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B1 with Korg Triode
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Old 9th April 2020, 10:42 PM   #4611
KevinHeem is offline KevinHeem  United States
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B1 with Korg Triode
Originally Posted by avdesignguru View Post
Also, NuTubes vary in their microphonics. A good one will exhibit little or no ringing that dies out immediately when tapped lightly with a fingernail. A bad one will ring either a long time or continuously when tapped. This is typically caused by the filament vibrating, usually somewhere around 5KHz.
I've got a bad one then...it will ring continuously. Weird though, it varies depending on which equipment it's paired with.

Pearl II -> B1 Korg -> FW M2 = No problems.
NuVista Vinyl -> B1 Korg -> FW M2 = low rumble sound.
VPI traveler -> (built in phono) -> B1 Korg -> Forte M 4 = continuous ringing.
Pearl II -> B1 Korg -> Quad 405 = Screams like a siren. (I mean loud!)

I'll give some different damping materials a try. At the moment the only damping installed is some packaging foam underneath.
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Old 9th April 2020, 10:45 PM   #4612
drpro is offline drpro  United States
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B1 with Korg Triode
Thanks, Itsikhefez. I will have to check Par Metals out.
I must build.F4s, F6, M2, Aleph J, BA-3, B1Korg preamp, Wayne's Linestage, MoFo, ImPasse preamp, Whammy headamp, Aksa preamp, Salas DCG3 headphone/preamp, XRK971 PCA & DCA headamp Bruno's balanced preamp, Doug Self preamp, Pete Millet Korg headamp.
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Old 10th April 2020, 01:02 AM   #4613
audionut is offline audionut
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Location: Cleveland ohio
B1 with Korg Triode
Hi all...

I am building a Korg Nu Tube Preamp according to the Pass Plan, and all parts and boards from the DIY Audio Store.

This preamp will go in front of a passive line level crossover...using inductors and capacitors. There will be a high frequency output for the tweeter channel and a low frequency output for the woofer channel.

there will be a master volume control in front of the preamp channels. But I would like to trim the gain of each high and low channel separatly. So the signal would go from master volume control to pots after the master volume control to the pre amp channels to adjust the signal to each channel. This way I can adjust Tweeter level and Woofer level to taste.

My question is: how would I do this??? if Master Volume control is say 20k, what should value of following trim pots be? and how connected?

the "adjusting" pots could not go at the output of the preamp because they would change the output impedence of the preamp and alter the response of the crossover filter at different levels...

Thanks in advance for any help on this.
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Old 10th April 2020, 02:20 AM   #4614
brian92fs is offline brian92fs  United States
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B1 with Korg Triode
I believe you'd need want a buffer between the Master Volume and Trim Volume controls. Otherwise, the output impedance of the master volume would load the trim pots causing problems.
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Old 10th April 2020, 07:41 AM   #4615
ClaudeG is offline ClaudeG
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Perhaps you may want to consider 2 pots at the output of the B1K, leading to your 2 filters?

The output of the B1K is between 160 and 300R ish depending on the fets you use, so you could potentialy use a 5K pot at the output, or even less. You want is as low as possible as I don't know what input impedance your filters will have, but that needs tp be very high for a filter, say at anything between 10k and 100kish, other wise you will need a kind of buffer at the input.

Just thinking loud, never done this, I guess most people would adjust the required level once once for all in their filter already adjusting levels between bass and treble, as is done in LS Xover?

Good luck

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Old 10th April 2020, 12:15 PM   #4616
audionut is offline audionut
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B1 with Korg Triode
Thanks for your answers...

I find it a nice advantage to change the tweeter and woofer levels...some recordings need a little more bass, some a little more treble...

Can the intrinsic gain of the korg pre amp be adjusted with a pot?? Thats what I do with my BOSOZ.
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Old 12th April 2020, 05:55 PM   #4617
dtaylo3 is offline dtaylo3  United States
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I am finishing up a B1K build. Do I need to ground my 50K volume pot to chassis, or just run the gounds to the B1K board's inputs?
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Old 12th April 2020, 06:02 PM   #4618
6L6 is offline 6L6  United States
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Ground the pot body if it hums.
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Old 14th April 2020, 03:02 PM   #4619
b4bz is offline b4bz  Canada
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Finished my build last week. Case of Spanish Cedar (ode to Dylan). Tung oil finish. Rear panel has 1 mm aluminum laminated to it and all switches are back there to keep the front cleaner and have less internal wiring. I polished the aluminum to 800 grit to leave a matte finish to match the volume knob I wish had a replacement for. Lid is held on with 4 very small magnets that work very well - strong enough to lift the whole thing up with the lid. Sounds excellent in front of the F5s. No microphonics, thankfully. Sealed wooden case might have helped with that and I cut a block of Magic Eraser for under the NuTube. Thanks to all of you for contributing your insights; Mr Pass, Jim, et all. I liked how the case turned out so I'm making a few more, one for an analog active crossover and another for a Bugle 3 phono stage.
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Old 14th April 2020, 03:14 PM   #4620
TungstenAudio is offline TungstenAudio  United States
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Very nice! I love the woodwork.

It is probably helping to prevent the microphonics that sometimes plague the Korg NuTube.
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