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-   -   Doug Self Preamp from Linear Audio #5 (https://www.diyaudio.com/forums/analog-line-level/280458-doug-self-preamp-linear-audio-5-a.html)

AndrewT 31st January 2018 09:28 AM

Quote:

Originally Posted by brian92fs (https://www.diyaudio.com/forums/analog-line-level/280458-doug-self-preamp-linear-audio-5-a-post5325903.html#post5325903)
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.

Mixi 19th February 2018 08:12 PM

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 ?

JohnWalker 2nd March 2018 09:11 AM

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

hadihf 2nd April 2018 12:55 PM

Hi,

Will a 5k log pot for volume work OK?

Regards
Farooq

scottjoplin 2nd April 2018 01:23 PM

The volume control circuit functions logarithmically with a linear potentiometer, why do you want to use a log pot?

Carl_Huff 2nd April 2018 04:37 PM

Quote:

Originally Posted by hadihf (https://www.diyaudio.com/forums/analog-line-level/280458-doug-self-preamp-linear-audio-5-a-post5392453.html#post5392453)
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.

hadihf 2nd April 2018 04:59 PM

Quote:

Originally Posted by Carl_Huff (https://www.diyaudio.com/forums/analog-line-level/280458-doug-self-preamp-linear-audio-5-a-post5392673.html#post5392673)
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.

scottjoplin 2nd April 2018 05:11 PM

You may find more options if you use 4.7k ohm pots

hadihf 2nd April 2018 05:39 PM

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."

asuslover 2nd April 2018 08:47 PM

Where can I get a stereo set for this preamp?
Thanks


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