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Question about preamp+amp performance

REK2575

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Recently picked up a couple of Rotel components, RC-1572 MKII preamp & RB-1552 MKII stereo amp. The amp is rated at 130W per channel @8 ohms. It's replacing a 20+ year old Denon AVR that was rated for 60W @8 ohms.

Most of my listening is via streaming Qobuz:

Bluesound Node 2i --coaxial--> RC-1572 preamp --XLR--> RB-1552 amp --> ELAC DBR62 speakers (6 ohms)

Overall I'm very pleased with this setup, but I'm a little surprised at the performance of the preamp+amp: namely, not as powerful as I would have expected.

The RC-1572 volume control is from 0 to 100. It defaults to 45 when powered on. At 45, the volume from the speakers is surprisingly low, much quieter than is viable for even casual listening in my living room.

Am I interpreting this correctly? At 45% power, my 130W amp doesn't put out enough volume for even casual listening? It has more than twice the power of my old 60W Denon AVR. At ~50% volume the Denon was definitely louder than 'very quiet'!

I'm finding that the practical volume range is all between 50 and 80 -- i.e. from moderate-soft to Loud. Lower than 50 volume is essentially useless. Higher than 80 and things are getting QUITE loud.

Does this sound normal? I guess I don't understand why 45-50% of the volume range on the preamp is useless i.e. too quiet. I figured with 130W things would already be very loud at 50%?
 

MaxwellsEq

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There isn't that much difference between 60W and 130W in terms of how loud an amplifier will drive speakers. You would assume it will be twice as loud, but it won't be.

This is really about amplifier gain and how the volume control works. It doesn't really mean very much where the volume control is for a certain sound level.
 

DVDdoug

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...not as powerful as I would have expected.

...Higher than 80 and things are getting QUITE loud.
So it's not a question of power, it's just the volume control "profile". I assume the volume control is an rotary encoder so that depends on the software (firmware) and it was a design choice.

It tends to be less of a problem with a rotary encoder because it can be programmed so that it takes more than one turn for 0-100% and you can get finer control. Or you can program-in acceleration for a bigger change when you move the knob faster, etc.

The thing the preamp designer doesn't know is the exact-level your feeding-in and different hardware will be different. And with a preamp you might not be using the "matching" power amp so they don't know how much gain the power amp has. And they don't know the sensitivity of your speakers or how close you are to the speakers.... i.e. They have no idea how "loud" "45" is.

A regular analog volume control is a potentiometer with an "audio taper" (approximately logarithmic, or maybe it's anti-logarithmic). It's similar to your setup with most of the voltage/signal change happening at the loud-end, but it's more natural and yours is probably more extreme.

A regular-linear pot would be at 50% (-6db from the maximum) at the mid-point and that would be way too loud and you'd have the opposite problem.
 
OP
REK2575

REK2575

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I appreciate the explanations. Many thanks.

@DVDdoug -- I see what you mean by preamp not being able to 'predict' (so to speak) pairings with a vast array of other hardware, and so the volume # can only be a very relative measure of actual volume. However, I thought because the Rotel 'MkII' preamp was clearly designed to complement the 'MkII' power amp, there would be more refinement / nuance in how the preamp's volume control affects the power amp. In other words, I would have expected more of the 0-100 volume range to register meaningful differences in volume, whereas I'm finding I'll never even use 0-40 range because it's way too soft.

Anyway, the most important point for me is that there's nothing actually 'wrong' with my setup! I was worried that I was somehow not getting the full potential of the power amp.
 
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