What is the name of this topology? - Page 2 - diyAudio
 What is the name of this topology?
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 1st October 2010, 09:04 AM #11 diyAudio Member     Join Date: Jan 2003 Location: UK (south west) I still think the analysis will be, more or less, the same as an LTP where the tail resistor is R4/R5 in parellel and Re is R7/2. Assuming C1 is large enough, and of course, the dc analysis is different. dc Last edited by DRC; 1st October 2010 at 09:08 AM.
 1st October 2010, 10:35 AM #12 diyAudio Member   Join Date: Jul 2004 Location: Scottish Borders no. The separate tail sinks defeat the LTP action. An LTP uses the constant current draw of the tail to influence how the other half amplifies it's input signal. __________________ regards Andrew T. Sent from my desktop computer using a keyboard
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Join Date: Jan 2003
Location: UK (south west)
Quote:
 An LTP uses the constant current draw of the tail to influence how the other half amplifies it's input signal.
thats what R7 + C1 do !

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Join Date: Jul 2005
Location: D-55629 Schwarzerden
Quote:
 Originally Posted by DF96 This is an emitter-coupled amplifier. The valve analogue is called the cathode-coupled amp. It is a form of differential amp. Differences from a normal LTP are: not necessarily balanced, often quite a 'short' tail, often AC coupling, not necessarily the same transistor type. To a first approximation all BJT behave in exactly the same way: exponential response. That is why changing the transistor had little effect. A normal LTP uses a matched pair in order to maintain DC balance. The ECA will typically have lower even-order distortion than a common-emitter amp. As the output is in phase with the input it might have greater risk of oscillation due to capacitive feedback.
I can also call that emitter coupled cascode (another form of the good known normal cascode or folded cascode).
check out US Patent 6,600,367
http://www.patentstorm.us/patents/66...scription.html
http://www.pat2pdf.org/patents/pat6600367.pdf
and
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This topology I get often automaticly, when I transform a power amp from the non inverted mode to an inverted mode.

But an additional fact is of interest:
After replace R4 and R5 each through current sources (two independend current sources instead commonly used one pcs. for both halves) and R7 through a potentiometer, you get the possibility for easy variation of the open loop gain/damping factor from your whole power amp stage.

Last edited by tiefbassuebertr; 1st October 2010 at 12:19 PM.

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Join Date: May 2007
Quote:
 no. The separate tail sinks defeat the LTP action.
Get rid of R7 and you have a short-tail pair. The tail is just R4 and R5 in parallel. Obviously this doesn't go down to DC because of the capacitor.

 2nd October 2010, 12:06 AM #16 diyAudio Member   Join Date: Oct 2008 Location: Vancouver A diff amp needs a diff input. T2s base is ac grounded. You have 2 outs, the first from a CE amp, the second from a 2 stage amp (cascode) CC then CB (common base). Thats the way it should be analized, not as a diff amp which is possible but thats over complicating things for no reason. (draw the second transistor rotated 90 degrees clockwise, the usual way to draw a CB amp, and maybe it will be easier to understand) Last edited by cbdb; 2nd October 2010 at 12:10 AM.
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Join Date: Jul 2005
Location: D-55629 Schwarzerden
Quote:
 Originally Posted by cbdb A diff amp needs a diff input. T2s base is ac grounded. You have 2 outs, the first from a CE amp, the second from a 2 stage amp (cascode) CC then CB (common base). Thats the way it should be analized, not as a diff amp which is possible but thats over complicating things for no reason. (draw the second transistor rotated 90 degrees clockwise, the usual way to draw a CB amp, and maybe it will be easier to understand)
Yes, the kind of drawing often determines, how well you understand the right working of a certainly circuit.
Independend of this - despite of the fact of grounding the inverted input it is still a diff amp - then the different between non inverted input and GND.

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