prone to noise?

[uranium235]

which is prone to noise switch mode or linear type power supply specially when used in audio equipments?  

[saturation]

Switching.  Even lab grade supplies have more noise than a cheaper but well made linear.

[uranium235]

is it possible to reduce or eliminate the noise in switchmode?

[Kiriakos-GR]

No , simple as that ..

Thats why any audio device coming from the respectable manufacturers,
uses high quality transformers , with shields and all . 

[slburris]

How about running a switcher to slightly above the voltage you need,
then use an LDO linear regulator to get the final voltage?

Scott

[saturation]

It can be, but the cost and effort often rise enough to match those of a more costly linear PSU, which rise as power requirements rise, then the question becomes why not just do the linear then?  The main consideration is size and weight, as linear tend to get farily large and heavy proportionate to it max power capacity.

Noise is more than just the power ripple, its the high frequency being radiated into whole circuit, pretty much slburris like the problem you have with that CS power supply you reviewed elsewhere, this will go through any linear front ends you put on the PSU, its basically a radio frequency riding on DC.  You can filter it down to a tiny %, but in linear supplies unless its being picked up from the power lines or other sources, its nonexistent.  The next question is, given its high frequency, it shouldn't be audible anyway, so why worry, maybe its moot.



  

How about running a switcher to slightly above the voltage you need,
then use an LDO linear regulator to get the final voltage?

Scott

is it possible to reduce or eliminate the noise in switchmode?

[alm]

As long as you use a modern switcher with a high switching frequency, I think you'd be fine, since the majority of the noise is most likely harmonics from the switching frequency, plus noise from the diode and MOSFET (both pretty high frequency). Your speakers make a fine low-pass filter, but I wouldn't be so comfortable with an ancient 30kHz switcher, which is too close to audio frequencies for my comfort.

A switcher + LDO actually pretty common, I believe. The efficiency of the LDO can actually be pretty good, since you can set the switcher to slightly above the dropout voltage. But I wouldn't expect the LDO to reject much high-frequency noise either, check the NMRR vs frequency graph in the datasheet. As a general rule, it's quite hard to get clean output from a switcher, which is why low power low noise loads like multimeters and low-power lab supplies are still linear. But it should be doable to make it good enough for audio (including the NMRR from the amplifier), since there's tons of audio equipment around with switching regulators, and even PWM amplifiers (class D?). Especially if you're not trying for studio quality.