What is the best way to hook up a subwoofer

Al and Tiffany, I touched indirectly on the point Al makes in criteria 1) above, to wit, "[t]he sub provides separate line-level inputs for the two channels, not just one input jack that is intended to receive a summed mono signal."

That is the precise problem I was dealing with in the other comments I posted about the issue of summing the left and right channels. In other words, assuming you can use a y-adapter to split the single main output, the leg going to the sub will of course be both left and right channels. If the sub only has one input jack, i.e., the sub only plays one channel, then simply plugging the "sub-leg" into the sub will short the signals. I suspect you would wind up having only mono coming out of the other leg going to the amp.

In my case, I also run only one sub which is fed a summed signal via a special made impedance buffer. The buffer (1) presents a high impedance load to the output main feeding the sub and (2) sums the signals without shorting the outputs of the preamp. Take a look at my posts.

After absorbing what Al and I are trying to get across, I suggest running the idea by Calvin at ARC to check that the idea has "legs" (pun intended).

Bruce, I'd feel pretty certain that the tape outputs are not volume-controlled by the preamp, and therefore can't be used. If the sub doesn't provide speaker-level inputs, using y-adapters with the single pair of main out jacks would be fine, IMO, provided that three criteria are met:

1)The sub provides separate line-level inputs for the two channels, not just one input jack that is intended to receive a summed mono signal.

2)The paralleled input impedance of the sub and the main power amp is at least 20K, as you indicated.

3)The total capacitance of the cables to the sub and the main power amp is less than 1000 pf.

If the sub provides high passed line-level outputs, connecting it between the preamp and the main power amp would be another possibility to consider.

Best regards,
-- Al

Al, you are 100% correct about the outputs. Odd the SP-9 has two tapes and only one main output. That means the SP-9 will drive the sub full bore out of the tape output unless there's some way to control the output gain from the tape output. Just thinking outloud, I wonder if the single main output can be split???

Pdspecl and Bruce (Bifwynne), I had looked at several pictures of the rear panel of the SP9, including at ARCDB.WS, and they show only one pair of main outs (plus two pairs of tape outs).

Excellent comments otherwise, Bruce. I would just add that according to the specs shown in Stereophile's review, while a load capacitance of 100pf (or less) is recommended, up to 1000pf is acceptable. That would seem to make sense given the 250 ohm nominal output impedance, and might particularly be a significant fact if a y-adapter turns out to be the best approach.

Best regards,
-- Al

I own an ARC Ref 5 line stage and also have a self powered sub woofer. I mention this because we may share similar issues.

I just checked the ARCDB web site and note that the SP-9 has two main outputs. Al asks the correct questions. Also is the sub woofer self powered?? Does the sub permit you to adjust low frequency rolloff, phase and loudness. These adjustments are important in order to blend the sub with your main speakers. If the sub does not provide these types of adjustments, you may need a separate cross-over.

Also, very important point. What is the input impedance attributes of your amp and the sub? The ARCDB web site mentions that the SP-9: "[r]ecommended load [should be] 60K ohms and 100pF. (20K ohms minimum)." In other words, if the combined input impedance of your amp and sub are less than 20K ohms, you will overload the SP-9, which could cause sonic degradation.

I've posted a number of comments about this issue and provide the formula for computing combined impedance, as well as the somewhat unique solution that I employed.

After answering the questions raised by Al and me, I think the group can provide better advice.

I use the second set of Preamp RCA outputs to the subwoofer.

The answer will depend on what kinds of inputs the particular sub provides. What make and model is it?

Regards,
-- Al

I use a second set of speaker cables and go from the amp to the speaker inputs on the sub.
This way you get full range to your speakers and a clean signal to your speakers.