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

[karl dalen]

--- James Patchell <patchell at cox.net> skrev:

> 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.

Yes but you didnt say "if" you used 78xx in that 0,4n/hz system!
and i seriously doubth you did.

Besides the droop voltage of 78xx series is something people
often oversees, and the droop caused by load or irregular
loading can be devastating for a VCO regarding to tuning
aspects, so way use a 78xx in a VCO if you can use the 317
with way better performance at the same cost? 

>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.

Thats is simply false.

No system is better then its power supply, if it was
we all would be running on 220V AC straight away!
And no decoupling capacitors!!

REg
KD


> 
> 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
> ***************************************************************
> http://www.oldcrows.net/~patchell
> 
> ***************************************************************
> 
> 
>