Magnepan LRS power amp compatibility?

For a load impedance that is essentially resistive (as is the case with the LRS, per John Atkinson’s measurements in Stereophile) the amount of power that is delivered equals voltage x current.

So for a given load impedance power (watts) and current (amperes) are directly proportional. (Or to be more precise, power is proportional to current squared, since voltage is also proportional to current). And given that relation together with the fact that per Ohm’s Law current equals voltage divided by resistance, it follows that providing a given amount of power into low impedances requires more current and less voltage than providing the same amount of power into high impedances.

JA characterized the speaker’s impedance as averaging about 3.33 ohms. I assume your amp provides a 4 ohm tap, which should be a reasonable match, that would allow the amp to come reasonably close to being able to provide 36 watts into this speaker. But the potential issue would be the maximum volume 36 watts could generate with this speaker, given its very low sensitivity. JA’s measurements indicate the speaker’s sensitivity as being 80.1 db/2.83 volts/1 meter, which given its 3.33 ohm average impedance corresponds to about 76.3 db/1 watt/1 meter.

Providing 36 watts into a pair of planar speakers each capable of producing 76.3 db at 1 meter in response to an input of 1 watt will result in a sound pressure level (SPL) at a distance of say 10 feet of approximately 90 db. That is enough for some listeners with many or most or all of their recordings, but is certainly not enough for many and I suspect most others.

So as is usual in audio, it depends :-)

Happy holidays! Regards,
-- Al

My LRS with monoblocks each 250 watts into 4 ohms sounded good, when I went with 500 watt into 4 ohm Bryston 4BSST noticed bass improvement although to be fair different room.  Your amp seems about 1/3 of what might be needed with a tube amp on these.  Call Eric @ factory he was driving them with 100 watt/channel tube amp. 

I have a vintage Dynamic 70 and LRS. It is not my main amplifier but a backup but the ST 70 offers an almost magical combination with the LRS if you drive it with a quality preamp. I know of another LRS owner who also fell in love with the combination. You will not max out the sound level capacity if thé LRS with the ST 70 but for a great majority of my listening the amp plays quite loud in a more modest sized room. The added sense of sound space is wonderfully captivating with the ST 70/LRS combination. Yes you can get better performance from more expensive and powerful amplifiers but the pairing of these two might provide you with many hours of great listening. Try both the 4 and 8 ohm tap as well as reversing wall plug polarity to find the optimal setting.