How to bias Long tail pair....??

RRITESH · 2nd August 2011, 11:14 AM

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

sregor · 2nd August 2011, 12:07 PM

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)

AndrewT · 2nd August 2011, 12:10 PM

Self and Leach both have an understandable explanation of the long tail pair (LTP).

wahab · 2nd August 2011, 12:14 PM

Quote:

Originally Posted by RRITESH

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

RRITESH · 4th August 2011, 03:41 PM

Hi,

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

thanks

Andrew Eckhardt · 4th August 2011, 03:54 PM

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.

RRITESH · 4th August 2011, 04:18 PM

Quote:

If you like cheapnis just use resistors.

what about value of resistance??
and if i want to make hi-fi (Good) then??

Andrew Eckhardt · 4th August 2011, 04:41 PM

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.

RRITESH · 5th August 2011, 04:05 AM

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

AndrewT · 5th August 2011, 08:31 AM

Forget LT spice and go and learn how transistor circuits work.

2nd August 2011, 11:14 AM	#1
RRITESH diyAudio Member Join Date: Aug 2011 Location: Earth	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

2nd August 2011, 12:07 PM	#2
sregor diyAudio Member Join Date: Jan 2006 Location: massachusetts	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) __________________ Steve

2nd August 2011, 12:10 PM	#3
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Self and Leach both have an understandable explanation of the long tail pair (LTP). __________________ regards Andrew T.

5th August 2011, 08:31 AM	#10
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Forget LT spice and go and learn how transistor circuits work. __________________ regards Andrew T.

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4th August 2011, 03:41 PM	#5
RRITESH diyAudio Member Join Date: Aug 2011 Location: Earth	Hi, I have seen that links, but what is the use of Long tail (diff. pair) amplifiers and how to bias it?? thanks

4th August 2011, 03:54 PM	#6
Andrew Eckhardt diyAudio Member Join Date: Nov 2005 Location: PA	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.

4th August 2011, 04:41 PM	#8
Andrew Eckhardt diyAudio Member Join Date: Nov 2005 Location: PA	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.

5th August 2011, 04:05 AM	#9
RRITESH diyAudio Member Join Date: Aug 2011 Location: Earth	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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