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Old 21st July 2012, 02:08 PM   #1
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Default Resistor To Ground - What is the purpose?

In the picture attached you will find a resistor to ground and another section with a capacitor/resistor to ground. What is the purpose for this type circuitry?
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Old 21st July 2012, 02:11 PM   #2
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With the two diodes above it, it forms a voltage reference, referenced against the upper supply rail, resulting in Vsupply - 2x diode drop.
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Old 21st July 2012, 02:19 PM   #3
BV is offline BV  Slovakia
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R-C: Boucherot cell
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Old 21st July 2012, 02:34 PM   #4
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Thanks gentlemen.
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Old 21st July 2012, 02:35 PM   #5
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Without R621 there would be no current through the diodes and they would just sit there rather stupid

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Old 21st July 2012, 02:36 PM   #6
PChi is offline PChi  United Kingdom
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I agree with BV. An alternative name is Zobel (not sure of the spelling) network.

I believe that it ensure that the output stage is loaded by a low impedance that helps to control the high frequency gain of the output stage so helps to maintain stability.
Another reason that I have read is that it partly compensates for the inductive part of a typical loudspeaker load.
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Old 21st July 2012, 02:42 PM   #7
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Could I also refer to the R-C combo in my schematic as a snubber?
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Old 21st July 2012, 08:47 PM   #8
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A snubber is used to snub or quench a transient or arc. They are normally used across a switching element and a current will shunt through it as the switch starts opening (not closing) so that an arc will not form across the contacts.

A zobel is a network that if placed at the input of a filter network and if looking into the filter, it appears as a constant impedance over a wide frequency range.
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Old 21st July 2012, 08:52 PM   #9
Boscoe is offline Boscoe  United Kingdom
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The RC combo is there to help reduce DC offset is it not? The cap is high impedance at low frequencies lowering the gain?
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Old 21st July 2012, 08:58 PM   #10
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This RC is Zobel at output.
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