Pete, please ask your brother his opinion of a guitar effects/processing box where each unit sold performs differently for each different user, seemingly at random.
Here is a possible explanation for the random but relatively high variation in vibration susceptibility and filament longevity, for which I have NO evidence but nonetheless may be plausible:
Korg developed the NuTube for music instrument (MI) applications, which as Bob notes is often subject to vibration and shock in use. Korg understands, as a typical large Japanese company following QA/QC principles (first established in the US), that any manufactured components is subject to a bell curve of performance. To ensure customer satisfaction for its primary MI business, it subjects each NuTube to some kind of screening process to weed out poorly performing NuTube units that fall below a Korg-determined internal specification level. Those units that pass the screening are entered into the MI manufacturing stream. Rejected NuTubes, which still test operational, are then sold off into secondary channels; one of these channels is to third party purchasers such as Pete Millet and the DIY Store (there might even be a grading process with tiered pricing to different kinds of third party purchasers). I consider this one plausible explanation because that is what appears to happen with respect to traditional tubes such as 12AX7 and 6080. There are only a few companies who actually manufacture tubes such as 12AX7. Other companies buy tubes in bulk, and may test to meet their screening. Rejected tubes are then placed back into the stream and resold to other users (at a lower price).
In any event, I believe that there are some actions that every new builder of the B1K should consider, according to each individual's risk tolerance, pocketbook and technical capabilities to troubleshoot and repair improperly functioning units:
1. Measure the value of every resistor and capacitor, and use only units that are within spec (matched if you have enough raw units).
2. Verify correct operation of every zener diode.
3. Use a socket or pins on the NuTube to permit easy changeout for testing and replacement.
4. Use dampened PCB standoffs.
5. Use one type of damping for the NuTube itself - there are many possibilities mentioned in posts on this thread.
6. Do not use a case which has open slots, if at all possible.
7. Consider adding case dampening materials, such as sorbothane; and/or case mass increasing materials such as polymer slabs.
8. Use isolation-type feet.
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Error is a use B1K without cover lid on.
Why not switch the power on of the B1K preamp always with the cover lid on the top of the chassis box so is closed ?
Is possible you not need to buy another new Nutube..
That is both an interesting & viable concept. Computer CPU manufacturers have done something like this for years, assigning different units/within production batches to different maximum (stable) operating speed batches after testing. Even highly sophisticated electronics production facilities can’t make every chip exactly the same.
Pete
Interesting thought. I wonder if we source the Korg elsewhere if results would be better. At this point mine has shown zero bad habits and I've had it for a long time. The issues still concern me though.
It may be possible to purchase the NuTube directly from US Korg as an end-user, or more likely ordering a replacement form an authorized US Korg service center (if this warranty model is being used by US Korg).
Purchasing the NuTube from any other buyer would probably not solve the issue as I am conjecturing that all "good" NuTubes are kept by Korg for internal use (manufacturing and warranty service) - assuming my supposition is true and remember, I have no evidence of this. Perhaps if additional screening were done, then there would be a higher probability of acceptable performance, but this would require a lot of $$$ and the volumes may not be high enough to justify any company undertaking it. Perhaps if someone could devise a DIY series of tests on newly-purchased NuTubes that might prevent a bad NuTube from going into service on an individual DIY's build, but it definitely would NOT support a warranty return because US Korg (and any reseller) has not bought into the testing regime and pass/fail criteria.
It may be that DIY builders simply have to accept the possibility of purchasing one or more poorly performing NuTubes and figure that into the overall cost and more generally, the risk in determining whether to build the preamp. The reward/risk ratio seems to be very high in favor of reward, and the overall cost - even with the need to purchase two replacement NuTubes - is probably still far below the cost of purchasing something comparable (in fact, I tend to doubt there is anything comparable in the retail market as an assembled and warranted component). Plus, there is the satisfaction and learning that comes with DIY which is absent in purchasing a retail product. Some DIYers expect perfection and miracles and expect too much; we need to have a good sense of perspective here. I, for one, am extremely thankful for the efforts of Mr. Pass, DIY Audio Store, DIY Audio forum, and the moderators of this forum.
I've never had an issue with anything purchased from the DIY store. Including this nutube. And I sincerely doubt that if they are indeed receiving second tier hardware from Korg, that they are unaware of it. As I posted days ago, remember these are relatively inexpensive components in the grand scheme of Audiophilism. And cost to performance ratio is off the charts from Mr. Pass' and DIY's efforts. Plus figuring it out is all the fun! I think...
And it would be beneficial to look at MI circuit design. Even modest amounts of NFB reduces or eliminates ringing which would explain how MI gets away with it.
These are all very insightful and relative comments. Many thanks for the various points made. Out of the 8 different units that I have made using the SP1 tube, 2 of them have had this same problem. The others were simply great sounding units. FWIW, 5 of the units were from Pete Millett, and were various products such as a buffer amp, a headphone amp and a power amp. 3 of the units were from the DIY store. All 3 are the B1K unit.
Frankly, I would pay more for a tube that has no issues, especially since there is the dismantling of a unit and de-soldering involved just to replace a tube. AFAIK a socket would not be a good idea because of the fragility of the pins on this tube.
Frankly, I would pay more for a tube that has no issues, especially since there is the dismantling of a unit and de-soldering involved just to replace a tube. AFAIK a socket would not be a good idea because of the fragility of the pins on this tube.
I meant to say I doubt that they are AWARE they were receiving second tier hardware if they indeed are. Wanted to correct that! Really should proofread stuff.
It's cool that a magnet changes the glow pattern of the cathode. It might be fun to hear what that does to the sound.
This talk about part grading led me to wonder if grade information is encoded in the NuTube part number. The little corstat box that my NuTube came in has what looks like the part number DIYE-NU6P1-1K0 followed by EXWWV: Electronic Component, Nutube 6P1, 1 Piece, Korg, Release 1. I'm not seeing anything that obviously looks like a parts grade, though.
This talk about part grading led me to wonder if grade information is encoded in the NuTube part number. The little corstat box that my NuTube came in has what looks like the part number DIYE-NU6P1-1K0 followed by EXWWV: Electronic Component, Nutube 6P1, 1 Piece, Korg, Release 1. I'm not seeing anything that obviously looks like a parts grade, though.
My (biased) opinion? I listened to it w&w/o the magnet and with the magnet it sharpened up the signal a bit, less warm and fuzzy overall, but the airiness and presence remained the same. Definitely different than the B1. It certain cut down the length of the ringing when one tapped on the case or did anything that would induce such an event.
The magnet actually doesn’t need glue to stay on (it’s attracted to that round, metal plate on the back of the Nutube) but it will slide from side to side. I glued a plastic spacer onto the Nutube so the magnet didn’t touch that metal disk and then just used very small dots of glue to prevent the side to side movement. Very easy to remove.
Cheers,
Pete
Got my Korg control board up and running on the bench using LEDs to show relay position. These are latching relays so current flows for a very brief time, and only while the relay is switching. No magnetic fields around the signal path.
1. At power on all relays are tested (about 50ms each) and reset to OFF.
2. Input select switch is tested for Input 1 or Input 2 position and appropriate Input relay is turned ON.
3. At about 3 seconds -- after the turn-on thumps are over -- the Output relay connects the Korg to the power amp.
During operation:
When the Input is switched, the Output relay is momentarily disconnected while the Input relays are in transit and then turned back on. Total time is maybe 500ms, and there should be no switching noise. I'm going to remove the resistors from the input sockets that were previously recommended to reduce input switching noise.
When 24V power is intentionally removed or accidentally lost, the Output relay and both Input relays are instantly disconnected, disconnecting the Korg from all sources and the power amplifier.
I haven't tested the trigger circuit yet, I need to reconsider the current limiting resistor value.
1. At power on all relays are tested (about 50ms each) and reset to OFF.
2. Input select switch is tested for Input 1 or Input 2 position and appropriate Input relay is turned ON.
3. At about 3 seconds -- after the turn-on thumps are over -- the Output relay connects the Korg to the power amp.
During operation:
When the Input is switched, the Output relay is momentarily disconnected while the Input relays are in transit and then turned back on. Total time is maybe 500ms, and there should be no switching noise. I'm going to remove the resistors from the input sockets that were previously recommended to reduce input switching noise.
When 24V power is intentionally removed or accidentally lost, the Output relay and both Input relays are instantly disconnected, disconnecting the Korg from all sources and the power amplifier.
I haven't tested the trigger circuit yet, I need to reconsider the current limiting resistor value.
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A question regarding ground planes -- I see that the Korg pcb does not have one, and am wondering if there is an audio-based rule-of-thumb to not use them in audio circuits. I have mostly done digital of late and have always used one, but perhaps this add-on board I'm doing should not have one in the audio signal area of the board? I'll still have the plane in the power & digital portions but I could easily leave the audio portion of the board without one.
Any guidance is welcome . . .
Any guidance is welcome . . .
Pearl2 has a ground plane.
ACP+ has a double-deck PCB arrangement where the bottom board is a ground plane.
Wayne's BA2018 linestage has a ground plane.
DIY Sony VFET front end cards Scourge, Bulwark, Marauder, Dreadnought, and Relentless all have ground planes.
Quasimodo V.4 has a ground plane -- but it's a digital circuit.
Noir headphone amp has a ground plane.
Bob Cordell's Super Gainclone has a ground plane.
SMPS inline filter PO89ZB has a ground plane.
VRDN regulated power supply has three ground planes (on a 4-layer PCB)
ACP+ has a double-deck PCB arrangement where the bottom board is a ground plane.
Wayne's BA2018 linestage has a ground plane.
DIY Sony VFET front end cards Scourge, Bulwark, Marauder, Dreadnought, and Relentless all have ground planes.
Quasimodo V.4 has a ground plane -- but it's a digital circuit.
Noir headphone amp has a ground plane.
Bob Cordell's Super Gainclone has a ground plane.
SMPS inline filter PO89ZB has a ground plane.
VRDN regulated power supply has three ground planes (on a 4-layer PCB)
LOL, that's a list! Good, I'm sticking with mine, then. Wayne's BA2018 seals the deal -- it has caught my attention and I want to try that next using the diyaudiostore B1K chassis.
I have a batch that says Korg Nutube 6P1 and also CH2322G 7BA
Hmm, thanks Mr. Pass! I looked at the top and edges of my Nutube & didn't see anything like a batch number. I get that this info was most likely from the factory and not on the NuTubes themselves. Unless it's on the bottom.
DIYE-NU6P1-1K0 is just the diyAudio store's own internal SKU for "A box that contains one unit of Korg Nutube 6P1".
We reached out to Korg to settle the debate about grading. I quote verbatim:
As for settling on a good mechanism of mitigating microphonics, that's clearly something we need to work towards. Korg's own products usually mount the tube in a mechanical suspension to minimize transmission of vibration to the tube.