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Pass 250.5 shuts down driving Magnepan 3.7

This is my first post so please bear with me.

My Pass labs 250.5 protection circuit shuts the amp down when I drive my new Magnepan 3.7s at high volume. I'm talking about a volme higher than I might consistently listen, but not an unbearable level.

I'm using a Cary Slp 05 preamp with long balanced ICs (25 ft,) The amp is close to the speakers with less than 6 feet of speaker wire. The system works fine at normal volumes. I've tried the same thing with a pair of Cary MB500 (750 W @ 4 ohm) and they too shut down at high volume.

I believe the maggies drop below 4 ohms and I wonder if either amp can handle the impedance drop below 4 ohms.

Has anyone experienced this issue ?

Any suggestions ?
gcoxsom

Showing 7 responses by magfan

magfan
1,583 posts
 
Are the amps in a well ventilated place? They very big and heavy with LOTS of heatsink.
If in restricted space, they could simply be not getting enough air.

I don't know that Magnepan has ever made a speaker that was a 'bad load'.
Low sensitivity? sure. Low impedance? yes again. But I've never seen any data showing bigtime dips or huge phase angles. Is the new 3.7 an exception? It does use a new design series crossover, so MAYBE, but don't bank on it.

If you haven't popped a speaker fuse, I'd look back at the amp......Onemug's bias meter suggestion is good.
magfan
1,583 posts
 
I LIKE that idea. If the wall voltage sags...badly, that'd do it.

Try a SINGLE channel at the offending level.

Borrow / buy a DVM and check line voltage during use. A 'Kill-a-Watt' meter would work, also. As long as you're on the same leg of the circuit as the amps, you'll be OK.

The Pass site also formerly listed output voltage of the amps, which would be another possible check.
magfan
1,583 posts
 
That would be nice if the Maggies dropped that low....

See AA for resolution to OPs problem.....
magfan
1,583 posts
 
Who's 'in a world of hurt'?
magfan
1,583 posts
 
Over at the Asylum, the OP posed the same question.

He has resolved his problem...which didn't get updated over here.

So, painful as it was, problem solved...........
magfan
1,583 posts
 
I'll be sure to be as unhelpful as possible if you ever have a problem, ebm.
Nice attitude.
magfan
1,583 posts
 
The OPs answer on the planar asylum: I can't figure out what he did except hook it back up after litle success with Cary amps.....?

I finally went back and hooked up my Pass Labs 250.5 and I've had nothing but great music since. The fact that my pass amp overheated was apparently not related to the Cary amps shutdown.

The Cary amps are new because just purchased off of Agon. I wanted mono blocks to place behind the speakers, But after listening to both amps there's no way I could go back to the Cary's. The pass amp just sounds so much better in every way. This is not to discredit the Cary but to my ears there's no comparison. Not to mention that the Cary's don't appear to be a good match for the Magnepan load. I should have known

Now these go back on Audiogon and someone will get a great deal. I now would like to see if I could get a another 250.5 and use one 250.5 to drive each channel. Not sure that would work with these amps but I guess that's for another post.

Thanks for all the suggestions and help
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