smps switching frequency and noise

[soundnovice]

hi
arjen helder ebay lists a smps power supply

Switchmode Power Supply 11-14 volts ADJ 3.5 A power max | eBay

the description says that the switching freq. is 50khz so noise is not an issue.
for t-amp, will this smps power supply give good results or atleast comparable with linear supply? or do u prefer linear supply as a better option? need your valuable suggestions.

 

[sachu888]

I am using DIY regulated power supply based on Rod Ellot design and modified by FM Omisra for B1,and DIY Phonostage(very sensitive to noise).It can be built under Rs 2000(including R-core trafo).I am very happy with the result and its definitely better than any wall wart or SMPS type PS.
Few pics:
By [URL=http://profile.imageshack.us/user/sachu888]sachu888 at 2011-12-24[/URL]
By [URL=http://profile.imageshack.us/user/sachu888]sachu888 at 2012-03-02[/URL]

Regards,
Sachin

 

[quad]

Sachin,
Om's supply board will not provide enough current for the OP's
application which required 12V, 3A or so.

soundnovice, since Arjen deals with Tripath amps, that supply is likely
to be suitable. T-amps run pretty good with SMPS.

 

[omishra]

Sachin,
Om's supply board will not provide enough current for the OP's
application which required 12V, 3A or so.

soundnovice, since Arjen deals with Tripath amps, that supply is likely
to be suitable. T-amps run pretty good with SMPS.

Yes, my PS is only for small current of pre amps and not for power amps.

Also that SMPS will be good option with Class T and class D amplifiers. But that is single rail ps it seems -V looks deceptive. So useful for 2020 & 2024 amps and not for amps which required dual PS.

 

[soundnovice]

well....my original doubt is.....
"the description says that the switching freq. is 50khz so noise is not an issue."
i.e. if switching freq. is 50khz, then does it mean that its quality is as good as linear supply? having a switching freq. of 50khz will not cause any noise in the output?

 

[sashijoseph]

unregulated supplies typically produce a mains induced audible hum at their outputs...a 50kHz smps would push this 'hum' beyond audibility and this is probably being touted by the manufacturer....
but emi noise in a smps is of more concern and emi will increase with the switching frequency...so the designer better have taken measures to suppress the additional garbage.

 

[soundnovice]

unregulated supplies typically produce a mains induced audible hum at their outputs...a 50kHz smps would push this 'hum' beyond audibility and this is probably being touted by the manufacturer....
but emi noise in a smps is of more concern and emi will increase with the switching frequency...so the designer better have taken measures to suppress the additional garbage.

got the answer! thanks

 

[omishra]

unregulated supplies typically produce a mains induced audible hum at their outputs...a 50kHz smps would push this 'hum' beyond audibility and this is probably being touted by the manufacturer....
but emi noise in a smps is of more concern and emi will increase with the switching frequency...so the designer better have taken measures to suppress the additional garbage.

These are from some older fellows, -

I also prefer SMPS and batteries than heavy transformer.
However, in SMPS, I found that there is always a high ~10mV ripple due to the switch.
The frequency of the voltage ripples is depends on the switching frequency of SMPS.
Normally, the ICs' PSRR (Tripath, LM317, etc.) always performs badly at this frequency range.
So they introduce noise at 10Khz~20Khz range, even the switching frequency is up to 40Khz.
(Because the ripples are not perfect sine waves, and if you do the Fourier transform to the waveform, you will know that it contain lower frequency components)
The higher the switching frequency, the smaller noise in audible range. (of course you can't go too high to the Tripath swithing frequency, that will cause another problem.)
IMHO, you should choose SMPS with higher switching frequency (>80Khz), and beware that many industrial SMPS switching frequency is around 25Khz.

Ref.A reliable 30-0-30 switching regulated PS

 

[soundnovice]

These are from some older fellows, -


Ref.A reliable 30-0-30 switching regulated PS

thanks for the details. however i just need one good reason why i should go for linear supply to expect the best possible sound. i think its safer to spend bit more and go for a linear supply which gaurantees low noise power.

 

[omishra]

For preamps you must go for linear well filtered PS. There is zero tolerance of PS impurity though current requirements are low.

For Power Amps ( specially class-T and class D), it does not matter SMPS or linear. Only purpose here is to get High current, lowest output impedance of PS and ripple is minimal (few Milli volts). Linear PS is bulky and difficult to build high current regulated with higher efficiency (w/o heat loss). SMPS is beneficial on all aspect. You get small ripple which anyway no matter with switching amplifier. So for 20KHz audio, anything >=50KHhz switching frequency (>= 2.5 times) should not matter.