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6V6 line preamp
6V6 line preamp
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Old 17th April 2018, 06:21 AM   #3341
skrstic is offline skrstic  Serbia
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Preamp is up and running. Q1 is IXTP08N100D2. Thanks.

When I play music on tpa3118 amplifier with 20 db gain there is an unpleasant buzzing, when music is over Folsom tda7297 amplifier with 32 db gain buzz is even more pronounced. There is buzzing recording "11 Apr 21.53.mp3.txt" (rename to mp3). I do not have oscilloscope and my knowledge of electronics is 0. Any suggestions about what the problem is?
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File Type: txt 11 Apr 21.53.mp3.txt (130.4 KB, 9 views)
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Old 17th April 2018, 10:09 AM   #3342
Salas is online now Salas  Greece
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6V6 line preamp
Foobar shows main activity around 2.2kHz and it sounds like an oscillation. Try with only passively filtered PSU and if it goes then it should be something with the B+ regulator build or its application. Try it in two wire output mode then by shorting F+ to S+ and F0 to S0 locally at its output connector. Put a 0.1uF across the reg's input connector too. That rectification valve is being asked for too much constant current or it sees a bigger than allowed smoothing capacitor is another suspicion. If on the other hand its a wiring or build style issue see about shorter wires and bad loops or the grid stopper resistors physical distance to the grid pins and their values.
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Old 17th April 2018, 11:54 AM   #3343
skrstic is offline skrstic  Serbia
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Thanks Salas.
F+ to S+ and F0 to S0 are shorten. PSU is as in image. Rectification tube is 5C3S (5Ц3С), tefo is 250mA and smoothing capacitor motor run 4uF.
I will put 0.1uF at SSHV2 input. Wiring is bad as I'm only in trying mode, first tube project.
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Old 17th April 2018, 12:28 PM   #3344
Salas is online now Salas  Greece
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6V6 line preamp
That's a 5U4G equivalent, see not to overload it with a bigger than 40uF capacitor on its output. As you don't have an oscilloscope the only debugging method is to remove and change or substitute things and see what happens. You will not easily know what to look for by guessing.
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Old 17th April 2018, 12:48 PM   #3345
skrstic is offline skrstic  Serbia
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Originally Posted by Salas View Post
That's a 5U4G equivalent, see not to overload it with a bigger than 40uF capacitor on its output. As you don't have an oscilloscope the only debugging method is to remove and change or substitute things and see what happens. You will not easily know what to look for by guessing.
It's max 20uF and i know it is mission impossible. When I put it in a box I'll ask some one locally for help
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Old 17th April 2018, 12:52 PM   #3346
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So its half than for the original 5U4G. Yes, better overview the build along with someone equipped for debugging.
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Old 17th April 2018, 02:25 PM   #3347
Lingwendil is offline Lingwendil  United States
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6V6 line preamp
Do you guys think that one of these would be able to drive a 5k~ or so input impedance, like on the BA3 output stage or pass F4 "crippled" (input buffer removed)

It would be setup as a triode connected gain stage.
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Old 17th April 2018, 03:50 PM   #3348
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Not really adequate because it has about 1.5kOhm output impedance. It will lose some max output voltage and it will up its THD by 6-7dB
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Old 17th April 2018, 04:20 PM   #3349
Lingwendil is offline Lingwendil  United States
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Maybe I'll direct couple a mosfet follower to it then. I've got a pile of IRF820 I can press into service. That should give plenty low output impedance.
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Old 17th April 2018, 05:30 PM   #3350
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Lingwendil- so the easy answer is run the F4 with the buffer. It’s sonically invisible anyway, plus it lets the 6V6 breathe easily. Win-win.
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