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Old 19th August 2006, 03:23 PM   #1
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Default Linearizing diodes in amp circuits.

Greetings.
Are linearizing diodes ever used to linearize the transfer characteristic of transistors in audio amps? I haven't seen any examples in the schematics. Google indicates that the technique is used in RF amps and diode lasers, but no examples in audio amps that I can find. Is there any role for them? what are the difficulties in using the technique? Are there any casualties among you from attempts to make it work? I look forward to your views with interest.
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Old 19th August 2006, 04:29 PM   #2
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Quote:
Are linearizing diodes ever used to linearize the transfer characteristic of transistors in audio amps
Where to put diode in the transistor? You got example drawing?
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Old 19th August 2006, 04:59 PM   #3
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Take a look at this:

http://ca.search.yahoo.com/search?p=...-web-t912&b=11

Go to number 12.
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Old 19th August 2006, 05:45 PM   #4
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It is LM13600

Is the linearizing diode is D2 and D3? What are they doing there? What's the mechanism to obtain the "linearizing"? Won't the DC offset annoyed?
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Old 19th August 2006, 06:21 PM   #5
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>Where to put diode in the transistor? You got example drawing?

I haven't sketched any examples yet. I will study the examples referenced in the reply from member lumanauw before spending time on it. I am putting off working on this idea in case there are some compelling reasons to avoid it.
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Old 19th August 2006, 06:32 PM   #6
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>Take a look at this:
>http://ca.search.yahoo.com/search?p...b-web-t912&b=11
>Go to number 12.

There is plenty of material to study there. I am still curious why there are no examples of discrete amps using linearizing diodes.

I expect it is easier use them in ICs due to better matching of diode and transistor properties when they are on the same die.
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Old 19th August 2006, 06:37 PM   #7
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>Where to put diode in the transistor? You got example drawing?

I expect I would use them to linearize the input transistors which give voltage gain. Small signal transistors; FETs and tubes all seem to have a non linear transfer characteristic and so there might be a role for linearizing diodes. This would be an alternative to high open loop gain with feedback to achieve linearity.
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Old 19th August 2006, 06:53 PM   #8
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You can "linearize" current driven common emitter stage to current mirror. You will get lower gain, but better linearity. Good basic example?
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Old 19th August 2006, 10:51 PM   #9
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Very hard to do right, except by experts.
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Old 19th August 2006, 11:00 PM   #10
latala is offline latala  United Kingdom
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The first think that comes to my mind is the baxendall diode as used inthe Linsey Hood 75 watt design ! This is used to match the transfer characteristics between the quasi-complimentary output stage transistors !
A similar technique is also used in the old Phase linear 400/700 power amps
Regards Trev
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