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Old 8th April 2008, 12:15 AM   #1
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Default Mini-a Versions

I am on the brink of flowing solder in attempt to build a MINI-ALEPH. I managed to find a set of BrianGT's blue boards only to find that the circuit is somewhat different than Grey Rollins design and seems to be more in line with an actual Aleph.

I will have +/-16 volt rails to power the amp and am wondering which componebt values to use particularly in the output section. For instance resistance values in the CCS are quite different . Which values are preferred ?? Would appreciate advice from the many builders of these amps . Or should I just go ahead and build according to Brian's schematic. I have really searched this subject over the past weeks and just cant put my finger on where to go with this.

questions as to why one has 2 -.47 sensing resistors and one has 4 come to mind . I'm a believer in the get it right before you do it wrong philosophy. Perhaps I'm in a mountains -mole hill lockup?? what say you??
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Old 8th April 2008, 12:57 AM   #2
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I'm not sure what values BrianGT specified, but I'm sure either set of values will work. I was short on some parts at the time I was pulling together the Mini-A and changed a few to match what I had on hand. Some things, like the biasing resistor for the Zener that programs the front end current source, definitely need to be smaller than the standard Aleph values due to the lower rails. That said, there's a lot of leeway in biasing a Zener, just as there's leeway in other parts of the circuit.

Grey

EDIT: I'm not sure about the .47 Ohm resistor thing. Lacking a schematic for BrianGT's version, I'm reduced to guessing.
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Old 8th April 2008, 01:05 AM   #3
troystg is online now troystg  United States
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Brian has a schematic and excel SS's with parts on his site. I am not on my home PC so give me a few to locate them on the web.
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Old 8th April 2008, 01:41 AM   #4
troystg is online now troystg  United States
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http://diyamps.com/aleph/

That be it!

And here are some good threads...

New Aleph Mini PCB GB

new batch of mini Aleph amplifier and PSU boards
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Old 8th April 2008, 02:04 AM   #5
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There is a formula somewhere on here that shows you how to calculate the output node resistor array. The easy way is, say you have two source resistors (two fets as well for mini-a) at 0.47R, so 0.47/2 = 0.235, the array at the output end should consist of values of resistors that equal that or come close. So you could use two 0.47R for the array. On Brian's schematic he uses four at the end, you'd have to recalculate for R12 (ac current gain) to get the figure you think sounds best. Thats where the formula comes in handy, I'll dig around and see what I can find. My current Mini-A has 0.20R sources (0.20/2= 0.100), and I have 4 0.47R on the array, (0.47/4 =0 .118), close enough. I am however running 25V rails at 3 amps, 75w dissipation per fet....dangerous territory, hasn't burned up yet, but it will, and it sounds great.
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Old 8th April 2008, 03:48 AM   #6
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Thanks for your replies. I've been all over the threads brought to light here and of course this is where I realised that I would'nt be building Grey's version on Brian's boards. We can take it for granted that Brian's version on Brian's boards is a good sounding amp. Is there anyone who has built it with lower value rail voltages who might comment?? Why would it be called Mini if the rails are at 25volts?
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Old 8th April 2008, 04:08 AM   #7
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"Why would it be called Mini if the rails are at 25volts?"

The "mini-A" was devised by Grey <and thank you Grey for this contribution, I for one appreciate it!> on 12 volts.. It was "adapted" to an A30 front end with higher voltage.

There are 2 tabs on the excel SS's for components. One for the Mini-A, one for the A30.

Also did you see the original thread Grey started?

Do a search for "Austin Powers" in the Pass labs forum and it will show up.

I absolutely love the way the "big guys" have such a sense of humor.
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Old 8th April 2008, 04:40 AM   #8
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Big guy? Me? I'll have you know I'm 150 pounds on a 5'10" frame. The very picture of...er...well...me.
An Aleph with 25V rails is an Aleph 3 or a Volksamp/Aleph 30. I had some mismatched MOSFETs left over after building four channels worth of Aleph 2 and (being possessed of the Scottish "frugal" gene on my mother's side) couldn't bring myself to just throw the things away. So I asked myself, "Self, what can we do with these lonely MOSFETs?" To which came the reply, "Myself, I guess we'll just have to do something that doesn't need matched parts." And since the easiest way to do that was to use the MOSFETs one at a time, I figured a miniature Aleph would be fun.
The name does seem to have suffered a bit over the years, what with people calling theirs "Aleph-M" and such. Oh, well.
Plenty has been written about building Alephs of most any random size. No need to stick to any particular path unless you just want to. Remember to bow deeply towards Foresthill, California, take a deep breath and say: Thanks, Nelson.
Gentlemen, start your soldering irons!

Grey
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Old 8th April 2008, 05:26 AM   #9
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tomato, tomata......it's got 2 fets on the end. I personally hold you and nelson in the highest regard, and I Thank You.
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Old 8th April 2008, 05:37 AM   #10
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Quote:
Originally posted by troystg
"Why would it be called Mini if the rails are at 25volts?"

The "mini-A" was devised by Grey <and thank you Grey for this contribution, I for one appreciate it!> on 12 volts.. It was "adapted" to an A30 front end with higher voltage.

There are 2 tabs on the excel SS's for components. One for the Mini-A, one for the A30.

I had not encountered the EXCELL parts list prior to this. Guess What?Calls for two resistors in the array!!Looks like I've run out of excuses.Nothing to do but sober up and get on with it!!
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