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B1 with Korg Triode
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Old 24th May 2019, 09:54 AM   #2381
BrianGasberg is offline BrianGasberg  Denmark
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Quote:
Originally Posted by Grunnet View Post
I have started building the B1 Nutube, but have become confused about the number of transistors. With the Diyaudio kit, I received a total of 4xQ1 plus 4xQ2 with 4 resistors. However on the print are marked for a total of 8xQ1 and 8xQ2.
Whats wrong? I cannot find mention of this in neither this thread or Nelsons paper?

You can find it in page three of the paper (see the picture ):
http://www.firstwatt.com/pdf/art_diy_nutube_preamp.pdf

b1_korg_FETs.jpg
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Old 24th May 2019, 10:04 AM   #2382
Grunnet is offline Grunnet  Denmark
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Default missing transistors 2

Sorry to have bothered everybody, it has just dawned on me, J or K transistors right:
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Old 24th May 2019, 10:22 AM   #2383
Erlend Sæterdal is offline Erlend Sæterdal  Denmark
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B1 with Korg Triode
Use the fairchilds. People can not detect any difference in resulting sound.
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Old 24th May 2019, 10:29 AM   #2384
Grunnet is offline Grunnet  Denmark
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It is morning here and I have only had one cup of coffee, bear with me
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Old 27th May 2019, 06:46 AM   #2385
avdesignguru is offline avdesignguru  United States
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Default Recommended NuHybrid Headphone Amp Mods

After building and listening to the Nelson Pass B1 Korg preamp and comparing it to the Pete Millett NuHybrid Headphone amp as well as Pete's Nutube Buffer, I like Papa's Korg tube setup a bit better than Pete's. So here is what I did to modify the NuHybrid Headphone amp to have it sound more like the B1 Korg. This build was done in a DIYaudio Galaxy chassis with all jacks, power switch, LED and volume pot all mounted off the PCB and on the chassis panels.

1. Since the triode circuit inverts the signal polarity and it is difficult to reverse the headphone transducer connections which would require taking the headphones apart, I added Jensen JT-11P-1 1:1 line input transformers with the primary winding connections reversed. Best USA price I found was Markertek at $63 each including shipping. I first tried some inexpensive Triad TY-250P transformers but their lack of shielding, excessive phase shift in the low bass and higher THD proved unacceptable. The Jensen inputs were connected to isolated RCA input jacks. The outputs directly to the volume pot. The can and electrostatic shield connections were connected to the right input jack ground/mounting PCB location. Not shown in the photos, I later lifted the direct chassis ground connection at that point and added the series resistor/cap to chassis ground connection shown in the data sheet. A dedicated ground wire was run from the volume pot to the left input jack ground/mounting PCB location. Since I was using a 10K pot, the recommended damping network was not required. Even though the pot is an Alps RK27, it has excessive noise at the extreme CCW rotation, which seems to be a problem with 10K pots in general. If I change it to something like a 50K, I'll add the damping network shown in the Jensen data sheet.

2. I bypassed the on board PCB volume pot connections altogether and went straight from the pot to some upsized Kemet 220 nF input caps at C20 and C21. One side of each cap is hanging off the edge of the board. Shielded connection from the pot to the cap is grounded only at the pot end, although best practice would typically reverse that scheme.

3. I changed the voltage divider resistors R19, R20, R22, R23 from 475K to 332K.

4. I changed the plate resistors R13, R14 from 475K to 332K.

5. I set the plate voltage at TP1 and TP2 to somewhere around +9.7 volts. I found this is best adjusted while listening to music and set to your preference. I also found that anything over +10.5 volts made the magic go away.

So how does it sound? With the resistor and plate voltage mods, it sounded better than stock. Much smoother with no loss of dynamics. Correcting the signal polarity with the transformers made a significant improvement in detail and imaging. Yes, they cost as much as the PCB, tube and board components combined but once you hear the difference, there is no going back.
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Old 27th May 2019, 08:31 AM   #2386
R-K Rønningstad is offline R-K Rønningstad  Norway
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Great idea. I did consider a transformer to “correct” the polarity of my B-1 Korg NuTube also.
But that part of my implementation is on hold. Great to see someone has done it.
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Old 27th May 2019, 08:45 AM   #2387
Bassivus is offline Bassivus  Serbia
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Nice! I also consider using transformer to get polarity back, only I was thinking on using top line Jensen output transformer that I have around
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Old 27th May 2019, 08:46 AM   #2388
Erlend Sæterdal is offline Erlend Sæterdal  Denmark
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That means it could be an idea to reverse polarity on balanced input for my Aleph 1.7 "Buffer" after the Korg. Or at the output.
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Old 27th May 2019, 04:34 PM   #2389
avdesignguru is offline avdesignguru  United States
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Quote:
Originally Posted by Bassivus View Post
Nice! I also consider using transformer to get polarity back, only I was thinking on using top line Jensen output transformer that I have around
I think output transformers are almost half the cost of equivalent performance input transformers and are therefore a good option for a preamp. However, they are harder to find in general distribution than the inputs. You have to buy direct from the manufacturer, pay full price plus shipping.
But for a headphone amp, I wanted to keep the low output impedance of the opamp driver connections and opted for the shielded input transformers.
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Old 27th May 2019, 05:14 PM   #2390
Bassivus is offline Bassivus  Serbia
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Quote:
Originally Posted by avdesignguru View Post
I think output transformers are almost half the cost of equivalent performance input transformers and are therefore a good option for a preamp. However, they are harder to find in general distribution than the inputs. You have to buy direct from the manufacturer, pay full price plus shipping.
But for a headphone amp, I wanted to keep the low output impedance of the opamp driver connections and opted for the shielded input transformers.
I'm not sure how's the quality performance ratio in this specific circuit but the Jensen JT-11-BMCF are over 200$ a pair.
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