Power Amp

zeus_threat · 12th October 2007, 02:12 PM

Hi could anyone comment on this amp. Its still at simulation stage.
Thanks

traderbam · 12th October 2007, 02:45 PM

Hi. Just a couple of questions before I comment to help me understand.
What is C14 for?
Why are C14, R7 on the right side of R20 rather than the left?

zeus_threat · 12th October 2007, 04:38 PM

Sorry don't understand your point. R7 is the emitter resistor for the CCS defining the current going to VBE and VAS. R20 is the resistor connected in parallel to the output inductor to improve damping. Can you provide your comments. Thanks

traderbam · 12th October 2007, 04:46 PM

I meant R19 & C7.

AndrewT · 12th October 2007, 05:08 PM

Hi,
there is nothing wrong with the Thiele network on the output.
Thiele originally showed the grounded components on either side of the output inductor. It's just that the before location has become more popular.
Dr. Cherry did a paper on the correct selection of these components for both locations and if he is right then almost everyone has copied the wrong values.

Leach uses the after location as one example.

Why have you chosen such a low value (0.3mA/leg) for the LTP current?
Have you read the recent posts describing the clipping behaviour and potential failure of the Self arrangement of EF before the VAS?
The ratio of R11 to R12 seems wrong. 1k/310+1=4.23. For a triple stage EF output you will need nearer 6 to 7times to bias the output stage correctly.
Q4 & Q12 have similar dissipation yet one is To92 and the other To126, why?
Have you deliberately chosen to omit the DC blocking on the input? That leaves the input resistances on the inverting and non-inverting inputs very unmatched.
Why bc546a for the LTP? better to use b grade as minimum or c grade if you buy them from the group buy for which stock is still available. Buy at least 20pairs of 546/556c for matching.

zeus_threat · 13th October 2007, 12:11 PM

Thanks for the reply, the TO92 transistor has been changed to a BD139. R11 and R12 ratio modified. What current would you suggest for the LTP?

Thanks

12th October 2007, 04:38 PM	#3
zeus_threat diyAudio Member Join Date: Nov 2005 Location: Mauritius	huh??? Sorry don't understand your point. R7 is the emitter resistor for the CCS defining the current going to VBE and VAS. R20 is the resistor connected in parallel to the output inductor to improve damping. Can you provide your comments. Thanks

12th October 2007, 05:08 PM	#5
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, there is nothing wrong with the Thiele network on the output. Thiele originally showed the grounded components on either side of the output inductor. It's just that the before location has become more popular. Dr. Cherry did a paper on the correct selection of these components for both locations and if he is right then almost everyone has copied the wrong values. Leach uses the after location as one example. Why have you chosen such a low value (0.3mA/leg) for the LTP current? Have you read the recent posts describing the clipping behaviour and potential failure of the Self arrangement of EF before the VAS? The ratio of R11 to R12 seems wrong. 1k/310+1=4.23. For a triple stage EF output you will need nearer 6 to 7times to bias the output stage correctly. Q4 & Q12 have similar dissipation yet one is To92 and the other To126, why? Have you deliberately chosen to omit the DC blocking on the input? That leaves the input resistances on the inverting and non-inverting inputs very unmatched. Why bc546a for the LTP? better to use b grade as minimum or c grade if you buy them from the group buy for which stock is still available. Buy at least 20pairs of 546/556c for matching. __________________ regards Andrew T.

13th October 2007, 12:11 PM	#6
zeus_threat diyAudio Member Join Date: Nov 2005 Location: Mauritius	Thanks Thanks for the reply, the TO92 transistor has been changed to a BD139. R11 and R12 ratio modified. What current would you suggest for the LTP? Thanks

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12th October 2007, 02:45 PM	#2
traderbam diyAudio Member Join Date: Jan 2002 Location: Earth	Hi. Just a couple of questions before I comment to help me understand. What is C14 for? Why are C14, R7 on the right side of R20 rather than the left?

12th October 2007, 04:46 PM	#4
traderbam diyAudio Member Join Date: Jan 2002 Location: Earth	I meant R19 & C7.

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