[Roger A. Modjeski]

I have been corresponding with an RM-10 owner concerning the effect of choosing different output taps on his amplifier. The RM-10 has a 4 and an 8 ohm tap. BTW, the RM-200 has 8,4,2,1 ohm taps so you can see, I like taps even though it raises the cost. I think it's asking a lot to require the owner to go inside the amp to change impedance.

His Question: I noticed that several internet sites are reporting that 80% of the power is available from the 4 ohm taps and the loss is only 1 dB. You said 3 dB, which sounds more consistent with what I heard. Does this mean that 50% of the power is available from the 4 ohm taps?


My Answer: The internet figure of 80% is meaningless as it will differ from amp to amp. The voltage difference is about all we can talk about. In a good amp like the RM-10 you get 35 watts by putting a RESISTOR load equal to the tap value. So the 4 ohm tap puts out 100% power into a 4 ohm load.  The 8 ohm tap puts out 100% into and 8 ohm load.

There are other factors that differ from amp to amp (like damping factor and output transformer winding resistance) that will determine the SPL difference you get by changing taps. Again 3dB is the right number when an 8 ohm speaker is connected to the 4 ohm tap with a high damping amplifier.

[Nilanjan]

Hello everyone,

I am the RM-10 owner that Roger referred to. Actually, I am a future owner. I have an order in for an RM-10 and am using a loaner from my dealer until my new amp comes in. I have the loaner RM-10 hooked up to my Vandersteen 2Ce Signature speakers.

We must have exchanged over 10 e-mails and Roger was always helpful and courteous. Coming from solid state amps, I had a few nagging doubts that were cleared up along the way -

1. Can a little 35 W/ch amplifier like the RM-10 really be used with large, low efficiency speakers?
2. Are there any real benefits to tube amplifiers or is it all related to a pleasant type of distortion?
3. What are the real tradeoffs with the 4 ohm taps? How much do you give up for the higher damping factor, and is there any audible benefit?
4. Is there only a certain type of music that works with a small tube amplifier? Can it handle large scale orchestral music or is it only suited for small chamber music ensembles?

Now for some general comments about the RM-10 -

1. It has a beautiful, solid build and all the parts are of high quality.
2. Audible distortion is very low - i.e. this is not the classic "tube sound".
3. It works very well with my Vandersteens in my 18 x 10 x 9 listening room. It throws a huge soundstage and has a beautiful midrange and adequate control over the bass.
4. Above all, it is backed by Roger - a designer who knows his stuff, answers all questions and can even tweak the amp a little if needed. In my case, he may raise the gain a little with the 4 ohm taps. This level of expertise coupled with personal interaction is rare in this age of commercialization, mass production and outsourcing.

Both the amp and its designer are highly recommended and worthy of support.

Nilanjan