My Nutube stopped working last year after two months of occasional use. It wasn't turned on continuously; after turning it on, a loud beeping noise suddenly came from the left channel.
Hi guys!
I bought a Korg Nutube kit that I finally have put together also. It was good fun and easy. I have done several other "pass kits" in the past and usually all is good.
However - I have problems with my Korg. It gives the 9.5 V where it should, but no sound comes out of it except a lot of humming- I have gone through the plans again and again but can not find any error.
As a final resort – should the trimmer potentiometers be adjusted to something specific ? I cant seem to find any information hereon. A certain voltage somewhere that I have wrong??
Any help would be much apprechiated. Thanks, carsten
I bought a Korg Nutube kit that I finally have put together also. It was good fun and easy. I have done several other "pass kits" in the past and usually all is good.
However - I have problems with my Korg. It gives the 9.5 V where it should, but no sound comes out of it except a lot of humming- I have gone through the plans again and again but can not find any error.
As a final resort – should the trimmer potentiometers be adjusted to something specific ? I cant seem to find any information hereon. A certain voltage somewhere that I have wrong??
Any help would be much apprechiated. Thanks, carsten
Hello everyone,
I've built a B1 which is working well so far.
I was wondering if it is necessary to change the bias, which is 9.5V as recommended. I have seen here and there that choosing a voltage slightly higher than 12V gives better results. What's your opinion on this? Is there a real improvement in sound (less distortion)? is there a risk to the Nutube?
Thanks in advance for your enlightened opinion!
Configuration: DSD files, Audirvana Studio, B1 Nutube with linear power supply, AAdac Audio Analogue, PASS F6 diy, Highland audio ORAN + Mosscade TItan Sub. Dirac Live Room Correction.
I've built a B1 which is working well so far.
I was wondering if it is necessary to change the bias, which is 9.5V as recommended. I have seen here and there that choosing a voltage slightly higher than 12V gives better results. What's your opinion on this? Is there a real improvement in sound (less distortion)? is there a risk to the Nutube?
Thanks in advance for your enlightened opinion!
Configuration: DSD files, Audirvana Studio, B1 Nutube with linear power supply, AAdac Audio Analogue, PASS F6 diy, Highland audio ORAN + Mosscade TItan Sub. Dirac Live Room Correction.
The trim pots are set correctly if you are measuring at the points given in the manual. Since it seems that this happening to both channels, the power supply is where I would start, checking every single voltage. I had a similar problem and in my case, I had accidently misread the 475 ohm resistors as 475K. Yah, I had no sound either until that was changed. You can bet that it is simple and right in your face. That's good.
Changing the bias voltage gives a different sound character to the unit. In the description, Nelson gives very good advice about choosing what you like to hear. 12 volts won't be a problem, and if you don't like the sound try other settings. Seems like 9.5 volts gives the least amount of 2nd harmonics.
From Nelson's DIY Nutube Preamp writeup (pdf download @ post #1):
After a few minutes and no smoke, we adjust the T7 and T8 voltages as follows:
Voltage at 12 VDC is approximately the 2nd harmonic null point where we get about .3 %
distortion in 3rd harmonics. As we go lower we start getting positive phase 2nd harmonic, and it
will hit 1.5% at 1 volt AC output with about 9.5 VDC on the T7 or T8 test points. Voltages
higher will give negative phase second harmonic.
This is a reasonable calibration - 0.1V either way changes the distortion by about 0.1%
Clockwise on the pot from the null spot makes for less Plate voltage, and positive phase
second harmonic, counterclockwise makes for more negative phase second harmonic.
If you have a distortion analyzer which gives you the percentage but not the phase, then just
start out with the Plate voltage high (CCW pot) and turn it clockwise to the point where it is
minimum, and then go further for + phase, or back up for - phase.
The reference setting for this project, are 9.5V on T7 and T8, which gives a positive phase at
about 1.5% at 1 volt output. You are free to set it elsewhere.
After a few minutes and no smoke, we adjust the T7 and T8 voltages as follows:
Voltage at 12 VDC is approximately the 2nd harmonic null point where we get about .3 %
distortion in 3rd harmonics. As we go lower we start getting positive phase 2nd harmonic, and it
will hit 1.5% at 1 volt AC output with about 9.5 VDC on the T7 or T8 test points. Voltages
higher will give negative phase second harmonic.
This is a reasonable calibration - 0.1V either way changes the distortion by about 0.1%
Clockwise on the pot from the null spot makes for less Plate voltage, and positive phase
second harmonic, counterclockwise makes for more negative phase second harmonic.
If you have a distortion analyzer which gives you the percentage but not the phase, then just
start out with the Plate voltage high (CCW pot) and turn it clockwise to the point where it is
minimum, and then go further for + phase, or back up for - phase.
The reference setting for this project, are 9.5V on T7 and T8, which gives a positive phase at
about 1.5% at 1 volt output. You are free to set it elsewhere.