LuFo Lite - a 1 Transistor SE Class A Headphone Amp

jwjarch

Member
Paid Member
2017-03-23 6:19 pm
Denver, CO
You’re welcome X! It is a great and simple design. And 8 watts is more than enough for my speakers.

I still need to try the negative bias circuit. You’re telling me, about not having time! Life is ridiculously busy right now! Good luck finding that block of time. I’m off to listen to the LuFo Lite for a few minutes before bed. ;)
 

jwjarch

Member
Paid Member
2017-03-23 6:19 pm
Denver, CO
Thanks Vunce! I was enjoying some great SACD’s tonight: Getz/Gilberto, Miles Davis - Kind of Blue, and Diana Krall. I noticed the imaging is really pinpoint with the LuFo Lite. I think X mentioned that should be the case, and IT IS! Soundstage depth is pretty good too. I do feel there is still some body missing compared to my other amps. That may also be due to speaker placement. I’ve been moving them around a bit. I’ll have to switch back to one of my other amps soon and do a comparison.

Good luck on your build Vunce! I might try out some MOT’s again too!
 
Well flipping the capacitor didn't work, same behaviour. No current flow till the pinch off threshold is reached then taps fullly open and my negative supply reads pos 0.9V and cannot be adjusted. Back to resistor and it works normally. Final Temps after an hour of playing music. JFET 45degC, resistor 55 deg C and heatsink is 42 deg C

.. dB
 
No, bass doesn't seem to be impacted, I ran a frequency sweep (off the chesky test disc) and it behaves similar to my other amps on the test bench.

The natural bass test track I tend to use is "aeris" from the Legacy Sampler III (not sure it is good form to share a link), it is a solo cello piece that has a lot of low harmonic decay (beautiful composition). This track sounds deep and natural.
 
I was wondering if adding a diode / zener to prevent the voltage flip. still not sure how this occurs given the independent negative supply - common ground perhaps.

I can tell you it sounds great, although not as spacious as a DIY F8 I have on the bench to repair. ( successful repair last night ;) )

I think one problem with building these amps is the bar for "better" gets set exceptionally high. I would say that despite the lufo lite being optimized for headphones ( which I have yet to test ) , it offers a very delicate / responsive performance with a sense of ease and naturalness that is typical of all good class A amplifiers. It's soundstage ( on my test bench ) is focused but deep while the F8 offers a similar soundscape but throws a wider sound stage with a sense of more air.

an unfair comparison perhaps given the design intention for each.

..dB
 
Don’t forget this is a 1 transistor amp not counting PSU cap multiplier.

More fair of a comparison with an F8 would be standard LuFo and running at similar 25w power.

Actually, I was not even aware that there was an F8!

Looks like a SIT driven by a P junction FET with an NMOS CCS in a mu-follower? Is there a DIY version already?

3.jpg
 
this amp got damaged in shipping when the transformer came loose and there was a little pin ball inside the chassis - so mechanical damage ( one of the mosfets snapped the bolt holding it on and all 3 pins broke off , traces on PCB broken etc )

It actually made me want to create a "how to ship a heavy amp" tutuorial. People forget that any amount of movement inside a box creates immense inertial forces which have the potential to destroy precious work.

I was fortunate enough that after managing to repair all necessary connections ( I missed one initially and had the full negative rail on the output ) but it was just a matter of resetting the DC offset and all worked ( at least thus far ).

I found this older FS thread this morning and am glad it was nothing more or else I may have been up the creek without a paddle.
F7 clone kit and WHAMMY PCB
"One of the most difficult parts of building the F7 is biasing the JFETS. This is done for you via prematched and preadjusted pots, which must go in the correct position according to the instructions. You still need to adjust the bias current by ear or with measurement, so this is not "plug and play", but much closer than if you sourced parts yourself."
 
Received my LU1014D kits yesterday, soldered boards, then p2p'd both channels using 10uf input cap, 56k gate to ground, 2200uf ouput cap, 12ohm 42mH air core chokes, 19V PSU, 1,2A idle current.

Sound is very detailed on higher frequencies, easier to perceive lyrics, but the bass is reduced, compared to direct DAP output.

Only thing that comes to my mind is that the choke is not good enough, too high DCR, too little inductance. But with speaker as test load low frequencies seem fine though.