I have upgraded beyond my means

I have a problem.

After spending some serious pennies I have got a hifi I love the sound of.

There is a small problem.

Two components do not combine wel.

I have a stunning Rotel RB-991 perfect apart from one small problem.
It is a 200w rms Class A amp. At all but low levels it sounds divine.
at low volumes it sounds poor!

When combine with my old 87db/w speakers it was great...only at whisper quiet volumes could the drop in quality be heard.

I have bought a pair of Acoustic Energy 309's that have a sensitivty in the high 90's

The low volume amp failing now appears at anything below 25% on the volume.

Guess how loud 25% is withhigh sensitivy speakers combined with Rotels flagship amp.

Is there anything i can do to correct this?

The only reasonable solution i can think is buy the house next door and listen to my hifi from there.

 

only what you already know I suspect..

a lower power amp or lower sensitivity speakers..

you could attenuate the signal, but do you really want to go there?

 

You could try reducing the line level signal from your CD player Peter. I'm not entirely sure this would work as required tho'. Rothwell Audio market in-line attenuators.

Lowering the sensitivity of your AE's with an L series attenuation circuit is the other solution but this would also skew the crossover frequency of your loudspeakers to some extent.

http://www.mhsoft.nl/spk_calc.asp#att

 

Go into SET territory with only 4 Watts.
It's the first Watt that counts!

JJ

 

Attenuate your cables yourself, I did and it worked great. It costs about 30p if you have the soldering iron already, and that includes the solder and electricity

and if you don't like it, take out the resistors, re-terminate the ICs and what have you lost? 30p. Hell, if it's not worth spending 30p to find out if you can avoid buying new amps or speakers then there is no pleasing you

 

Stumblin's got it right ......attenuate the output of the cdp

 

Unless I am overlooking some basic knowledge (which i probably am) The CDP is output is much easier to attenuate by using the volume control.

I think i would need to attenuate the speaker cable for that to be of use.

Is that possible? How would i do it? Would it be cheaper and easier in the long run to buy a new house?

 

Yes you are...!

with a high signal from the cdp the amp just ticks over...reduce the level of input the amp works harder. This gets the amp to do the things that the designer wanted. As the volume range of an amp varies so does the quality...vol pot are not linear most are mis matched between channels at low levels. Its only IME the range 40-60% of max does the amp really start to sing. So you can see why these attenuators can help.

 

Is worth a shout. Lots of Quad and Naim owners use this trick, as modern kit outputs more than the equipment was designed for.

 

yeah, worth a go for what it costs.

You may find attenuating the interconnect gives you a more muddy sound with less dynamics - I did. BUT! for what it costs its got to be worth a try, as its the cheapest option

 

OK you need to explain this in simpler terms! my brain cannot hack this...answers in crayon would be prefered.

As I see it, my cd player puts out a signal. for simplification lets call it 5v.
this signal enters my preamp and is cut down to 2v.
the new 2v signalenters the back of my power amp gets multiplied by ten and heads to the speakers.

I can assume that you believe the faliure is down to a poor quality preamp.

I believe the problem is with the power amp. If it is not using a significant proportion of its power then the bass is distorted.

Are you suggesting that if a quieter signal enters the poweramp then it willbe using more of its potential with a more reasonable output. That seems sensible. But surely that is what the volume pot is for?

 

There is a simpler answer. Sell the Rotel and buy a Sugden. Seriously.

 

I attenuated the CD on my dads gear.

Before 20% on the volume knob was normal listening levels, after 50% was normal listening level (same percieved volume).

So in theory your amp will be working harder and be more in it's normal operating range.

 

There seem to be some basic misunderstandings here. The volume pot is an attenuator. It divides the input signal and sends some of it to the power amp whilst shunting the rest to ground.

Adding an extra attenuator at the input to the pre-amp and then turning the volume up to compensate will not change the signal going into the power amp. The power amp will see exactly the same signal it saw before and will most definitely not be "working harder".

The pre-amp will be working less hard though as it is working with a smaller signal. This may or may not be a good thing depending on the pre-amp.

Both the pre-amp and the power amp have fixed gain. The overall gain is set by how much of the pre-amp output is passed into the power amp. This is why volume controls are sometimes known as gain controls.

 

Okay, this will ge getting nerdy. We are looking at the gain structure of the hi-fi chain here.

First of all, are you sure the problem exists and you are not running afoul of Fletcher Munson curves? The ear hears diferently at low and high volumes, bass and treble are subjectively less loud relative to the midrange at low levels than at high levels.

Second, some speakers also need a bit of welly to come alive. The spiders which fix the membrane put up a bit of initial resistance which can distort the sound mor at low levels than at high.

It only makes sense to spend money on fixing the problem there when you have determined that there really is a problem wih your amps.

So, thirdly: Red Book specification for CD players fixes the output at 2V. Most manufacturers stick to that spec, but some - mostly those which are seeking a quick in a demo comparison through the louder = better effect - put out even more voltage, up to 8V have been measured on some 'merican designs.

A power amp these days generally needs about 1V input for full output. Some require even less, a few valve amps neeed more. The input sensitivity of your Rotel should be in the manual.

Since you normally won't listen flat out, a typical requirement for a signal at the power amp's input is about .1 V. Having seen that the CD player puts out 2V, you can see that the preamp generally doesn't have any amplification to do, only attenuation, hence why so-called passive preamps can work.

Your problem may have two causes: either you have to turn down your volume knob too much and the pot is misbehaving (highly technical term, that). Or, more likely, your amp is just ticking over and you are in a region where the amp has more distortion than at higher power levels - a reasonably common phenomenon in Class B amps but not in Class A amps, which you claim your Rotel to be (I know nothing about that specific model).

Solution: find out if the problem comes from the pre or the power amp. Change the component responsible, or change your speakers back to something less efficient.