[sdiy] Opionions on Switchmode PSUs for analog synths?

Richie Burnett rburnett at richieburnett.co.uk
Thu Oct 31 00:48:46 CET 2019


---- Mattias Rickardsson wrote ----
>
> How likely is a linear regulator to properly suppress the high-frequency noise from SMPS?
> 

Not very likely. Linear regulators typically have plenty of loop gain at low frequencies, so they are great at removing 100Hz / 120Hz ripple, but HF switching noise from the hundreds of kHz up to the 10's of MHz often just blazes straight through linear regulators with very little attenuation. That's what LC filters and common-mode chokes are for. These are much more effective at RF filtering.

It is technically possible to make a very quiet SMPSU, but it requires careful design with generously sized filtering components and proper screening. Your typical "Grand Dynasty" wall wart type SMPSUs typically uses the flyback topology below about 70W which is incredibly noisy to start with.  And they go on to skimp on input and output filtering and screening because these increase size, weight and cost.

Just look at the cost difference between a Chinese budget SMPSU and the equivalent offering from a reputable manufacturer like XP power, Lambda, Traco, etc. Filtering is one place they cut corners. Safety is the other! 

-Richie,




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