Anyone compared BAT Rex vs. Atmasphere MP-1?

08-27-10: Raquel
If you have long IC runs (2+ meters) to your amp, I would be inclined to consider the top solid-state pre's in order to avoid the impedance issues and problems running long cables that almost all tube preamps (except those using output transformers) suffer from.

Both these preamps are fully balanced/differential from input to output. No output transformers(Ralph Karsten doesn't use them in any of his products). The MP-1(& MP-3) put out 32v@600ohms, the Rex 200ohms. The Atma preamps are claimed to easily drive cables of up to 200ft long. So, cable influence is essentially a non-factor when run to true balanced inputs of a power amp.

Output impedance measurements for tube preamps are typically made at 1 khz., and the story will usually be very different at the frequency extremes, especially in the low bass. As for the BAT Rex, Atkinson's measurements in Stereophile revealed, "[I]ts output impedance was a little higher than specified, at 1000 ohms at 20kHz, 415 ohms at 1kHz, and 4.8k ohms at 20Hz. The last is due to the necessarily finite size of the output coupling capacitors. As MF noted, it should not be a significant issue in listening to music as long as the power amplifier has an input impedance greater than about 50k ohms." Atkinson's measurements of the BAT VK-51SE revealed similar performance.

Generally speaking, you need ten times the maximum output impedance of the preamp as compared to the input impedance of the amp to avoid frequency roll-off, i.e., this is why Fremer and Atkinson state that a BAT Rex with a maximum output impedance of 4.8K ohms needs to be used with an amp featuring an input impedance of 50K ohms or higher. There are a lot of amps featuring input impedances of less than 50K ohms, so this is going to be an issue at times.

I know that Atma-Sphere pre's don't use output transformers. Perhaps Ralph can explain how the MP-1 get around this problem?

Aaah, I get what you are saying now, thanks for the tip. Luckily, everything that I am considering is 100k and up.

Sonic attributes of the Rex include:

Very dynamic, clean, energetic.
Highlights midrange texture and harmonies.
Bass is excellent.
Treble is open and extended.
Noise is very low.
Very powerful sound.
Switch between 6C45 and 6H30 provides two flavors.
Build quality is at the top.

Those looking for warmth and forgiveness should look elsewhere. This will dig deeper into the music. I have no clue why people say BAT is 'dark'. I would never charactarize this preamp as dark.

Adding NOS 6H30DRs will up the excitement factor (2 out of 8 in the power module is enough for me).

I think the Joule LA450 and the Audio Reference Anniversary Preamp could be intriguing alternatives, but I have not made a comparison and am not particularly concerned to do so at this time.

Hello,

I am not familiar with MP-1 except its excellent reputation. I am familiar with REX and its the best (along with my current Joule-Electra LA-300ME) preamp I ever auditioned or used.

When I heard REX first time (using my reference tracks) my jaws literally dropped to the floor. Word "magnificent" is understatement.

Regarding the long cables - its the best if you call Victor. In this situation,I would not care at all if preamp balanced or not but if it has a buffer driver. Victor is perfect man to address your specific concerns, He is extraordinary nice person (well may be not in all his writing... ;--) ;--) He will help you and advise you. You meet daily at "Outside" and Victor will do everything he can to help you in any way possible.

Good Luck !
Simon