Soulution amp and tubed preamp

Psag,
Al gave you very good information. Here's an exception to the rule. Australian member Pap said he used a Coincident Statement Linestage quite successfully with a Soulution amplifier. The Coincident has an output impedance of 500 ohms. So an unexpected outcome given the numbers. Al's point is certainly the general rule of thumb is these situations. I have no idea why the Coincident is an odd exception.
Charles,

Hi Charles,

As you know the CSLS has transformer coupled outputs, which I suspect maintain a fairly constant output impedance across the audible frequency range. I'm pretty certain that the ARC Ref amps have capacitively coupled outputs, which causes their output impedance to rise significantly at deep bass frequencies.

As I'm sure you know, it is often recommended that there be a minimum of a 10:1 ratio between power amp input impedance and preamp output impedance. And to be safe that ratio should be applied to the preamp's highest output impedance at any audible frequency, which especially in the case of capacitively coupled outputs may be much higher than the spec provided by the manufacturer, since unless otherwise stated that spec is probably at a mid-range frequency. Or if the preamp's highest output impedance at any audible frequency is not known, and there is reason to believe that the outputs are capacitively coupled, a much higher ratio than 10:1 should be applied to the manufacturer's spec. I've suggested 50 or 75 to 1 in past threads, to be completely safe in those situations.

The adverse effects which may result from failure to adhere to that guideline, such as rolloff of the bottom octave, result mainly from the COMBINATION of substantial impedance VARIATION as a function of frequency and the low ratio, not just from the low ratio in itself.

I see, btw, that ARC's web page on the Ref10 which Psag indicates he is using does in fact have the same 20K minimum load recommendation that I indicated earlier applies to many of their models.

Best regards,
-- Al

Hello Al,
Well that makes plenty of sense! The transformer coupled Coincident would
avoid the potential wide impedance fluctuations of a capacitor coupled
preamplifier. Pap's experience isn't the odd exception after all and his
success with the Soulution amplifier is now logically understood.
Thanks,
Charles,

Hi Psag, I am sure there are higher input impedance SS amps that you could look into besides Soulution. For example, Gryphon amps are 20kohms (balanced) so you'd likely be in safer waters with your ARC preamp. Not the same character as a Soulution but do let us know what other amps you are considering. Good luck.

I haven't heard Gryphon. I heard Soulution at RMAF with Focal speakers and was impressed with the clarity and effortless presentation. But I listen to a lot of rock music and I wonder it would sound lean.