Bi-Amping 2 Interconnects or Y Cable?

If I understand correctly, you are referring to the possibility of using a pair of 1-rca female to 2-rca male y-adapters at the power amp inputs, and running a single pair of rca cables from there to the preamp. Vs. running a separate pair of rca cables from each power amp to the two sets of output jacks that apparently are provided on the preamp (which I am pretty certain, in the case of your MC-7 and most other preamps that provide two sets of output jacks, are simply wired together inside the rear panel of the preamp, rather than being separately buffered).

If my understanding of the question is correct, the first issue you would face is that most off-the-shelf y-adapters are very short, and might not be long enough to reach between the input jacks of the two amps. And if a custom-made adapter would be necessary to provide enough length, you might as well purchase a second pair of rca cables, it seems to me.

In any event, given that your preamp probably has a low output impedance, and your power amp has a high input impedance, the one possible technical issue I can foresee with either approach would be a slightly increased likelihood of ground loop issues (hum and/or buzz) with the single-cable + y-adapter approach.

FWIW, here are a couple of y-adapters having the correct genders, including the one from Monster that Hifihvn referred to:

http://www.bhphotovideo.com/c/product/469394-REG/Monster_Cable_600450_RCA_Female_to_2.html

http://www.audioadvisor.com/prodinfo.asp?number=TRS3YFMM

Regards,
-- Al

Follow-up to my previous post: Upon further thought, I suspect that you are referring to a passive vertical bi-amp arrangement, so each y-adapter would be connected between two input connectors of a single amp. Given that, the increased possibility of ground loop issues that I mentioned goes away, and the length issue probably does as well. So I see no problem going with y-adapters. And doing that would have the benefit of substantially reducing the amount of cable capacitance loading the preamp output, vs. having two cables, although that probably won't make any difference given a low preamp output impedance.

Regards,
-- Al

I have been trying to find that review for years, I dont know if they just finally posted it or what.

As a matter of fact, I see that they did indeed just post it. At the top of the first page of the review, in the byline showing Martin Colloms' name, it says "Posted: Aug 24, 2011 • Published: Dec 1, 1990"!

Best regards,
-- Al

Hi Toby,

I have no particular thoughts about additional mods.

Let me make sure, though, that I understand the reference to "500 watt mono biamps." Was I correct in thinking that you are planning to vertically biamp, i.e., having one channel of an amp drive the woofer on one speaker, and the other channel of the same amp drive the midrange & tweeter on the same speaker?

Best regards,
-- Al

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

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