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Old 12th July 2013, 09:33 PM   #4951
stajo is offline stajo  Sweden
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I'm not building a balanced amp. I'm building a true symmetrical amp. Tail is SE. Hopefully Andrew or/and ZM gets the itches now
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Old 12th July 2013, 09:35 PM   #4952
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name of the game is Fun
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Old 12th July 2013, 09:36 PM   #4953
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I'm not building a balanced amp. I'm building a true symmetrical amp. Tail is SE. Hopefully Andrew or/and ZM gets the itches now
I surrender before beginning.
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Old 12th July 2013, 09:36 PM   #4954
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ZM, this forum was not the same without you for the last weeks :-)
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Old 12th July 2013, 09:37 PM   #4955
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..... Tail is SE. Hopefully ......


when you have idea , everything else is just semantics

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Old 12th July 2013, 09:39 PM   #4956
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ZM, this forum was not the same without you for the last weeks :-)
yup

The Court is dry without The Jester

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Old 14th July 2013, 03:23 AM   #4957
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Default F6 Amplifier

Some experience from Saturday playing with my F6(no THD analyzer yet, only ones attached to my head):
1. I had F6 with no FE degeneration and R13=0.1R R=0.
Very deep soundstage, but too much distortions -- harshy sound.
2. Same but R13=0.05R. Better distortion and almost same soundstage. Just didn't like its tonal balance.
3. Symmetrical one with variable 2nd harmonic from the F6 article. Very clean like F5.
4. Made 5 turns of trimpot to make a neg. phase shift (I.e. R13). That's it! Like it better than everything. Soundstage, clean and very soft and pleasant tonally.
:-) for what it worth.
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Old 16th July 2013, 03:28 PM   #4958
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Boys, how can I measure THD spectra of F6 FE? If I make output Rs symmetrical and measure the whole amp will it be enough?
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Old 16th July 2013, 03:37 PM   #4959
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Just measure whole amp while adjusting. At the end of the day, it is the final sound you are trying to manipulate. You may find lowest distortion on FE does not result in best sound. I am not 100% sure lowest THD on FE will result in lowest THD in final product, but could be wrong. Perhaps Ilquam or others can comment. If you want t measure just FE, you can pull transformer and load FE with 10K resistor to ground and measure.
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Old 16th July 2013, 03:45 PM   #4960
lhquam is offline lhquam  United States
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Boys, how can I measure THD spectra of F6 FE? If I make output Rs symmetrical and measure the whole amp will it be enough?
I recently tried adding a 10 ohm pot between the source pins of the JFETs with the wiper to the transformer primary. Measuring the end-to-end THD, I could not detect any significant change with different wiper positions. My conclusion is that the FE distortion is so low compared to the output stage that source resistors make no difference other than to reduce the JFET current.
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