RM200 / RM300 on 1 ohm?

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chan_

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RM200 / RM300 on 1 ohm?
« on: 10 Dec 2007, 11:01 pm »
Hello Roger,

For some time now I am looking around for tube amplifiers which can drive Apogee Scintilla. Their impedance drop as low as 1 ohm.  Will the low impedance have any effect on the musical character of the RM200 or RM300?

Regards,
Chan

jeffreybehr

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Re: RM200 / RM300 on 1 ohm?
« Reply #1 on: 11 Dec 2007, 02:43 am »
If the 200 has 4-Ohm output taps, if you parallel them (and the inputs, too) the amp will deliver 400* Watts into 2 Ohms.  Will that be good enough?

* Assuming it's a 200WPC amp.

chan_

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Re: RM200 / RM300 on 1 ohm?
« Reply #2 on: 11 Dec 2007, 10:45 pm »
As I understand the Scintilla's are hard to drive because of their sensitivity. Only 85db/watt. It will need quite some current to make them sing...
Probably the power is not the main problem, but delivering it at 1 ohm will a be problem for most amps.

Chan

jeffreybehr

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Re: RM200 / RM300 on 1 ohm?
« Reply #3 on: 12 Dec 2007, 02:48 am »
Well...you didn't answer my question about whether 400 Watts into 2 Ohms would be enough, but here's another thought.  C-j's Premier Eleven and P-12 output transformers can be wired for 2-Ohm outputs.  If one puts a P-11's two 2-Ohm channels in parallel, one gets a tubed amp that'll deliver 140 Watts into ONE Ohm.  How's that?

The P-11s are inexpensive enough for you to buy a couple to play with.

Roger A. Modjeski

Re: RM200 / RM300 on 1 ohm?
« Reply #4 on: 12 Dec 2007, 04:59 am »
Are you certain about the drop to 1 ohm? At what frequency? The speaker is resistive in nature. Is it the ribbon that goes to 1 ohm? How did the maker intend for this to be driven?

chan_

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Re: RM200 / RM300 on 1 ohm?
« Reply #5 on: 12 Dec 2007, 06:44 am »
140 watts will be sufficient  :) , as long as those CJ's can provide the current, it will be an interesting choice, Thanks!

Yes, I am afraid 1 ohm is a certainty. The Ribbons of the MR and TW play from 500HZ and up. I have no measurements at hand, but I read from an other owner (and amp builder) that the impedance characteristics are quite "flat". At introduction this speaker was driven by Krell KSA 100 or KMA 100/200.

I saw on a picture of the backside a 1 ohm tap at the RM200. How much current could the RM200 deliver?

Roger A. Modjeski

Re: RM200 / RM300 on 1 ohm?
« Reply #6 on: 17 Dec 2007, 08:29 am »
chan,

I was testing a RM-200 MK II the other day and took some measurements for you. You can get 14 amps peak from the 1 ohm tap. That corresponds to 196 watts peak or 98 watts on an RMS basis. You can connect a one ohm load to the 2 ohm tap and get 17 amps which is 289 watts peak or 144 watts on an RMS basis.

These are quite high figures if one notes that the 8 ohm tap on a typical 100 watt amp delivers 5 amps peak and the 4 ohm tap delivers 7 amps. An important aspect of the RM-200 is its ability to drive difficult loads which often drop to 1/2 or 1/3 of the nominal value.

The RM-300 will roughly triple the RM-200 numbers.

chan_

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Re: RM200 / RM300 on 1 ohm?
« Reply #7 on: 17 Dec 2007, 10:06 pm »
Roger,

Thank you for taking the time to take these measurements.
Are both models voiced the same? Or do they have different characters?
Any pictures available on the RM-300?

I sent you an email as well.

Chan