Recent builder here chiming in with my story.
Last Friday night, I finished baseline wiring up of both channels into the half-assembled chassis, enough to bring them up on power with a DBT and a variac. As I had the bias pots fully minimized, it took me a long time to get current flowing and registering bias on R2. I thought something was wrong and even took a break to ponder what I was missing, but then, one last turn and the bias started climbing from 0.000 V up to .01, .1, and into the hundreds. Whew!
I got both channels fairly well balanced to 500 mV and low offset and called it a night.
Saturday morning I went through the chassis assembly and hooking up inputs, outputs, getting wires routed and the whole thing assembled enough to carry it down to the listening rig once the bias and offset were in range. I then spent an hour listening and tweaking the bias, letting it warm up and settle in. I think I spent five minutes with the scope and a sine wave, "Yap, it's amplifying the signal. Next!"
I did lose an R2 up in smoke, I don't know why, but it was easy enough diagnose (not so many components on the board to check, eh?) and replace, and it's been a rock since then.
I've been around solid, quality audio for 30+ years; have various generations of well known amps and assorted front end components, but as this F6 opens up, it continues to open up and show me what's really in the music, and new levels of what's possible in hi-fi.*
I'm gushing.
Anyway, music is a new experience, the build was shockingly straightforward, resources here, at the store and on YouTube were like having a mentor at my beck and call. Over the last four days I've been enjoying listening to this thing sing to me.
Thanks Papa for the design, and all that support this site for the boards, the store, the help, and the knowledge!
*By the way, this thing is dead silent. If you want to sit in silence and contemplate the universe, I highly recommend turning this thing on and playing nothing. You'll just get more silence, but with a better sense of the room where nothing is going on.
Last Friday night, I finished baseline wiring up of both channels into the half-assembled chassis, enough to bring them up on power with a DBT and a variac. As I had the bias pots fully minimized, it took me a long time to get current flowing and registering bias on R2. I thought something was wrong and even took a break to ponder what I was missing, but then, one last turn and the bias started climbing from 0.000 V up to .01, .1, and into the hundreds. Whew!
I got both channels fairly well balanced to 500 mV and low offset and called it a night.
Saturday morning I went through the chassis assembly and hooking up inputs, outputs, getting wires routed and the whole thing assembled enough to carry it down to the listening rig once the bias and offset were in range. I then spent an hour listening and tweaking the bias, letting it warm up and settle in. I think I spent five minutes with the scope and a sine wave, "Yap, it's amplifying the signal. Next!"
I did lose an R2 up in smoke, I don't know why, but it was easy enough diagnose (not so many components on the board to check, eh?) and replace, and it's been a rock since then.
I've been around solid, quality audio for 30+ years; have various generations of well known amps and assorted front end components, but as this F6 opens up, it continues to open up and show me what's really in the music, and new levels of what's possible in hi-fi.*
I'm gushing.
Anyway, music is a new experience, the build was shockingly straightforward, resources here, at the store and on YouTube were like having a mentor at my beck and call. Over the last four days I've been enjoying listening to this thing sing to me.
Thanks Papa for the design, and all that support this site for the boards, the store, the help, and the knowledge!
*By the way, this thing is dead silent. If you want to sit in silence and contemplate the universe, I highly recommend turning this thing on and playing nothing. You'll just get more silence, but with a better sense of the room where nothing is going on.
You sir, win the internets for the day!
Congrats on that build. Also love the 4004. Still have a 2004 for some fun stuff. Had a 4004 and an 8008BB. Wish I had the 8008BB back.
Thanks!
That 4004 has had some adventures. I bought it off of Ebay in, oh, 2002; seller was in Augusta, Maine shipping to me in the Denver area.
Fast forward a few years and I'm living outside of Augusta, Maine and it needs some servicing. Turns out there's actually a tech in town. I take it in, he looks at it, asks where and when I got it. Yep, it was originally his. Small world.
I recently repaired/cleaned up the speaker relays and reset the bias (one channel way low, the other way high) on the outputs and adjusted the DC offset, which if I recall correctly was off some 70 mV per channel. It certainly changed the sonics of the amp. It does control that bass, but is very, very laid back on the treble.
It's the Mark 1 version. I'm considering doing the changes to make it into the Mark 2 (a few resistors, a diode, some new capacitors in the circuit), which is the version that got the attention of the industry back in the day. But I've got a bunch of other projects lined up and only a couple of places for listening setups in my house, all occupied with an amp or two.
It is, however, winter in Maine, so time to stay inside and work on stuff.
That 4004 has had some adventures. I bought it off of Ebay in, oh, 2002; seller was in Augusta, Maine shipping to me in the Denver area.
Fast forward a few years and I'm living outside of Augusta, Maine and it needs some servicing. Turns out there's actually a tech in town. I take it in, he looks at it, asks where and when I got it. Yep, it was originally his. Small world.
I recently repaired/cleaned up the speaker relays and reset the bias (one channel way low, the other way high) on the outputs and adjusted the DC offset, which if I recall correctly was off some 70 mV per channel. It certainly changed the sonics of the amp. It does control that bass, but is very, very laid back on the treble.
It's the Mark 1 version. I'm considering doing the changes to make it into the Mark 2 (a few resistors, a diode, some new capacitors in the circuit), which is the version that got the attention of the industry back in the day. But I've got a bunch of other projects lined up and only a couple of places for listening setups in my house, all occupied with an amp or two.
It is, however, winter in Maine, so time to stay inside and work on stuff.
^ Great story. Lived in the southwestern part of Maine for a summer ages ago doing an internship (Bridgeton, to be specific). Loved it. My first "hifi" rig was a 2004, VTL TL2.5 pre, Rega Planet, and Vandersteen 2c's. I still have (or friends and family have borrowed) all of it. Never getting rid of it ...
It's not really a voltage divider, since the series resistor is on the fet side, and not on the input jack side.
Although some of the NP amps do have it that way.
So I have a couple of more interesting questions. What concerns me here is the presence of a DC current in the transformer primary. I think I'd like to have it decoupled so I'd be able to use smaller Nanoperm toroidal cores I have in leftovers. Also what the purpose of FET source resistors R1 and R2 other than for passive protection? With bipolar push-pull EF stages they from my understanding limit the transconductance and thus it's Vbe dependency. But this trick simply won't work with FETs due to their very different curve.
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I just finished the final bias adjustment for my first non-kit project, an F6 in a Modushop case. I ended up going to 620 mV - hopefully it won't get too hot. I had no trouble whatsoever setting the bias thanks to the suggested mods. There is no hum. In fact it's dead silent with the DAC cranked and no signal. I still need to do a little wiring housekeeping and hook up the power button LED. I also plan to add snubbers to the bridges when the parts get here. This amp sounds absolutely wonderful. It really shines with live recordings - especially strings and percussion. I'm listening to some Nils Lofgren and it sounds like he's sitting in my living room. I'm blown away. Thanks to Nelson Pass and all the folks who make this site possible.
