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Old 9th January 2009, 11:51 AM   #11
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I have modified a cambridge 840 or 2, it sounds ok, I couldnt pick up when the exchange happens, feel the frontend needs attention, I wasnt really deep listening for this technique they use, but it does have its flaws. The measurements they did seem to show some improvement.
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Old 9th January 2009, 01:02 PM   #12
atiq19 is offline atiq19  United Kingdom
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what is that sabistor thing doing in technics scheme?

I really don't know what a sabistor does.
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Old 9th January 2009, 01:19 PM   #13
atiq19 is offline atiq19  United Kingdom
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Is it worth while to integrate a simple mod to RMI-fc100 output transistors like the technics? in this case i would need a 'sabistor' and few resistors.

does it make sense?
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Old 10th January 2009, 01:59 AM   #14
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Quote:
Originally posted by AndrewT
there are a lot of designers and builders that disagree with me, notably Prof. Leach where he describes the operation of his drivers in LO Tim as staying in ClassA simply because he has arranged that they never switch off. I contend that he is wrong.

You have to make up your own mind.

My "clarification" is not fact. It is my opinion.
Andrew,

I agree with you. Just because one of the transistors is conducting some current does NOT make the operation class A and does NOT eliminate static crossover distortion. The spirit of class A (and the good performance that derives therefrom) is that both transistors contribute to the signal over the full cycle. If a transistor goes into essentially a constant current mode by its being prevented from cutting off, it is not contributing to the signal.

Cheers,
Bob
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Old 10th January 2009, 12:41 PM   #15
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atiq19, Although I cannot answer your questions about Technic's biasing scheme I would suggest that the inspiration for it came from Peter Blomley's February/March 1971 articles in Wireless World. The basic thinking behind Blomley's idea is that if neither class B output device enters cutoff the linearity in the crossover region becomes more controllable. An added complexity is that we need a "signal splitter" stage to direct the audio signal half cycles to the appropriate output devices.
On this forum I did a search using the terms "Blomley Amplifier" and found several threads. One is called "Question about signal disection" that includes a link to the circuit diagram. At the time of publication the amplifier had a distortion performance that exceded the capabilities of the measurement instrumentation available. It was not a DIY construction project as only the circuit schematic was given.
Keith
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Old 10th January 2009, 01:09 PM   #16
atiq19 is offline atiq19  United Kingdom
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Keith, Thanks for your post.

I couldn't find the Blomely post. Do you have a link.
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Old 10th January 2009, 02:00 PM   #17
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atiq19, Try this one for the circuit diagram http://www.diyaudio.com/forums/attac...amp=1110777721 Also check the spelling of Blomley.
Keith
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Old 10th January 2009, 05:18 PM   #18
atiq19 is offline atiq19  United Kingdom
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my mistake.

cheers.
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Old 10th January 2009, 07:35 PM   #19
jkeny is offline jkeny  Ireland
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If this biasing scheme or Krill amp biasing scheme prevents crossover distortion & only leaves static distortion can anyone quantify these?

What I am asking is lets not deal in absolutes - how big is crossover distortion relative to static distortion - is it 90% compared to 10%? If so we are removing 90% of the class AB distortion which seems like a good idea to me - no?

Sometimes we dismiss good ideas because they do not give us the 100% solution. So lets quantify what we're talking about
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Old 10th January 2009, 09:38 PM   #20
jkeny is offline jkeny  Ireland
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So Andrew or Bob,
Willing to put some figures on these distortions or their relative importance?
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