Bi-Amping 2 Interconnects or Y Cable?

Or! You could add shunt resisters on the amp inputs. ;-)

Hi Dan,

I don't see any problem there. Martin Colloms' measurements in the review I linked to indicate that the power amp's input impedance is 50K (although the quoted specs say 100K!). So the two channels in parallel will present to the preamp a combined load of 25K. That won't result in a significant reduction in sensitivity (or significant frequency response unevenness, either) with nearly all preamps, especially solid state ones such as Toby's MC-7, since the preamp's output impedance will be vastly lower.

The lack of separate buffering on the two output jacks also means that the two-cable approach Toby was considering would result in the preamp's output stage seeing nearly twice the amount of cable capacitance as with the y-adapter approach. That could result in perceptible upper treble rolloff if cable lengths are long, the cables do not have low capacitance per unit length, AND preamp output impedance is high. But again, in this case the output impedance of the preamp is most likely low enough for that to be a non-issue, regardless of which approach is chosen.

Best regards,
-- Al

Thanks, Al. I didn't mean to suggest a mis-match, only that IME it can change the sound, usually a reduction in bass impact.

IME it can change the sound, usually a reduction in bass impact.

Hi Dan,

Yes, that's exactly what will happen under some circumstances. The voltage divider effect that occurs between preamp output impedance and amp input impedance will approximately double in significance if the amp's input channels are paralleled. That will approximately double the severity of the deep bass rolloff that will occur if the preamp has a coupling capacitor in series with its output (which most tube preamps and some solid state preamps have), the rolloff occurring because the capacitor's impedance rise at low frequencies increases the severity of the voltage divider effect at those frequencies.

In the case of a solid state preamp working into 25K, though, I wouldn't expect any of that to be quantitatively significant.

Best regards,
-- Al

Thanks again, Al!