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Old 9th June 2002, 11:13 AM   #1
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Join Date: Jan 2001
Default aleph bias, ...

hello

i am building aleph 30 and i have some questions.

1. is it good to bypass 220uF capacitators ?

2. how much VA have transformer in original aleph 30 ?

3. i would like to incrise bias current. if i replace siurce resistrs
from 0.47 to 0.39 the current will be higher. do i need any other
changes in circuit to increse bias. am i correct?

thanks


janey
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Old 10th June 2002, 01:43 AM   #2
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Join Date: Feb 2001
Location: Columbia, SC
1-Certainly wouldn't hurt.
2-If you were planning on building a stock 30, then I'd say 350-400VA minimum, but since you appear to be planning on increasing the bias, this won't be large enough.
3-Depends on what bias current you're shooting for. If you decrease the Source resistors from .47 to .39 ohms, yes the bias current will increase. But the actual value you end up with will depend on the heatsinking, etc. You may need to adjust R19 to get the exact target value you want.
Again, keep in mind that the VA rating you were asking about in your second question will need to be increased to accomodate the increased current demands.

Grey
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Old 10th June 2002, 11:43 AM   #3
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thanks Grey for your reply.

in original aleph 30 the source resistors are 0,47 ohm
the bias is 0,25V/0,47ohm is 0,53A per mosfet, total 1,6A

if i put 0.4 ohm resistors in circuit
0,25V/0,4ohm there is 0,625A bias current per mosfet so total
1,875A.

am i right?

do i need to adjust R19?

janey
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Old 10th June 2002, 01:40 PM   #4
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Join Date: Sep 2001
Location: Europe, Slovenia
...actualy there is an error in Aleph30 schematics. One chanell will draw approx. 2A idle. Nelson confirm this in:
http://www.diyaudio.com/forums/showthread.php?threadid=1235&highlight=aleph30

I am in the middle of Aleph30 also...

Regards
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