As luck would have it, a kind soul lent me a Nagra BPS phono stage for a week to conduct an analog workshop for a small group. The BPS was handed over to me in a small plastic flightcase, which was a refreshing change from the equipment I have had to handle recently (which could double up as weights in the gym !)
The Nagra BPS is slightly larger than the palm of my hand, and operates from a single 9V battery. It has a variety of loading and gain options, which should make it easy to mate with a variety of cartridges. MC gain is partly accomplished using in-house wound transformers.
The top cover of the BPS removes easily using the supplied hex key, giving access to various jumpers and the loading board. A separate hatch allows you to swop the 9V battery easily without having to open the top cover.
The front panel has a single toggle switch with three positions, "on", "off" and "test" (for battery life). The rear panel has two pairs of RCA sockets and an incredibly small grounding post. A DC socket allows you to use the BPS with an external power supply (7-10 V DC). I used this feature only to keep the circuit warmed-up and switched to the battery for listening sessions.
Gain is a very healthy 53 db for MM and 64 db for MC. Jumpers allow you to attenuate the gain by 16 db if you require. The resistive load settings for the BPS are 100, 150, 220, 330, 470 and 1000 ohms.
I was a bit concerned about battery life in use, but the manual states that the battery life is 100 hours, and in the 4-5 hours that I used the unit, the dealer installed battery held up fine.
I tried it first with my high output MC cartridge, a Sumiko Blackbird. The high frequencies were distorted, but using the 16db attenuator fixed all of that. Compared to my Whest Two phonostage, the Nagra had a lighter and faster tone.
The workshop host was using a midrange Pro-ject deck with an Ortofon 2M Blue MM cartridge. The differences between the Nagra and Whest were clearly audible, with some members of the audience preferring the more linear and extended sound of the Nagra and some preferring the more romantic tone of the Whest. The Nagra had a more neutral tone, with a very tight and fast bass line, and a drier but more extended top end. I also felt that the Nagra's soundstage presentation was more distant, but with better separation and more precise imaging.
Moving the Nagra back home, I tried it with my main rig, a Soulines Kubrick DCX with Jelco SA-750 tonearm. I tried a Hana SH cartridge - a high output MC cartridge (review coming) and a Shelter 5000 MC cartridge. I used my Graham Slee Reflex M and Elevator as a comparison phono stage. The Nagra sounded quite different in this setup. On both cartridges, midrange had a more laidback and subtly creamy quality to it, while both frequency extremes were clean and tightly controlled. The Graham Slee had a much more dynamic presentation, with a more vibrant and tonally dense delivery. Staging wise, the Graham Slee projected a more three dimensional stage, with a greater sense of depth and height. In comparison, you could describe the Nagra as being subtly expressive, but with a more restrained delivery.
Performance wise, I would put the Nagra to be on par with the Graham Slee duo, although their tonal balance are quite different. As a matter of reference, both phono stages are in a similar price bracket locally. Assuming that you like a more neutral tone, the Nagra is an impressive phono stage.