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Salas DCG3 preamp (line & headphone)
Salas DCG3 preamp (line & headphone)
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Old Today, 02:01 AM   #2871
Salas is offline Salas  Greece
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Salas DCG3 preamp (line & headphone)
Originally Posted by nashbap View Post
I bought 200 of the German Diotec 327-40 from a source on Ebay. Sorting indicated a range in hfe from 358 to 408, with several greater than 400. This is with a new MM and a new battery. Another MM showed 438 as the high one and the all component tester thingie sold on Ebay showed 379 for the same. Anyway, I got 8 exact matches of 406 hfe at around 67F referencing the first tester mentioned and I tested the matching five separate times. I also checked the eight 560C’s that were removed which TeaBag had sent me. Using the same tester and similar conditions the 560’s measured from 420 to 428. Tea’s sets were marked as 436, 440. So on average the 560’s had 19 higher hfe then the 327’s that I put in.

After a suitable burning in of around twenty hours, playing music at full volume into turned off power amps, I started some serious listening with speakers only, no headphones.. The tonality of the violin has changed. It is lighter, and more extended. It was as if the violinist had refined his/her style and was playing with a less heavy hand. Clearer vibrato. The surprise to me was the improvement in clarity of the piano notes especially the lower ones. Not a subtle but significant improvement. Listen to a softly struck note and you can hear the difference. Massed instruments also sounded clearer. Brasses, woodwinds, male and female voices all sounded clearer without any apparent loss of body and weight of the music. Transient speed gave the impression of being even faster because the notes were clearer.

Summing up, I’d say that the overall sound is clearer and somewhat brighter and nothing has been lost, only enhanced. And it’s more enjoyable. You need to burn it in for at least twenty hours. I found some harshness especially in the highs and a lack of smoothness before I let it burn in.

I noticed that in some recordings, for example, a violin concerto where the artist usually performs in the front and center of the orchestra that the artist seemed to be a bit further forward and a bit higher relative to the orchestra than I remember. I have not listened enough to be conclusive about this but perhaps there is slightly better focusing. Any thoughts? No other changes were made.

Subjectively it appears that the H2/H3 balance is slightly changed. Salas, any chance you have run an FFT comparing the DCG3 with the 560 vs 327?

With this mod, you have certainly raised the bar! Thank you!

You are welcome. Subjectively I generally agree with your findings. On the focusing too. I did not hear on speakers the pre run-in bit rougher state you mention though. Maybe because I had given it a longish run on headphones with the newly installed alternative BJTs the night before. Or its an ambient temperature difference. Would you also remind us what speakers you use?

In simulation I could not see any THD % difference or H2/H3 balance difference with 1kHz and 5kHz test tones at 3V RMS output. So I did not bother setting up the real FFT measurement rig just for confirming as I know it satisfactorily follows my dcg3 analysis trends from previous sessions. I could see 4nVrtHz less input referred noise in simulation though. Input referred noise multiplies by times the voltage gain. Thus a minus 12nVrtHz output noise improvement at gain of three. My idea was to intrinsically lessen the mirror's noise contribution without degenerating it with emitter resistors as its normally done. I shaped the original open loop gain max plateau more extended with using less impedance than shooting for highest possible number at a narrower region. I did not want to change that but to enhance it even. Emitters degeneration with 150 Ohm resistors test makes much less output noise difference in simulation now. Because the active part itself has lowered the mirror's noise contribution.
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