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19 July 2010:


The Proteus ~ The Design of Sound

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Sound Quality vs. Measurements

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From the outset the English Valve Amplifiers Ltd. Proteus has been designed for the sound it produces not what the figures say on a sheet of paper. The whole design ethic is to get an amplifier to sound the best it possibly can in the real world throughout its power ranges and concentrating on the lower levels of volume.

Most of us listen to music at below 5 Watts, any more than that and our ears start objecting. In our homes we are right in front of the speakers, the sound comes at us like wall, so how can we possibly expect it to sound like it should, like a live concert. The point is we can't, the live sound is exactly that, live and unrecordable, we can get quite close though.

In the real world, all the sounds we hear are actually distorted in some way, to try and capture all that is difficult and to reproduce impossible and so it's a compromise at best.

Whilst developing the Proteus it became very clear that there were two things that was need; the lowest distortion at low power levels and control of the frequency response especially at the extremes.

The basic "sound" of this amplifier is mainly down to the output transformers, the power supply and a rather unusual line stage.

Fine Tuning The Proteus

During the later stages of development it was decided to see what would happen if we extended the frequency from 20Kz to 30Kz, we though it"The Proteus has a high-end sound that is also remarkably uncontrived..."
HiFi Critic
sounded better at first and then after a week of listening and comments from others it was found that a lot of the dynamics had been destroyed and the top end was edgy. We messed around with the feedback system and fine tuned the driver stages but ultimately most of the things we did damaged the original sound and concept.

We tried getting rid of the lift at 70Hz and found the dynamics at the bottom end went haywire, the bass was ill-defined and fluffy.

We moved the distortion characteristics around and found it ruined the top end dynamics, so we put everything back to how it was.

We then did it all over again just to make sure we weren't going mad or the results a product of psycho acoustic problems.

Don't Believe All That You Read!

If you measure the Proteus using all the latest equipment the results look pretty unencouraging. The frequency response is not uniform and it falls off rather alarmingly at 25 kHz, there is a hump at 70Hz, and the overall response extends below 5 Hz. (The very low end response bought it's own instability problems. We finally found that, occasionally, the whole thing was oscillating at about 2 Hz, cured by a change of valve type without affecting anything else).

The distortion figures are also not particularly attractive, below .08% for 3 Watts at some points and above 1% at other levels . We didn't bother measuring phase relationships!

But then listen to it! The dynamics are some of the best of any amplifier made, its production of the frequency spectrum effortless and accurate, and with every speaker we've tried it on!

It's very easy to get lulled into a situation where one thinks "it's got be good because it looks good on paper" only to find that, this is not the case!

Time and time again I've listened to amplifiers both valve and solid state that claim dead flat frequency responses, zero distortion and whopping power outputs, they all sound the same---- horrible! A good test is to listen to a set-up for half an hour or more, if you want to carry on listening because you are enjoying it, it's probable that this set is actually very good. If, on the other hand, you can't wait to get out because your ears hurt or your bored, there's a good chance that it sounds pretty bad and you are feeling the strain. You should never have to work at listening to hi-fi, it should be natural to be able to enjoy it ---- you should be able to hear the music, not the equipment.


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