Another solid state gain stage after it or it will get too complicated and not worth it?
Pass Korg B1
I'm also working on a BOM also. I am wondering about the JFETs. The Pass B1 board had an option of purchase with matched JFETs. I wonder if the Korg B1 board will also have this option. What do you think? Also are the Bourns 10K trimmers which I assume from the silk-screened board single turn or multi turn?
I'm also working on a BOM also. I am wondering about the JFETs. The Pass B1 board had an option of purchase with matched JFETs. I wonder if the Korg B1 board will also have this option. What do you think? Also are the Bourns 10K trimmers which I assume from the silk-screened board single turn or multi turn?
I am examining two options for the Jfets, one with 2SK370 followers
(same as 2SK170 w/ package difference) and the other with the Fairchild
J113's. Both require selected parts, and the Toshiba parts are a lot more
expensive.
Single turn pots.
Speaking of selecting parts, has anyone noticed any variations in the NuTube itself? I ask, because on my first NuTube adventure (using the Millett buffer board and recommended circuit values), I set the grid voltage for G2 to 1.9 VDC to see what hitting the sweet spot on the plate curve would sound like. This yielded 9.43 VDC on anode A2. It took around 2.0 VDC on grid G1 to get the same 9.43 V on A1. I listened both ways, and most assuredly preferred the sound of matched anode voltages (both at 9.43) to the sound of matched grid voltages (both at 1.9). A-B comparison with my standard B1 preamp revealed the B1 having a bit more detail but the NuTube sure makes me smile (unlike my Akido with 6N1Ps, which has been relegated to recording studio duties). Oh, BTW, mid-high amplification is an F6.
Thanks for the clarification. Looking forward to building and listening to your version when it becomes available. There's something about the NuTube that reminds me of traditional tubes run with low plate voltages in a quasi "space charge" mode (over driven cathode). Rounds off the rough edges without losing too much of the good stuff.
I will compare each to my B1 passive buffer which is my reference standard. The B1 is fitted with JFets that were supplied with the board by PassDIY and it was built using his recommended parts standards:
Akido (12AU7 LV version with J. Broskie supplied parts), although quiet and accurate, is a bit withdrawn and lifeless, lacks some detail and is soft in the bottom end compared to the B1.
NuTube Buffer (P. Millett 24V version using his recommended plate resistor values) sounds like the B1 with a bit of warmth dialed in with no added softness and no loss of excitement. However, setting the tube bias is critical to getting a good sound. That said, bias that was set listening to mid-1980s ADS L980 12" 3-way studio monitors (91dB nominal sensitivity, bi-amplified) still worked reasonably well for a pair of LX Minis.
Loudspeaker polarity was properly reversed when listening to the NuTube preamp and yes, you can hear the difference, although it seemed to mainly affect imaging.