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

Silverlight99,

I took a look at the following documents:

MusicianIII Specs
211FE Manual
SLP05 Manual
Stereophile's SLP-05 measurements, particularly output impedance

The 211FE input impedance appears to be specified as 150K unbalanced, 300 ohm balanced. If that is correct (and I would suggest verifying the 300 ohm number with Cary), you don't want to use the balanced input, because it's input impedance is vastly too low in relation to the preamp's output impedance.

Otherwise, I don't see any problems in relation to impedances. The power amp's 20K input impedance is not quite ideal in relation to the preamp's output impedance at 20 Hz of 3400 ohms (1500 ohms at higher frequencies), but that will result in a low frequency rolloff of less than 1db at 20Hz, which is insignificant.

You WILL need passive attenuation on the inputs to the Musician III's. They are spec'd for a voltage gain of 26db, apparently in stereo mode. Bridged mode will increase that to 32db. Using the balanced inputs may or may not increase that to 38db, depending on the internal design (you should ask Spectron that question).

The gain of the 211FE's is a little unclear. It says that 2 volts input results in full power, but full power is specified with 3 different numbers for Class A, Class AB2, and Class B operation. My guess, and it's just a guess, is that the 2 volts corresponds to the 110W Class AB2 number. For an 8 ohm speaker load (connected to the 8 ohm taps) that would be a voltage gain of about 24db (which would be 25db if the 2 volt sensitivity rating is based on the 150W Class B number). For a 4 ohm speaker load, those numbers would be about 20db and 22db, respectively.

So once you've pinned down the uncertainties I've described that enter into the gain calculations for each amp, the amount of attenuation that is required can be calculated by subtracting the resulting gain number for the 211FE from the gain number of the Musician III's.

All of this assumes that speaker sensitivity (spl out vs. voltage in) is the same for the low frequency drivers as for the mid/hi frequency drivers, which is probably the case if all drivers are part of the same speaker.

Hope that helps,
-- Al

Addendum to my previous post: I see on this spec sheet that the 211FE's balanced mode input impedance is listed as 300K, not 300 ohms, so the indication in the manual of 300 ohms is most likely a mistake, and using the balanced input is most likely fine.

Regards,
-- Al

Almarg - thx very much for the response, most helpful. slow delay as I didn't get a notifier for a response (don't know if that's a possibility on this forum). so I'm now getting closer to giving this a run. The speakers I'm using are the new eFicion F300's. they're an excellent speaker, with two separate units - bass and then mid/high. I'll check with the manufacturer if they're both rated at 8 ohms and how consistent. I will let you know what success I have! I'm guessing as a check if I set up the system without the attenuator on the bass from the Spectron's I can measure the actual voltage arriving at the speakers as a confirmation, but not sure.

Silverlight (and Almarg) I thought I should post a follow-up to this thread, given that it was me who asked the original question.

I have since bought a pair of JL Audio F110 subwoofers, and a Behringer CX2310 crossover to remove low bass from the main speakers. The result has been a substantial improvement in bass clarity up to the midbass, and improvement in dynamic headroom of the system. The cost is from loss of midrange and upper treble resolution, as well as an annoying hum. No doubt this is due to the poor quality of the Behringer. A Marchand is on the way.

I think a much better solution is to forget about bi-amping from the SLP-05, and buy an external crossover. It would be even better if it were possible to bypass the internal crossovers of your speaker and go active. The extra cost of doing so is negligible, since you already own two pairs of power amps.