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Old 18th February 2004, 09:18 PM   #21
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jh6you,
If you want to experiment with rail voltage vs. bias current, feel free. I've got more freedom in that than most--at least for the Aleph 2s--since they are water cooled and can dissipate a tremendous amount of heat. Just keep an eye on device dissipation; don't so wrapped up in the output that you forget the front end. It may need a little fine tuning as far as resistor values if you change the rail too much.
I've varied the bias quite a bit. If you lean it out, it starts sounding "hi-fi" which may suit some, but it's not to my taste. I've only varied the rails by about 5-8% or so. Not much to tell in that tight a range (by comparison, I've run the bias probably +-50%).
bertram,
The front end current source will be happy with any reasonable source of 9V. You could, for instance, use a voltage divider from one rail to ground or to the opposite rail--might be a good idea to have regulated rails. Zeners work. I haven't used them in this application, but a voltage reference should be fine.
I used the blue Panasonic metal film resistors from Digikey. What might be available where you are, I do not know.
The MPSA18 is not particularly critical. Nelson uses the Zetex 450 in some of the Aleph schematics. That would be perfect. The MPSA18 is a pretty ordinary 45V NPN. The circuit won't come unglued if you toss in another NPN. I used MPSA18s because I've got a zillion of them.
Two rectifier bridges would be great. Or you can use just one. Whatever suits you.
Wind your own chokes. It's much cheaper.
Although I'm sure Nelson wouldn't turn down a good French wine, I believe he's on record as leaning towards the California product. I'm prone to French, Australian, and Californian wines, but not necessarily in that order. Just depends on what's going on. Being a fan of red wines, myself, Germany doesn't get too high on the list....however, there are some stunning German beers.

Grey
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Old 19th February 2004, 10:24 AM   #22
Lucas_G is offline Lucas_G  Netherlands
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This forum has become one of the most interesting places for DIY audio in the world. It is always a joy to see how people of different nations and cultures can participate in the exchange of ideas and experiences. It has helped making DIY audio a very dynamic and sophisticated affair. People with all kind of levels and skills have learned so much from the contributions of men like GRollins, Dieckmann and so many other members, that we must try to protect this forum from unwanted resentments.

When sharing ideas in a forum, one is bound to engage with people that have different backgrounds, methods, and characters than your own. If it becomes difficult to respect that, the best next thing is to ignore the other person. That at least prevents the forum from being obstructed by personal resentments, which really do not help any of us...

This very thread will become more and more important when so many members will start constructing their Aleph-X's in these coming weeks and months.
I hope that after the two days pause, both (really highly estimated) members will continue to contribute in a postive way to this thread. They have both (each in his own way) presented so much knowledge, experience, and inventions to this forum, that it would be a pity for all the other members when we would have to continue without them.

May this thread flourish just as much as the sound of all the newborn Aleph X's that will come to life!
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Old 19th February 2004, 12:40 PM   #23
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Default FET's to use

Nelson said to not run below 25volt rails - was this in respect of 244's only (and therefore 044's are ok at say 19v)?
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Old 19th February 2004, 03:59 PM   #24
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Default Re: FET's to use

Quote:
Originally posted by Jason Hubbard
Nelson said to not run below 25volt rails - was this in respect of 244's only (and therefore 044's are ok at say 19v)?
You can run them at any rail voltage you like, but below 25
volts or so you start into the part of the curve where every
volt counts, so I recommend that at least as a + to - figure.
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Old 20th February 2004, 12:59 AM   #25
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I need a source for .22 ohm wirewounds for the X. I was able to get both .2 and .25 Vishays so which of these would be the preferable one to use in a stock amp?

Also as far as matching these low ohm resistors goes would a 5-1/2 digit meter suffice with direct resistance readings or is it better to measure voltage drop across them(with the same 5-1/2 digit meter of course......?

Thanks for the help!
Mark
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Old 20th February 2004, 01:54 AM   #26
MikeW is offline MikeW  United States
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.2or.25 close enough. I used.33 on the last AX.
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Old 20th February 2004, 05:28 AM   #27
moe29 is offline moe29  United States
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I'm a little confused... It seems that the First Watt Aleph X's will
have 24 volt rails and run at aprrox. 15 watts.

15 Volt rails for the DIY Aleph X gets you close to 35 watts

these figures are just off the top of my head... but there seems
to be a discrepency between the two amps in this area.

I know these aren't identical amps, but why the difference?

thanks for putting up with questions from the back of the class


m.
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Old 20th February 2004, 06:52 AM   #28
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Default Choice of FET's

I already have lots of 244's - should i sell them and go for 044's instead (given that my rails are +-19v) or will 244's be just as applicable in this case?
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Old 20th February 2004, 01:35 PM   #29
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Mark,
Choose the resistor value according to how much bias you want and how much heat you can safely dissipate. Lower resistor values (all things being equal, meaning you don't fiddle the current source, etc.) will, of course, lead to higher bias current. Look at your speaker load impedance and decide what its minimum value is. Work backwards from there, then throw in a bit of extra bias, just for spice.
5 1/2 digits will do fine for matching. What tolerance are the Vishays? 1%? I wouldn't even bother matching them, myself, but then I'm short on time. Someone with more time on their hands might feel that tweaking the R values would be worthwhile.
moe29,
I think it's safe to say that the First Watt Aleph-X will turn out to have a slightly different topology than the Aleph-X that I designed. I have at least two possibilities in mind as to what Nelson's up to, but haven't had time to think either idea through yet.
Jason,
No need to go for '044s unless you want to. Use the '244s.

Grey
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Old 20th February 2004, 05:34 PM   #30
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Default Heat Protection for Alephs

I'm posting this question here because I recently got hifiZen's boards and may build the X next. However, I also bought some regular Aleph boards, courtesy of Coulomb, and might do that first.

Here is the question: The Aleph manuals are contradictory on heat protection: both the 5 and the 2 manuals say in one passage that a 70 deg. C thermal protection switch is installed, yet say in another that a 75 deg C switch is installed. Yesterday (before I discovered the contractictory passages) I bought a bunch of 70 deg C switches from DigiKey, thinking no matter what Aleph I build--2,5, or X--its going to get hot, even with the R Theta heat sinks at 2 per channel. Did I screw up in buying the lower temp value? Am I obsessing again?......Dang! Where are my meds?

Larry Wright
Seattle area
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