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Rega Brio (one channel dead)
Rega Brio (one channel dead)
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Old 19th June 2018, 12:06 PM   #91
Depaj is offline Depaj  France
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Join Date: Aug 2015
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Well this wasn't completely for nothing because I learned something (thank you Nigel Pearson) but almost. I jut now noticed (wanting to test maximum power output) that the connectors to my 8ohm dummy loads (yes both of them) weren't making contact so I was scoping without any load. With the 8ohm load correctly connected the square wave looks actually quite good, although the rise time isn't that great compared to other amps I've worked on but I assume this isn't that surprising with this amp.
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Old 20th June 2018, 09:49 AM   #92
nigel pearson is offline nigel pearson  United Kingdom
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We all do it. I was much more alert at your age and get worse with age. You are one of the few who questions these things, well done.

In my experience the Brio type is far better than would be imagined. I don't think it would impress Jean Hiraga much. Mr Hiraga liberated my thinking circa 1980. He approximately said the ear can not hear distortion if the relationship of harmonics is the same as music. That is 2nd higher than 3 rd and so on with exponential decay. Second can easily be 1% and yet totally inaudible. A valve design I built respected this ideal and sounded just like live music. It had almost no negative feedback and what is did have was minute cathode degeneration. It had feed-forward distortion cancellation by curve matching. It was 1% THD 6 watts and 0.2% 1 watt. 15 Hz to 50 kHz - 3db 25 Hz to 30 kHz - 1 dB. It could not produce a square wave above 2 kHz. In some ways it out performed a commercial design using 300B ( I lie, it was far better ), it used EL34. What the amplifier gave was layers in the music seldom heard. Even with modern speakers it was fine and ideal with Quad ESL63. My design is nothing like the RH34 as I built one and wanted more. RH84,34,88 etc are very good projects and cheap to do. I am not a valve fanatic except the SE types. I don't think 300B is a good choice.

Hiraga said approximately that a very low distortion design with harmonics unlike music will sound distorted even if the percentage is very low. Negative feedback risks that. What happens is distortion that should not be there is not corrected whilst more benign distortion that would have made a better spectrum is removed. If a bottle of wine what has been made is vinegar with little fruit. Class AB is not easy. I suspect 1 watt of class A is a possible to overcome this. Douglas Self would say it's an abomination to do that. I am not so sure. 5 watts would be better, alas far too hot.

Before you think Hiraga a fool you should factor in the distortion of typical microphones and loudspeakers. 2% would not be unusual. However most have OK spectra. The Quad ESL would be about 0.1% and some microphones also. The Quad ESL has no real need for damping factor which helps. However my amp always sounded very impressive in the bass with them. I could imagine the Brio would be OK with them. The old test was 8R+2uF. That's very nasty.
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