LuFo Lite - a 1 Transistor SE Class A Headphone Amp

I did a quick FFT of the LuFoLite with halogen bulb today and as we can see, it resembles the output of a SE Class A amp with triode like behavior. There is only 2nd and 3rd order harmonic distortion and this is for driving a 10ohm dummy load to 1.0Vpp - a typical level for moderately loud playing on a headphone. The THD is about 0.21% and the 2nd harmonic is about 20dB higher than the 3rd harmonic. This is for 20v rail, 13v source and 12v at the lamp below the inductor with 1.63A bias current:



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Thanks for all the info on the LuFo Lite X.

I'm collecting parts to build one (and I'll include the latest halogen bulb mod). Just to check if I may.

I am planning to use a pair of Triad C-56U chokes I have available. They're rated at 35mH, 2Amp and 790mOhms - a little lower inductance and slightly higher resistance compared with your MOT, but I think the Triads will be fine for headphone listening.

The halogen bulb equates to a 7.2ohm resistor and with the choke that gives a total of about 8ohms so, with a 24V SMPS, I reckon the LU1014D current will be around 1.5A and a dissipation of circa 18W - do I have that about right?
Hi X. Just wondering if you considered a SuSyLu Lite - I thought it might be an interesting project? The only complexity would seem to be around the choke, finding something suitable off-the-shelf is unlikely so it may require a custom wind (but it should be smaller/cheaper than your SuSyLu chokes) but I'm also wondering about just using two standard chokes (like the Triad C-56Us I already have)?
Yes, you can use two standard chokes (not magnetically coupled). The distortion will be a tad higher and you can’t call it SuSy… anymore as there is no “super symmetry” from the coupled chokes. However, you could arrange two Erse 40mH speaker crossover chokes side by side and there IS significant coupling as Jwjarch found that the 40mH rating was boosted to like 56mH or something like that when they were side by side. This was discussed earlier in this thread.

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