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-   -   question about Aleph-3 , need help (http://www.diyaudio.com/forums/pass-labs/125314-question-about-aleph-3-need-help.html)

space2000 23rd June 2008 02:39 PM

question about Aleph-3 , need help
 
hi,

i just made aleph-3 its working fine as far i can see. i want to ask few questions about the voltage.

its says 25vdc + - but i applied 29v+- as i had the transformer. should it be any problem with bit higher voltage?

as my main voltage is 29vdc + - . i used two pair mosfets insted of 3 pair at output just for testing purpose. when i checked the main voltage, i have found it's drop to 27v. if i add more its drop bit more voltage. is it normal in class A to drop some voltage like this or my amp have some problem?

my heat sink temperature count after run 20mints rum 41c. our room temperature is 30c.

anyone can help me pls as i am new to class A amp.


thank you
michael

hifimaker 23rd June 2008 05:03 PM

You can run the amp at 29vdc, if you have adequate heat sinking or adjust the bias. If needed, place additional resistance in the CRC portion of your power supply to drop the voltage a bit.

Also be sure to check the heat after 1 hour and every 30 minutes. The amp will get a lot hotter as it runs.

The rule of thumb is not to exceed 50c, or the output devices will be short lived. In a commercial set-up the temp sould be lower than this for trouble free longevity. My Aleph runs just below 50c after 2-3 hours with 28c ambient temp.

Search the forum, since there has been TONs written on tis topic.

-David

space2000 23rd June 2008 10:12 PM

hi,

i want to know is this very common in dropping voltage as adding more output mosfets?

like mine two pair of mosfets drip main voltage 29 to 27v.

thanks

hifimaker 23rd June 2008 10:36 PM

The original Aleph 3 had 4 output devices and the Aleph30 had 6 both per each stereo channel. Perhaps this will provide some benchmark. Look around the forum for A30 schematics to see the idea. The notion of paralleling more output devices is to distribute the load for reducing the stress of the output devices.

Also toss in some 3w or 5w resistors in parallel, in the "R" section of the CRC power supply, to drop some volts as needed.

Paralleling the resistors better dispates the heat.

-David

space2000 23rd June 2008 11:10 PM

hi dw8083 ,


Also toss in some 3w or 5w resistors in parallel, in the "R" section of the CRC power supply, to drop some volts as needed.

i couldn't understand this. what is CRC?

my original voltage is 29 after connect the amp is now drop to 27, there is 2v short so the transformer gets hot.

thank you for helping,

hifimaker 24th June 2008 12:18 AM

2 Attachment(s)
After the rectifier in the power supply, the Aleph has a large capacitor, followed by resistor(s), followed by another large capacitor to smooth out the ripple in the unregulated DC output. Thus the designation CRC - Capacitor, Resistor, Capacitor.

The greater the resistance the greater the voltage drop.

Attached is a circuit diagram from Duncan Tools PSU simulator. It's worth Google-ing it up for experimentation. I found it to be pretty accurate and a great learning tool.

What is the VA rating of the transformer? It does tend to get hot.

-David

space2000 24th June 2008 12:29 AM

hi,

thank for info. i thought related to the circuit problem. ok i will add few 3ohms 3w resister to the power. my transformer is 10ampire.

best regards
michael

hifimaker 24th June 2008 02:20 AM

Michael,

Download the Duncan's PSUD2 power supply simulator.
http://www.duncanamps.com/psud2/index.html

If memory serves me, the Aleph 3 draws something like 2.5amps of current per channel.

It will help you find the right values for the resistors. Here's a link to a parallel resistor calculator: http://www.1728.com/resistrs.htm

Once you find the right resistor, duplicate that value through the calaculator above for 5 or 6 3-5w resistors in parallel to share the load.

-David

space2000 25th June 2008 05:44 AM

hi,

now my psu is working fine. slightly voltage drop. every things is working fine. i have little bit hum, i know its require a air coil at power supply. how can i make my own? or can use others things?

second question is, i want to adjust output voltage(bias). now it is showing 0.330v at output. is it too low or i have to adjust higher?
how can i adjust higher?

my amp is 30w RMS.

thank you.
michael

hifimaker 25th June 2008 06:28 AM

Perhaps you could post the exact schematic and parts used.

-David


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