your wiring you should hear some crackling in your music / sounds coming out of a speaker at some point. When you are playing some music you could try wiggling, pulling and shaking your wiring going into the wall. If you can locate a problem it would indicate which one, perhaps, and a bit of vinyl tape on the split conductors to insulate them from each other and the metal parts in the wall may fix the problem.

No such cracking or any diminished sound quality........ until it stops casting music and gives a continuous loud buzzing.

Edited January 28, 2022 by asbril

[larryllix]

15 minutes ago, asbril said:

No such cracking or any diminished sound quality........ until it stops casting music and gives a continuous loud buzzing.

That sounds more like a preamp problem with some kind of input burning out something on an input / mixer etc. not a shorted output on a speaker. Burned out speaker stages don't usually buzz. They would just go dead or pop the speakers really loudly.

Do you remember if both channels buzzed or just one?

[asbril]

50 minutes ago, larryllix said:

That sounds more like a preamp problem with some kind of input burning out something on an input / mixer etc. not a shorted output on a speaker. Burned out speaker stages don't usually buzz. They would just go dead or pop the speakers really loudly.

Do you remember if both channels buzzed or just one?

both channels. Furthermore, as this happened 3 times, each time I got a new amplifier they would work for a few days with perfect quality..... until they popped.

 

 

Edited January 28, 2022 by asbril

[apostolakisl]

7 minutes ago, asbril said:

both channels. Furthermore, as this happened 3 times, each time I got a new amplifier they would work for a few days with perfect quality..... until they popped.

 

 

Like I said.  If you have normal sound coming from the speakers, then you almost certainly don't have a short.  A dead short would result in silence and an amp that blows very quickly (typically amps would not blow but rather trip a safety shut down).  Any sort of partial where you still get good sound seems crazy unlikely.

I have to agree that if you are getting buzzing, that sounds more like the input to the amp, not the amp itself.  In which case your speakers or speaker wiring would have nothing to do with any of this.

[asbril]

3 minutes ago, apostolakisl said:

Like I said.  If you have normal sound coming from the speakers, then you almost certainly don't have a short.  A dead short would result in silence and an amp that blows very quickly (typically amps would not blow but rather trip a safety shut down).  Any sort of partial where you still get good sound seems crazy unlikely.

I have to agree that if you are getting buzzing, that sounds more like the input to the amp, not the amp itself.  In which case your speakers or speaker wiring would have nothing to do with any of this.

This is the input; A chromecast connected to a hdmi to rca :

 

[apostolakisl]

"Input" can also refer to the pre-amp portion of the "amp".  If your amp has a volume control on it, then it has a pre-amp.  But this still does not answer the question as to why.  Perhaps the hdmi split out you have there has some sort of intermittent electrical  issue where it is trashing the pre-amp portion of your amp.  I don't know, seems unlikely, but at this point I would replace it.

[stillwater]

Very possibly the problem is the power supply (wall wart) for the HDMI to RCA converter, or less likely with the HDMI converter or chromecast.     Unless -- I assume you didn't reuse the same power brick for the 3 amplifiers...  

Maybe the power supply leaking high voltage  into the HDMI converter.  Otherwise  I'd be surprised the amps are permanently damaged due to an input condition from a 5 volt powered source. (assuming the HDMI converter is powered from a USB wall wart -- if not maybe it's 12 volts...  but still ...).  Or maybe it's leaking a lot high frequency from the switching power supply and that is overheating the amps.  

How do you know the amps  are toast?    (Just re-read your original post.  One or more of the amps could have turned themselves off with overheat protection.)  If you haven't tested them separately from that input configuration it's possible they aren't actually destroyed.  Even if they aren't destroyed the most likely culprit is still the wall wart for the HDMI converter (failed capacitor).  

(If the amps are not destroyed what could be happening is the following -- something in the HDMI wall wart or HDMI converter (less likely in chromecast) is failing.   You unplug everything or turn off the power strip and these components cool down.  You replace the amp.  It works again until something warms up and fails and you think the amp has died... repeat.,   

 

 

 

Edited January 28, 2022 by stillwater
for clarity x5