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Old 11th September 2011, 11:51 AM   #1
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Default output inductor//resistor placement

What is the best placement for the L//R output network?

Keeping it off the amplifier PCB would probably be a good idea. Maybe mounting it to the amplifier speaker output terminals would be a good placement?
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Old 11th September 2011, 01:13 PM   #2
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The take off point for the negative feedback path is critical, so if its already there on the PCB its there for a fairly good reason, study some of Doug Selfs Blameless amp discussions into this subject to observe just how critical. Also observe a Zobel Network is not to be confused with other output stage parts, the Zobel has a stability function.

hope this helps / Chris
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Old 11th September 2011, 01:16 PM   #3
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Quote:
Originally Posted by Chris Daly View Post
The take off point for the negative feedback path is critical, so if its already there on the PCB its there for a fairly good reason, study some of Doug Selfs Blameless amp discussions into this subject to observe just how critical. Also observe a Zobel Network is not to be confused with other output stage parts, the Zobel has a stability function.

hope this helps / Chris
Making my own boards.

The rest I know.

Just wanted to know if it was a good idea to mount the inductor//resistor combo away from the PCB. It wouldnt affect the NFB path or the Zobel network.
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Old 11th September 2011, 05:30 PM   #4
AndrewT is offline AndrewT  Scotland
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I have very slowly come to the conclusion that the Thiele Network must be split into at least two main parts.
The R+C which is the high frequency load seen by the output devices needs to be very closely coupled to the loop from the decoupling through the outputs into the Zobel and back to the decoupling. I reckon that for the Zobel to work well at very high frequencies that the total loop length must be kept very short to minimise inductance due to long traces or long wires.
The Zobel must be on board.

The second part of the Thiele consisting of the L//R can be anywhere, provided it does not interfere with the other circuits and it itself is not prevented from doing it's job properly.
The inductor requires to be kept away from the sensitive circuits of the amplifier. But the Air cored coil must also be kept away from other coils and from major metal work, particularly iron. I have started putting L//R in as part of the two core cable that joins the amplifier PCB to the Speaker Terminals.

Finally, the alternative version of the Thiele Network shows the R+C after the L//R. Thiele reduces this R to zero ohms. This is best placed directly across the speaker terminals.
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regards Andrew T.
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