I've received Korg's microphonics reducing case for the NuTube and have started to rebuild the BK1 around it. Instead of using the cloth-based adhesive tape that comes with the kit I'm using Sorbothane tape from 3M. Using the kit requires some changes to the physical set up (the case needs to sit on the board) and the wiring of the NuTube (the wiring kit for the case only has eight wires instead of 10 pins of the tube). A review of the BK1 schematics, the NuTube site, and the BK1 board present a very simple solution to this difference. At least, I hope so. I will report back next weekend as soon as the rebuild is complete.
Thanks TYM
Although it was more the Aluminum knob i meant, in order to ensure that is fits in the recess of the frontpanel.
I found and ordered this one:
2PCS AUDIO KNOB 30x22mm Machined Aluminum VOLUME POTENTIOMETER AMPLIFIER CD Knob | eBay
It looks like it could be a good fit.
For the power connector i have ordered this one:
PC-GM2.1 NINIGI - Socket | DC supply; male; 5,5/2,1mm; 5.5mm; 2.1mm; soldering | TME - Electronic components
To be used with this PSU:
SGA25E24-P1J MEAN WELL - Power supply: switched-mode | 24VDC; 1.04A; Out: 5,5/2,1; 25W; 87.5% | TME - Electronic components
Now i am only missing the switch
(and the chassis )
I tried Kong's Nutube accessory kit in an attempt to reduce the ringing of the tube from environmental noise. In my case, environmental noise constitutes sitting in the listening position and clapping my hands or snapping my fingers. Or listening to music. While using the kit didn't completely prevent the ringing the reduction is significant. The kit's holder has basically saved the build for me.
The kit consists of several parts offering several different kinds of Nutube mounting options.The kit parts that I used were the converter board, the harness (wires only), and the holder. There are others I won't discuss since didn't use them. After removing the Nutube from the BK1 board I mounted it to the converter board. This board largely functions the same way as the converter board for the volume control in the BK1 kit; that is, it allows for simple wire soldering to the board to connect the tube to the preamp's main board. Korg supplies a set of "cushions" for mounting the various parts, however, I substituted the cushions for sorbothane tape from 3M. One piece of tape connects the tube to the converter board, one piece connects the board to the holder, and a final piece of tape connects the holder to the preamp board.
Since the Nutube no longer connects directly to the preamp board wires must be used to connect the converter board to the preamp (or other application) board. Korg supplies a harness for this purpose, but the harness connection end is female, while the BK1 board is also female. Also, the pin configuration of the harness does not match the physical positioning of the Nutube pins as does the preamp board. I don't have wire small enough to fit in the preamp board's soldering positions for for the Nutube (something smaller than AWG19) so I cut the wire from harness. This turned out to be a good option since the wire i have on hand (Cardas hookup wire) is too stiff be used in this application as well last too large.
Another important note is that Korg apparently intends for the user to twist the wire if the pin order of the preamp board is in the same order a the Nutube. Since the BK1 maintains this polarity, for lack of a better term, I wired the converter board backwards compared to Korg's instructions. That is, the wires exit the board in the direction of the Nutube pins instead of the instruction's indicated orientation of away from the Nutube pins. The only drawback to this is the builder needs to be very careful not to cut or tear the wires on the pins. It turns out I could have shortened the wires prior to soldering, but I didn't know this before the installation, and, frankly, I was afraid of cutting the ridiculously fine and soft wire sourced from the harness.
I mounted the Nutube in the holder after soldering the wires, but before mounting the holder. I had to change the mounting height of the Nutube in the holder, and the holder on the board. The first because, since I'm using sorbothane tape, I had mounted the Nutube using too many layers and the mounted Nutube was too high for the case. In the second case I wanted to maintain access to the solder points on the preamp board, which would be covered by the holder (the holder is much larger than the Nutube), and I used enough layers of sorbothan that the holder sat too high to fit in the BK1 chassis. With all the re/mounting I also broke one of the fine wires. I want to reiterate that the mounting kit wires are fine.
Korg's instructions say to till any gap in between the wires and the holder using (what I'm assuming is) a hot glue gun. I used trimmed sorothane to fill in the gap.
The holder doesn't feel particularly rigid using the sorbothane tape, but it seems to be holding well. The tape uses 3M adhesive, after all.
In my first test powering up my new Nutube mounting configuration the Nutube lit up and there was a conspicuous absence of flashes, sparks or smoke. I took this for a good sign. Without testing the preamp via test points on the board, I inserted the preamp into a system consisting of Zu Dirty Weekends, ACA 1.7 in mono block configuration and a old MacBook Pro with a Dragonfly as the d/a converter. Before even plugging in the MacBook the ringing at power up was greatly reduced and the clap test indicated greatly reduced ringing response. Ringing resulting from tapping on the preamp chassis is greatly reduced, too. Even the ringing from switching sources is reduced significantly.
While the Korg accessory kit didn't relieve all of the ringing in my preamp it has reduced the ringing to a level that is tolerable. Generally, I view it as a success and will leave the kit in place. I recommend the kit to others that are experiencing the same problem, and I now consider my build done.
Now, off to finish my partially completed Aleph J, M2x and Pearl 2 builds.
The kit consists of several parts offering several different kinds of Nutube mounting options.The kit parts that I used were the converter board, the harness (wires only), and the holder. There are others I won't discuss since didn't use them. After removing the Nutube from the BK1 board I mounted it to the converter board. This board largely functions the same way as the converter board for the volume control in the BK1 kit; that is, it allows for simple wire soldering to the board to connect the tube to the preamp's main board. Korg supplies a set of "cushions" for mounting the various parts, however, I substituted the cushions for sorbothane tape from 3M. One piece of tape connects the tube to the converter board, one piece connects the board to the holder, and a final piece of tape connects the holder to the preamp board.
Since the Nutube no longer connects directly to the preamp board wires must be used to connect the converter board to the preamp (or other application) board. Korg supplies a harness for this purpose, but the harness connection end is female, while the BK1 board is also female. Also, the pin configuration of the harness does not match the physical positioning of the Nutube pins as does the preamp board. I don't have wire small enough to fit in the preamp board's soldering positions for for the Nutube (something smaller than AWG19) so I cut the wire from harness. This turned out to be a good option since the wire i have on hand (Cardas hookup wire) is too stiff be used in this application as well last too large.
Another important note is that Korg apparently intends for the user to twist the wire if the pin order of the preamp board is in the same order a the Nutube. Since the BK1 maintains this polarity, for lack of a better term, I wired the converter board backwards compared to Korg's instructions. That is, the wires exit the board in the direction of the Nutube pins instead of the instruction's indicated orientation of away from the Nutube pins. The only drawback to this is the builder needs to be very careful not to cut or tear the wires on the pins. It turns out I could have shortened the wires prior to soldering, but I didn't know this before the installation, and, frankly, I was afraid of cutting the ridiculously fine and soft wire sourced from the harness.
I mounted the Nutube in the holder after soldering the wires, but before mounting the holder. I had to change the mounting height of the Nutube in the holder, and the holder on the board. The first because, since I'm using sorbothane tape, I had mounted the Nutube using too many layers and the mounted Nutube was too high for the case. In the second case I wanted to maintain access to the solder points on the preamp board, which would be covered by the holder (the holder is much larger than the Nutube), and I used enough layers of sorbothan that the holder sat too high to fit in the BK1 chassis. With all the re/mounting I also broke one of the fine wires. I want to reiterate that the mounting kit wires are fine.
Korg's instructions say to till any gap in between the wires and the holder using (what I'm assuming is) a hot glue gun. I used trimmed sorothane to fill in the gap.
The holder doesn't feel particularly rigid using the sorbothane tape, but it seems to be holding well. The tape uses 3M adhesive, after all.
In my first test powering up my new Nutube mounting configuration the Nutube lit up and there was a conspicuous absence of flashes, sparks or smoke. I took this for a good sign. Without testing the preamp via test points on the board, I inserted the preamp into a system consisting of Zu Dirty Weekends, ACA 1.7 in mono block configuration and a old MacBook Pro with a Dragonfly as the d/a converter. Before even plugging in the MacBook the ringing at power up was greatly reduced and the clap test indicated greatly reduced ringing response. Ringing resulting from tapping on the preamp chassis is greatly reduced, too. Even the ringing from switching sources is reduced significantly.
While the Korg accessory kit didn't relieve all of the ringing in my preamp it has reduced the ringing to a level that is tolerable. Generally, I view it as a success and will leave the kit in place. I recommend the kit to others that are experiencing the same problem, and I now consider my build done.
Now, off to finish my partially completed Aleph J, M2x and Pearl 2 builds.
Attachments
One more important point I forgot in my previous post. You will notice that there are no wires leading to F1 and F3. This is because in NPs design these pins tie into the same path in the circuit. Using the converter board accomplishes this tie in at the end wires. I have left the F1 and F3 positions empty, although I could have jumped them to be conservative. A review of the Korg info sheet and NP's info sheet for the BK1 indicates that this shouldn't be necessary, although it may be better engineering/building than I completed here.
I still believe the best way to kill the microphonics is to treat it like a turntable and damp down everything that can ring or resonate and transmit back into the Nutube. I've now got heavy perspex bolted to the original base plate that the PCB is mounted to. It makes the base very dead when I tap it. I need to replace the perspex lid I've got with the same combination to block out unwanted RF/EFI and sound deaden that too.
Nice bit of timber would do the same, just anything that doesn't clang when you hit it with a screwdriver. Galaxy case lids are as good as cymbals.
Nice bit of timber would do the same, just anything that doesn't clang when you hit it with a screwdriver. Galaxy case lids are as good as cymbals.
Taming the Microphony
I purchased a couple sheets of Sonic Barrier damping sheets with the adhesive backing to damping the B1 Kong chassis and to cover up the vent slots on the top and bottom panels of the chassis to further isolate the Korg NuTube from acoustic-born microphony.
I bought the Sonic Barrier sheets from Parts Express:
Sonic Barrier Lightweight Vinyl Sound Damping Sheet 10" x 13"
I cut the sheets using a hobby knife and straight edge. Then, I applied strips of black electrical tape onto the adhesive backing side of Sonic Barrier sheets where the vent slots were covered, so that dust wouldn’t make its way through the slots and stick to the adhesive backing. It actually turned out well.
I am now able to crank up the volume without any microphonic ringing. Previously, I covered the vents with paperback books. Mission accomplished!
As I mentioned before, the B1 Korg chassis kit should be sold with top and bottom panels without the vent slots. I would still recommend using the Sonic Barrier sheets as it really dampens the metallic ringing of the Aluminum chassis.
Next up is installing the Tocos Cosmos volume pot and film caps as ClaudeG has recommended.
I purchased a couple sheets of Sonic Barrier damping sheets with the adhesive backing to damping the B1 Kong chassis and to cover up the vent slots on the top and bottom panels of the chassis to further isolate the Korg NuTube from acoustic-born microphony.
I bought the Sonic Barrier sheets from Parts Express:
Sonic Barrier Lightweight Vinyl Sound Damping Sheet 10" x 13"
I cut the sheets using a hobby knife and straight edge. Then, I applied strips of black electrical tape onto the adhesive backing side of Sonic Barrier sheets where the vent slots were covered, so that dust wouldn’t make its way through the slots and stick to the adhesive backing. It actually turned out well.
I am now able to crank up the volume without any microphonic ringing. Previously, I covered the vents with paperback books. Mission accomplished!
As I mentioned before, the B1 Korg chassis kit should be sold with top and bottom panels without the vent slots. I would still recommend using the Sonic Barrier sheets as it really dampens the metallic ringing of the Aluminum chassis.
Next up is installing the Tocos Cosmos volume pot and film caps as ClaudeG has recommended.
Great advice on dampening, Rich
That reads like the most effective dampening approach yet. And smart move with the electrical tape. Excited to have the kits available soon and really thank all you "Pioneers" out there to help troubleshoot and tip. Having so utterly enjoyed my stereo ACA, I'm looking forward to building the Korg pre and maybe two more ACAs in mono (need those watts, NP!).
That reads like the most effective dampening approach yet. And smart move with the electrical tape. Excited to have the kits available soon and really thank all you "Pioneers" out there to help troubleshoot and tip. Having so utterly enjoyed my stereo ACA, I'm looking forward to building the Korg pre and maybe two more ACAs in mono (need those watts, NP!).
I couldn't find the RK27 PCB as a stand alone offering either at the diyaudio store or over at Peter Millett's site/store.
I know I don't need it but I like the concept in that it offers neatness/tidiness and offers a pro look.
Any leads to get some?
If not, should be an item to offer separately?
I know I don't need it but I like the concept in that it offers neatness/tidiness and offers a pro look.
Any leads to get some?
If not, should be an item to offer separately?
Seems a shame that the kit doesn't include the circuitry and XLR outputs to mate with the ACA - there was a post about Jensen transformers but no diagrams showing how such a thing would be wired up.
Flex your search muscles over at eBay and you'll come upon many possibilities. For example, the attached image.
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