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Old 23rd May 2005, 11:03 AM   #1
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Default beginners q's

input diff pair is SO common, why not simple single transistor with feedback to the emitter? (current feedback)

And which is best, double or triple darlington OPS for BJTs?
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Old 23rd May 2005, 02:41 PM   #2
anatech is offline anatech  Canada
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Hi cdr data,
NAD used a single bjt input instead of a diff pair. This design does not compete well sonically with other approaches. If it did, that would be the prevailing design. The diff pair can be far more linear, over a greater input signal range. It is self balancing for DC offset and there is no DC offset between the error input and signal input (0.6V for the single bjt).

There are enough variations between input device types and configurations to keep one busy for an awfully long time. At least you are on ground that is proven and stable.

You have only listed a couple output configurations. Lots of different ways to do things here too.

The answers depend one what you intend at the end, and cost. One circuit may not fit all situations.

-Chris
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Old 23rd May 2005, 07:20 PM   #3
AndrewT is offline AndrewT  Scotland
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Hi,
single input transistor is reputedly quieter than LTP.
JLH and many others use it.
The single will probably be more difficult to stabilise the DC offset at the output but I have never yet seen a design using a DC servo to control that parameter.
Swot up on it and give us a new design.
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Old 23rd May 2005, 09:59 PM   #4
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Try this address: http://sound.westhost.com/amp_design.htm
Rod Elliot is well known audio master. You might find some answers there.
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