• These commercial threads are for private transactions. diyAudio.com provides these forums for the convenience of our members, but makes no warranty nor assumes any responsibility. We do not vet any members, use of this facility is at your own risk. Customers can post any issues in those threads as long as it is done in a civil manner. All diyAudio rules about conduct apply and will be enforced.

Korg NuTube is now available online

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
The Nutube is definitely a bit microphonic. Korg has experimented with several ways to try and mechanically isolate the tube from the PCB, including connecting it with thin wires and mounting it with a rubber sponge.

I have not seen the case that you showed, so I'm not sure how it works.

In the headphone amp I designed, I did not isolate it from the PCB. You can certainly hear a noise if you tap the PCB, but I don't think it is excessive.

If you were going to use the Nutube in a low level signal application (like a microphone or phono preamp) you would probably need to address it.

Pete

I've found (with the NuHybrid amp) that mounting the PCB vertically helps somewhat with the microphony issue, although further isolation of the boards from the chassis, or the chassis from the environment would definitely help as well. Am looking into trying to mount the boards to an interstitial chassis plate isolated in a similar manner as mechanical hard drive isolation (rubber grommets with through-bolts).

However, the sound quality is worth it!

-D
 
I used the double sided tape on foam that Pete supplied with my board and tube. In addition, I also put rubber grommets over my standoffs (they are just a little taller than the short standoffs), and then I screwed down the PCB onto the standoffs but not too hard. The rubber doughnut type grommet my help a bit in "floating" the PCB. Who knows? Just got the unit fired up and all seems to be working, which is good given my soldering skills. Will adjust bias tomorrow. Wall wart is 19 volts, so I will go with 9.5 volts as my plate voltage.

What kind of pot and how many ohms are folks using on this little gem?
 
Last edited:
First, you will need a soldering iron. For less than $25 you can get a Weller unit at Lowes (and maybe HD) that has 3 LED's on it to help with lighting and comes with 3 tips and a small amount of solder. You will need more solder, so try and get solder that is thin, not the huge thick stuff they sell at HD or Lowes. You will need a small sponge to help you clean the tip and perhaps a brass scrubbing pad like you can buy at grocery store, also for some tip cleaning. You could buy a small pad of tip cleaner/tinner. You will need some hook up wire, some basic 18 gauge will work, maybe in both black and red, and 4 RCA panel mount terminals. You will need an inexpensive wall power supply (wall wart) that produces 9 to 24 volts DC. You will probably want some type of case or box to put the project into. You will need a DC input jack in which to plug the wall supply, and a 50K ohm potentiometer (volume control) so you can adjust the units output level. You will have gain (increased volume) with the NuTube, so you will need to adjust that volume as if you were using a preamp. You will also need some small screw drivers, an inexpensive multimeter and some sharp wire cutters to strip the hook up wire ends. Soldering takes a little practice, so I would purchase some kind of inexpensive printed circuit board and practice on that with some cheap resistors and capacitors. Pete's board is small and the soldering somewhat close for a nooby, but it was only my second project and it is an excellent board and the solder flowed easily onto his solder pads. Just realized you are not in the U.S., hopefully you have a decent electronics store nearby where you can buy much of this stuff. For many, including myself, soldering at first is a major mystery. Watch tutorials on You Tube. Then practice. After 20 or 30 solder joints you will get the hang of it and then all the sudden it will be easy, even in tight locations. Get a soldering iron for $18 or more and ensure it produces the right temperature. You may go through a few tips early on and make a mess of them. Don't let that bother you.
 
Member
Joined 2017
Paid Member
Finished building the pre. Hooked it up to my ACAs and FHXLs and I think it gave both the extra punch they needed. Very happy with the sound and don't think I have any problems with microphonics (although I maybe I just don't notice after many years of listening to router "music"). My only problem is that the volume goes from nothing to full with just a nudge on the knob. I have a 25k taper pot on the front. Is there a better pot I can use that will solve that problem or did I maybe do something else wrong?
Doug
 

Attachments

  • 0330191149.jpg
    0330191149.jpg
    976.2 KB · Views: 546
  • 0330191156a.jpg
    0330191156a.jpg
    849.6 KB · Views: 517
  • 0330191155.jpg
    0330191155.jpg
    917.5 KB · Views: 504
Balanced preamp / headphone amp PCB Current needed?

I have a power supply question for the balanced headphone amp.

I plan to use Salas SSLV1.3 UltraBiB shunt regulators to power the two boards.

I know a +/-15V supply is needed, but i'm not sure about the mA consumption the headphone amp board needs from the power supply.

What mA should I plan for? The manual says I should allow 50 - 100 mA extra.
 
Pete,
Can the Opa551 opamp be replaced with other audio op amps like LME49710, Opa134 etc? The output current of Opa551 is 200mA. Should I find an op amp to match that to make it work? Thanks.

Spoon109,
I am also planning to use Salas ULtraBiB v1.3 to power it;please let me know what resistor values you finally decide on. Thanks.
 
Pretty much any single opamp will work. You do need one that supports +/- 12V power rails. How much current you need depends on the impedance headphones you want to drive, and to a lesser extent how loud you listen. Opamps like LME49710 will work OK into higher impedance headphones, and will drive low-Z OK but not to a very high level.

There's lots of discussions about opamps for headphones online. Like this: The Opamp thread | Headphone Reviews and Discussion - Head-Fi.org

Pete
 
Hello all, What are the lowest replacement resistor values that could be used to substitute for R29 & R30 on the Korg HA-Kit? I am trying to power very low impedance in ear monitors and need the damping to support them.

You can go as low as zero. A couple of caveats, though: The resistor helps with short circuit protection. Most opamps are pretty robust so it's usually not a big concern. And occasionally some opamps can have stability problems driving some headphones that present wacky reactive loads.

If you are driving low-Z IEMs I'd stick something like 1 ohm there.

Pete
 
Mains hum

Hi Pete,
I finished building the NuTube headphone amp but there seems to be a hum when I plug in my iPhone with a spilt cable. Whereas if I use RCA cable with my DAC there is is no hum. Is this a grounding issue or a power supply issue. Any advise how to resolve this hum.

And of course there is microphonics everytime I touches the volume pot.
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.