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Old 13th June 2002, 09:28 AM   #1
rbroer is offline rbroer  Netherlands
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Question Improved LM317 ?

Searching the archives I came up with this "better than datasheet" implementation of the LM317 regulator according to some...

I think the idea is to fixate and isolate Adj from noise of the output, so the LM317 only regulates to keep 1.25V difference between Vout and Adj ?
Or do you effectively break the feedback loop, making the regutor "worse" and have the output caps do all the AC work, but sonically better due to removing regulator induced sonics ?

I'm puzzled.

Same questions with TL431 shunt regulator and capacitor decoupled reference...

Rudolf.
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Old 13th June 2002, 10:02 AM   #2
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Many questions here are about how good is 7815, LM317 etc. If we deside to that the load are rather constant and the load regulation aren't very important nor the stability, then you only have to filter the voltage, before and after the regulator. If you do that you will have a "quite" voltage.

If you check my QSXM3 phono amp, you will see how I have done. I have C+R+C+R+C for smoothing with makes very smoothe incoming voltage.

Check also datashets and application notes at Linear Tech for LM317/LT317. They have some ideas to make it better but for unknown loads!

Check also my extreme regulator QSXPS for MC-amps.
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Old 13th June 2002, 10:50 AM   #3
UrSv is offline UrSv  Sweden
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Off topic, but where do you have your PCBs made peranders?

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Old 13th June 2002, 11:37 AM   #4
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Default improved 317

Rudolf,

Since the 317 does its best to keep 1.25V between Adj and output, the quietness of the Adj has a direct effect on the final result.

In the diagram you posted, Adj is made as stable and quiet as possible by using a current source and a ref diode. That is at any rate better than just the customary resistive divider with decoupling cap. The 'resistive divider' formed by I1 and D1 - for noise etc - probably is something on the order of 1 million to one, which will be hard with an R and C, especially at low freqs.

The other question on the 'musicality', whatever that is, is another matter altogether. The 317 is there to approach an ideal volt source. After all, the amp is designed with the assumption that it is fed with a DC voltage. If you think a less ideal volt source makes the amp sound better, there is no overriding reason to use a 317 or whatever regulator you can think of.

Cheers, Jan Didden
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Old 13th June 2002, 12:48 PM   #5
ALW is offline ALW  United Kingdom
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Default Oh my - it's Jan Didden!

Just thought I'd say Hi!

As I'm in the process of building some Walt Jung regulators, based on his updated bootstrapped design, you're currently in my mind as I've been reading and studying the original TAA articles you contributed extensively to.

Any hints, tips or updates would be gratefully received by all, I'm sure

Anyway, thanks for the work you all did on the originals.

Regards,

Andy.
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Old 13th June 2002, 02:04 PM   #6
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Default regulators

Hi yourself,

There is one additional change I did in one of my implementations which as far as I know hasn't been documented, and that is replacing the current source on the input side (you know, the LED & transistors and couple of Rs) with a current reg diode (CRD), which actually is a FET connected as a current source. IIRC I used a J50x, try to find the highest value, like 10mA. This does further improve input noise and ripple rejection especially in the higher freq area. There is one caveat though: you need at least 7 or 8V difference between the input and output to have the CRD function correctly. But other than that, I find it worthwhile towards measurable better performance. Whether it's worth it sonically is something I cannot decide for you for obvious reasons.

Cheers, Jan Didden
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Old 13th June 2002, 02:11 PM   #7
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Default Re: regulators

Quote:
Originally posted by janneman
a current reg diode (CRD), which actually is a FET connected as a current source.
To be precise, it is a JFet with gate tied to source and then sorted for current.
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Old 13th June 2002, 02:19 PM   #8
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Quote:
Originally posted by UrSv
Off topic, but where do you have your PCBs made peranders?

/UrSv
Cogra makes very nice pcb's and we at work are satisfied by them. Notice: They use Macintosh in production!

http://www.cogra.se/index_e.html
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Old 13th June 2002, 04:14 PM   #9
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Default Jan

Thanks Jan for taking the time to update.

I seem to remember that one of Walts design aims was to reduce dropout, hence the choice of LED-biased current source. In many POOGE-type applications though the extra dropout could be handled, so I will try it at some point in order to assess the sonic effect.

Certainly the lashed-together Sulzer style regulator, and my own modified version of the POOGE 5.x discrete reg's have astounded me with their sonic abilities.

I was surprised actually that no-one AFAIK saw what seemed an obvious mod to the POOGE reg's, that had been implemented in all the op-amp based reg's i.e. tailoring the feedback response to unity at AC. It effectively lowers output impedance by a factor of 10, and noise by a significant margin, for just one extra capacitor. I guess it was largely due to preoccupation with the better designs.

The real benefit being these can be made small and cheap, relative to the AD797 based units, making them a good 3-terminal replacement. They are also wonderfully stable.

Thanks again,

Andy.
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Old 13th June 2002, 04:38 PM   #10
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Default improved 317

Yes, you're right.

Of course if drop out is an issue, the CRD is a no-go, but you should give it a try if you have the excess voltage available. And it is more compact.

Jan Didden
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