I think the correct spelling is now the same as the headphone amp company, "Schiit".
That said, I am unaware of any divine status they may have or has been conferred upon them...
Remember that the lower pot is for bias, and the upper pot is for offset. Read the biasing instructions very carefully,
because you may just need to tweek it the right way to zero out the offset.
I had one channel that had almost permanent 18~20v offset in negative polarity. One of the JFET died. That happen just after finish building. Started turning, nothing happen, nothing happen then jump to negative. Maybe there was a current spike, but I now recommend a wait period after turning the pot, the current doesn't go up immediately
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I have a run of F6's with the Mosfets (believe it or not, most of my listeners prefer them over the JFETs in this application) and I use 6.25V references for the biasing, formed by TL431's.
IRFP240 are as good as any in this regard.
Be sure to include Gate stopper resistors and some
Source ballast resistors, maybe 0.47 ohm.
OK, removed all extra LEDs, replaced the 5k pot for offset. Bias voltage is OK in both channels.
The offset is still 20v in one channel, the other is well behaved.
Anyone have a pair of R100A semisouth jfets they could sell me?
PM me!
Thanks
Vince
Contact SemisouthFan, he has an inventory of R125 which basically is the same as the R100.
I don't remember saying that , but I'm saying it now - do that as test of functionality of biasing circuits , both upper and lower
then back it down , put JFets in and proceed with true setting procedure
not really penalty ; as I wrote in last post - leave it or remove later - your choice
Hi PKI,
Thanks for that bit of enlightenment.
What I realized was that if I were to run the leads even longer, I could have bundled the wires at the base plate of the amp, instead of running them the shortest path. I can be penny wise, pound foolish. It's just the way I grew up. It's a behavior I'm trying to break. Also, the wiring is mostly 12 gauge and a bit of 14 gauge, so it's a bit harder to "hide".
Also, if I used a PCB for the cap banks, it might have looked more tidy.
I could have made a PCB out of perf board and just flipped everything and it might have looked "cool" with all the caps nicely presented, but hind-sight is best left to those who can see the future, or those better at building amps.
I like access to things inside, so I can reach them without taking heat sinks off or generally dismantling everything.
What you don't see (obviously) are the 8 primary leads and 6 thermistors.
That's probably because they are at the base plate of the amp. Also, some of the extra wire allows me to remove the back plate and make connections with little difficulty. Again, coming full-circle, longer wiring runs could have allowed for the same.
I know it's nauseating to some, this horrible wiring. I feel the same way about builds with plexiglass or acrylic with LEDs lighting up large fonts that are advertising the make and brand they didn't design, but that's just me!
With the cover on, all this doesn't matter much. When you hear it, you will not care. Trust me!
Thanks!
Vince
Thanks for that bit of enlightenment.
What I realized was that if I were to run the leads even longer, I could have bundled the wires at the base plate of the amp, instead of running them the shortest path. I can be penny wise, pound foolish. It's just the way I grew up.
It's a behavior I'm trying to break. Also, the wiring is mostly 12 gauge and a bit of 14 gauge, so it's a bit harder to "hide". Also, if I used a PCB for the cap banks, it might have looked more tidy.
I could have made a PCB out of perf board and just flipped everything and it might have looked "cool" with all the caps nicely presented, but hind-sight is best left to those who can see the future, or those better at building amps.
I like access to things inside, so I can reach them without taking heat sinks off or generally dismantling everything.
What you don't see (obviously
) are the 8 primary leads and 6 thermistors.That's probably because they are at the base plate of the amp. Also, some of the extra wire allows me to remove the back plate and make connections with little difficulty. Again, coming full-circle, longer wiring runs could have allowed for the same.
I know it's nauseating to some, this horrible wiring. I feel the same way about builds with plexiglass or acrylic with LEDs lighting up large fonts that are advertising the make and brand they didn't design, but that's just me!
With the cover on, all this doesn't matter much. When you hear it, you will not care. Trust me!
Thanks!
Vince
Vince, is the amp quiet? If so, make no apologies for the wiring.
Yes it is quite. The Jensen's are close to the toroids, but there is little noise at the 94db FR drivers. Have to stick your ear in the driver to hear any noise.
You know Jim, after 3+ months of building this amp, the pay off is the great sound. By the same token, I could have been more patient and considered the wiring more carefully.
BTW- I didn't expect it to sound that much different than the Zen 9 or L'amp CSS amps in the room. It does though. There's some resemblance to the others, but it's its own thing. I could go on and on about its sound. Most important, it has a shocking amount of power. Makes the other two amps sound polite by comparison. I heard the F5T v3. You'd think the F6 is 100w amp as well. Maybe it's just a good pairing with the drivers!
What they say is true. The instruments are huge in the sound stage and it has great depth.
I know the Semisouth FETs are a bit hard to get, but the DIY F6 is another great amp in the blood line, and should be strongly considered. Should be interesting to see what people say about the mosfets F6. If it's anything like this, build it!
As always thanks for your help!
Vince
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