[sdiy] Switched-mode power supply module in synths... good orbad?

[Jean-Pierre Desrochers]

Linear power supply  are SO EASY TO REPAIR !!!!

Just my 2 cents..
JP


----- Original Message ----- 
From: "ASSI" <Stromeko at nexgo.de>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Wednesday, January 25, 2012 4:10 PM
Subject: Re: [sdiy] Switched-mode power supply module in synths... good 
orbad?


> On Wednesday 25 January 2012, 21:04:39, Mattias Rickardsson wrote:
>> It would then probably be a +/-15 V supply, regulated down to +/-12 V
>> with the linear regulators on the Living Vocoder pcb in order to get
>> rid of the switch ripple. I expect the ripple (on the order of 100 mV)
>> would be way too strong to use directly.
>
> These TRACOs are pretty noisy IIRC, so you might want to look further.
>
> Check the datasheet for ripple specification and get a PSU that has low
> ripple to start with (they usually have different circuit topology and are
> more expensive, though).  Fixed frequency switching is a definite plus and
> higher switching frequencies make the filter components smaller (that may
> come at the expense of more radiated emissions).  A linear regulator will
> _not_ be effective to attenuate the ripple in the 100kHZ+ region you have 
> to
> expect, you should use a passive low-pass for that, maybe in combination
> with a voltage follower output or shunt transistor.  You need a very good
> voltage reference for these and again passive filters to take care of any
> noise above audio.  Again some PSU have those filters and transistors
> already included and unless you have at least a good scope they'll do much
> better than you can achieve yourself — in fact often better than typical
> linear regulators with noisy references.  Unless the Vocoder produces
> pronounced load transients, just use a 12V PSU directly.  Some further
> reading:
>
> http://cds.linear.com/docs/Application%20Note/an70.pdf
> http://cds.linear.com/docs/Application%20Note/an75f.pdf
> http://cds.linear.com/docs/Application%20Note/an83f.pdf
>
>
> Regards,
> Achim.
> -- 
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>
> Waldorf MIDI Implementation & additional documentation:
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