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

[Barry Klein]

Which makes me think of a PPG Wave I fixed one time.  Had a bad 5V supply.  Huge National linear TO3 part that ran hot.
Swapped in a 5V (switcher) wallwart....  :-)

Barry


-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Jean-Pierre Desrochers
Sent: Wednesday, January 25, 2012 5:20 PM
To: synth diy
Subject: Re: [sdiy] Switched-mode power supply module in synths... good orbad?

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.
> --
> +<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+
>
> Waldorf MIDI Implementation & additional documentation:
> http://Synth.Stromeko.net/Downloads.html#WaldorfDocs
>
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