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Old 2nd August 2011, 11:14 AM   #1
RRITESH is offline RRITESH  India
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Default How to bias Long tail pair....??

Hello,

I am trying to make an amplifier ( using transistor) of 5watt ( near by this) for this a long tail pair is required in many circuits...
I have seen many link but i don't understand its biasing.
Please tell how to make it.??


Thanks
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Old 2nd August 2011, 12:07 PM   #2
sregor is offline sregor  United States
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Please supply circuit. LTP (long tail pair) operating points are usually determined by current source or resistor to supply rail going to the emitters, then a resistor to ground or to input circuit on one base, and a circuit from feedback to the other base, so that both bases are about the same voltage, and the emitter current is supplied. (I prefer the term operating point rather than bias - YMMV)
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Old 2nd August 2011, 12:10 PM   #3
AndrewT is offline AndrewT  Scotland
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Self and Leach both have an understandable explanation of the long tail pair (LTP).
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Old 2nd August 2011, 12:14 PM   #4
wahab is offline wahab  Algeria
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Quote:
Originally Posted by RRITESH View Post
Hello,

I am trying to make an amplifier ( using transistor) of 5watt ( near by this) for this a long tail pair is required in many circuits...
I have seen many link but i don't understand its biasing.
Please tell how to make it.??


Thanks

Transistors
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Old 4th August 2011, 03:41 PM   #5
RRITESH is offline RRITESH  India
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Hi,

I have seen that links, but what is the use of Long tail (diff. pair) amplifiers and how to bias it??

thanks
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Old 4th August 2011, 03:54 PM   #6
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What's the use? Matched high impedance +/- inputs. Tons of gain. Some even harmonic suppression. The best way to bias depends on what you expect from the circuit. If you like cheapnis just use resistors.
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Old 4th August 2011, 04:18 PM   #7
RRITESH is offline RRITESH  India
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Quote:
If you like cheapnis just use resistors.
what about value of resistance??
and if i want to make hi-fi (Good) then??
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Old 4th August 2011, 04:41 PM   #8
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Find and inspect/analyze the old Accuphase P-300 circuit. Just resistors for current sources can easily be hi-fi. At some point it becomes a matter of taste. You'd have to build or listen to a lot of circuits to really know what you're after. Generally, more transistors is not always the solution.

Far as ballpark figuring out how much collector current you have in an LTP, just figure the emitters are one junction drop beyond the bases, and do V/R on the emitter resistors. Divide the answer in two to find per transistor operating point. To decide how much current you Want requires a lot of mental fiddling with facts about how that changes circuit response alongside the available graphs in the datasheets, or a bunch of messing around in spice. Around 1mA is often pretty close for input stage transistors.
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Old 5th August 2011, 04:05 AM   #9
RRITESH is offline RRITESH  India
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I have seen many pdf of Acc. P-300, but the cicuit where overmy head please give some basic information for designing it and circuit......
I use Lt spice.

thnaks
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Old 5th August 2011, 08:31 AM   #10
AndrewT is offline AndrewT  Scotland
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Forget LT spice and go and learn how transistor circuits work.
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