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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.

--dan
dgaylin
daverz
487 posts
 
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.
dgaylin OP
255 posts
 
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?
daverz
487 posts
 
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.
dgaylin OP
255 posts
 
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.
onhwy61's avatar
onhwy61
5,216 posts
 
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.
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