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B1 with Korg Triode
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Old 31st March 2020, 01:56 PM   #4591
North America Hornet is offline North America Hornet  Taiwan
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Join Date: Jul 2015
Location: Taiwan
hi, everyone

since i finished building my B1k, i’ve been impressed by this amazing pre-amp that gives much musicality to the sound.

while reading the forum, i found an interesting article from japan by Mr. Shin, and it says that if you put an magnet near to the nutube, then it would suppress the vibration of the filament.

1721 :真空管 KORG Nutube、 磁石でマイクロフォニック・ノイズを消す | ShinさんのPA工作室

so i put some Neodymium magnet in the back of the nutube, and i found out that the spatial perception of sound improved a bit. the glowing zone of nutube converged from an area to a thin line by my raw-eye observation.

the article shows that the THD has changed while magnets influencing the nutube filament, and i’m wondering how it changes the harmonic features of this circuit, however, i don’t have an spectrum scope to analyze the alternation
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Old 31st March 2020, 05:24 PM   #4592
ClaudeG is offline ClaudeG
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Join Date: Jan 2015
You may want to use the search function on this thread, I believe I read somewhere the response to what you are asking.

I can't remember exactly, but while some seemed initialy quite positive on this tweak, it turned out it had in fact the same effect as playing with the bias pot. So nothing new... apart perhaps some help in resolving the ringing issue some Nutubes seem to have?

Good luck with your search and sorry for the little help

Claude
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Old 31st March 2020, 05:31 PM   #4593
ghitus is offline ghitus  Italy
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Join Date: Nov 2017
Location: Bari
Did you try putting a magnet ON the nutube? What kind of magnet did you use? Did you solve or reduce the ringing issue?
Gaetano.

Last edited by ghitus; 31st March 2020 at 05:33 PM.
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Old 31st March 2020, 11:26 PM   #4594
itsikhefez is offline itsikhefez  United States
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Join Date: Aug 2015
B1 with Korg Triode
The new zeners arrived along with various damping materials. I replaced the parts and everything is looking good now. I went overboard with damping and there is no ringing now on volume change. I still think my Nutube is overly microphonic, as moving my finger gently on the top of the damping material will cause low (but audible) ringing.

I also had the chance to measure it with my amateur test suite (ARTA+pmillett SCI+EMU soundcard). In my setup, it's measuring ~1% THD with 1V output at the 9.5V bias point. FR is pretty flat, which is nice. If I ever swap in film caps for coupling, atleast I have a good baseline on what sufficient capacitance should look like.

One nice bonus is that the volume display shows -16db at 0db gain (1V in 1V out).. I thought that was cool since the circuit has about 16db of gain.

Really happy with how this came out.. Thanks Nelson!!!
Attached Images
File Type: jpg 2020-03-31 15.26.09.jpg (91.5 KB, 640 views)
File Type: jpg 2020-03-31 15.27.47.jpg (111.3 KB, 639 views)
File Type: jpg 2020-03-31 15.25.34.jpg (184.9 KB, 643 views)
File Type: png FFT 1V.png (66.6 KB, 597 views)
File Type: png FR 1V.png (60.7 KB, 563 views)
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Old 1st April 2020, 11:16 AM   #4595
cubicincher is offline cubicincher  Germany
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Join Date: Mar 2016
Location: Hechingen, South of Germany
Default to itshikefez #4594

Hello itshikefez,


a very nice build with a clean design! I like it!



Enjoy the sound! Don't forget to play with the 10kOhm trimpots and

try to reverse polarity of your speakers at the poweramp / speakeroutput.
Will be an 'interesting journey' for you - as it was for me...


Perhaps you will need a lot of time to listen to your music / CD's / vinyl
in a new way.
Greets
Dirk
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Old 1st April 2020, 12:17 PM   #4596
Bassivus is offline Bassivus  Serbia
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Location: Novi Sad, Vojvodina
Quote:
Originally Posted by itsikhefez View Post
The new zeners arrived along with various damping materials. I replaced the parts and everything is looking good now. I went overboard with damping and there is no ringing now on volume change. I still think my Nutube is overly microphonic, as moving my finger gently on the top of the damping material will cause low (but audible) ringing.

I also had the chance to measure it with my amateur test suite (ARTA+pmillett SCI+EMU soundcard). In my setup, it's measuring ~1% THD with 1V output at the 9.5V bias point. FR is pretty flat, which is nice. If I ever swap in film caps for coupling, atleast I have a good baseline on what sufficient capacitance should look like.

One nice bonus is that the volume display shows -16db at 0db gain (1V in 1V out).. I thought that was cool since the circuit has about 16db of gain.

Really happy with how this came out.. Thanks Nelson!!!
Wow! Beautifull build! Congartulations. Enjoy
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Old 1st April 2020, 05:20 PM   #4597
itsikhefez is offline itsikhefez  United States
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B1 with Korg Triode
Thanks both for the kind words and suggestions!
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Old 2nd April 2020, 04:34 AM   #4598
jb2004 is offline jb2004  United States
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Join Date: Dec 2006
Sense the preamp is phase-inverting. Can you invert the phase of the wires from the board to the RCA connector to get the correct absolute phase?
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Old 2nd April 2020, 06:18 AM   #4599
PKI is offline PKI  United States
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Join Date: Aug 2011
B1 with Korg Triode
Quote:
Originally Posted by itsikhefez View Post
The new zeners arrived along with various damping materials. I replaced the parts and everything is looking good now. I went overboard with damping and there is no ringing now on volume change. I still think my Nutube is overly microphonic, as moving my finger gently on the top of the damping material will cause low (but audible) ringing.

I also had the chance to measure it with my amateur test suite (ARTA+pmillett SCI+EMU soundcard). In my setup, it's measuring ~1% THD with 1V output at the 9.5V bias point. FR is pretty flat, which is nice. If I ever swap in film caps for coupling, atleast I have a good baseline on what sufficient capacitance should look like.

One nice bonus is that the volume display shows -16db at 0db gain (1V in 1V out).. I thought that was cool since the circuit has about 16db of gain.

Really happy with how this came out.. Thanks Nelson!!!
Beautiful build! Is that selector and volume control from Maxim?
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Old 2nd April 2020, 06:28 AM   #4600
ClaudeG is offline ClaudeG
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Join Date: Jan 2015
Quote:
Originally Posted by jb2004 View Post
Sense the preamp is phase-inverting. Can you invert the phase of the wires from the board to the RCA connector to get the correct absolute phase?
No...

Claude
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