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Old 6th December 2014, 02:34 AM   #1
BRSHiFi is offline BRSHiFi  United States
Previously known as kingden
Join Date: Aug 2008
Location: Evanston, IL
Default Simple Line Stage

I just constructed this preamp out of parts I had accumulated over various projects. It is a CCS long tail and a cathode follower. I have a schematic for both the right and left channel complete with voltages I measured at each node.

The goal was to produce a system that takes 0.5 to 1 volt peak in and amplify it to 2 volts peak (the high-z input to my power amp).

It passes completely flat into 10k ohms somewhere well into the subsonics into the triple kilohertz range. Fooling with the 51k feedback resistor seemingly changes the dynamics of the audio and the tone (especially the sharpness/dullness of instruments in the mid-range). Is this just my imagination? If not, what improvements do you recommend?
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Old 6th December 2014, 05:09 AM   #2
seppoa is offline seppoa  Sweden
diyAudio Member
Join Date: Feb 2013
Well, the right tube seems to have unbalanced heaters. So one half of the tube is not doing what it should, the other neither. So fooling with feedback maybe gives the results you hear. Also understand, that small differences in volume make big impacts in perceived sound quality.
And my opinion is, that the circuit for a amplification of 2-4 times seems too complicated, no need for NFB at all.
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Old 6th December 2014, 07:19 PM   #3
BRSHiFi is offline BRSHiFi  United States
Previously known as kingden
Join Date: Aug 2008
Location: Evanston, IL
This may be a false alarm. I have not had quality sleep for the past few days. When in my chair, I started to doze off. Now that I am more fresh and alert, took a good walk, and rested well my preamp is sounding better.

My perception of volume vs. sound quality I just learned is a function of how alert I am. This morning, I had to turn it down as it was clearly too loud. Not when I was feeling zombish, as last night it was "way too soft".
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