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

[Paul Maddox]

My PPG had the classic PSU problems.... I replaced it with a SMPSU, worked a treat from then on! and I stopped burning my fingers when I switched it off (the 5A 5V reg was right next to the on/off switch).

On 26 Jan 2012, at 01:37, Barry Klein wrote:

> 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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> 
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