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DIY Marantz 7 phono preamp
DIY Marantz 7 phono preamp
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Old 19th January 2019, 09:51 AM   #21
vpapanik is offline vpapanik  Greece
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Slightly improved version
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Old 19th January 2019, 06:21 PM   #22
vpapanik is offline vpapanik  Greece
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Now finalized, with a detailed SPICE model. All settled.
Thanks a lot to tron_ic for the valuable info in his site.


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Old 20th January 2019, 09:50 AM   #23
vpapanik is offline vpapanik  Greece
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Now perfected ! Ready for shopping.
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Old 20th January 2019, 10:49 PM   #24
TonyTecson is offline TonyTecson  Philippines
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DIY Marantz 7 phono preamp
Quote:
Originally Posted by ejp View Post
Really? GNFB in a preamp? With equalisation? How does that work?
look here: cascaded 12ax7 has mu of 100 so open loop gain is 10000 ideally. but in reality much lower than that, perhaps around 2500 tops....furthermore, gain with feedback when the loop is closed is way lower than that..the RCA tube databook gives a design that did not use global feedback, it is also known as passive equalization, in contrast with this active equalization..

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Old 21st January 2019, 02:29 AM   #25
ejp is offline ejp  Australia
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That's just the phono stage. It is NFB but not GNFB. The original claim was for the Marantz 7, not just the phono stage.
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Old 21st January 2019, 02:32 AM   #26
rayma is offline rayma  United States
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Quote:
Originally Posted by ejp View Post
That's just the phono stage. It is NFB but not GNFB. The original claim was for
the Marantz 7, not just the phono stage.
You can't have a volume control inside a feedback loop.
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Old 21st January 2019, 05:14 AM   #27
TonyTecson is offline TonyTecson  Philippines
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DIY Marantz 7 phono preamp
Quote:
Originally Posted by ejp View Post
That's just the phono stage. It is NFB but not GNFB. The original claim was for the Marantz 7, not just the phono stage.
we are talking phono stage here, global as used here means from the output of second stage to the cathode of the first stage...

even the line stage section of the marantz 7 also used global feedback also to take the gain of the 12ax7 to line levels...
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