What is a better alternative for 317 337?

[Sunsun22]

I recently burned my Mark Levinson 431's 337 regulator. Since 317 and 337 are quite old, is there a better alternative for them?

Input 80.5V
Output 68V
Current: don't know but let it be the max of 317 & 337.

Thanks

[abraxalito]

When you want 'better' do you mean lower noise? Or more ripple rejection? Given that you've got 12.5V of headroom, you'll get better ripple rejection from using two in series - so long as you have enough space.

[wintermute]

I'm assuming that since the max voltage output of the LM317 is 37V that the 68V is actually + to - ie +34V 0V -34V.

In this case there is only about 6V of headroom per device. My (simulation) experience is that if you go for less than 5V differential in to out, that the ripple increases quite substantially.

I searched for alternatives to the LM317, some people were extolling the virtues of the LT1085 at the time I was looking, but I ended up deciding to stay with the LM317, actually an LT317A which is a closer tolerance version of the original LM317.

If one has burned, you might want to consider upping the heat sinking!

Tony.

[Sunsun22]

I am repairing a factory amp therefore regret that there is no room for using dual regulators.

The input voltage is +80V - 0 - -80V, so the output is +68V - 0 - -68V. These regulators are for the driver board only. As of "better", I really don't know what would make an amp better in its performance? The amp is pretty quiet as original but you know people never get satisfied!

I burnt the 337 because of my own fault, nothing to do with the amp's design. The amp is scratching therefore I tried to "observe" which could be the problem. I saw a cap looks like swelling therefore I de-soldered it from the board and measured but nothing wrong with it. When I put it back to the board, I wrongly placed the polarity therefore the cap blasted and the 337 is dead. Luckily, the amp returns to working condition when I replaced the 337 and the cap but the scratches are still there.

[abraxalito]

Originally Posted by wintermute

I'm assuming that since the max voltage output of the LM317 is 37V that the 68V is actually + to - ie +34V 0V -34V.

Since these are floating regs, there's no maximum output voltage as such, just a max input-output voltage. Its risky though running them at such high voltages as under short-circuit conditions they can easily exceed the 37V in-out differential and need some protection.

I searched for alternatives to the LM317, some people were extolling the virtues of the LT1085 at the time I was looking, but I ended up deciding to stay with the LM317, actually an LT317A which is a closer tolerance version of the original LM317.

And being LT I'm guessing at least 20dB more expensive?

[QSerraTico_Tico]

LT317/337 sound better

[wintermute]

Thanks abrax, I was taking the 37V as being an absolute (ie max 40V input - 3V dropout = 37V). I never thought of it as being relative to the input voltage and the adjustment just being how much you drop that voltage by (though I guess since I'm using a positive reg in the -ve rail of my circuit I should have!)

Yes the LT's are more expensive but 6db would be a closer approximation but at an extra $6 in total for two I'm not going to quibble too much

Tony.

[abraxalito]

Originally Posted by wintermute

Yes the LT's are more expensive but 6db would be a closer approximation but at an extra $6 in total for two I'm not going to quibble too much

$6 over here would get me half a gross of LM317

[wintermute]

Originally Posted by Sunsun22

Luckily, the amp returns to working condition when I replaced the 337 and the cap but the scratches are still there.

Are these scratches worse when you move the volume (or other) pot(s)? you may have a noisy pot. Some contact cleaning spray squirted into the pots may help.

Tony.

PS. Abrax, I know stuff is cheap in China but that is ridiculous I've often been tempted to order some stuff from Farnel China (yes I know they aren't cheap but compared to the Australian pricing they are!), get it delivered to one of my wife's relatives and ask them to ship it to me... just not sure they would accept a foreign credit card...

[jean-paul]

Never ever use contact spray on potentiometers and/or switches. The whole device will be greasy, dirty and the problem will return. There is only one good solution and that is thorough inside cleaning of the potentiometer or switch if it is not worn out. Replacement will be less time consuming if the parts can be bought at all.

Contact spray should not be on workbenches of good tech people. It is in the category of using aluminium foil for replacing blown fuses, or like using brake cleaner to start an engine etc. It is the last inadequate solution to a problem that will end the life of that part faster.

Sunsun22, when turning potentiometers (if a 431 has those) does not change the scratching my guess is that you have a leaky transistor or SMD ceramic/electrolytic cap.