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Graham Slee Power Amplifier

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Post Options Post Options   Thanks (0) Thanks(0)   Quote morris_minor Quote  Post ReplyReply Direct Link To This Post Posted: 20 Feb 2016 at 9:07pm
Welcome to the forum, Dave!

Graham's posts are always interesting, and it's great to see the development process "up close". The posts about what was to become the Accession phono stage were made into a series of blog posts, which make for very interesting reading Wink.

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Accession MC/Enigma, Accession MM, Reflex M, Elevator EXP, Era Gold V
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Post Options Post Options   Thanks (1) Thanks(1)   Quote BAK Quote  Post ReplyReply Direct Link To This Post Posted: 21 Jan 2020 at 5:47pm
Originally posted by BAK BAK wrote:

Efficiency is more important than power handling for sound quality.
It is a matter of physics.
Every time a quantity of energy is transformed from one energy form to another there is a loss of energy. The loss can be quantified by measuring the efficiency of the transformation.
With a lower efficiency transformation, less of the original information from the energy source is reproduced in the end result.
 This amounts to less of the original sound energy is reproduced in lower efficiency speakers.

The dissertation below will prove that any quality-built amplifier (like the Proprius) with greater than 20 watts rms power output is sufficient enough to drive speakers available today with very pleasing results.

 (By quality-built I mean: one that has enough current and voltage "headroom" designed-in, wide enough frequency response to not hinder delicate or powerfull sound passages, and extremely low distortion measurements at loud and quiet sound levels.)

A little-known fact is:
 In old-school electronics,
less than 1 watt rms = low power,
from 1 watt to 10 watts = medium power,
greater than 10 watts rms = HIGH POWER...(100 watts rms is extra high but was not mentioned in the reference)

This rating scheme came from early radio days.
 It was found that less than 1 watt rms was all that was needed for "personal" listening; with  headphones or a pocket radio.
 1 watt to 10 watts was needed to fill the average room with sound as with a table radio (most were between 1.5 and 5 watts).
 Greater than 10 watts rms was only needed to fill large rooms.

Average commercial speaker sensitivity today is about 85 dB @ 1 watt rms measured @ 1 meter, in short form...85 dB @ 1 w/1m. That means that you get 85 dB at 1 watt when measured with a sound pressure measurement instrument with a calibrated microphone from a distance of 1 meter directly in front of the speaker, in the center of the speaker's radiating pattern...or straight in front.

 The below is a way to approximate decibel levels.
Note: An increase in Acoustic power (dBw) is ... 10 Decibels = 10 x log of 10watts / 1watts.

Now with acoustic power you add 10 dB for every multiple of 10 watts rms... or each time you multiply the power by 10.
 If with 1 watt you get 85 dB,
 then at 10 watts you get 95 dB,
 at 100 watts you will get 105 dB!
Again with acoustic power you add 3 dB for every multiple of 2
watts rms... or each time you multiply the power by 2.
 If with 1 watt you get 85 dB,
 then at 2 watts you get 88 db (+3 dB),
 at 4 watts you get 91 dB (+3 dB),
  and at 8 watts you get 94 dB (+3 dB),

 from above, at 10 watts you get 95 dB,
 then at 20 watts you get 98 dB (+3 dB).

If you have an 8 ohm speaker capable of producing 95 dB @ 1w/1m,
 you will get 105 dB @ 10 watts / 1m,
 and then 108 dB @ 20 watts / 1m,
 and about 110 dB @ 26 watts / 1m (Proprius power @ 8 ohms),
 and 115 dB @ 100 watts / 1m.

You see from above that, if you have a higher efficiency speaker, you will get more sound measured in decibels at any
acoustic power level than you will from a lower efficiency speaker.
You will also be able to drive the higher efficiency speaker with less power to get the same amount of sound!

This is why professional sound systems use very high efficiency speaker drivers.

 Good to repeat.

AT-14SA, Pickering XV-15/625, Technics SL-1600MK2, Reflex M, Lautus, Technics SH-8066, Dynaco ST120a, Eminence Beta 8A in custom cabs;; Using Majestic DAC
Enjoy Life Your Way!
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