Surprising results from bi-amping the Uniti Atom and NAP 250.2 with B&W Signature 705

Hi-Fi Corner
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I started my hi-fi journey a year ago with Naim Uniti Atom and a pair of KEF LS50s connected with Audioquest Rocket 22. Over the last few months, I have been trying to upgrade the current system step by step. First, I found a good deal on B&W Signature 705s and upgraded the speakers.
The 705s have impressive highs, but I would say they sound different rather than better than the LS 50s.

After a while, I found a good deal on a pre-loved NAP 250.2, recently serviced and upgraded with Naim’s the NAP 300DR Trafo. With the NAP 250.2, I found the undiscovered potential of the Signature 705. My experience with this upgrade was shared in a recent post: Suggestions for Naim Uniti Atom vs Atom HE as a pure streamer/DAC/preamplifier.

Last week, I found a couple of NAC-A5 cables in very good condition. Replacing the Rocket 22 cable with the NAC-A5 isn’t “better”. The soundstage is wider, but sometimes I felt there was more grain in the background, less clarity, although the difference is not huge. The overall impression is slightly better with the NAC-A5, but this could simply be a subjective impression due to the “Naim” on the cable.

While I was wondering of what to do with the Rocket 22 cable, it occurred to me that I could experiment with the 705 Signature speaker. The speaker supports bi-wiring / bi-amping.
Having read some bi-amping experiences with either Atom or Nova shared on this forum, I connected the Rocket 22 cable between the Atom and the HF, leaving the NAP-250.2 to concentrate on the LF.
I know that the the Atom and the NAP 250.2 have different power outputs, and the cables are also different, so it is not theoretically “right” to do this experiment. However, the results are surprising: the HF resolution is significantly improved and the HF and LF work in good synergy.

My wife and I repeated the A/B tests blindly (one setting the cable, the other blindly listening to the system without knowing the current setting), and each time we found the bi-amp to be notably better than the 250.2 alone: better resolution, better separation, and an overall better listening experience. Concerned that the LF response might be too pronounced with bi-amping (driven by NAP 250.2), I measured the frequency response at our primary listening position between the two settings. Surprisingly, the curves look very similar, and I did not see any extra decibels in the lower frequencies.

The difference of bi-amp is much more pronounced than swapping the cables, similar to the upgrade by adding a NAP 250.2 as a power amp. Of course, this may only apply to my speakers. This experience may not apply to other speakers or systems. My own opinion is that HF is relatively easy to drive, and with only 40W from the Atom it is sufficient to drive it properly. When it came to relatively harder LF, the higher output of the NAP 250.2 was just right. But that doesn’t explain the better resolution even in the HF range. Is it possible that B&W speakers are designed to work better with be bi-amp?

I can only conclude that it takes a lot of experimentation to achieve the ideal listening experience: The room setting, the room treatment, good equipment, and good synergy between the individual components of the system. But Atom is definitely an interesting little guy with a lot of potential.

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It’s worth just removing the supplied links on those B&Ws and replacing with link wires - nothing fancy just experiment with some RS56 hook up cable. I came into possession of a pair of 3 way B&W floor standers some years back and decided to try them out before deciding what to do with them. Initially I was somewhat underwhelmed and felt that there was far too little precision and definition to what was a prodigious, if somewhat wooly bass and indistinct midrange. Removing the supplied metal links and replacing with 56 strand cable link with the terminals done up nice and tight brought a total transformation.

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Good point. I hadn’t considered that this connection could be the bottleneck in my system. I’ll definitely give it a try and update here with the results of the experiment.

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Managing as best possible LF more often than not cleans-up HF (and mid-range) performance too, hence the many advocates of room treatment, to this end. I suspect you are also hearing that the B&W’s prefer the better current control of the 250. Legacy B&Ws can be very current hungry and, in general, speakers always respond to more control from enhanced power.

Of course, you can also try and manage LF via the bungs which are supplied.

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I completely agree that the 250.2 offers better current control. That’s what I experienced after adding the NAP 250.2 to the Atom. What I don’t understand is why the HF performance improves after driving it exclusively with the Atom (40W) in bi-amp mode? Doesn’t the NAP 250.2 (80W) as a single amp (for both HF and LF) theoretically deliver more current to the HF?

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You should try it the other way around; the better amp should be driving the hf.

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tried it and it did not sound better. I remember reading somewhere that the LF needs more power to drive compared to the HF

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I bought a pair of Chord jumpers and tried to replace them with the B&W links supplied and used 250.2 to drive them. However, it still does not sound as good as bi-amping and I would say that the difference between the Chord jumpers and the B&W jumpers is not very obvious.

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