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Has anyone bi-amped with a Cary SLP-05?

I have this rather weird problem I am hoping the collective wisdom of Audiogon will be able to help me sort out.

The SLP-05 preamp has a pair of RCA outputs, and a pair of XLR outputs. I recently tried bi-amping using both outputs, and the result is the SS power amp always fails to work, no matter what output it is connected to. Here are the configurations which I tried:

SLP05-> (RCA)-> Cary CAD2000-> speaker
(Full range). Result: success

SLP05-> (XLR)-> Cary CAD200-> speaker
(Full range). Result: success

SLP05-> (XLR)-> Cary CAD211AE-> mid/tweet
SLP05-> (RCA)-> Cary CAD200-> woofer
(Bi-amped). Result: CAD211AE works, CAD200 produces no sound from the woofer.

SLP05-> (RCA)-> Cary CAD211AE-> mid/tweet
SLP05-> (XLR)-> Cary CAD200-> woofer
(Bi-amped). Result: CAD211AE works, CAD200 produces no sound from woofer.

SLP05-> (XLR)-> Cary CAD200-> mid/tweet
SLP05-> (RCA)-> Cary CAD211AE-> woofer
(Bi-amped with valve amp on bottom). Result: Now here is the interesting thing. Put the SS amp on the mid/tweet and the valve amp on the woofer, and it works! I am succesfully bi-amping!

Now obviously this is not what I want, because I would rather have the SS amp on the woofer. I checked and rechecked the connections and there was no problem. I swapped RCA and XLR cables to my spares and there was no problem. I swapped speaker cables and there was no problem.

I even borrowed another two SS power amps and the result was the same - each time, the SS power amp refused to power the woofer in bi-amp configuration.

I am wondering whether there is something about the higher input impedance of the valve amp that makes the SLP-05 preferentially drive it.

This problem has me beat. I can't figure it out. Can anyone help?
amfibius
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almarg
9,670 posts
 
SLP05-> (RCA)-> Cary CAD211AE-> mid/tweet
SLP05-> (XLR)-> Cary CAD200-> woofer
(Bi-amped). Result: CAD211AE works, CAD200 produces no sound from woofer.

SLP05-> (XLR)-> Cary CAD200-> mid/tweet
SLP05-> (RCA)-> Cary CAD211AE-> woofer
(Bi-amped with valve amp on bottom). Result: Now here is the interesting thing. Put the SS amp on the mid/tweet and the valve amp on the woofer, and it works! I am succesfully bi-amping!

... I even borrowed another two SS power amps and the result was the same - each time, the SS power amp refused to power the woofer in bi-amp configuration.

These are the key clues, it seems to me. And I think that they indicate that the preamp-to-power amp interface is not where the problem is; it is somehow in the power amp-to-woofer interface. The preamp would have no knowledge, so to speak, of which drivers (mid/hi or woofer) each power amp is connected to.

Are you sure that in the cases where you get sound from the woofers (running the ss amp full range, or running the tube amp into the woofer) you get the full expected volume from the woofers, distortion-free? Perhaps some problem has arisen in the woofer or its crossover elements that is causing the impedance presented to the power amp to drop down too low, causing the ss amps to go into protective shutdown, while the tube amp perhaps manages to keep functioning.

Or perhaps the woofer and its crossover elements by themselves present a highly reactive load to the power amp (probably inductive), and the ss power amp's protection circuitry is unhappy with that. When you run full-range, the capacitive reactance which is probably seen looking into the mid/hi terminals would to some extent cancel out the inductive reactance seen looking into the woofer terminals, resulting in a more purely resistive (and hence easier) load.

Regards,
-- Al
amfibius OP
282 posts
 
Thanks for your reply Almarg, I am finding it a bit difficult to follow your argument but what you say makes sense. To answer your question - every time I get sound from the woofers it sounds OK.

To clarify matters I am going to ask an engineer friend of mine to help measure the impedance curve of the woofers. I do not understand why the SS power amp is happy to power the speakers full range, but not happy to power the woofers alone.
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almarg
9,670 posts
 
To clarify matters I am going to ask an engineer friend of mine to help measure the impedance curve of the woofers. I do not understand why the SS power amp is happy to power the speakers full range, but not happy to power the woofers alone.

That sounds like an excellent idea. What I was speculating, and it's just a guess, is that the impedance looking into the woofer terminals alone is too highly inductive, such that it would trigger the ss amp's self-protection mechanisms. When you parallel the woofer and the mid/hi elements for full-range operation, the somewhat capacitive load which is probably presented by the mid/hi crossover elements would tend to partially cancel the inductive component of the impedance of the woofer and its crossover, making the overall load more purely resistive and therefore perhaps not triggering the amp's self-protection mechanisms.

Just a guess, as I say, but it's the only theory I can think of that seems to fit all of the facts.

Good luck!

-- Al
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almarg
9,670 posts
 
Also, if at all possible try to arrange for the impedance measurements to provide the phase angle of the impedance (vs. frequency), not just the magnitude of the impedance (vs. frequency). That will allow the inductive, capacitive, and resistive components of the impedance to be distinguished from one another.

Regards,
-- Al
ajackson1
156 posts
 
Amfibius,

I have tried all the combinations you list with my Cary SLP-05, Cary MB 500 and Cary 120s tube amp and they all work for me.
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