Joule Electra LA -150 ii/ 200 and impedance issues

BTW, I'll mention another potential biamping issue that isn't generally realized.

In the case of a preamp driving a single power amplifier, if the output impedance of the preamp is high (at high frequencies), and the interconnect cable is long and also has high capacitance per unit length, the result can be a slight but perceptible rolloff of the upper treble. Although in most circumstances that effect won't be great enough to be audibly significant. But in the case of a preamp driving two power amps from a single output stage, the possibility of that kind of issue increases significantly, because the combined (total) capacitance of the interconnect cables to BOTH amps will affect the signal seen by the high frequency amp.

So in the situation where a single preamp output stage is driving two power amps, and the preamp has a highish output impedance, it becomes especially important to minimize the TOTAL of the lengths of BOTH interconnects, and/or their capacitance per unit length.

All of these considerations, btw, are also applicable to the situation where a preamp is driving both a power amp and a powered subwoofer.

Regards,
-- Al

Springbok, yup it's just like Al said. Take a look at some of my posts which discussed how I loaded my ARC Ref 3/5 preamp's 2 outputs: Main 1 -- drives the main amp. Main 2: -- drives a single subwoofer. ARC recommends that the combined load impedance presented to the Ref 3/5 NOT be less than 20K Ohms.

Using Al's formula, I realized that I overloaded my preamp. In my case, I found a gent who custom designed a built a buffer device for me that presents Main 2 with a much higher impedance load. The device also (i) sums the left and right channels for the subwoofer without shorting the Mains and (ii) enables me to tap both loads into the preamp's balanced outputs.

It's a cool device and was NOT terribly expensive.