Atmasphere ma1,VTL mb250, Jolida JD 3000

I'm a dealer for Atma-Sphere, SoundLab, and JoLida.

The difference between 140 and 200 watts is less than 2 dB. However, none of these three amps will really be delivering exactly their rated power into the load the SoundLabs present, so let's take a closer look.

The main challenge that SoundLabs impose on most amplifiers is this: In the bass region, the impedance is up north of 30 ohms.

Let's start out with a look at a typical solid amp that delivers 200 watts into 8 ohms. The amp may well double and do 400 watts into 4 ohms, but into 16 ohms it's halved to a 100 watt amp, and into 32 ohms it's only a 50 watt amp.

Most push-pull tube amps do a better job than this at high impedance; most of them will probably give you closer to 100 or 150 watts into 32 ohms (assuming you start with 200 watts into 8 ohms).

The 140 watt Atma-Sphere amp will give you probably a good 200 to 250 watts into 32 ohms.

Now the impedance curve doesn't stay up there of course - assuming you have high-impedance backplates (necessary with Atma-Sphere amps) the impedance will come down to about 6 - 8 ohms at 500 Hz. There, your MA-1 will probably give you 120 to 140 watts or so. The impedance then rises to 15 ohms ballpark, and then descends to about 2 or 3 ohms in the high treble. This sounds scary, but in practice it doesn't tax the amplifier because there's very little power demanded of the amp way up there. Now the frequency response curve of the SoundLabs does slope down a bit at high frequencies because of that impedance curve behavior, but the detail and nuance is still there - it's just a warmer sound overall.

So in practice, the difference in output level you get driving SoundLabs with a 140 watt OTL amp and a 200 watt push-pull amps is probably small, and the edge might well go to the OTL amp.

If you shoot me an e-mail, I can give you some subjective impressions that might be helpful.

Best of luck,

Duke

Thanks Duke;check your email.

What a great response! Thanks for the detail.

Duke, I agree with Jafox. What a great response and a model for how folks in the business-of-audio can interact positively and constructively to share their knowledge. Thank you!

Rlef, one thought I would add is that the Atma-Sphere MA-1 will deliver exceptionally transparent, highly resolving sound, with accurate timbre and excellent bass authority, when the impedance match works. I can't speak to the VTL or Jolida equipment because I haven't hear them.
.

The impedance of current Sound Lab models, namely the PX series, is being measured by Roger West at this time. I requested it since we are looking at a large installation which may involve driving more than one speaker from an amplifier, possibly Atma-Sphere. When the impedance curves are developed I will try to make them available.

Amplifier power output ratings are nominal only, especially when driving difficult loads. I have had 100 watt amps drive the U-1s here well, while 250 watt amps fell flat on their faces. Interestingly, both were tube amps with output transformers. The speaker load is a challenge for any amplifier, whether tube or solid state. Amps with robust power supplies tend to do better. Not all OTLs are necessarily well suited to drive big ESLs like Sound Labs, either.

Disclaimer: I'm a Sound Lab and Atma-Sphere dealer.

Brian

Brian, thank you. The impedance measurements would be very interesting to see if you can share them.
.