Biamping with very different amps

roberjermanYou really need an active crossover to split the signal into high and low pass outputs to drive the bass and mid/high amps! An active crossover will allow you to set the roll-off slopes (not doeable with passive) and levels for the best sound! Been there, done that!

To do that successfully with an active xover, he would also have to completely by-pass the internal xovers inside his Kefs, way too much work.

No, passive by-amping will be fine, as those Kefs have a very well thought out quality passive xover network, with for memory conjugate matching circuitry as well.

Cheers George

Thank you George! You are correct in this matter!

While the KUBE equalizer I believe you are using with the speakers would probably allow you to avoid the gain matching issue some of the others have mentioned, that is the least of the issues that would come into play.

I suspect that many of those who have responded do not realize that the Cary is a 20 watt tube amp (and rated at only 15 watts for 1% distortion), while for the 4 ohm nominal impedance of the speakers the Parasound is rated at 800 watts!!

As Imhififan correctly indicated, if you were to passively biamp using those amplifiers you would in effect be converting the 800 watt amp into not a great deal more than a 20 watt amp. That is because while a passive biamp configuration reduces the amount of current and power each amp must supply, both amps must still output voltages corresponding to the full frequency range of the signal. And therefore if the volume control is turned up high enough to utilize a substantial fraction of the power capability of the 800 watt amp the 20 watt amp would be driven into clipping.

But that’s not all. The speaker’s crossover between the two sections that are accessible via its input terminals (i.e., the crossover between the low frequency driver and the mid/hi drivers) occurs at 150 Hz. Most music has most of its energy above that frequency, most of the time. Which means that a passive biamp configuration would require the 20 watt amp to supply most of the power most of the time, while the 800 watt amp would be doing very little most of the time.

And if you were to use an external active crossover with its crossover point set high enough to avoid asking too much of the 20 watt amp, I suspect you would have to set that frequency somewhere in the treble region. The result would be little or no sound between that frequency and 150 Hz!!!

And all of that is not to mention the potential for loss of coherency due to differences between the intrinsic sonic characters of the amps.

Yes, to use your words it’s a crazy idea IMO. In audio, IMO, simpler is generally likely to be better. And in a case like this especially.

Regards,
-- Al

Thanks Al, I value your opinion.  The current drive train for the 107/2s is Parasound (JC 3), JC 2 BP, 107/2 KUBE, and JC 1.  When I replace the Esoteric SA-60 with an Ayre DX-5 DSD, a Bryston SP3 may replace the JC 2 BP so HDMI can be used for SACD and BD surround.

I've used a CAD 572 SE to drive LS50s with surprisingly good results, so that stirred my imagination without thinking it through.  The sensitivity of the LS50s is 5 dB less than that of the 107/2s, so I may try setting up a switch between the amps, but the 107/2s do sound magnificent driven by the JC 1s -- a JC 1 also drives the Reference 204/2C center.

db