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Old 12th March 2001, 07:37 PM   #41
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Default Offset

When driving things with current sources, you can pretty much expect things to "fix themselves". In this X100 case, I would not expect the output voltages to drift unless there was an unbalance in the current sources. Kind of neat don't you think?
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Old 13th March 2001, 02:58 AM   #42
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Default dc offset & others

Fiddling with R36 & R37 will probably help you null out any offset allright. They'll also vary your feedback loop, so some caution may be required. As I mentioned, I haven't actually simulated your version of this design, my version is closer to what Pass described in his patent (very similar to what mefinnis posted). I'll have to plug in your schematic and see how it fares.

Bypassing R36 and R37 with a cap is one of those things that you wouldn't think you needed, but is a good idea. For lowest distortion, particularly at high frequencies, it's important to have the N and P type devices being driven equally. At higher frequencies, the current sources begin to act less ideal, and the bias circuit impedance starts to become significant. Mefinnis used a 220uF cap, I think that's a bit large. I usually use something around 0.5 - 0.1uF, and make it a good quality film cap. Take a look around, I've never seen an amp without this bypass.

Sounds like you're closer to building your amp than I am, keep us posted, I'm very interested in what you find! My X350 project won't get really going for a bit. First I have to finish my Aleph 2's!
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Old 13th March 2001, 05:11 PM   #43
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Good point about the feedback. I have also seen another version of this using two resistors, one going each way with a lower impedance voltage source between them.
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Old 24th March 2001, 03:21 PM   #44
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Default Meci line filters

Got the line filters today. Very very nice and highly recommended. Beware though, they were physically larger than I had imagined.

Another good thing is that they had flat stud-mounts and so testing forward/backwards direction is simple and would not involve soldering.

The ground did not have a series inductor. I don't have grounded outlets in my living room, so this may be a mute point -- but still a fair thing to point out. I recommend a thermistor in that position as a minium, but would normally use a small inductor on component side if connected.

Still waiting for thermal washers.

Detail design almost completed. Due to time constraints, I am considering getting a friend to built it.

I am also considering making teflon based PCB's to simplify construction.
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Old 28th March 2001, 10:48 PM   #45
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Smile X1000 backengineered here

Very nice job, I am flattered.

The X1000 actually has 80 output devices per channel,
not 16, and the input devices (IRF610)are also
cascoded to keep the dissipation down on them.
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Old 29th March 2001, 02:49 AM   #46
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Exclamation wow

Wow you never really know who is watching or reading as it is!
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Old 29th March 2001, 08:35 PM   #47
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Default Wow indeed!

A message from the Master -- very nice indeed.

NP is the only designer I have heard of who would respond positively to something like this. Most designers are "closed" and operate in the twilight zone of audio crap/hype. Not so with NP.

So this reinforces my impression that if you need to purchase excellent audio gear, you could do worse than picking up a piece of Pass gear.

BTW: This is an X100 ...
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Old 30th March 2001, 01:13 AM   #48
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Actually, Nelson is guest of the week over on the AVS forum:

http://www.avsforum.com/ubbcgi/Ultim...i?action=intro

Some quite interesting points made and worth a read.

I was quite worried I would be "out-of-line" when I made my Aleph4, but the reply from Passlabs was basically very positive. I suspect for several reasons. Mostly that NP has a genuine committment to help the DIY'er, but also if you think about it, none of us are likely to buy an X1000. Hell, most of the posts I get are from people trying to find cheaper FETs!! Conversely, serious X1000/100 buyers are unlikely to be frequenting DIY lists .... we are really mutually exclusive groups on the whole and Nelson is not jeopardizing his income to any significant degree. Plus, I imagine most of us would heartily recommend any of his products to anyone asking for advice ;-)
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Old 30th March 2001, 01:53 AM   #49
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Exclamation Pass Rules!

Among high end designers, Nelson Pass is one of the few who encourages people to 'roll their own'. His articles in various magazines, describing design techniques, and specific construction projects are 'must' reading for anyone interested enough in audio to learn how to solder.

I'll echo Petters comments here, although I'm currently building a pair of Aleph 2 clones, and considering a pair of X350's, as I write this, my Threshold/Pass NS10 preamp is playing very musical music.

Cheers, Dave
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Old 30th March 2001, 02:55 AM   #50
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Mark,
Your comments about potential customers and DIY being (for the most part) separate groups are noted, but in a world where people seem to want to take things for granted, I'd prefer to have permission (implicit or explicit) before taking liberties with someone else's intellectual property. Speaking as a published science fiction author, I find this 'information wants to be free' nonsense disturbing. Information wants nothing; it is an inanimate, abstract entity. Only people want something, and those who take something without permission or payment are stealing, period. Napster and its ilk are just as much a concern to authors as they are to musicians, as sites are out there doing the same thing with the printed word.
That said...if it's okay with Nelson, then that's all the permission needed. It's his intellectual property to do with as he pleases, and if he chooses to allow us access to his ideas then I'm one happy camper.
Onwards and upwards--as I understand it, the X-series uses class AB output. Now, granted, it's a trivial matter to up the bias until it's class A, but that's not 'fanatical' enough.
Has anyone considered that the Aleph topology is primarily a rear-end topology, and that the X topology is primarily a front-end topology?
Why not combine the two?

Grey
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