Hi. I was wondering (IF I even hook it up at all.) the best way to ad a powered sub to an SE84UFO2. The sub is an Hsu vtf-3. The very first, front firing version. It does have both high level ins/outs and low level inputs. The source for now will be an Oppo player using analog outs. Thanks much! ~Mike

I use the speaker output for my sub from my SE84UFO.  It worked out pretty easy.  I use banana plugs from the amp to the sub and then direct connect the bare wire to the holes in the terminals.  

I don't use the high pass filter in the sub so the mains are still running full frequency but that allows the sub to be crossed over lower and requires very little gain from the sub amp.

The only other issue with connecting subs, I believe, is that you can only use high / speaker level connections when the amp has a true not floating ground. And I don't believe that the SE84UFO has a true ground. Steve could obviously advise. In terms of sound quality, both options can sound good. Some prefer the speaker level connection to give the same "flavor" to the sub. I prefer it at least when going long distances vs an rca.

Tony wrote on 12/06/21 at 23:42:01:


Thanks
I can't say there is necessarily a gain in sq, but my brain tells me to run wires separately to both the speakers and the subs.
Probably doesn't matter one way or the other.

I have 2 SE84UFO25s with 2 active subs wired directly from the speaker terminals to the corresponding high level inputs of the subs. This method was recommended as ideal for sound quality and does not reduce power to the speakers. Sounds great!

Sending separate lines from amp to speakers and amp to sub(s) is parallel connection. This is the cleaner way.

Run in series, separate loads add arithmetically, e.g. 8 + 8 + 8 = 24 ohms.  Run in parallel the load is the 'reciprocal of the sum of the reciprocals' of the individual loads; 1/8 + 1/8 + 1/8 = 3/8, reciprocal is 8/3 = 2.7 ohms.

The common active subs for sale rarely give the input impedance for speaker level, but through many searches I found one claiming 100 ohms and two stating 1k ohms. From one amp  channel's speaker out to one 8 ohm speaker and also to one sub input, connected separately (parallel), this would show 7.4 or 7.9 ohms, respectively, to the main amplifier. Hardly an imposition on the amp either way. But with series connection, who knows?

Aside that, there is issue of  the main speaker driver's back EMF that would be translated to the sub if connected in series (amp ->speaker->sub).

So, as related above: "[Parallel] method was recommended as ideal for sound quality and does not reduce power to the speakers."