DIY Pass B1 Preamplifier with Korg Nutube Triode

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marantzfan

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Very soon, I plan to get underway on a new build project!

While I was building the Aleph J, I also became intrigued by another recent Nelson Pass DIY project, the B1 with Korg Nutube Triode. Not a "traditional" tube, but a dual triode nonethless.

Korg.jpg

The implementation of it in this circuit is really interesting. For those who haven't seen it, here is the original thread on Diyaudio.com by Mr. Pass himself:


Also, a fairly recent write up by 6 Moons:


Now, with this build I'm thinking of adding a little luxury I don't normally afford myself; a remote control! Does anyone have experience with this little piece of audio candy?

64steps_khozmo.jpg

 
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I was interested by that project. I built one of Pete Millett's NuClassD amps that also uses the 6P1 triode. The one heads-up I will give you is that the 6P1 is microphonic as hell. You will really need to isolate the board and preamp.
 
Interesting that it is mounted on a daughterboard in the photo above. Perhaps that will help with isolation?
 
Interesting that it is mounted on a daughterboard in the photo above. Perhaps that will help with isolation?

To be completely transparent, I'm likely going to just piggyback on this fine build which I believe uses that daughterboard:

 
Those Khozmo attenuator's look awesome. If I ever build a preamp one of them will be part of it. I sort of lost any desire after getting my Audio Research SP8 though. I still want to build something using one, it will come to me someday.

BillWojo
 
I would recommend skipping this one if possible. If you look at Pete's and Nelson's implementations, a fet or two drives the input of the Nutube, and the Nutube drives a fet or two that handles whatever is at the output. The Nutube's grid current causes it to have input impedance that is rather low, and the tiny amount of current that the Nutube can run and its very limited (0.0017W) dissipation makes it incapable of driving interconnects or the input of an amplifier. It can't even really run another device with voltage gain. Being a small directly heated tube, it's not all that surprising that it's a bit microphonic too.

The idea is pretty cool, but the device itself is far too small to be of any real use. If they made a 1-5W device compatible with CPU heatsinks, I'd be on board, but as it is, I lump this device in with the old Sonic Impact tripath amp. It can be a fun novelty to mess around with, but probably not the best place to throw in a bunch of high dollar components.

The Pass version is kind of two B1 buffers stuck on either side of the NuTube, you could just go with the B1 instead! It should cost much less, probably sounds a bit better, and won't bother you with microphonics.
 
I would recommend skipping this one if possible. If you look at Pete's and Nelson's implementations, a fet or two drives the input of the Nutube, and the Nutube drives a fet or two that handles whatever is at the output. The Nutube's grid current causes it to have input impedance that is rather low, and the tiny amount of current that the Nutube can run and its very limited (0.0017W) dissipation makes it incapable of driving interconnects or the input of an amplifier. It can't even really run another device with voltage gain. Being a small directly heated tube, it's not all that surprising that it's a bit microphonic too.

The idea is pretty cool, but the device itself is far too small to be of any real use. If they made a 1-5W device compatible with CPU heatsinks, I'd be on board, but as it is, I lump this device in with the old Sonic Impact tripath amp. It can be a fun novelty to mess around with, but probably not the best place to throw in a bunch of high dollar components.

The Pass version is kind of two B1 buffers stuck on either side of the NuTube, you could just go with the B1 instead! It should cost much less, probably sounds a bit better, and won't bother you with microphonics.
Do I sense a revised Paul edition on the horizon?
 
I would recommend skipping this one if possible. If you look at Pete's and Nelson's implementations, a fet or two drives the input of the Nutube, and the Nutube drives a fet or two that handles whatever is at the output. The Nutube's grid current causes it to have input impedance that is rather low, and the tiny amount of current that the Nutube can run and its very limited (0.0017W) dissipation makes it incapable of driving interconnects or the input of an amplifier. It can't even really run another device with voltage gain. Being a small directly heated tube, it's not all that surprising that it's a bit microphonic too.

The idea is pretty cool, but the device itself is far too small to be of any real use. If they made a 1-5W device compatible with CPU heatsinks, I'd be on board, but as it is, I lump this device in with the old Sonic Impact tripath amp. It can be a fun novelty to mess around with, but probably not the best place to throw in a bunch of high dollar components.

The Pass version is kind of two B1 buffers stuck on either side of the NuTube, you could just go with the B1 instead! It should cost much less, probably sounds a bit better, and won't bother you with microphonics.

Interesting. Before building my first Bottlehead kit, I built an F5 clone and a B1.

My first thought was to build another B1 to go with the Aleph J before I saw this new design.

I really did like the B1 and it was a very simple and straightforward build.

I’ve already got the pcb, matched transistors and Nutube but haven’t started putting anything together yet do all options are still on the table...
 
Do I sense a revised Paul edition on the horizon?
I hope they make something like that, but I would wonder just how expensive such a device would end up being. Then there's also the fun of replacing something like this when the cathodes are exhausted. Large surface mount devices don't exactly come off that easily!
 
MarantzFan,

What ended up happening with the B1 Korg Triode build?

I would love to hear how it worked out or if it happened?

Thanks!
 
It hasn’t happened....yet. I have most of the parts minus a chassis and some hardware.

I also have a set of the plain B1 boards too...

Man, how many projects do I have backlogged? :p
 
It hasn’t happened....yet. I have most of the parts minus a chassis and some hardware.

I also have a set of the plain B1 boards too...

Man, how many projects do I have backlogged? :p
Don't let Nate know about this one or you'll never hear the end of it...
 
It hasn’t happened....yet. I have most of the parts minus a chassis and some hardware.

I also have a set of the plain B1 boards too...

Man, how many projects do I have backlogged? :p

Lots of projects is a good thing! That way life is never boring. What amp do you think you would try to the B1 with?
 
I missed that also. MarantzFan, it sounds like you have lots of build or diy experience. What Pass amps have you built? It sounds like you build an F5? I ask because I am wondering what Pass/First Watt you have heard/built that you enjoyed the most. Also, what speakers did you run your F5 clone with?

Thanks!
 
I missed that also. MarantzFan, it sounds like you have lots of build or diy experience. What Pass amps have you built? It sounds like you build an F5? I ask because I am wondering what Pass/First Watt you have heard/built that you enjoyed the most. Also, what speakers did you run your F5 clone with?

Thanks!

I've built two FirstWatt/Pass class A amplifiers; the F5 and recently the Aleph J. Both are outstanding performers (especially for the meager investment). I used the F5 with Altec Model 19's and right now I have the Aleph J hooked up to my Altec 604-8G speakers. So, my only experience with these has been on very sensitive speakers.

They sound similar to a single ended tube amplifier but to me they lack a little of the "flesh and blood" feeling you get with SET's. Both the F5 and Aleph J are outstanding and unfortunately I didn't own them at the same time to compare.

If you're contemplating a build, I would recommend you do it. With the way these have been put together on the DIY Audio Store and the build threads on that site they are a very easy first time build.
 
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