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Doug Self Preamp from Linear Audio #5
Doug Self Preamp from Linear Audio #5
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Old 31st January 2018, 09:28 AM   #1001
AndrewT is offline AndrewT  Scotland
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Join Date: Jul 2004
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Quote:
Originally Posted by brian92fs View Post
Question on variable gain - would it be practical to connect the pads for R42 and R45 to a switch that allows 2 or more discrete values to be selected? For example, going to a toggle switch that allows 0 db or 10 db gain to be selected? Or would the length of the wires going to the switch compromise performance?
switchable gain is possible.
One should check that stability margins do not change adversely at some of the options.
Switching a gain stage to unity gain gives no useful advantage. It would be better to either switch select to a buffer stage or bypass and go completely passive if the source can drive the resulting capacitances.
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Old 19th February 2018, 08:12 PM   #1002
Mixi is offline Mixi  Europe
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does anyone know what the values for input & output impedance are?

will the performance of the amp be affected if the gain is lowered or set to 0 ?
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Old 2nd March 2018, 09:11 AM   #1003
JohnWalker is offline JohnWalker
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does anyone have the backpanel (1U format) of these amp in the 'panel designer format' or in DXF-format available for me ?
kind regards,
John
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Old 2nd April 2018, 12:55 PM   #1004
hadihf is offline hadihf  Pakistan
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Hi,

Will a 5k log pot for volume work OK?

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Farooq
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Old 2nd April 2018, 01:23 PM   #1005
scottjoplin is offline scottjoplin  Wales
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The volume control circuit functions logarithmically with a linear potentiometer, why do you want to use a log pot?
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Old 2nd April 2018, 04:37 PM   #1006
Carl_Huff is offline Carl_Huff  United States
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Location: Bakersfield, CA
Quote:
Originally Posted by hadihf View Post
Hi,

Will a 5k log pot for volume work OK?

Regards
Farooq
Nope sorry Farooq. It's got to be a 5K dual linear pot. A log pot will not work.
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Old 2nd April 2018, 04:59 PM   #1007
hadihf is offline hadihf  Pakistan
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Originally Posted by Carl_Huff View Post
Nope sorry Farooq. It's got to be a 5K dual linear pot. A log pot will not work.
Thanks Carl...I am still in collecting parts phase...found a good quality pot but it is a log type.
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Old 2nd April 2018, 05:11 PM   #1008
scottjoplin is offline scottjoplin  Wales
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You may find more options if you use 4.7k ohm pots
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Old 2nd April 2018, 05:39 PM   #1009
hadihf is offline hadihf  Pakistan
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Default 5k pot

Page 33 of DS book...Self on Audio.. made me think otherwise but I might be missing something.

"It can be readily shown by simple algebra that the control track resistance now has no effect on the gain law, and hence the channel balance of such a system depends only on the mechanical alignment of the two halves of a dual linear pot."
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Old 2nd April 2018, 08:47 PM   #1010
asuslover is offline asuslover  Romania
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Where can I get a stereo set for this preamp?
Thanks
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