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Old 17th October 2019, 11:30 AM   #21
grahamgraham is offline grahamgraham  United Kingdom
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Quote:
Originally Posted by FauxFrench View Post
Hi Graham,

I have seen it before but not had one to test. I am a low power guy (says my wife). It may be able to go further down in loading without noise.
Thanks, man. Its interesting because it is very small and passively cooled. It could go in a 1u rack case for sure.

Sorry to thread hijack but this has some interesting info on it....

I am looking at the 3e audio tpa3251 4x 100wpc. What power supply would you reccomend and what would the effect if underpowering with a lower wattage psu be other than reduced output?

This psu looks good:

£38.78 | 400W 24V/15.5A 12V/2A Mini Digital Power Amplifier Switching Power Supply With PFC For Amplifier
AliExpress
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Old 17th October 2019, 11:37 AM   #22
grahamgraham is offline grahamgraham  United Kingdom
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Originally Posted by Kjaerlarsen View Post
Most interesting will be to hear how it compares to my rather old Rotel class AB amplifier (2x80W), especially with vinyl!
It will definetly have enough power, that's for sure!
Anyone have any idea what to expect?
I've never used a class d on my main system so await your impressions!
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Old 17th October 2019, 12:00 PM   #23
FauxFrench is offline FauxFrench  France
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Quote:
Originally Posted by grahamgraham View Post
Thanks, man. Its interesting because it is very small and passively cooled. It could go in a 1u rack case for sure.

Sorry to thread hijack but this has some interesting info on it....

I am looking at the 3e audio tpa3251 4x 100wpc. What power supply would you reccomend and what would the effect if underpowering with a lower wattage psu be other than reduced output?

This psu looks good:

£38.78 | 400W 24V/15.5A 12V/2A Mini Digital Power Amplifier Switching Power Supply With PFC For Amplifier
AliExpress
24V supply will allow 70W in 4 Ohm or 35W in 8 Ohm. With 4 Ohm speakers, the power supply is fine and with good margin. With 8 Ohm speakers, the power supply is "overkill".

The TPA3251 chip can operate down to 12V so 24V is fine for the chip. The 3E-board is recommended to operate with a supply voltage in the range 24-32V, thus 24V should be fine. Only the output power should change (reduce) with less supply voltage, not the SQ. SQ with Class D amplifiers is less supply voltage dependent than for class AB. A clear advantage with less supply voltage is that the heatsink becomes less warm.
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Old 17th October 2019, 01:24 PM   #24
Turbowatch2 is offline Turbowatch2  Germany
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You must be aware that you loose headroom, if you use less voltage than optimal for any amp. This might compress the sound even at moderate levels, if the music has high dynamics.
Even very small high quality speaker, today can take very high bursts, which makes them sound so amazing. I write "high quality", because we are in a DIYS forum and many build their speakers, too. So if you have a pair of small Scan Speak, Seas or Peerless etc. based speakers, you might be right to use a high power amp on it.
I never found any disadvantage by using amps that are 5 times stronger than the speakers are rated.

This question is asked very often, because people want to use something as a power supply, that is already in their possession. So, yes, you can use a mismatched power supply, if it has less volt than possible with the amp, but do not expect the optimum result. For a first test, this maybe OK, but if you are disappointed, donīt blame the amp module.
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Old 18th October 2019, 09:31 AM   #25
grahamgraham is offline grahamgraham  United Kingdom
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Interesting, thanks for the reply. I suppose what I don't understand is what wattage the PSU needs to be in order for the TPA3252/TPA3255 to function and best capacity. What is most presumably obvious is that it needs to have more watts than the amp power output?

For instance, Kjaerlarsen has picked a wattage higher than the amp output. Is this because the amp is not 100% efficient?
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Old 18th October 2019, 10:08 AM   #26
Kjaerlarsen is offline Kjaerlarsen  Denmark
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Originally Posted by grahamgraham View Post
Interesting, thanks for the reply. I suppose what I don't understand is what wattage the PSU needs to be in order for the TPA3252/TPA3255 to function and best capacity. What is most presumably obvious is that it needs to have more watts than the amp power output?

For instance, Kjaerlarsen has picked a wattage higher than the amp output. Is this because the amp is not 100% efficient?
I guess I did it due to what we used to do in the past with class-AB amplifiers and traditional power supplies, the bigger the supply, the better.
I chose the size of the power supply based on the maximum power the amp can deliver in 4 ohms, it may be overkill, but the price difference was very small. Also, I chose voltage in the upper range of the amps working limits, which should ensure that no headroom is lost.
I do hope I got it right, only time will tell.
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Old 18th October 2019, 10:56 AM   #27
sajunky is offline sajunky  South Africa
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Originally Posted by grahamgraham View Post
Interesting, thanks for the reply. I suppose what I don't understand is what wattage the PSU needs to be in order for the TPA3252/TPA3255 to function and best capacity. What is most presumably obvious is that it needs to have more watts than the amp power output?

For instance, Kjaerlarsen has picked a wattage higher than the amp output. Is this because the amp is not 100% efficient?
It is obviuous requiment for a bigger PSU wattage. You must also take out efficiency of the amp. And you don't want to force PSU to work on the maximum load for two reasons:

1. Overload protection and there are 3 types. Some PSU's make smooth transition from voltage regulation to current limiting, this one is the best for you. The other one will temporary pause conversion and restore operation after removing a cause. You will definitely notice it when happens. The third type will permanently lock-up PSU output. You will have to complete power cycle to restore operation.

2. Working on the limits increase PSU noise, as rectifiers works harder there are bigger requirements for the size of capacitors in the output filter. In addition, the best PSU (see #1) has apparently the poorest noise parameters on the maximum load, so it is not a good idea to depend on the current limiting feature anyway.
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Old 18th October 2019, 12:21 PM   #28
FauxFrench is offline FauxFrench  France
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Quote:
Originally Posted by grahamgraham View Post
Interesting, thanks for the reply. I suppose what I don't understand is what wattage the PSU needs to be in order for the TPA3252/TPA3255 to function and best capacity. What is most presumably obvious is that it needs to have more watts than the amp power output?

For instance, Kjaerlarsen has picked a wattage higher than the amp output. Is this because the amp is not 100% efficient?
For a class D amplifier you have a typical efficiency of 90%. That means, that per channel of the amplifier, you divide the maximum output power the amplifier may deliver in any actual load (2-8 Ohm) with 0.9 to come to the power needed from the power supply, per amplifier channel. Then you multiply with the number of channels, if they all operate the same load impedance, to arrive at the total power demand from the power supply.

What you sometimes see mentioned as the "crest factor of music" allows us to use a power supply with less power (down to half) than calculated above.
Using the calculation above and stepping up in size to the next standard power value of the power supply is safe play.

Last edited by FauxFrench; 18th October 2019 at 12:24 PM.
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Old 18th October 2019, 12:36 PM   #29
amplidude is offline amplidude  Denmark
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Many have praised the class d boards by ljm, they are based on iraud amplifier, there are several threads here on topic, and they are dirt cheap, then u can spend more money on a good psu and chassis
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Old 20th October 2019, 04:39 AM   #30
Turbowatch2 is offline Turbowatch2  Germany
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The type of power supply is indeed the cause for the different answers to this "simple" question, if you ask different people.
There are parts even with good DIYS, where you can not find the perfect single solution.

Example one: I want to use low cost stuff. I buy at Alibaba, eBay or Amazon.
The amp module has been used by others and found to be OK. The amp should put out itīs maximum power of 160 W for a small sub woofer for a home cinema. It may run with constant high load and distortion sometimes, which is no problem with very low frequency.
I buy a no name OEM supply, rated at 240W, to feed my 36V amp. This takes into account, that the Chinese producer of the PS is rating it very optimistic, the amps 90% efficiency and the possible lowest load a 4 ohm rated woofer may have. Seen from this perspective, 1/3 or 50% of of a reserve seems to give some peace of mind.

2. Example: I want a high quality amp for my Dadīs floor standers. It may cost a little more. He usually listens low volume, just sometimes likes an opera loud.
I take a good 2x 140 amp module from a reputable constructor/ seller, use the recommended power supply of 200 W and will be fine.
Even as I only have 2/3rd or 65% of the amps nominal output power, the PS will have enough reserve to play some peakīs that may be in the music sometimes.

Both amps do nothing wrong, one with 65% PS, the other with 150% theoretical power.
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