Hi there, I suspect I may have a bad J113 jfet somewhere.. I’ve swapped in a new Nutube and still can’t get a stable 9.5vdc on the right channel. The voltage drops over time. All perfectly stable on the left channel. I can actually see the right triode glows less brightly than the left after about an hour.
Could someone advise (link me to):
How to test the jfet?
How to match a new pair if I buy a bunch of them?
How to determine the tweaking resistor value?
Cheers
Could someone advise (link me to):
How to test the jfet?
How to match a new pair if I buy a bunch of them?
How to determine the tweaking resistor value?
Cheers
B1 works great with any VFET amps , i wonder if the B1 Korg will not be too creamy with them .
someone tried the Combo ?
Swap the Jfets left for right ch, one at a time if you like, until the problem
goes to the other channel. If it doesn't then it's likely the tube.
If it's a bad Jfet, email me.
Ok so after realizing the last measurements I posted had some things wrong with it and wanting to know if I just didn't know how to measure properly or if something was wrong with my preamp, I spent some time trouble shooting it.
I figured out that my Focusrite sound card is probably the issue plus there was some interference from my desktop monitors, amps and other electronics.
So I took some new measurements and they look much better.
My signal generator is battery powered and even when plugging that into my sound card i still get a 60hz bump. Even when I plug nothing into my sound card that 60hz bump is there so I don't think it's the preamp.
This is 1v out and the nutube set at 9.4v.
Hopefully this is what it's supposed to look like.
I figured out that my Focusrite sound card is probably the issue plus there was some interference from my desktop monitors, amps and other electronics.
So I took some new measurements and they look much better.
My signal generator is battery powered and even when plugging that into my sound card i still get a 60hz bump. Even when I plug nothing into my sound card that 60hz bump is there so I don't think it's the preamp.
This is 1v out and the nutube set at 9.4v.
Hopefully this is what it's supposed to look like.
Attachments
Running B1 Korg with F4 and Cornwalls. The sound is excellent. Se more in F4 thread. F4 power amplifier
Cool! That amp looks awesome. I'm sure the Cornwalls will drive you out of the room at about 5 watts so I'm betting the F4 is running class A+ ;-). I would love to hear that setup. My F5 board and components were delivered to day. So that's on the TTD list after the B1K build.
B1 Korg with Pass Clone VFET to Stax headphones is excellent in both positive and negative phase (to switch them, just switch the outputs). B1 Korg also sounds great with Yamaha B2 VFET to planar speakers. It does not seem to overdose the harmonics in the 1V or below range.
Thanks Nelson. Swapped two pairs of jfets today. Tricky to get them out! No change yet.
Had a bit of a setback swapping the last two pairs of jfets.. Broke a leg off the last one trying to get it out.. Anyway, the problem didn’t move from right to left with the swapping so the jfets must have been ok. Must be something else..
I finished the preamp and tried after 72 hours of heating, the B1 Korg.
A small report was needed because this preamp is well worth it.
I wanted to make it as minimal as possible and for a cost not exceeding $ 200:
One input, a potentiometer, the Korg card of Nelson with its Meanwell 75/24 power supply and one output.
Optimization of the links so that they are as short as possible and use of an excellent potentiometer: the Alps RK40.
The listening base: CD pro2, Dac PCM 1704, VFet from N.Pass, Tannoy GRF + ST100, Belden and Mogami cables.
Although with a sensitivity of 95db GRF, no hum.
However if you tap on the card, a microphone noise is heard, but who would enjoy playing the battery on the card?
In this configuration, the best sound (for me) is to associate with T7 / T8 at 9.7V and the wiring to the out of phase speakers.
The sound is ample, with a nice bass base, well timbre and associated with a great speed on transients (eg CD: The Ozelltapes Marcus Miller disc 1 / band 4)
I compared the Korg B1 with 3 other preamps: Accuphase C2000, Luxman CL360, and a DIY SE 5687 WOT in the same configuration as written above.
The Korg has nothing to envy to these 3 preamps, it is closer to the DIY SE5687.
Now, he misses it to be universal, an excellent phono input.
Thank you Nelson for this great exercise.
Good DIY to all,
Christophe
A small report was needed because this preamp is well worth it.
I wanted to make it as minimal as possible and for a cost not exceeding $ 200:
One input, a potentiometer, the Korg card of Nelson with its Meanwell 75/24 power supply and one output.
Optimization of the links so that they are as short as possible and use of an excellent potentiometer: the Alps RK40.
The listening base: CD pro2, Dac PCM 1704, VFet from N.Pass, Tannoy GRF + ST100, Belden and Mogami cables.
Although with a sensitivity of 95db GRF, no hum.
However if you tap on the card, a microphone noise is heard, but who would enjoy playing the battery on the card?
In this configuration, the best sound (for me) is to associate with T7 / T8 at 9.7V and the wiring to the out of phase speakers.
The sound is ample, with a nice bass base, well timbre and associated with a great speed on transients (eg CD: The Ozelltapes Marcus Miller disc 1 / band 4)
I compared the Korg B1 with 3 other preamps: Accuphase C2000, Luxman CL360, and a DIY SE 5687 WOT in the same configuration as written above.
The Korg has nothing to envy to these 3 preamps, it is closer to the DIY SE5687.
Now, he misses it to be universal, an excellent phono input.
Thank you Nelson for this great exercise.
Good DIY to all,
Christophe
Beautyful build 
Congratulations and thanks for sharing description about audio.
Have a nice day
Congratulations and thanks for sharing description about audio.Have a nice day
Nice built, congrats Christophe!
I share your findings and enthousiasm regarding voltage setting and tha Alps Black Beauty.
You may want to upgrade the caps in the signal path, that made really a big difference in my case and IMHO takes the amazing B1 Korg to another level...
Enjoy it very much
Claude
PS: very small phono pre is my next project, on it (Salas' Chipomatic) 🙂
I share your findings and enthousiasm regarding voltage setting and tha Alps Black Beauty.
You may want to upgrade the caps in the signal path, that made really a big difference in my case and IMHO takes the amazing B1 Korg to another level...
Enjoy it very much
Claude
PS: very small phono pre is my next project, on it (Salas' Chipomatic) 🙂
Hello Claude,
I have a second PCB B1 Korg.
At the sight of your experience, I will experiment MKP Mundorf caps on ranks 1 and 2 of the signal path.
But do I need to put caps on the 3rd row of the signal path? knowing that this preamp will be associated with the diyAudio Sony Vfet.
A+
Christophe
I have a second PCB B1 Korg.
At the sight of your experience, I will experiment MKP Mundorf caps on ranks 1 and 2 of the signal path.
But do I need to put caps on the 3rd row of the signal path? knowing that this preamp will be associated with the diyAudio Sony Vfet.
A+
Christophe
I see Cornell caps 940 have a rated voltage of 600VDC.
It seems to me huge at the sight of the voltages of B1.
100V is this enough? this will also allow for smaller MKP caps.
It seems to me huge at the sight of the voltages of B1.
100V is this enough? this will also allow for smaller MKP caps.