SV: Re: [sdiy] Linear PSU options .. 7815/7915 vs LM317/LM337 vs 723 etc

[James Patchell]

All I can say is that I have designed systems with less that 0.4nV/root Hz, 
which is a lot better than almost any audio systems, and have used 
78xx/79xx regulators without any problems at all.  A properly designed 
amplifier, or any circuit for that matter, will not care what the noise 
level on the power supply is.  Generally, all I care about is that the 
power supply have a good low impedance.

At 12:46 AM 1/10/2006 +0000, Seb Francis wrote:
>This is a very good point, but nevertheless many hi-end audio circuits do 
>seem to use better than 7xxx PSUs.  Maybe this is kind of over the top 
>audiophile engineering, but I'm not so sure.
>
>In my application there isn't anything like a VCO that needs a really 
>precise voltage, but there are however hi-end audio components (THAT VCAs 
>in the compressor) that need to pass/process the audio with as little 
>added noise as possible.  Also, the distortion processor elements have 
>very high gain which will probably amplify any power supply noise.
>
>So while I don't want to get over-complicated, if a 317/337 PSU can give 
>lower noise than a 7815/7915 PSU with only an extra couple of resistors 
>then it seems worth it (maybe I have some traces of audiophile in my genes! ;)
>
>Seb
>
>P.S. The only digital bit (a PIC micro for the MIDI interface) has its own 
>78L05 driven power rail.
>
>
>
>Paul Perry wrote:
>
>>There's another side to this regulator debate, and that is:
>>just how good does the regulated supply need to be?
>>When one looks at precision analog circuitry, you often see
>>power rails no better than you would get from a LM78xx,
>>but wherever a *really* precise voltage source is required, there is a 
>>precision source dedicated to just that. And it is right there on the 
>>board where it is wanted.
>>Which at a stroke solves the problem of noise generated on the power 
>>rails by switching transients etc.
>>And, speaking of transients...... anyone serious (including some
>>members here, I notice) have separate power rails for the digital stuff,
>>and for the analog that they try to keep noise free.
>>I personally think, the difference between the 78xx and other regs,
>>is swamped by these other techniques..... and if you want to go the whole 
>>distance, you are going to need to have precision voltage
>>diodes & separate analog/digital lines anyway!
>>
>>paul perry Melbourne Australia
>>
>>
>>
>

         -Jim
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