stupid question about sources, amps, and loudness

Okay, so I really should know this, but I don't, so your help is most appreciated.

My speakers are a fairly tough load to drive 86db efficient, 6 Ohms nominal.

That suggests that I need reasonably powerful amplifier(s). Currently I use solid state amps rated at 100 WPC.

The amps are Kharma MP150s. They drive the speakers quite loud, although they do start to "flatten out" at 95 db (which is much louder than I typically listen, even when I've turned it up).

I have some issues with not having enough range of volume control either with a pre-amp or with a CPD with a volume control -- that is to say, if I turn the volume control much past 10 or 11 it is too loud.

I know that I can use attenuators to fix the volume control problem, but that they also can have sonic consequences.

Here's the question: less powerful amps are NOT the answer right? It's input sensitivity. Right?

So, if for example, I am thinking of trying tube amps, I still need to be mindful of the difficult to drive speakers and thus need to get some pretty beefy tube amps (i.e., 100 WPC+). Because less powerful tube amps won't have enough current to drive the speakers effectively.

BUT: I would want amps with a lower input sensitivity?

Do I have this right?

Thanks for clearing the cobwebs for me.

Sounds like a gain issue. What is the gain rating on your current amp? I have several different amps with different gains each, having nothing to do with power rating. If amp X has more gain than amp Y then the speakers playing from amp X at a volume setting at 10 o'clock on the same preamp with be louder.

Seems like the common component is the CD player, whether direct or through the preamp. Maybe it is your CD player that has more gain and is causing the issue? I have two CD players with volume control. One I can turn up all the way and have tolerably loud music. The other CDP gets too loud at about 60% of full volume. Note - this is when they are being run variable output direct to the amp.
Ckoffend, thanks. I can't find a gain spec on the amps. They do have an input sensitivity of 1.2 V.

I actually tried the amps with a different CDP. Same issue. I can attenuate the output of the pre-amp with internal jumpers by 20 db. But the sound quality is reduced.

So there's gain, current, and input sensitivity. How can you ever know what components are going to work.
The gain is probably the better number to pay attention to because it is not relative the the power rating of the amp.

If only the power rating and the sensitivity is given, gain in dB is related to the power rating (at 8 Ohms) and the sensitivity by

gain = 20*log10(sqrt(power*8)/sensitivity)
Daverz, thanks very sensitivity, you mean input sensitvity of the amp, right?
Yes, input sensitivity of the amp. So your amps would have a gain of

20*log10(sqrt(100*8)/1.2) = 27.4 dB

Which is on the moderate side.

It would be nice if more amps had switchable gain like some Brystons or variable gain like the Parasound amps.
Daverz, yeah that's what I got too (good to know I can do math even if I can't figure out component matching). Thank you.

So...back to my main question. As a separate issue, I am interested in trying tube amps (never had them before). So what I want are amps with good current 100+ per some of the Atmasphere technical papers and posts on this. But I want amps with a lower gain.

This way, not only will I have the ability to try appropriately powered tube amps, but I will have the added benefit of better volume control with the CDP or the preamp.

Do I have this right?
One thing about tube amps is that you'll typically get about 3dB less gain from the 4 Ohm taps.

Looking for a low gain amp seems like an awkward way of solving this problem. I would suggest trying attenuators first.
Yes that's probably right...just helpful to keep all this in mind as I think about what tube amps to get.

Thanks so much.
I do not think your current set up has any gain mismatch issues. If you are listening at the 9 or 10 o'clock position, it is okay. I would say you have a problem only if you are always below 8 o'clock.

The factors involved are the output of your digital source, input sensitivity of your preamp and amp, preamp and amp gain and speaker sensitivity.
Please describe what you mean about the loss of sound quality when the preamp -20dB jumper is used. The fact that your unnamed preamp has this feature means it could be modded to other values. You might want to contact the manufacturer.

Your unnamed speaker are not such a tough load unless their impedance varies wildly. They may not be the current monsters you think they are.
>>"I have some issues with not having enough range of volume control either with a pre-amp or with a CPD with a volume control -- that is to say, if I turn the volume control much past 10 or 11 it is too loud.
I know that I can use attenuators to fix the volume control problem, but that they also can have sonic consequences."<<

What's the problem??
I had a similar problem when I use balanced ic's. Except I could not even get to 11 o'clock which is why I bought the rca version.

As far as tube power I had a Bryston B100 rated @ 100w into 8ohm and 180w into 4ohm. My speakers are Dyn C1's rated at 85 db but a steady 4ohm. Then I bought the Octave V70SE rated at 70w into 4ohm. The Octave has everything all over the Bryston especially the control of instruments and vocals. 2 things I would consider when looking at a tubes is a soft start to make the tubes last longer and a good output protection circuit (all tubes will eventually fail) and you don't want to have to have it repaired after a tube failure.
Great comments from Onhwy61! I agree that you need to know the voltage out put of your digital sources as they can often exceed the 2.0 volt standard. Preamp gain plays major role also. I had rhis same issue a few months ago. My DAC has 3.1 volt output,preamp had 20db of gain, amp input sensitivity=0.7v and speakers are 94 db sensitivity. I solved the problem by having Coincident reduce rhe preamp gainfrom 20 to 10db, problem solved completely.
Good Luck,
All --

Thanks for the many helpful comments.

Specifics are as follows: speakers are Wilson Benesch Curves; pre-amp is Nagra PL-L. Sources are EAR Acute CD player (yes very high 5V output) but also Northstar DAC (2 volt ouput).

Here's the experience:

with the Northstar into the Nagra, volume on the Nagra was at 8-10 o'clock. Over 10 too loud. When I changed the jumpers on the Nagra to -20db, the volume needed to be at 3-6 o'clock (7 is maximum). But the sound was noticeably less clear -- sort of compressed sounding.

with the EAR into the Nagra, the EAR's volume is set at 12 o'clock, and the Nagra then has a nice range of volume control (10 o'clock to 2 o'clock). Seems good. BUT...

The very best sound of the system, despite the fact that the Nagra is an absolutely wonderful pre-amp, is to connect the EAR directly to the amps. Surprisingly much better: more details, greater warmth, greatly improved soundstage.

In this set-up, the EAR's volume control is between 8 and 11.

Sebrof -- the problem is that fine volume control is difficult with such a small range, and as I understand it with volume controls, using them at the extreme range is not good in terms of sonics.
I don't know the steps in volume control for the EAR CDP. But my question is when the EAR is running into the PLL preamp, why don't you have the EAR's volume/output set to fixed (is this not possible with the EAR?)?

I have heard very good things about the EAR Acute and have owned the Northstar DAC (good, but not better than the EAR from what I have heard). Doesn't the EAR have digital inputs?

Are you running balanced or SE? Maybe try a pair of Attenuators (either RCA or Balanced) running at negative 10dbA. I think this may help give you what you are seeking.

Finally, the EAR Acute is supposed to be pretty warm. Unless you are looking for a lot of warmth I would definately try it with a tube amp before buying one.
Yeah the EAR has no fixed volume option. Yes it does sound warm, which I like, and while the Northstar is good, the EAR is substantially better. Agree that tube amps may be too much of a good thing. Also agree that maybe I have less of a problem than I originally thought. Will probably try some attenuators since it is an easy and relatively low cost experiment.

thanks all!
I missed the part about the jumpers on the pre-amp. That's a thoughtful feature. Dgaylin, are you sure about the sound degradation? Make sure you are matching levels when you compare before and after.
Generally, almost all audio systems have TOO MUCH Voltage gain, resulting in various combinations of not enough volume-control range, more electronic noise out of the speakers*, etc. The most-common culprit is too much gain in poweramps and secondly too much gain in linestages.

Nelson Pass recognizes this and makes one of his FirstWatt amps with NO Voltage gain--yes, it's just a 'preamp-output buffer', converting the preamp's Voltage to the same Voltage but lots higher current to drive speaker systems.

Dgaylin, your goal of more than 100 tubed Watts for your 86dB-(in)sensitive speakers seems reasonable to me, but I doubt if you'll find an amp with little-enough gain (such as maybe 10dB). Using the 4-Ohm taps will indeed lower Voltage gain AND increase speaker-damping factor compared with using the 8-Ohm taps. The easy thing to do is try the in-line RCA/RCA attentuators.

I just bought Monarchy SE-160 poweramps that use a 12AT7 for frontend gain and a class-A-biased output stage that uses MOSFETS. With the designer's approval, I'm now using 12AU7s, and the amps have c. 9dB less gain. About 10dB still-less gain will be about right, and I'll have to get that by changing something within the amp or adding a resistive dividing network at the amp's frontend.

IF you fall in love with a tubed amp that has too much gain, a technician can fairly easily add a gain contol at its frontend.

* which is more likely to occur with relatively hi-sensitivity speakers
Is anyone going to mention potentiometer taper?
Linear or log, for example?

Want more vol control range? Get a different taper pot.