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Old 30th May 2003, 03:45 PM   #1
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Default X-lite

Note: This IS NOT a proven design. If you build it, it will be at your own risk. All info based on simulation:
If you are familiar with the AlephX, you will see that there is nothing new here- just re-hashing some old ideas into something different. I was asked to write up a description and include a readable schematic (see the zenlight thread). So, if you're interested- here goes:
refering to the attached schematic (zip file)
The input stage:
Q1 and Q2 form a differential pair, biased by current source mosfet Q3. R13 (1.21K) is there with C1 to divide the rail and decrease dissipation on the current source mosfet. D1 sets up a 9.1V reference, filtered by C2, and R22 sets the current. R22 will also determine what voltage the speaker outputs of the amp are at, and should be set so that both outputs are at +3-4 volts for maximum voltage swing. R12 sets the current through the zener D1 to around 4mA, and should be adjusted if the + rail voltage is changed. R29 and R2 are the load resistors for the differential pair. R25 (2k pot) is used to adjust the balance between the output stages, so you can null out DC voltage across the speaker terminals caused by imbalance between the output stages. For those who are experienced with the AlephX design, you may also substitute the HH current source.

The output stage:
L1-L6 are 110V 250W incandescent light bulbs, as found everywhere in the US. They are used with the high + rail to create a current source. I used Nelson's chart in the Zenlight article to approximate the resistance of each bulb for the simulation. Your results may vary... (you have been forewarned- this is not a proven design at this point). The output mosfets can be whatever you would use in the zen/soz/aleph/alephX amps... typically IRFP240. The .3 ohms resistors are there to help balance the mosfets, so that any one dosen't hog all the current. There are the typical 221 ohm gate resistors to prevent oscillation, as used in all the aleph amps, etc.

Other stuff:
R14 and R15 are the "magic" resistors, which you know about if you have been following the AlephX thread. They stabilize the amp. Along with these, you might want to use 33-100 ohms at each speaker output terminal to ground to help with stability.

Some things to note about the design:
The power supply will be massive- needs to supply 10+ amps at each rail, all the time. It should do about 45 watts into 8 ohms, and should drive down to 6 ohms (actual impedance- not rated speaker impedance) without current limiting. There is about 150 watts dissipation among the mosfets, so a good heat sink is required.
If you don't need as much power, you could get rid of one bulb and one mosfet on each side. The reason I decided to go with so much bias is to guarantee that it won't current limit before reaching max voltage output into 8 ohms. If you don't need a lot of power, you could get away with less bias.

Any suggestions or improvements are definitley welcome!

Steve
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File Type: zip x-lite_schematic.zip (36.2 KB, 608 views)
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Old 30th May 2003, 04:10 PM   #2
Variac is offline Variac  United States
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Wow! Now that the schematic is clear, I'm even more impressed. Thanks for adding the resistor ratings, etc.

This one has it all! Like a walk through the history of Pass DIY


x-circuit ,lightbulbs ,
decent power output , huge power supplies , simple circuit

How do you get the 12v on the negative supply vs. 50 on the positive?

Thank you for sharing, maybe the mods will move some of the other postings regarding this amp over to this thread.
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Old 30th May 2003, 05:06 PM   #3
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Quote:
How do you get the 12v on the negative supply vs. 50 on the positive?
The 12V on the negative supply is to keep the dissipation in the output fets down. The 50V is needed to make the bulbs act like current sources- basically a somewhat high voltage and a resistor, like in the balanced line stage.
These rails will have to come from seperate transformers, with the + of the 12V rail tied to the - of the 50V rail to make a ground reference point...
So, 2 transformers, 2 rectifiers, 2 sets of caps, etc.
Thanks for the interest.
Steve
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Old 30th May 2003, 05:32 PM   #4
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Do X circuits always require split supplies?
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Old 30th May 2003, 06:14 PM   #5
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Thanks Steve . I was afraid that might be one of those stupid questions! I guess it was OK after all. I know I should do SOME of the work, but any clue on the VA of the big transformer and the 12 volt one? I assume they are different loads.

Hey guys, go to e-bay and search on "projector bulbs"
Some VERY cool options- including 750 watt 120 volt models
I really hesitated mentioning this, cause I'm not ordering yet!
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Old 30th May 2003, 06:46 PM   #6
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mrothacher,
I don't think that split supplies are a necessity for X feedback, but i think the circuitry used generally lends itself to that type of setup. Nelson could tell you for sure! How's that for answering but not saying anything! Sorry I can't get more specific.

Variac,
No stupid questions, just stupid people, right? haha Just kidding. Actually, my sig is directed at myself more than anyone else. I have been known on occasion to ask a question that 1. I already know the answer to, but have not taken time to think through clearly, or 2. That is just plain stupid in general. I should listen to Mark Twain more often.
The big tranny will probably have to be 40 to 45 volts @ a bunch of amps. Think somewhere around 750-1000VA minimum! Per channel! Yikes!
As for the 12 volt- a filament tranny with a lot of current should do nicely. I know allelectronics has one for sale (they call it 12.5 volt @ 25A). I'm using some of these for my Aleph X's. The currents will be the same for both trannies (or, should I say the draw on each rail will be the same). The upper rail will have to be a lot higher VA because it is supplying the same current and a lot more voltage.
Are you actually thinking of building one of these monsters?
Steve
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Old 30th May 2003, 08:18 PM   #7
Variac is offline Variac  United States
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I am definately in the lazy question asker camp
Didn't Stefano say he has actually built one of these?

Well... I have these 2 1000 VA toroids @ 37.5 volts that I was planning to use for an Aleph 2. BUT the x amp designs came out, so I wanted to be trendy, but they use about half the voltage so no go. But your amp seems like it would be OK with the 37.5 volts. Then the problem of all those expensive heat sinks which your design at least partially addresses. The biggest problem is I have a 15 watt SOZ in the works for the treble so the combo of the 2 amps would REALLY suck up the power-maybe more than my house wiring can handle!
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Old 30th May 2003, 08:27 PM   #8
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Quote:
maybe more than my house wiring can handle
You are not kidding! I can see how you could easily overload the circuit with a biamp setup like that. I hope to find out soon. I wonder when Nelson's new amp will be out at Passdiy? I've been watching non-stop for it.
Well, if you decide to give it a go and I can be of any help, I'll be around. You and I may be the only ones to build one, from the looks of it. Oh well... the rest might just miss out on something great!
Steve
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Old 30th May 2003, 09:09 PM   #9
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Quote:
Originally posted by Variac

Didn't Stefano say he has actually built one of these?


Yes but single ended .I am drawing my own schematic for the X-lite yet.
But I will use much less power than a kilowatt/channel ...
let's say 4-5 Amp par channel max ...
And 2 mosfets par channel .Also becouse 4 heatsinks are just waiting for it.
And I've got 2 tranny with 37-0-37volt and 15-0-15 each.
Actually they are connected for 57volts.


Thanks guys!
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Old 30th May 2003, 09:16 PM   #10
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Quote:
Originally posted by Variac
Thank you for sharing, maybe the mods will move some of the other postings regarding this amp over to this thread.
Too busy to go through the whole thing, but tell me the post numbers and I will move them for you
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