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Bob Cordell's Power amplifier book
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Old Yesterday, 09:13 PM   #9701
shadders is offline shadders  United Kingdom
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Hi,
Hopefully this is a simple question - in the latest book, page 88, Figure 4.1, the feedback resistors R7 and R8 are rated at 1watt each.

When i run a simulation of a similar amplifier, using resistors with a much lower resistance, approx 10x less, but still similar ratio to one another, only then does the power rating meet or slightly exceed the 1watt rating.

Therefore, what is the reason for such a power rating for the feedback resistors given that they are higher in resistance requiring less than 120mW peak power for the highest resistance power ?
Thanks and regards,
Shadders.
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Old Yesterday, 09:41 PM   #9702
rsavas is offline rsavas  Canada
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Quote:
Therefore, what is the reason for such a power rating for the feedback resistors given that they are higher in resistance requiring less than 120mW peak power for the highest resistance power ?
see p370, 16.7 Resistor Distortion
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Old Yesterday, 11:15 PM   #9703
mjona is online now mjona  New Zealand
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Quote:
Originally Posted by RNMarsh View Post
Well, maybe you can look at some yourself, including DVD/CD combo players and see how well assumptions that nothing exists within amplifier BW is out there to be amplified by PA gain.

Sometimes there have been idle tones just there all the time within audio band and only 65 dB down, for example. Whats that doing there?


Attachment 788577


here you see an idle tone. Then afterwards some Stuff comes thru. Also well within some amps BW. [ Note the measurement BW is 1KHz to 1 MHz log.]

I have lots of this stuff that should not be there IS there.

To the degree yours does also, it is a potential problem for insufficient SR amps (IM). Take it for what is worth.


My basic distortion T&M. Partial... no network analyzers etal....

Attachment 788579

THx-RNMarsh
The Australian magazine Silicon Chip magazine has published projects for a pre-amplifier and a power amplifier which use RC in series with the input with the pre-amplifier -this a Miller 5250 low permeability ferrite sleeve wedged in series between R and C in the diagram.

The feedback path has 2.2k//470p, closed loop gain is 2 and this is followed by the volume pot and a unity gain buffer stage with another sleeve in series with the output resistor.

For the power amplifier the input inductor is a ferrite bead FB1 which precedes the RC section.

The articles were published in November 2011 and January 2017. Silicon Chip have Audio Precision test equipment however that said your laboratory setup looks seriously impressive.
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Old Yesterday, 11:52 PM   #9704
mjona is online now mjona  New Zealand
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Default Point of Clarification

Quote:
Originally Posted by mjona View Post
The Australian magazine Silicon Chip magazine has published projects for a pre-amplifier and a power amplifier which use RC in series with the input with the pre-amplifier -this a Miller 5250 low permeability ferrite sleeve wedged in series between R and C in the diagram.

The feedback path has 2.2k//470p, closed loop gain is 2 and this is followed by the volume pot and a unity gain buffer stage with another sleeve in series with the output resistor.

For the power amplifier the input inductor is a ferrite bead FB1 which precedes the RC section.

The articles were published in November 2011 and January 2017. Silicon Chip have Audio Precision test equipment however that said your laboratory setup looks seriously impressive.
The September 2019 issue of the magazine has a six stereo input module for the pre-amplifier involving Miller L5250 in series with each relay output - parts of separate RLC filters where R=100 and C=470p.

FB1 in the quote in the third paragraph above is a Miller L5250.
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Old Today, 12:24 AM   #9705
anatech is online now anatech  Canada
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Bob Cordell's Power amplifier book

Hey mjona, you know you're not supposed to quote the previous post in it's entirety - right? You quoted yourself for Pete's sake! Please, use some common sense when you are going to quote something.

-Chris
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