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Class D Switching Power Amplifiers and Power D/A conversion

Problems Sure amplifiers
Problems Sure amplifiers
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Old 21st December 2017, 07:29 AM   #1
taita is online now taita  Netherlands
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Default Problems Sure amplifiers

I have two Sure amplifiers that have problems.

AA-AB013V120: This one has never done it. I have used different power supplies. The Hmute light is on indicating there is a problem.

AA-AB32971: This one I bought recently. It sounded very good with this power supply Gratis Verzending 240 w 24 v 10a Enkele Output schakelende suppy in Gratis Verzending 240 w 24 v 10a Enkele Output schakelende suppy van Stroomvoorziening op AliExpress.com | Alibaba Groep

Unfortunately one of the channels suddenly failed and a red light on the board is indicating an error occured.

In both cases the manual gives no information what to do. Any suggestions from this forum?
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Old 28th December 2017, 12:15 PM   #2
ICG is offline ICG  Germany
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Location: Too many amps, too many speakers, too little time
Is it possible you got one of the outputs (- or +) somehow connected to the other channel, + or ground? That destroys the most bridged amps instantly. The - on the speakers may not be 'collected', you have to wire them separately.
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Old 28th December 2017, 02:17 PM   #3
FauxFrench is offline FauxFrench  France
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A lot of these power supplies are intended for powering LED lights. This means that their dynamic (transient) behavior may not be suited for audio amplifiers. With sudden changes in in the current consumption of the amplifier (caused by transients in the music) the output voltage may vary a lot. And, such supply voltage variations may cause voltage spikes to be generated in the amplifier that can destroy the amplifier chip.
Power amplifiers normally need good size power decoupling capacitors preferably on the amplifier board, alternatively at the output of the power supply.
Your AA-AB32971 has got 6 times 470uF in total just below 3000uF for decoupling of a 2x100W amplifier. Clearly insufficient for more loud music.
Your power supply has probably got a current source characteristic with voltage limitation of 24V. If so you could have put some 15000uF-20000uF at the output to stabilize the supply voltage. But, it may be too late now.

For a start, remove the fan and see what kind of switch-bridge is used (it is the small black IC that is being cooled by the heatsink and fan). It is likely to be a STA505, STA508 or something like that.

Do you have a multimeter?
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Old 28th December 2017, 04:36 PM   #4
FauxFrench is offline FauxFrench  France
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The way I know to find a fault in a monolithic class D amplifier (bridge coupled) is to measure with a multimeter, put in the 20KOhm range, all permutations of the 4 output terminals and the 2 power supply terminals. If any of these combinations give a multimeter reading of less than 10 Ohm steady state the fault is likely to have been found.

Be aware that measuring across the two power supply terminals should give readings that steadily increase when the power line decoupling capacitors are recharged.

If you want to see how a switch-bridge IC of the type you may have on your board, and the IC that may be defect, looks give DIYBudgetAudio.com a glance under the article "TK2050 based class D power amplifier". The so called TK2050 is likely to be the chip-set combination in your Sure amplifier.

It may be this IC that is defect in your amplifier. Dare you give repair a try if that turns out to be the defect IC?
I can tell you how I do (with success until now) but it is not trivial due to the very small dimensions.
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Old 28th December 2017, 07:51 PM   #5
taita is online now taita  Netherlands
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Quote:
Originally Posted by FauxFrench View Post
The way I know to find a fault in a monolithic class D amplifier (bridge coupled) is to measure with a multimeter, put in the 20KOhm range, all permutations of the 4 output terminals and the 2 power supply terminals. If any of these combinations give a multimeter reading of less than 10 Ohm steady state the fault is likely to have been found.

Be aware that measuring across the two power supply terminals should give readings that steadily increase when the power line decoupling capacitors are recharged.

If you want to see how a switch-bridge IC of the type you may have on your board, and the IC that may be defect, looks give DIYBudgetAudio.com a glance under the article "TK2050 based class D power amplifier". The so called TK2050 is likely to be the chip-set combination in your Sure amplifier.

It may be this IC that is defect in your amplifier. Dare you give repair a try if that turns out to be the defect IC?
I can tell you how I do (with success until now) but it is not trivial due to the very small dimensions.
Thanks for your quite extensive answer. I tried to remove the fan but need a special device for the screws. But removing the fan won't be enough, removing the cooling block is needed to get access to the chips.

I measured the resistance between the different connections. They all have high values, nothing close to 10 ohm, even the failing channel.

Its a good suggestion to increase the output capacity of the power supply. But to be honest I can't imagine that this was the reason as the amplifier failed at a low music level. For me no Sure devices any more.
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Old 29th December 2017, 04:34 PM   #6
FauxFrench is offline FauxFrench  France
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If there is no short circuit (internally) of the 6 terminals there is a chance that the chip is still alive.
A particular “chip killer” in class D amplifiers are the output filter chokes that can generate very nasty voltage spikes if the supply voltage is not stable or too much current is drawn for the outputs. I have seen a TDA8954 chip die from operation at 2x15V with a 1A limit. But, your output switches seem still to be intact.


Then, next step is probably measurement of the signals on each pin of the bridge IC with an oscilloscope. But, that also requires you have access to the IC and the cooling block is removed. If it is glued onto the chip it is very difficult to remove without damaging the PCB.
Be very careful not to short circuit more pins with the probe tip.


If you can get access to the switch-bridge IC and your hands on an oscilloscope, then: a sine-wave on the inputs, cheap 8 Ohm dummy loads or cheap speakers at the outputs and a moderate 15V supply voltage. If one channel still works you can compare the signals for each channel.
Another reason for the faulty channel can be that SMD components break or loose connection in a way that is very difficult to see without a magnifying glass


I guess that also Sure Electronics mainly gets their products from Far East where most is produced nowadays. If the amplifier used to work, it has passed QC and the fault may be due to something else than an obvious design mistake. But, I understand your disappointment – two good amplifiers lost. I tried to find the first amplifier you mention (AA-AB013V120) but I got no matches on the Internet.


Succes!
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Old 30th December 2017, 08:08 AM   #7
taita is online now taita  Netherlands
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Quote:
Originally Posted by FauxFrench View Post
If there is no short circuit (internally) of the 6 terminals there is a chance that the chip is still alive.
A particular “chip killer” in class D amplifiers are the output filter chokes that can generate very nasty voltage spikes if the supply voltage is not stable or too much current is drawn for the outputs. I have seen a TDA8954 chip die from operation at 2x15V with a 1A limit. But, your output switches seem still to be intact.


Then, next step is probably measurement of the signals on each pin of the bridge IC with an oscilloscope. But, that also requires you have access to the IC and the cooling block is removed. If it is glued onto the chip it is very difficult to remove without damaging the PCB.
Be very careful not to short circuit more pins with the probe tip.


If you can get access to the switch-bridge IC and your hands on an oscilloscope, then: a sine-wave on the inputs, cheap 8 Ohm dummy loads or cheap speakers at the outputs and a moderate 15V supply voltage. If one channel still works you can compare the signals for each channel.
Another reason for the faulty channel can be that SMD components break or loose connection in a way that is very difficult to see without a magnifying glass


I guess that also Sure Electronics mainly gets their products from Far East where most is produced nowadays. If the amplifier used to work, it has passed QC and the fault may be due to something else than an obvious design mistake. But, I understand your disappointment – two good amplifiers lost. I tried to find the first amplifier you mention (AA-AB013V120) but I got no matches on the Internet.


Succes!
Thanks again for your answers. I'm afraid I have to take my loss. Besides Sure I now know the service level of loudspeakerfreaks.com where I buyed the board: They don't give any reply on my e-mails and don't answer the phone.

I will install me some capacitors (2*10000uF electrolytical capacitor) to avoid the risks of the power supply with some new amplifier boards I ordered: Dual Channel Audio Stereo Versterker Boord XH M510 TDA7498 DC 14 34 V Versterker Boord van Klasse D 2X100 W in Dual Channel Audio Stereo Versterker Boord XH-M510 TDA7498 DC 14-34 V Versterker Boord van Klasse D 2X100 W van Geintegreerde Schakelingen op AliExpress.com | Alibaba Groep

Not so much hits on the first amplifiers, but this is it: https://www.parts-express.com/pedocs...nual-43666.pdf

Last edited by taita; 30th December 2017 at 08:31 AM.
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Old 30th December 2017, 09:44 AM   #8
ICG is offline ICG  Germany
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Quote:
Originally Posted by FauxFrench View Post
Power amplifiers normally need good size power decoupling capacitors preferably on the amplifier board, alternatively at the output of the power supply.
Your AA-AB32971 has got 6 times 470uF in total just below 3000uF for decoupling of a 2x100W amplifier. Clearly insufficient for more loud music.
Your power supply has probably got a current source characteristic with voltage limitation of 24V. If so you could have put some 15000uF-20000uF at the output to stabilize the supply voltage. But, it may be too late now.
Erm, that's the size you need on a conventional (transformator) power supply. On the high frequency loading of the SMPS, you need a lot less, it has to buffer for a much, much shorter time. 4-5000F is really enough with a SMPS.
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Old 30th December 2017, 09:58 AM   #9
ICG is offline ICG  Germany
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Quote:
Originally Posted by taita View Post
I will install me some capacitors (2*10000uF electrolytical capacitor) to avoid the risks of the power supply with some new amplifier boards [...]
You got a SMPS (switch mode power supply), it creates a DC voltage, chops it up at a high frequency, transforms and rectifies it again. The problem here is the high frequency, the load cycles are very short. That means, the ripple-current is quite high. If the capacitor isn't an low-ESR type, it heats up the capacitor which drasically shortens its lifetime. If it gets much too hot the capacitor can even burn or explode. So while big capacitors solve the one problem, you need low-ESR capacitors for that. If the power supply already killed 2 amps (and it didn't happen because of a cross-short of the outputs), I would suggest you just buy a different power supply which is proven to behave well, i.e. a Mean Well.
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Old 30th December 2017, 11:49 AM   #10
taita is online now taita  Netherlands
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Quote:
Originally Posted by ICG View Post
You got a SMPS (switch mode power supply), it creates a DC voltage, chops it up at a high frequency, transforms and rectifies it again. The problem here is the high frequency, the load cycles are very short. That means, the ripple-current is quite high. If the capacitor isn't an low-ESR type, it heats up the capacitor which drasically shortens its lifetime. If it gets much too hot the capacitor can even burn or explode. So while big capacitors solve the one problem, you need low-ESR capacitors for that. If the power supply already killed 2 amps (and it didn't happen because of a cross-short of the outputs), I would suggest you just buy a different power supply which is proven to behave well, i.e. a Mean Well.
Thanks for your suggestions. Adding a low-ESR capacitor is not a problem but I spotted 3 * 1000uF on the board of the output of the smps.

I didn't use this power supply for the first failing amplifier. I tested this one using a 12V battery. I think the first amplifier was already failing when I received it (buyed it second hand).

The power supply did it very well even on the highest levels before the second amplifier failed on a low level. I'm in doubt amortizing this power supply and buying a new one.
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