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Old 3rd June 2009, 03:27 PM   #1
NiklasJ is online now NiklasJ  Sweden
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Default Aleph 30 build by diyaudio newbie

Hi, my name is Niklas, I'm from northern Sweden and this is my first post in this forum.
I'm starting again in the hifi hobby, have been away from this 15 years.
I am planning to make 4pcs of Aleph-30 monoblocks to drive my Linn Keilidh's in active mode.
PCB's for amp and psu will be BrianGT's design if still available thru chipamp.com

Questions:
1) Speakers are about 4 Ohm so I think I'd better add more bias to take best advantage of the design, as I understand it I only need to change one resistor to accomplish this, which resistor would that be on BrianGT's boards? About 2.5A bias current. This would make the a30 deliver about 60W@4Ohm, correct?

2)Transformer...is a Nuvotem 0225P1-2-018K sufficient for each monoblock? Should give me about 25V rails if I'm not totally lost...? Data:
VA Rating 225VA
Input Voltage 230Vac
Output Voltage 2 x 18Vac
Output Current 6.25A
Regulation Typ. 9%
Temperature Rise 60C
Fixing Hole Dia. mm M6
Height x Diameter 52 x 126mm
Weight 2.25kg
Dimensions L x W x H 52 (H) x 126 (Dia) mm
Click the image to open in full size.

3)Heatsink, will 0.167 C/W total be enough for each monoblock (only counting flanges, not the rest of the aluminum chassis)
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Old 3rd June 2009, 04:30 PM   #2
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It will be running close to its VA rating. Perhaps one per channel?

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Old 3rd June 2009, 05:02 PM   #3
NiklasJ is online now NiklasJ  Sweden
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I'm very honored to get an ansver from you Nelson!
As I'm building monoblocks I was planning one toroid per channel, but perhaps you're saying that I need one per rail, ie 2pcs transformers per mono-channel?
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Old 3rd June 2009, 09:19 PM   #4
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No, I think one transformer per channel would do it.

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Old 7th June 2009, 12:28 PM   #5
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Hi Niklas,
Your numbers look pretty good, maybe a little low on the bias. 2.5A would be around 50W.
The heatsink rating could be a problem unless you have derated them for lower operating temperature. They should be fine for 2.5A bias. Go to the Conrad heatsink website and check out their charts, they do a good job of explaining the variables.
Have you read the WIKI.

Best, Bill
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Old 8th June 2009, 03:10 PM   #6
NiklasJ is online now NiklasJ  Sweden
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OK! Thanks for your input Bill, and of course another thankyou to you Nelson!
I havnt studied electronics in 20 years so I dont yet understand the aleph circuit completely.
But, finding that aleph 30 wiki sure helped alot...thanks for that Bill!
-Though I'm still totally lost on how to compute the value of R19? bias controlling resistor...
Found something in the schematic by algar emi but those values dont seem to match the expected results I got when fiddling with the modified AXE-1.xls by wuffwaf...?

Now I know how to calculate AC current gain... so according to that the stock Aleph 30 should be at about 61% AC current gain from the R21/R20 ratio mentioned in a linked thread in the wiki...But still confused as I found statements about keeping the gain around 50% to avoid distortion at high levels... Is there a "sweet spot" to shoot for here concerning the R21/R20 ratio?

This data, rail voltages and source resistor values from the a30 schematic put into the modified AXE-1.xls by wuffwaff all seems to compute, set up as close as possible to a standard a30 I think, example:
Bias 1.75 A total bias for one channel being one monoblock
Peak current 4.5 A maximum output current
Power 8 Ohms (RMS) 30 W here a voltage loss of 3Volts (fet + source resistor) is assumed
Power 4 Ohms (RMS) 40 W here a voltage loss of 3Volts (fet + source resistor) is assumed
Power 2 Ohms (RMS) 20 W here a voltage loss of 3Volts (fet + source resistor) is assumed

Dissipation for one channel 87 W With this you can calculate your heatsinks like shown further below.
Dissipation per fet 14.5 W Between 20 and 30 watts should be ok, look below for junction temp.
Bias per fet 0.582 A
Voltage drop on Source Resistor 0.27 V Adjust with R19 (ref. Aleph 2 schematics on Passlabs.com), l.e. 0.66

(Fairly close to the 0.25V in the schematic...or am I lost here...?)

Resistor to bias fet 0.47 Ohm choose nearest value (preferably lower so for 0,3 ohms choose 0,27)
Chosen value of source resistor 0.47 Ohm here you must fill in the resistor value youve chosen
Current through source resistor 0.58 A

Basically, I just want to build 4pcs of A30 monoblocks but with changed bias to give a little better punch than a stock a30 on the 4Ohm speakers I've got... About 60W should do it...
I dont have much electronic measuring equipment so I really would like to find right components at once and get something working right from the start.
Could someone point me in the right direction please?

Best regards,

/Niklas
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Old 9th June 2009, 12:07 AM   #7
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Hi Niklas,
I think it would be good to go through the Zen articles on Passdiy for a tutorial on the constant current source. Should be very helpful.

Bill
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Old 10th June 2009, 02:59 PM   #8
NiklasJ is online now NiklasJ  Sweden
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I'm starting to thing about the chassis for my amps...

Originally i figured wall hanged mono-amps would be original&nice (like a painting) but some extreme audiophiles insist the amps should stand steady on the floor, som even suggest puttin a huge 50+lbs block (brass, concrete etc) on the amps for better sound....
Have they been smoking stuff or is there really something to this - planting tha amps firmly to the floor I mean?

Anyway, In case there is some merit to that I thought I might as well build a true dual mono block, started sketching some...
I like the possibilities this solution has (one mono side and flange excluded), chassis size l*w*h~320x200x322mm but I do not know if some unusual features with this approach present a problem:
-Capacitors laying down, horisontal axis?
-Toroid standing upright (hanging from center hole really)?
- All pcb's mounted to the flange (by nylon fasteners I think)?
Click the image to open in full size.
Comments, suggestions anyone?
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Old 7th February 2012, 12:11 PM   #9
biju55 is offline biju55  India
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hai


where can i get complete kit of pass aleph 30 amplifier ? please send me mail on biju55@aol.com
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