[Guidof]

My RM 200 Mk II drives Martin Logan SL3s speakers whose impedance drops to 1.5 Ohms. They are driven from the RM 200's 1 Ohm taps, with excellent results.

My question, to Roger in particular, is: What is the output power of the RM 200 in this scenario?

Just curious, really.

Thanks for any enlightenment.

Regards,

Guido F.

[Roger A. Modjeski]

The RM-200 puts out 100 watts into any tap loaded with it's stated load.

[Guidof]

Thanks, Roger, for the information. I was under the apparently wrong impression that as the speaker impedance decreased (to 1.5 Ohms in this case) the RM 200 power output increased.

Regards,

Guido F.

[Roger A. Modjeski]

Thanks, Roger, for the information. I was under the apparently wrong impression that as the speaker impedance decreased (to 1.5 Ohms in this case) the RM 200 power output increased.

Regards,

Guido F.

There is more to this as the RM-200 is a very special amplifier when driving a miss-matched load. Virtually all transistor amplifiers increase their power as the load drops and the good ones double their power with each step down in impedance and halve their power with each step up. This is because transistor amps are voltage source devices that can put out more current (up to a point) as the load requires it.

Tube amplifiers do not respond this way. Their power actually peaks at the matched load and is less at either side (higher or lower than the marked tap). The RM-200 and RM-9 SE are a bit like transistor amps in that they have excess current available for a load that dips in some area. An RM-200 can put out about 150% of its rated power into a load that is half the rated tap impedance. Typical tube amps put out only 50-70% into a 1/2 impedance load, the balance going into overheating the output tubes.

Given all that, if your load does go as low as 1.5 ohms it really should not be on the 8 ohm tap no matter what the rating or highest impedance stated by the manufacturer of the speaker. It's the lowest impedance that really matters. That is why I take the time and expense to give you 8,4,2 and 1 ohm taps. As stated before, one should always use the lowest tap that sounds good and plays at your peak listening level without clipping.

Times have changed and many of us have more sensitive speakers and listen at lower volumes (because we have better definition equipment) than we did in the days of monster power amps. I find that most people are using just a few watts these days. The extra watts that are in "reserve" in a big amp are better traded for driving the speaker with a lower tap which provides more current. In many cases a 10 watt amplifier playing at a few watts sounds much better than a 100+ watt amplifier playing a few watts. When you go down on the taps you actually turn any amplifier into more class A with lower distortion in its low power range. While some think a big amp "controls" the speaker better this is totally untrue. It's more damping and more current that "control" a speaker and that is achieved by going down on the taps. This was first explained in 1990 in the RM-10 manual where I coined the term "light loading".

[Guidof]

Again, thanks very much, Roger, for the thorough explanation.

Over the years, I experimented with the various taps. In my current smaller listening room, I find that the 1 Ohm tap gives the best sound quality without any clipping. Even though the small room has been a challenge, the combination of bass traps, sound absorbing panels and DSPeaker AntiMode Dual Core has made your RM 200 Mark II amp sound better than ever through my Martin Logan SL3 speakers that are not known for being an easy load.

Regards,

Guido F.

[Roger A. Modjeski]

Again, thanks very much, Roger, for the thorough explanation.

Over the years, I experimented with the various taps. In my current smaller listening room, I find that the 1 Ohm tap gives the best sound quality without any clipping. Even though the small room has been a challenge, the combination of bass traps, sound absorbing panels and DSPeaker AntiMode Dual Core has made your RM 200 Mark II amp sound better than ever through my Martin Logan SL3 speakers that are not known for being an easy load.

Regards,

Guido F.

Glad to hear you like the 1 ohm tap. Speakers like yours are the reason for it's existence. With speakers that drop so low a 4 or 8 ohm tap just can't drive them. In addition, the low load on the high tap looks like a short so the power that isn't going into the load is going into overheating the tubes. People who have large impedance mismatches find their tube life is significantly reduced.