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Old 7th December 2007, 03:20 PM   #1
jol50 is offline jol50  United States
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Default amp PS design and performance?

For those of you that look at a lot of amps and test/use them, can you tell much about the amp by the power supply and outputs in general? Can it affect how the amp goes into distortion or its quality, does the capacity of the PS have a lot of bearing on the actual output of the amp? Does the use of BJTs in output mean anything? Or is it more about how the whole thing is put together and you really can't tell much from the components and this is a stupid question...lol.

What set me off is for example I have a 2x75rms at 12.6v at 1kHz and 4ohms amp that only has two irfz34 in PS and a smallish transformer, and it is 1 ohm/ch stable while most amps that size can't do that. Given 1kHz rating might not be the best but that seems like a lot of stress for the PS unless this amp is regulated in some way. It has four BJT for output, the D998 sets from Korea. I think it is new enough to be a Maxxsonics crunch. Or did they just hogwash these ratings?
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Old 8th December 2007, 03:33 PM   #2
Tolik is offline Tolik  Israel
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Quote:
can you tell much about the amp by the power supply and outputs in general?
Generally yes...

Quote:
Can it affect how the amp goes into distortion or its quality
Of course, noisy SMPS is able to kill the sound of even of any good amplifier. The noise, & voltage spikes of bad SMPS almost
impossible to kill with any filters.

Quote:
does the capacity of the PS have a lot of bearing on the actual output of the amp?
Not capacity only. The reactive impedance of capacitors is ricing with frequency of ripple current. SMPS are working at frequencys 20kHz and more. In addition the current drawn by amp is very far from contenious if it`s not class A amp. So capacitors should be ``fast`` enouth to provide good filtering at these conditions.
It`s mean that caps should to to have low ESL. Capacitance of SMPS filter is very depanding on charge current frequesy - with higher frequencys it is possible to go with lower amount of capacitance, if low ESL caps are used.

Example of some good capacitors

Quote:
Does the use of BJTs in output mean anything?
Almost nothing. There are both good & bad designs are avaible with either BJT`s or MOSFET`s at any stage.

Quote:
Or is it more about how the whole thing is put together and you really can't tell much from the components and this is a stupid question...lol.
There are lot of good engeneered commercial designs was ruined by production with cheap low quality components... Try to fill gas tank of your Porshe or Ford GT with oil or 99premium fuel - in both cases your car still be great, but for the drive preformance I`m not sure
Quote:
I have a 2x75rms at 12.6v at 1kHz and 4ohms amp that only has two irfz34 in PS and a smallish transformer
Power of pulse transformer is not only size dependent.
Working frequency, magnetic saturation lewel , even amount of wire inside of window of toroid are important.
Even relative small cores from good ferrite are able to transfer hundreds of watt.
IRFZ34 - has Id.max 26A , so 26x12.6= 327.6 Watt peak power
Quote:
unless this amp is regulated in some way.
It`s should to be PWM-regulated

Hope this was some helpful
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Old 8th December 2007, 11:46 PM   #3
jol50 is offline jol50  United States
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Very helpful post thanks, I like to see the larger picture but I'm not familiar enough with them to know what points are more important.
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