I've been using the 9 pin 12AU7 VTA drivers in my MK3 clones for a few years. Always happy with them, although I did find some 12AU7s pretty bright. The best sounding to me were JJ ECC802 as they took off a bit of the edge. I did try the 12BH7, but had a hard time finding some that were not severely microphonic. I decided to try the octal version. No real need to, but it's a hobby, right?
Got them built and installed over the weekend. Ran all day Sunday.
I did make some changes over my installed 9 pin versions. Added the 100uF cap upgrade and didn't use the supplied Jantzen coupling caps. I had some Audyn caps I wanted to try. I don't think there's much difference, they are the same metalized polypropylene 400V build. About the same physical size too, just wanted to point out my comparison is not only a tube change. One other change that I've been looking forward to was adding 25 turn bias pots in place of the single turn hyper-sensitive supplied pots. Much nicer!
The boards differ very little in component selection. Only the resistors for the PI CCS regulation and gain stage grid leak resistor were changed. I'll add here that the drawn schematics for both boards differed quite a bit from the supplied components / BOM. It seems like the drawings were early versions and never updated as the circuit was tweaked.
I installed the LM335 on the bottom of the boards. Seemed too close to the larger ceramic tube socket to me. Possible heat issue.
Well. I really think after some time listing to familiar tracks that the 6SN7 is a much better tube choice for this circuit. The 12AU7 was fine, but immediately I noticed not more bass, but more bass punch / presence. Possibly the bigger 100uF caps, but there is more everything to be honest. Seems more dynamic / lively a bit more holographic. The pops at the end Deacon Blues were "wider" more pronounced. Nothing dramatic or night and day, but a quite a bit more than I was expecting.
Was hoping to get some decent before and after tests in, but my laptop that I use with ARTA kicked off. I think I fried the sound card with too much juice to the mic in... I did look at power out and SQ waves. Pretty much unchanged. Would have liked to see FR sweeps and distortion. Something for later when I can get back up with another laptop.
I'd say if you're looking at these and unsure, probably go for the octal if you have the PT to handle a little more filament current and are OK with the aesthetic. If you're like me with perfectly fine 9 pin boards and are just wondering, yeah, do it. They are pretty inexpensive and you could always flip them if you wanted. I'm keeping mine.
Got them built and installed over the weekend. Ran all day Sunday.
I did make some changes over my installed 9 pin versions. Added the 100uF cap upgrade and didn't use the supplied Jantzen coupling caps. I had some Audyn caps I wanted to try. I don't think there's much difference, they are the same metalized polypropylene 400V build. About the same physical size too, just wanted to point out my comparison is not only a tube change. One other change that I've been looking forward to was adding 25 turn bias pots in place of the single turn hyper-sensitive supplied pots. Much nicer!
The boards differ very little in component selection. Only the resistors for the PI CCS regulation and gain stage grid leak resistor were changed. I'll add here that the drawn schematics for both boards differed quite a bit from the supplied components / BOM. It seems like the drawings were early versions and never updated as the circuit was tweaked.
I installed the LM335 on the bottom of the boards. Seemed too close to the larger ceramic tube socket to me. Possible heat issue.
Well. I really think after some time listing to familiar tracks that the 6SN7 is a much better tube choice for this circuit. The 12AU7 was fine, but immediately I noticed not more bass, but more bass punch / presence. Possibly the bigger 100uF caps, but there is more everything to be honest. Seems more dynamic / lively a bit more holographic. The pops at the end Deacon Blues were "wider" more pronounced. Nothing dramatic or night and day, but a quite a bit more than I was expecting.
Was hoping to get some decent before and after tests in, but my laptop that I use with ARTA kicked off. I think I fried the sound card with too much juice to the mic in... I did look at power out and SQ waves. Pretty much unchanged. Would have liked to see FR sweeps and distortion. Something for later when I can get back up with another laptop.
I'd say if you're looking at these and unsure, probably go for the octal if you have the PT to handle a little more filament current and are OK with the aesthetic. If you're like me with perfectly fine 9 pin boards and are just wondering, yeah, do it. They are pretty inexpensive and you could always flip them if you wanted. I'm keeping mine.
