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

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.

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

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

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.

I notice this statement in the manual for the CAD200:

Short circuit protection activates if load impedance is about 1.6 ohms or less.

I'm not sure how the protection circuit would sense what the load impedance is, but presumably it would do it by some sort of measurement of the relation between output voltage and output current. If the load is highly inductive, the current drawn by the speaker will lag the voltage by a substantial fraction of 90 degrees (exactly 90 degrees for a pure inductor, that has no resistance).

Therefore at the instant that current reaches its peak, the voltage will be at a considerably smaller value than the instantaneous voltage which caused that peak, which occurred somewhat earlier in the sine wave cycle. The protection circuit may interpret, however, that the peak current was caused by the instantaneous voltage occurring at the exact time of the current peak, in which case it would "think" that a lower impedance is present than is really the case (recall Ohm's Law, resistance = voltage/current; therefore a lower voltage producing the same current implies lower resistance).

When you run the speakers full range, as I said earlier, the capacitance which is likely to be a significant part of the impedance of the mid/hi drivers is placed in parallel with the woofer and its crossover elements, which would partially negate the inductive component of the loading presented by the woofer (the effects of inductance and capacitance on the phase relationships between voltage and current work in opposite directions).

So I think the statement in the manual about the protection mechanism reinforces the theory I presented earlier. It could be that the design of the amp's protection mechanisms is incompatible with your woofers, when they are driven alone. While you are waiting for the measurements you may want to ask Cary if a heavily inductive load, such as the woofer section of a speaker connected by itself, can trigger protective shutdown of the amp.

Regards,
-- Al