1 Amp Per Expression, or 1 Amp For Both?

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ttocs

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In my quest to get my mind right about possible, or probable future mono amps for my Expressions I decided to do a seat of the pants experiment. I’ve been searching for info on comparisons of stereo amps vs monoblocks and I haven’t seen anything which is an actual apples to apples test, plus I really want to know how that would relate to driving a modern ML with powered woofers. So I thought I’d setup a test to find out.

The amps for this are a Krell S-1500 and an Emotiva XPA-200. Wattage is not horribly far off, signal to noise is close, filter cap storage is close, transformer on the Krell is waaay bigger.

Full disclosure: I’m extremely happy with how my system sounds. I want to experience dedicated amps whether it's monos or a matching S-1500, and also get educated on tubes. I never said I wasn’t crazy.

The listening test.
Each amp is only connected to 1 speaker. So, all I wanted to find out is if there would be a difference in dynamic impact. The simple answer is yes. And frankly I’m a bit surprised that the sound would be as good as it is. It’s not a huge difference, but it is readily noticeable and more enjoyable. What I initially interpreted as better articulation is probably better dynamics. That’s my assumption for now.

A little bit of science thrown in.
The Krell amp is driving the left Expression and a microphone is setup to record sound coming only from the panel. The right Expression is then connected to the Emotiva. I’ll record 20 seconds of Lester’s Methadone Clinic which is just voice and finger snapping, then I’ll connect the right speaker to the Krell and record the left speaker again. Recording into a DAW allows a close look at the wave forms. Zooming way in reveals differences in amplitude, small differences. When the Krell was driving only the LEFT speaker there was stronger waveform activity compared to when it was driving BOTH speakers. When I looked at smooth portions of the BOTH wave and compared it to the LEFT ONLY wave, the LEFT ONLY had more bumps in it which I interpret as the amp being able to exhibit better resolution. Also, smaller amplitude portions of the BOTH wave showed more rounding, or smoothing, whereas the LEFT ONLY had sharper forms which is partly why they were taller, having more amplitude.

What this means to me is that if I had another S-1500 I would use them each as mono amps and would enjoy an improvement. Splitting hairs, yes. Would I still do it? Yes. But that’s not all, because there’s something else going on here that I haven’t yet figured out, something in the soundstage. Maybe it’s the really tiny things coming through at the millisecond level (because that’s how far zoomed in I was), I dunno, but it’s intriguing.

I plan to reverse the experiment and record the speaker that’s connected to the Emotiva amp for the duration of the test. I would expect more pronounced differences from the cheaper amp with a much smaller transformer. I also need to make some short speaker cables as an extra credit test for when each amp is only running 1 speaker.
 
Well that was easy. Before I move the Emotiva back to where it belongs I decided to do the test today.

I did the same test using the Emotiva for left speaker duties. The results are very easy to see, the waveforms are noticeably different. When BOTH channels are driven the waveform shows reduced peaks without having to zoom all the way in. Not splitting hairs on this one at all. No contest.

With the Emotiva amp, driving one channel is better than driving both. Way better.

With the Krell, driving one channel is a really, really tiny bit better than driving two. I'm happy about how small the difference is, but there is a difference.
 

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