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Volume Controls better @ 11:00 and above

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    Posted: 22 Mar 2016 at 3:44pm
Volume controls sound their best at  or above 11:00 (or above 4 on a scale of 1 to 10).
WHY? It has to do with the transfer of electrical sound energy across the volume control to the next amplifier stage.
 This is called the "drive" to the next stage.

The output impedance of the amp circuit driving the volume control is applied directly across the volume control.

 BUT the next stage's input impedance is being driven by the variable output of the volume control.
When the volume control is set at a lower level, there is now an impedance mismatch such that the driving frequency response is not as flat and there is a loss at lower frequencies (hence the older amps used a "loudness" tap on the volume control to boost the low end).
 SO the input to the next stage after the volume control will be "frequency starved" at very low volume control settings ( below 9:00 or 3 on a scale of 1 to 10) and you will hear more treble.
 At 11;00 you will hear more midrange and some more bass . At 12:00 (1/2 volume) and above, you will get most of the bass added in. Above 1:00 there is very little change in the frequency response.



Edited by BAK - 23 Mar 2016 at 12:12pm
Bruce
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BAK Quote  Post ReplyReply Direct Link To This Post Posted: 22 Mar 2016 at 4:16pm
You can mitigate this "1/2 volume" level by using an attenuator in the signal chain before the volume control.
 Use a 20 dB attenuator if you can't get above 1 or 2 on a scale of 10.
 Use a 10 dB attenuator if you can't get above 3 or 4 on a scale of 10.

But there is another way ( which wastes power)... put a 4 ohm 50 watt resistor in series with each speaker to reduce a 1/3rd of volume on a 8 ohm speaker. A power amp can handle the now "12 ohms nominal" on it's 8 ohm nominal output. This resistor will not affect the frequency response. Of course you need to use a larger power-rated resistor than actually needed to keep a lower amount of heat radiated. (Use a 50 watt "R" for expected power output to be 50 watts or less, 100 watt "R" if you have a 200 watt or larger amp.)
(Any need for a higher power-rated "R" would be for a very loud power delivery system like in a concert hall !)

Note: A resistor in series with your speaker can act as a sacrifice device to prevent blowing your expensive speakers.
Just use a "R" with a power rating of 1/2 the power rating of your speaker.

OR you can use a smaller power-rated amplifier.
Remember, higher power does not equate to higher quality sound if you are not going to use that higher power.


Like Graham has described here:
http://audio-forum.gspaudio.co.uk/proprius-amp-tweaking_topic2758_page5.html
 the higher power amplifiers need to have more active components to achieve the higher power (more transistors or valves). And every active component added to the signal chain changes the signal quality.
So, the fewer active components used to achieve the desired result, the more close-to-the-original your system will sound.


This is the basis for the "minimalist" HiFi approach.



Bruce
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BAK Quote  Post ReplyReply Direct Link To This Post Posted: 22 Mar 2016 at 4:55pm
Another little-known fact:
 At lower volume control settings there is a lower Signal-to-Noise ratio.
This is due to the amplifier's stages after the volume control being designed for full volume driving them.
If a circuit is designed for a 1.0 volt signal drive, and you reduce it to less than half @ 0.5 volts, it will have 6 dB less signal than at full volume... @ 0.25 volts, it will have 12 dB  less signal.
You can equate the amount of dB attenuation on the volume control to how much you are reducing the Signal-to-Noise ratio.

Example:
@ Full volume you have 100 dB S/N ratio
then, @ -6 dB volume setting on the volume control you will have 100 - 6 = 94 dB S/N
  @ -12 dB vol setting you will have 100 - 12 = 88 dB S/N
And so on...

An added clarification to note is: the noise floor does not raise up as you turn your volume control  down ...
 the signal level is being reduced closer down to the noise floor... thus reducing the S/N ratio.
You will not hear the noise level changing as it will remain constant.


This is another reason for the volume control setting above 11:00 sounding better; especially with higher powered amps.


Edited by BAK - 23 Mar 2016 at 2:39am
Bruce
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BAK Quote  Post ReplyReply Direct Link To This Post Posted: 22 Mar 2016 at 8:50pm
All...
 The above stated information and all other posts of mine on this forum come from over 45 years of experience in electronics... all kinds of circuits require the following:
 low S/N ratios, low distortion, low digital interference, low RF interference, a wide enough frequency response for the given purpose, and efficiency enough to be power-cost effective.

 Where I state in my signature my experience, it is not to be in conflict with any one else' experience, including Graham's own.
 My motto, "Here To Help", means just that. I try to help where I see it is needed. The "old" knowledge is being whittled away by falsehoods in today's world. "More" of anything is not always better.

 Those who have more power than they need can keep their beliefs about power requirements.
I will not judge them to be any less knowledgeable.
 Yes extra current drive capability from a power amp allows for some considerable "headroom" above what would be used. This has the effect of making the sound reproduced to seem "wide-open" and "effortless" driving a pair of speakers... almost like the music has no bottom.
 
I have heard such systems (and repaired some very powerful amps; 2500, 1500, 1000, etc ).

 And, yes, at normal listening levels, the THD is lower than at full volume... this is a given for all amplifiers.

I have also heard low power amps achieve the same effect with very high efficiency speakers,
the high efficiency allows the speaker to sound more "effortless" in it's delivery.

 I
am only hoping to state that speakers do not require a lot of power unless they are very low efficiency.

Your ears will prove this out in any A - B speaker test using the same amplifier (with it's volume control at the same setting) with A being any low efficiency (< 85 db SPL) and B being any higher efficiency (> 90 dB SPL) speakers.


Edited by BAK - 23 Mar 2016 at 2:50am
Bruce
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 23 Mar 2016 at 5:23am
The usual exception, and I say usual leaving out S/N, is the virtual-earth or summing node, and for one good reason: the common mode gets "cancelled" (well, just about) in the math - the input never approaches saturation because it is the "fulcrum" in the input output circuit. That's why it's called a virtual earth, because the signal is virtually zero, and zero cancels common mode distortion.

(and this is why recording studio mixers get away with it)
Not simple enough for Google-Bot to understand...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DaveG Quote  Post ReplyReply Direct Link To This Post Posted: 23 Mar 2016 at 12:24pm
This is interesting & informative stuff. It begs the question though - what is the rationale behind using high powered amps for normal home use when it means you can't use anything like the full full volume range? When I bought mine I vaguely remember stuff like "reproducing dynamics, avoidance of clipping and the ability to drive difficult loads" being cited. Not that any of that particularly influenced me - I just bought after demo-ing vs a couple of other amps. I liked the sound then and still do. Just seems that all that power is going to waste....or is it? I've owned and liked, to varying degrees, amps at both ends of the spectrum. As ever in hifi opinions seems to be polarised with people getting behind whichever P.O.V. they have bought into and refusing to budge. Me I'm just curious.
Dave

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Post Options Post Options   Thanks (0) Thanks(0)   Quote morris_minor Quote  Post ReplyReply Direct Link To This Post Posted: 23 Mar 2016 at 1:53pm
Judging by how dynamic the Proprius amps sound into my PMCs, for my room, a higher powered amplifier just isn't required . . 
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