[jman66]

The RM-9, even with the gain toggle set at LOW, is very easy to drive.
Using the LOW toggle, the highest amount of feedback is used, MED toggle uses less and the HI setting uses the least - all with sonic differences.
How does one attenuate excessive preamp gain without mucking up the signal in order to obtain broader use of the volume control?
Would something like the EVS Ultimate Attenuators between the preamp and amp be in order?

[Roger A. Modjeski]

If you had my RM-5 preamp you would find 4 dip switches inside to lower the gain to unity if desired. How much gain does your preamp have? 20-30 dB is typical and that's often too much. You can use an attenuator but that increases distortion (the preamp has to produce more voltage). If you use just CD and other high/medium line sources, consider our passive "Pot in a Box". If you are going to install attenuation its better at the input of the preamp than the output, or a little of both.

We have the C-4 preamp coming soon which will have lower (more appropriate) gain. Check it out at www.ramlabs-musicreference.com. The pictures are in the gallery, the text isn't up yet.

Roger

[jman66]

Currently, my preamp has 10dB of gain and the source (DAC) outputs 2.25Vrms.
I've looked into the RM-5 and the C-4 but unfortunately the lack of remote is a show stopper for me.
And, I've considered a passive but don't want to lose dynamics.

Moving through the gain toggle settings HI - MED - LO and their respective, increasing negative feedback levels,
how would you characterize the impact on the sound?

[Roger A. Modjeski]

Where do these dynamics that you don't want to loose come from? Are they generated in the preamp? If so, how do you imagine that is done?

The impact on sound that changing the gain/feedback switch is just as one would expect. More feedback, more damping, less distortion, less noise. What do you hear when you change the switch? That's all that matters.

If you have a speaker with a rising impedance in some region you will experience more acoustic output in those regions as the feedback is decreased because the output impedance of the amp rises so as to follow the impedance curve of the speaker. Some years ago, a fellow brought over an OTL he had built which had little damping. I measured it and it was around 1. When connected to my QUAD 63's the bass was up 8 db at 50 Hz. I measured that too. The treble was down by about as much making the total frequency response error 16 dB from top to bottom. For someone who didn't know what was happening, he might ascribe this new sound to the new amplifier saying "Wow, great bass, great bloom, those speakers aren't bass shy anymore" Would he know that 99% of what he heard was simple frequency response error generated by the amplifier-speaker combination? Would he know that the response of the speaker was nothing close to how QUAD had voiced it? This fellow who made the amp said "one of my owners has 63's and he loves them with this OTL".

The RM-9 damping is given in the manual and its a lot better than 1. From memory it is about 20 in the lowest gain setting and one third that in the high gain setting. I am avoiding the "fxxxback" word by noting the gain difference. They go hand and hand.

[jman66]

The RM-9 damping is given in the manual and its a lot better than 1.

Yes, damping is listed in the manual: LO gain yields .7db, MED gain yields 1.5dB and HI yields 2.5db.
Those values are relatively close to 1. 
What you've stated about damping is converse to what the documented numbers portray. Higher feedback appears to yield lower damping.

Regardless, you said it best, it's what you hear that matters.

As for dynamics, that comes from the source component, or if you really want to get picky, from the actual source software being played. If it isn't in the source, then nothing downstream is going to recreate dynamics. The preamp attenuates or amplifies that signal true to the source, or so one would hope.

[Roger A. Modjeski]

Sorry for the confusion. When damping is expressed in dB (which I prefer) one has to do a bit of converting. Without getting into the math 1 dB is a factor of 10 and .5 dB is a factor of 20. So even in the high gain position the damping is about 7 minimum and it is 15 at the maximum. As it should be, the damping goes up with the feedback and the gain goes down.

There is a good reason for doing this and I bow to ARC for being the first I am aware of to express it that way in a printed spec. I had been measuring damping that way for a long time and converting it to the standard form as I did in the paragraph above. I was happy to see someone else state it as it is most easily measured. To measure it this way all one has to do is drive the speaker into the specified load, set a zero reference, remove the load and see how much the output rises. The smaller the rise, the higher the damping. ARC calls it output regulation. Doing it this way we know that the drive to the speaker cannot rise above the open circuit value and that's a good thing to know. If the damping was one, the output could rise as much as 6 dB.

As to your thoughts about the preamp I agree, it should just pass on the dynamics of the original recording. Therefore if one has enough signal from the source to drive the amp to the required level there is no need for a preamp.

I don't want to shoot myself in the foot here because I am offering a preamp in the SES series. This preamp handles two tasks:

1. The EM-7 has a gain of only 12 dB and some sources may need a little gain to drive the amp to full output on quiet CDs. 

2. The speakers I have designed for the SES system benefit greatly from a little passive EQ. That takes up about 8 dB of the gain making the preamp a necessity. I also plan to make a preamp with passive tone controls which will chew up gain also.

This is a good place to remind everyone that a preamp cannot increase the maximum power of a power amp.  I hear this misconception at least once a week in phone conversations with the public at large.

Your RM-9 allows for a passive preamp and I have used mine that way for many years. It's the main reason for the high gain position. Even a quiet CD will drive the amp to full undistorted output.

Roger

[jman66]

Roger,

As always, thanks for the explanation and setting the facts straight!