I got it. My guess is, based on the descriptions in both the 6Moons and the new Stereophile review, that Pass is using complementary MOSFETs in the driver stage (IRF240 and 9240's to drive the two IXFN60N80P's in opposite phase (like a bridged circuit).
The amp is advertised as delivering 25 w/channel into 8 ohms, but put out 80 w/channel on the bench before clipping. Pretty impressive. Pass replaced 28 IRF MOSFETs in the XA60.8 with 2 HiPerFETs and got better sound in the process. Pretty cool. I need to hear one of these things.
The amp is advertised as delivering 25 w/channel into 8 ohms, but put out 80 w/channel on the bench before clipping. Pretty impressive. Pass replaced 28 IRF MOSFETs in the XA60.8 with 2 HiPerFETs and got better sound in the process. Pretty cool. I need to hear one of these things.
Thanks, Zen Mod - I will take a look.
I just built an F3 (using Chinese boards from eBay - actually nicely laid out), and am halfway through building a Pass Sony VFET (although I think I'll need a couple shots of Balvanie Scotch before I put power onto those pixie-dust containing VFETs).
I have all the parts to build an F5 Turbo V.2, but I am looking for the next thing to try. (I've also built a lot of toob stuff, but, that is really like restoring Model A Fords.....nothing works without GOOD output transformers which are getting harder to find.)
I am driving a minty pair of Spendor SP-1's which are 8 ohms and reasonably efficient. They work really well with a Pass Aleph 5 (60 wpm), but the Firstwatt amps are a little to small.
I am looking for something with the power of the Aleph but with a triode transfer function....the IXFN140N20P SE circuit might be just right for the Spendors, BUT a push-pull variant using these new HiPreFET pucks might be better still.
Anyway having just retired after 39 years at Boeing, I am looking to get into a little mischief.
I just built an F3 (using Chinese boards from eBay - actually nicely laid out), and am halfway through building a Pass Sony VFET (although I think I'll need a couple shots of Balvanie Scotch before I put power onto those pixie-dust containing VFETs).
I have all the parts to build an F5 Turbo V.2, but I am looking for the next thing to try. (I've also built a lot of toob stuff, but, that is really like restoring Model A Fords.....nothing works without GOOD output transformers which are getting harder to find.)
I am driving a minty pair of Spendor SP-1's which are 8 ohms and reasonably efficient. They work really well with a Pass Aleph 5 (60 wpm), but the Firstwatt amps are a little to small.
I am looking for something with the power of the Aleph but with a triode transfer function....the IXFN140N20P SE circuit might be just right for the Spendors, BUT a push-pull variant using these new HiPreFET pucks might be better still.
Anyway having just retired after 39 years at Boeing, I am looking to get into a little mischief.
I tried with another beast mosfet (IXFK140N20P) which is pretty much the same one but in a plastic package and slightly cheaper.
There is a bit of distortion on the low end (the increasing 3rd harmonic) due to a bad input isolation transformer as I didn't use dual supplies then.
Performed alright at 1W but completely derailed at 10W and above (sadly I don't have the measurements uploaded to the net), my guess is due to the very large capacitances when VDS gets below 10V. I tried some different mosfets but the IRFP240 beat them all, it's like Nelson knows what he is doing
What was I thinking?
A year in the making and pondering this Building Guide Forum, I now have a beautiful sounding, F6 amp cool-running absolutely quiet and stable at .550V and zero DC offset. I found the idea of biasing totally intimidating but after putting screwdriver to pot how easy! Obviously, I'm a babe in the woods when it comes to this endeavor. Now I've ordered parts for a F4. What was I thinking? I can't help myself. Thank you all for your postings and guidance. Thank you, especially, 6L6. Still one question: What is the advantage of building dual mono versions aside from improved separation? Can you hear the difference, and where is the schematic presented? I'm hooked.
A year in the making and pondering this Building Guide Forum, I now have a beautiful sounding, F6 amp cool-running absolutely quiet and stable at .550V and zero DC offset. I found the idea of biasing totally intimidating but after putting screwdriver to pot how easy! Obviously, I'm a babe in the woods when it comes to this endeavor. Now I've ordered parts for a F4. What was I thinking? I can't help myself. Thank you all for your postings and guidance. Thank you, especially, 6L6. Still one question: What is the advantage of building dual mono versions aside from improved separation? Can you hear the difference, and where is the schematic presented? I'm hooked.
aside improved separation , what's difference between male and female ?
One is a sissy and one is not a sissy?
Hahahaha
Well IMO .. Possibly.. (assuming the single setup is somehow lacking)
IF ? your source is as good as the Amp is
And your speakers are at least as good or even better than the Amp.
Not many are.
Beyond that? yer into perceptual issues .. the bedrock of Audio Weenie dreams everywhere
That said it reads like yer liking the smell of solder/rosin.. which for many is reason enough.
Have fun.
I need some help with troubleshooting a distorted sounding f6.
About two years ago I built an f6 clone (pcb from the store) and, because I did not have any decent sources, I built a dedicated dac (Soekris dam 1021) and passive preamp to use with the amp. The combination works nicely and sounds fine.
But now I've changed my system and for the first time had to connect a different source to my f6 using a headamp/preamp as a pre by connecting its lineout with the input of the f6.
And suddenly everything comes out distorted as if the amp was clipping on louder passages, even though the music played is not very loud! The volume is maybe a quarter of my usual listening volume when used with the dac/pre combination I made for it.
The distorted/clipping sound comes on passages that I would not even consider very loud.
Then I've used a stereo jack->rca cable that I made and connected the amp straight to the headphone out of the headamp/preamp: undistorted sound, much louder, nicer and no clipping at all! I could even reproduce this with a nother headphone amp that I have here.
It seems like any normal line level source that I connect produces distorted sound/clipping except for the headphone amps.
Please: can someone explaing to me what is happening here? And: do I have to fix my f6 now?
About two years ago I built an f6 clone (pcb from the store) and, because I did not have any decent sources, I built a dedicated dac (Soekris dam 1021) and passive preamp to use with the amp. The combination works nicely and sounds fine.
But now I've changed my system and for the first time had to connect a different source to my f6 using a headamp/preamp as a pre by connecting its lineout with the input of the f6.
And suddenly everything comes out distorted as if the amp was clipping on louder passages, even though the music played is not very loud! The volume is maybe a quarter of my usual listening volume when used with the dac/pre combination I made for it.
The distorted/clipping sound comes on passages that I would not even consider very loud.
Then I've used a stereo jack->rca cable that I made and connected the amp straight to the headphone out of the headamp/preamp: undistorted sound, much louder, nicer and no clipping at all! I could even reproduce this with a nother headphone amp that I have here.
It seems like any normal line level source that I connect produces distorted sound/clipping except for the headphone amps.
Please: can someone explaing to me what is happening here? And: do I have to fix my f6 now?
Thanks for the quick answer - you just gave me the motivation to re-check this:
dac->preamp/headamp (headphone-out)->f6 ok
dac->f6 (bad hum but no cliping/distortion) ok
dac->preamp/headamp (line-out)->f6 (no hum, distortion) nok
phono-pre->f6 OK (no clipping/distortion)
phono-pre->preamp/headamp (line-out)->f6 (distortion) nok
So it could be that my nice new, excellent sounding (over headphones) headamp/pre has a bad preamp section :-(
Also, the sources, connected straight to the f6 develop a bad hum. Maybe I have a grounding issue that does not show with my own dac/ppre combo.
Have to connect some active speaker to pre and check for distortion. Also have to check f6 for the hum...
dac->preamp/headamp (headphone-out)->f6 ok
dac->f6 (bad hum but no cliping/distortion) ok
dac->preamp/headamp (line-out)->f6 (no hum, distortion) nok
phono-pre->f6 OK (no clipping/distortion)
phono-pre->preamp/headamp (line-out)->f6 (distortion) nok
So it could be that my nice new, excellent sounding (over headphones) headamp/pre has a bad preamp section :-(
Also, the sources, connected straight to the f6 develop a bad hum. Maybe I have a grounding issue that does not show with my own dac/ppre combo.
Have to connect some active speaker to pre and check for distortion. Also have to check f6 for the hum...
OK, re-checked w. active speakers: preamp via line out sounds fine w. active speakers.
Main issue remains mysterious: phono-pre->pre/headamp->f6 clips/distorts (except if you use headphone stage). I'm done for now and will immediately employ a beer in order to activate the troubleshooting area in my brain.
Almost sounds like something is filtered out by headstage, but left through by linestage.
Q: Would f6 happily amplifiy subsonic/hf noise? Could this make f6 clip?
Main issue remains mysterious: phono-pre->pre/headamp->f6 clips/distorts (except if you use headphone stage). I'm done for now and will immediately employ a beer in order to activate the troubleshooting area in my brain.
Almost sounds like something is filtered out by headstage, but left through by linestage.
Q: Would f6 happily amplifiy subsonic/hf noise? Could this make f6 clip?