Odyssey Stratos... or Stratos Plus, preowned. Around $750 or so. Not a tube amp but pretty nice.
11 responses Add your response
Energy lists the impedance as 8 ohms nominal, but notes that it may dip down to 4 ohms. Without more information from the manufacturer (like an impedance curve) it would be difficult to say whether it is tube friendly. There are professional reviews on the Energy website, though unfortunately none includes lab results.
What to do? Well there is anecdotal evidence: you can peruse the forums here to see if anyone else is using tube gear with the speakers (you'd want to pay attention to what kind of tube gear - sort of an "apples-to-apples" comparison to the amps you're interested in). Also, the SoundStage! review includes some information that might be helpful, for example:
The matching of a pair of loudspeakers to an amplifier is critical for achieving the desired sound. My Graaf Venticinque is a 25Wpc push-pull tube design running in pure class A. It is not an especially tubey-sounding amp in the sense of having a great deal of bloom in the low end, but it is still, electrically speaking, a tube amp. Although rated into 4 ohms, it will not drive all loads evenly. My Amphion speakers are exceptionally tube friendly, with an impedance that never drops below 7 ohms. In general, I felt that the RC-10s were very compatible with this amplifier, but I do suspect that a solid-state design, even of moderate power output, would have taken tighter control of the woofer and produced a more articulate bass.
Hope that helps.
The link that Mgattone provided had a link to the review measurements: http://www.soundstagemagazine.com/measurements/energy_rc_10/ where you'll find the impedance curve near the bottom. Since the scale is 0 - 50 ohms, the curve doesn't look too bad. But, from 2K Hz (guess the crossover point) to 5K Hz the impedance drops 10 ohms. And there's a 15 ohm rise from 200 Hz to 2K Hz. I guess you'd probably have less frequency response impact from the 8 ohm tap of the amp. I'll leave it to the tube guys to comment whether that much change will be audible. It looks like a roller coaster to me.
Regarding your initial comment about not needing a sub... The RC10 uses a small woofer and, even though your room is not huge, its sensitivity is low so you'll probably have to push the little guy. Look at the frequency response... It's great down to 100 Hz. I would high pass the RC10 and low pass a sub at 80 Hz, which would probably give a pretty flat response down to 40 Hz. In order to do this, you'll have to either use separates or an integrated with both preamp out and main amp in jacks or a stereo receiver with bass management.
It's not a matter of needing more power. That won't help. It's a matter of the disparity between the amp's output impedance and the speaker's impedance. For the 8 ohm tap, when the speaker's impedance is less than 8 ohms, less voltage will be available to the speaker (more will be dropped across the amp's output impedance) and the speaker will produce less SPL; when the speaker's impedance is greater than 8 ohms, more voltage will be available to the speaker (less will be dropped across the amp's output impedance) and the speaker will produce more SPL.
The question is whether these SPL output differences will be audible. Is it possible to use the sensitivity of the speaker to estimate the SPL differences?