LM317 for power amp regulation?

[leadbelly]

If you're talking about how the amp sounds before clipping, he may well be right.

We obviously do not share the same sonic taste.

Geez Louise! I'll just shut up now then

 

[SY]

Don't worry, analog loves poking me with a stick every chance he gets. You just got in the way.

 

[skyraider]

Apart from the technical details i would expect a 2A3 amp powered from a 317 and heated through a 317 to sound no better than a Gainclone; possibly worse.

So no one here has actually tried lm317 for a power amp? Currently I have 16uF,10H,470uF CLC before feeding into the regulator. The reason for regulator is to take out the need for another RC stage in the PS. In that way, I can also compared the regulator with conventional RC stage.

I will be building several designs I have found, including the zener reference type.

How to calculate the output impedance of a regulated PS?
Is the CLC stage before the regulator accountable for the impedance as well? Or is it just the output impedance of the mosfet/ control element?

Thanks!

 

[SY]

So no one here has actually tried lm317 for a power amp? ...

How to calculate the output impedance of a regulated PS?
Is the CLC stage before the regulator accountable for the impedance as well? Or is it just the output impedance of the mosfet/ control element?

Who said that? I've been using the Maida and Curcio designs for years. They're excellent; reliable and quiet. You do need to have a capacitor at the output to keep the impedance low at high frequencies.

The stuff before the regulator does not figure into the supply source impedance to a good approximation.

 

[paulb]

That's a matter of your interpretation of 'idiot' as related to amp design. I built 'Daniel' the same year as the article in AA came out and was monumentally disappointed. The fact that he had emptied an AR SP6 case to house the design was impressive but the sound was not. We obviously do not share the same sonic taste.

Or maybe you didn't build it quite right.

 

[skyraider]

Hi SY,

Who said that? I've been using the Maida and Curcio designs for years. They're excellent; reliable and quiet. You do need to have a capacitor at the output to keep the impedance low at high frequencies.

Maida & Curcio uses LM317 as the main control element? Or just for 'support'?
Do you have their schematic to share?

The stuff before the regulator does not figure into the supply source impedance to a good approximation.

Meaning the PS output impedance is mainly determined by the regulator output and not accounting CLC stage before it?
.
thanks

 

[SY]

Maida's app note is at the National Semiconductor site. The Curcio circuit was published in Glass Audio V1 #1 page 1 (a Stereo 70 modification project). Basically, the 317's input is fed by an emitter follower that's held several volts above the 317 output. The 317 is the main control element. It's pretty good, but it definitely needs some capacitance on the output to keep things dynamically stable and knock down the "inductive" nature of its output impedance versus frequency. For low noise applications, it also needs some capacitance at the sense terminal.

Errol Dietz published a very nice paper showing the effects of varying capacitances on the 317's behavior. It was in EDN, but might be sitting somewhere on the National Semi website. It was also reprinted in the back of Bob Pease's book "Analog Troubleshooting", which you ought to own.

 

[Gluca]

I could not find the AN @ national.com

Ciao SY,

could you post that AN or just indicate the number as I could not find it and would have the chance to look at it.

Gianluca

 

[SY]

Andy already posted that in Post #4 of this string.

 

[skyraider]

Thanks for the help SY.

What cap values do you use at the regulator output? 20uF motor-run works fine? I read that large caps has no benefit, but does not specify what is 'BIG'

 

[analog_sa]

Or maybe you didn't build it quite right.

Very possibly. I was newbie in '85. My other references ( Marantz 7C and AR SP10 - phono sections only) were probably equally poorly built but sounded a lot better. My naive explanation at the time was that neither Marantz, nor ARC made money out of writing magazine articles

 

[SY]

Thanks for the help SY.

What cap values do you use at the regulator output? 20uF motor-run works fine? I read that large caps has no benefit, but does not specify what is 'BIG'

I use a 20u cap in series with a small (2-4 ohm) resistor for most applications. You likely will not get benefit from using a much bigger value and you risk having the regulator fold up like a AAA map.

 

[SY]

Let me disagree with myself a bit. For low noise applications, a bigger output cap (along with a couple of uF across the voltage setting resistor) IS of benefit. It still carries smoke risk, but 100uF isn't unreasonable.

I mostly use the Maida in power amps and as a preregulator in my preamp and crossover. That's why the noise qualification never occured to me. Sorry.