What’s On the Bench Tonight (OBT)

[xrk971]

Custom CNC binding post plates for the LSA Sig 80. Paired with Viborg binding posts, the look is great and the fit and feel is solid. These are not the same posts for production but same construction and diameter.

 

[peppennino]

Beautiful!

 

[xrk971]

LuFoLite amp

12v 20w halogen lightbulb replaces the resistor under the inductor on the LuFo Lite. It really becomes a LuFoLite now. Using 24v SMPS and 4v drop across cap Mx for 20v rail. 1.63A bias current.

 

[xrk971]

I finally built the P2P crossover for the new LSA Signature 80 speakers. First listen to them and they sound amazing. Recorded with iPhone 12 Pro Max. Amazon Music HD playing through Behringer UM2 DAC and Emerald Physics 600.2SE amp. Mono speaker.

LSA Signature 80 Reference Monitor first sound - YouTube

Predicted crossover:

 

[adason]

So much stuff being build with power jfet lu1014, so i put together little headphone amp. It can drive bookshelf a little as well. No measurements yet, but it sounds good.

 

[adason]

Tube preamps next...

 

[xrk971]

So much stuff being build with power jfet lu1014, so i put together little headphone amp. It can drive bookshelf a little as well. No measurements yet, but it sounds good.

Hi Adason,

Nice work! You can drive HE400i’s with that?

I made a headphone amp years ago with LU1014D but with a JFET input stage for some gain. It sounded great.

 

[adason]

yes, it can drive 50 ohm planars to deafening spl from half of line level
it can even drive small bookshelf (not too loud though)
if someone needs more power, lowering the resistors and increasing power supply is the way to go, but for me this is plenty for headphones
I have seen your design, its different, yours is follower
mine is work in progress, there is still small hum, that's why I made no measurements yet
it needs better supply, regulated, likely because it has poor psrr
it should not be a problem, it only draws 0.1A per channel

 

[adason]

While i still have some hum, but not too bad, it sounds amazing. I was listening on 32ohm grado, and now it has been playing quietly on 8 ohm bookshelf.
Here is background noise.

 

[adason]

And the spectrum at pretty high level, -6dB, purely second harmonic, barely any 3rd, tiny bit 4th, not much else. No wonder it sounds great. I am sure it can be improved, but i am happy with it as it is. Just better supply. Cheers.

 

[xrk971]

Nice harmonic profile. Almost all SE Class A headphone amps will have this very pleasing g profile. It’s true that there is no PSRR so a very quiet PSU is needed. What I have found that works well is either a battery (LiPo driving DCDC boost), or a wall wart driving a DCDC boost followed by a cap multiplier. If you add an ultra low noise TPS7A4XXX regulator after that, it’s about as quiet as a battery.

There is a board in my shop that provides CLC / Cap Mx / low noise VR:
Simple Cap Mx Regulated Power Supply | Etsy

Easy enough to P2P if you don’t need a neat PCB.

 

[adason]

Thanks for the info, will check it out.

 

[adason]

I reduced 47ohm resistors to 22, just for fun, now it can drive small bookshelf to normal level. When i used betsy with ribbon, half of volume pot filled the room.
Resistors and jfet little warm, but not hot.
Plus it can rapture your eardrums with any headphones now.
Otherwise it sounds wonderfull.

 

[Vunce]

Neat project Adason! It’s easy enough, I might have to give this a go. I’m not much into headphones, but I probably can drive my Klipsch Forte speakers pretty loud

 

[adason]

That may be too optimistic, but you never know till you try

 

[xrk971]

What was the drain to source bias current at 22ohms? I am guessing close to 500mA?

Forte’s are 98dB so about 2 W would be too loud already.

 

[Vunce]

Oh Yeah!

 

[adason]

I have not measured current, but can easily do so. It was about 100mA with two 47 ohm resistors.
I assume it will roughly double with both 22 ohms.

 

[adason]

You need to put at least 1A through to get some power.
I am tempted to try this next. Credit goes to Juma.

 

[xrk971]

I have not seen that one before. It’s got an interesting feedback loop based on the response across the speaker load. Almost like an F7. I wonder how this sounds? Easy enough to simulate or to make with P2P.