How 'improved' it might be, I'm not sure. All he did was rearrange the current source to take an N-channel device instead of a P-channel.
It would be slightly cheaper, however, given that N devices are lower cost.
Sound quality? Dunno that I'd expect an audible difference. I once asked Nelson if he'd ever noticed a consistent sound quality difference between equivalent N and P channel MOSFETs. He said he wasn't aware of one. (This was one of those thought experiments I'm prone to whilst driving. The SOZ circuit would provide a convenient test bed for such experiments.)
It wouldn't be particularly difficult to build a Zen with plug-n-play current sources, nor particularly expensive (the heat sink & power supply are the hurtful parts). If you've got the time and inclination, try it and give a report.
I built one and it works just fine. I prefer using N-channels over P-channels. I truly don't think you'll hear any difference. N-channel devices are less expensive and therefore cheaper to match if you wish to use more than one device.
I'm assuming you're looking at the schematic at http://www.tanker.se/lidstrom/zeni.gif. The ground connection at the bottom is not the constant current mosfet. The CCS is the upper mosfet. The bottom mosfet is the signal or output mosfet.
The reason it is connected to ground is that, unlike the Aleph series, which uses +/- power supplies with little DC offset and no output capacitors, this design has a single ended power supply. The side opposite the + supply is therefore referenced to ground. This means that the output signal from the Zen amplifier is floating about 2/3 above ground with respect to the + power supply(in this schematic about 2/3 times 34 volts). This in turn is why an ouput capacitor is needed: to prevent putting around 22 V DC into your speaker. Without the cap, 22 V will instantly fry just about any speaker.
Yes I am looking at the same schematic as you. I know the top part of the circuit is the CCS. What I can't figure out is how the earth connection shown on the Pass ZEN schematic (to R6) has been done away with.
T'ain't no problem...R6 is still there, and is even labelled R6. What's confusing you, I suspect, is that in using an N-channel device for the current source, all the polarities were reversed (just for the current source). If you turn the schematic upside-down and kinda squint your eyes a bit (pretending that the positive rail is the ground in the original Zen schematic), you'll see that Alice went through the looking glass and brought your Zen back to you.
It's not that R6 needs to go to ground, per se, it's that it needs to go to a reference voltage.
I'm a little slow but I'm getting there.
Does this mean that in the original pass circuit that the ground shown is actually a connection to the reference voltage of the circuit at the drain of Q2?
I may have lost the plot here.
Now, I'm the one who's confused...I didn't know it needed fixin' before it would work. Granted, I haven't studied the critter in detail, nor have I built one, but I don't remember seeing anything that looked particularly wonky. I'd say go for it.
If I weren't up to my ears in fiddle-factor here, I'd build one of each and listen to them side-by-side, just to see which sounds which way.
I have finished a preliminary PCB layout for the Lidstrom ZENi. I have posted a new thread to let people know I require advice on this. Please check out my post and let me know if you want the design emailed to you and in what format