But do measure points on the board first, make sure it hasn't gone off due to some issue.
My completed B1K, sitting on top of a WHAMMY headphone amp. As you can see the B1K reuses the enclosure design I did for the WHAMMY.
Currently running 10V bias. Is there an easy way to invert the polarity when listening with headphones? I suppose I can build an inverting headphone cable.
Currently running 10V bias. Is there an easy way to invert the polarity when listening with headphones? I suppose I can build an inverting headphone cable.
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Hi Brijac, I followed the suggestions you gave me some days ago about my Nutube B1. For unknown reasons, it has broken the filament. So I pulled away the tube and then I measured the circuit at T points with a 24 wall wart psu of course without the tube. Here are my measurements:
•T1 23.95V
•T2 23.11V
•T3 22.299V
•T4 9.16V
•T5 9.235V
•T6 9.235V
•T7 19.93V
•T8 20.02V
What are your thoughts? Could the circuit be still healthy? Is it worth to replace the tube?
Thanks in advance,
Gaetano.
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T5 and T6 are way too high. Those are filament voltages and probably the reason why it had died. It should be around 0.6-0.65v. Also T7 and T8 are high, those are adjusted with trimpot. See if you can lower them to 9.5v.
As it is, do not insert new nutube. I would start with reflowing the joints, as components values as i see are correct. Then re measure.
As it is, do not insert new nutube. I would start with reflowing the joints, as components values as i see are correct. Then re measure.
Finished my Nelson Pass Korg Nutube B1 Preamp… …. I used Clarity Cap ESA 10uF polypropylene film caps for the input/outputs, BICC silver plated copper hook up wire for input sockets and volume, some DNM solid core wire for output and to connect the Clarity caps to the Wago 221 connectors with some of the supplied wire for the mains wiring, I modified some spade terminals to connect to a TKD 2CP-2511 50K dual log potentiometer, for easy maintenance (no unsoldering) I used some pitch screw terminal blocks.
I purchased a Mean Well (2 pole) Medical Grade GSM120B power supply with a R7BF-P1M adaptor plug.
All measurement points were spot on.
The pre amp that the B1 is replacing is (hopefully) a Glasshouse TVC.
On connecting up I had way excess gain with just a small turn on the volume, the B1 has 16 dB of gain and my Channel Islands Audio D•200 MKII Class D Monoblock amps have an Input Impedance of:100k ohms with 26db of gain, adding Rothwell 20dB attenuators to the power amps did the trick giving me the control on the volume, I also had to reduce the volume on my SVS SB-1000 Pro Subwoofers by the same amount, after a bit more tinkering I was able to do some serious listening, so far I only have about 6 hours playing time on the B1, bass is more detailed as is the highs and mids, it has very good clarity and sounds in a word organic, there’s absolutely no trace of any brightness or sibilance, as a test I turned off/on the pre amp a few times before the power amps and not even a hint of a thump let alone any trace of microphonics, so far I’m extremely pleased with the B1.
I purchased a Mean Well (2 pole) Medical Grade GSM120B power supply with a R7BF-P1M adaptor plug.
All measurement points were spot on.
The pre amp that the B1 is replacing is (hopefully) a Glasshouse TVC.
On connecting up I had way excess gain with just a small turn on the volume, the B1 has 16 dB of gain and my Channel Islands Audio D•200 MKII Class D Monoblock amps have an Input Impedance of:100k ohms with 26db of gain, adding Rothwell 20dB attenuators to the power amps did the trick giving me the control on the volume, I also had to reduce the volume on my SVS SB-1000 Pro Subwoofers by the same amount, after a bit more tinkering I was able to do some serious listening, so far I only have about 6 hours playing time on the B1, bass is more detailed as is the highs and mids, it has very good clarity and sounds in a word organic, there’s absolutely no trace of any brightness or sibilance, as a test I turned off/on the pre amp a few times before the power amps and not even a hint of a thump let alone any trace of microphonics, so far I’m extremely pleased with the B1.
ever read What is Gain Structure?
piling small boxes one by one, then introducing attenuator cells to ensure so-so travel of volume pot
in the end, your speakers are getting pale approximation of original signal energy
edit: better preserved on start of this thread: https://www.diyaudio.com/community/threads/what-is-gain-structure.186018/
piling small boxes one by one, then introducing attenuator cells to ensure so-so travel of volume pot
in the end, your speakers are getting pale approximation of original signal energy
edit: better preserved on start of this thread: https://www.diyaudio.com/community/threads/what-is-gain-structure.186018/
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The voltages at the test points without the Nutube installed appear normal. Before powering up with the Nutube installed, be sure to adjust the two trimmer pots to its centre position. This is part of Nelson's B1 Korg article:
The full article may be downloaded at post #1.
Follow Nelson's instructions.
Hello Forum: I am hoping someone can guide me as my knowledge is very limited. I have assembled the preamp following the excellent build guide and am getting sound only on one channel. Have reviewed the build guide and checked everything a few times. The same thing happens using Input 1 or 2; If I reverse the output RCA jacks - the music moves over to the other side; Both sides of the Nutube are lit in blue; Sound in one channel is clear but the other side sounds has a very low volume static pulse. Am adding pictures. Was able to build the ACA amplifier myself without any trouble but clearly I have made a mistake here. Am adding pictures hoping someone can spot the problem. Very grateful for any help and advice.
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Which channel is the bad channel?
What are the test point voltages for both channels? See Nelson's article for test point voltage measurements.
Check the 33.2K and 332K resistors on the board. Compare resistors between the good and the bad channels and see if there are any misplaced resistors.
What are the test point voltages for both channels? See Nelson's article for test point voltage measurements.
Check the 33.2K and 332K resistors on the board. Compare resistors between the good and the bad channels and see if there are any misplaced resistors.
