[Whit]

How much total capacitance do you have for C1?

 

[doobooloo]

Quote:

Originally Posted by Whit How much total capacitance do you have for C1?

1200uF x 9 = 10800uF

Definately on the high side...

 

[Whit]

I would try decreasing the C1 capacitance. What I believe is happening, is that the regulator can't handle the inrush current that begins when the C1 caps are first charging up. To the regulator it looks like a dead short.

 

[ECM]

for troubleshooting purposes, can you wire a resistor in series with the STEPS output to limit the current?

 

[tangent]

Quote:

10800uF

So here you are with a uniquely high rail capacitance and a unique power supply symptom. Sounds like we've found our problem.

Seriously, can you hear any difference at all with that much capacitance, relative to a half or a quarter the amount?

 

[doobooloo]

Strange, though, that the Motorola LM317T from RadioShack works perfectly fine.

I thought all LM317s, whoever makes them, should be of identical specs, no?

 

[doobooloo]

Quote:

Originally Posted by tangent Seriously, can you hear any difference at all with that much capacitance, relative to a half or a quarter the amount?

No, I can't hear the difference. But the FMs at that capacitance was available, and had lower impedance (since they're taller) so I thought, why not. Have done more than 10,000uF on a PPA before without problems, so this was completely unexpected for me.

Well now I have a regulator tough enough to do the job in the PPA now, so problem solved I suppose.

 

[S_Dedalus]

Quote:

Originally Posted by doobooloo Strange, though, that the Motorola LM317T from RadioShack works perfectly fine. I thought all LM317s, whoever makes them, should be of identical specs, no?

Look at the datasheets, it seems as though they all have a basic set of specs, but they all seem to be different in some way.

 

[S_Dedalus]

Quote:

Originally Posted by doobooloo No, I can't hear the difference. But the FMs at that capacitance was available, and had lower impedance (since they're taller) so I thought, why not. Have done more than 10,000uF on a PPA before without problems, so this was completely unexpected for me. Well now I have a regulator tough enough to do the job in the PPA now, so problem solved I suppose.

Its always possible that you just got a bad batch that couldn't handle a load. Did you ever hook the steps up to something like a cmoy or pimeta just to see?

 

[Megaptera]

Quote:

Originally Posted by doobooloo Well now I have a regulator tough enough to do the job in the PPA now, so problem solved I suppose.

Hopefully. But I'd keep my eye on it -- it might be a marginal thing where the one you're using now can do it, but won't be able to do it forever.

 

[Pars]

Quote:

Originally Posted by S_Dedalus Look at the datasheets, it seems as though they all have a basic set of specs, but they all seem to be different in some way.

From when I worked in the semiconductor industry in the '80s, that seems to be the way it is. Everyone's supposed xxxx chip is different, sometimes barely meeting the minimal set of accepted specs to qualify for that designation. This comes from working as a tech and noting how other manufacturers TTL chips behaved in our testers. One brand (Signetics, IIRC) would consistently suck, while others worked pretty well to great. Speed differences, you name it. So it would be no surprise that all LM317s were not created equal.

The other poster is right, however, regarding keeping an eye on it. Something else sounds like it may be marginal, with that drastic of failure in one brand.