Korg B1 completion kit pioneer batch feedback

[carlpsyd]

Finished Project

To deal with the microphonic ringing here is my final solution - I tried many others with little to no affect. I lined the chassis box with Noico 80 mil Butyl Automotive Sound Deadening mat from Amazon, closing the top and bottom vents, and 1" Platinum Silicone Hemisphere Isolation Feet. That fixed the ringing and made the box solid with no microphonics. I wanted to see the tube so I sourced a piece of 1/8" acrylic plastic and replaced the top of the box. It's more dense than the original metal piece. No ringing.
I've build two boards and sourced the parts from DigiKey. They both sound fantastic and both have very different microphonic characteristics.
I enjoy the clean, clear sound of the this preamp over many high priced preamps.
Thanks to all who have shared various ideas and insights.

 

[jf4828]

I had problem with left channel going out. It worked fine for a while but then started having issues so I reflowed the left side of the board and everything started working fine again. As I was probing around looking for things before and after, I realized channel matching is pretty far off. Any suggestions on how I might improve this? See attached picture. Note that YES, I did try swapping scope probes between channels as well as test signal source but the results indicate the left channel (blue trace) is lower in output then right (yellow trace). Also confirmed this with Fluke 87V. Also note that DC offset is very very close to zero and matches almost perfect between channels. The voltage difference between L and R output increases as a function of input voltage.

Any ideas on where to start looking?

 

[iWozza]

White (latex, not pink) pencil eraser taped to the top of the NuTube seems to be the best single thing to do to help the microphonics. Also taping the vent holes closed.

The NuTube seem to be wildly inconsistent in their propensity for ringing, some are pretty good, some are insanely bad. They all ring when you tap on the chassis though...

Hadn't realised other people were witnessing the same degree of ringing as me. Both my NuTubes ring like an orchestral triangle in a cave. The idea one is supposed to work in a portable headphone amp with a plastic case is just not realistic. Maybe ok in a HiFi unit with a heavy casing.
Interesting to learn of wild inconsistencies. I was told it rarely causes anyone any problems.
The ring decay time is way too long. I wonder if it is part electrical oscillation like electric guitar feedback rather than just a pinging filament wire.


I haven't bothered using it since I got a little Mojo.

Want to try the tube in the B1 circuit in a sturdy case and see how that works.

 

[alanhuth]

I ordered the kit and am eagerly awaiting its arrival. But messages like this make me wonder if maybe some more engineering is necessary. Is this a product design flaw or just the nature of the beast that happens rarely enough that the benefits outweigh the risks?

 

[b4bz]

I've done 3 Preamps with this board. The two that I installed the board into the case with rubber mounts make no noise. Neither of them needed anything mounted on the Nutube. The other with metal mounting posts was very microphonic. Link:
iFlight 12PCS M3X7+4.5... Amazon.com: iFlight 12PCS M3X7+4.5 Anti-Vibration Fixed Screws Mounting Hardware Spacer Standoff RC Screws kit with 12PCS M3 Nylon Hex Nut for Naze32 CC3D F3 F4 Flight Controller FPV Racer: Industrial & Scientific

 

[6L6]

Alanhuth- the microphony of the NuTube is extremely variable, ranging from “some” to “wow, that’s a whole lot.” I have one so bad that it is absolutely unusable without treatment, and the eraser is the best single thing I’ve found, and works very well with that super microphonic one. The new chassis will have no vent holes and that will help, and many people Have reported that softer PCB mounting can also be very beneficial.

I also have one that works beautifully with no treatment, so your mileage may vary. Hopefully in the future Korg will be able to address this, but in the meantime a little extra work is necessary for some builders. It’s worth it though, this circuit is very well loved for a reason.

 

[RobertHaze]

My NuTube saga is here.
YouTube

 

[Tuberoller]

Does this component as provided as kit by the store always sit between source and amplifier?

 

[aljordan]

Does this component as provided as kit by the store always sit between source and amplifier?

Yes.

 

[Tuberoller]

Thanks Al

What about preamp usage? Can it be added to another preamp?

What is the input output impedance of this device, per above kit?

Thanks again

 

[Manolo47]

Solved the ringing using bluetak...

I had a ringing problem with a unit I built for a friend. It was solved by covering the Borg “tubes” with bluetak. Does not need to cover the entire rectangle, only both ends.

 

[chanthing]

Build guide?

Hi,

I'm a little late to the party having recently received my completion parts. Got everything but the chassis because I want to build mine with 3 input pairs.

Is there an official build guide for the kit somewhere? I've looked to no avail and there are many many forum postings.

Has anyone done a version with > 2 inputs? Am interested in CAD files for the chassis as well as wiring diagrams for an input switcher. I will be glad to share mine if I am on untrod path here.

Thanks!

-- chanthing

 

[Jason]

The build guide should be up at guides.diyaudio.com in the next 24-48 hours. We're just ironing out a few bugs.

 

[chanthing]

Sweet! Thanks much.

 

[Jason]

The B1K build guide is now live at:

B1 with Korg Nutube - diyAudio Guides

Many thanks to 6L6 for producing this. Please direct any questions to the main B1K thread.

 

[Mark Johnson]

Just read the build guide HERE and it is fantastic. Congratulations and enormous thanks to member 6L6 !!

 

[Jason]

Thanks for the link correction Mark, copy and paste error (post updated)

 

[batty]

Didn't see this thread.
Here is mine, works great with M2X or ACA.