cabling a subwoofer to a NAD C356 integrated amp

For the B set I have my cables set for both right and left positive to go to positive in on Gallo, same for left.

The Gallo subs, or at least those that are presently listed on their website, have separate high level inputs for the two channels. So I think you are NOT saying that you would connect left and right positive to a single positive input of the sub, but rather to separate left and right positive inputs, respectively. And likewise for negative.

If so, and given that the Gallo subs are self-powered, there is no downside to what you are proposing. Also, I'll mention that you don't have to use heavy gauge speaker wire to connect to the sub, since you would be driving the high input impedance of the sub's amplifier and not the low impedance of its driver. Pretty much any gauge that is heavy enough to not be mechanically fragile should do.

The one thing you absolutely do NOT want to do is to connect left and right positive of the B output to a single input terminal on the Gallo, which could damage your amplifier. Although as I indicated I suspect that is not what you meant.

Regards,
-- Al

al:
the nad c356 has preamp outs and ins--would the poster be better served connecting the amp preout to the rca inputs on the sub (and rca outputs to to the amp prein)?

Hi Loomis,

I think you are referring to connecting the pre-outs to both the sub and to the inputs of the amp's power amp section, rather than connecting the pre-outs to the sub and the sub's line outs to the power amp section. If that is not the case let me know, although the considerations either way are somewhat similar.

That approach would probably work reasonably well. But I suspect the resulting sonics would be no better, and perhaps slightly worse, than connecting at speaker level. The main reasons being:

(a)The input impedance of the NAD's power amp section, at least for the C356BEE version, is specified as 20K in parallel with 1 nF (1000 pF). That is a large amount of input capacitance, which the output circuits of the preamp section would have to drive in combination with the added capacitance of the cables to the sub, as well as the input impedance of the sub itself. (The sub's input impedance is unspecified, but the input impedance of the line-level inputs of powered subs is often low enough to be an issue). The 80 ohm specified output impedance of the preamp section would seem to indicate that it could handle that reasonably well, but depending on the accuracy of that spec and on how it may vary as a function of frequency I wouldn't assume that the resulting effects on the signal path to the main speakers would be negligible.

(b)I suspect that the line-level connection approach would stand a somewhat greater chance of resulting in hum or other noise issues than the speaker-level approach, although chances are it would not be a problem either way.

(c)Although some folks would disagree, a philosophy espoused by REL among others is that it is preferable for the signals provided to the sub and to the main speakers to both reflect the sonic effects of the main power amp.

Best regards,
-- Al