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Old 17th February 2005, 10:59 PM   #1
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Default more aleph 2 questions

Ok, 2 questions. I've searched and searched and haven't found a great explaination about how to adjust ac current gain on an aleph 2. Most explainations tell what to set it to, not how to set it. Anyway, if someone could explain this to me, that'd be great, or at least give me a link that says how to adjust it. Some info, i'm going to be using 16 outputs per channel of irp240.

i'm using 1 ohm source resistors and for the output resistors i'm using mra-12 mills .22 ohm x3 in parallel. i'm gonna set the bias w/ a 100k pot for r19, and i may have a switch that can switch between 2 or 3 different parallel resistors eventually to have the bias set for fall/summer/winter settings (i can use a dpdt switch to adjust ac current gain as needed as well, but i need to know how to adjust ac current gain)

also, i'm using ztx450's, can someone look at the layout and make sure that they are the correct orientation? thanks!

-Matthew K. Olson
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Old 18th February 2005, 12:34 PM   #2
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Matt,

It is difficult to tell from the picture. If you look directly at the flat side of the transistor, the lead to the left is the emitter. Here is the PDF file for the ZTX450.
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Old 18th February 2005, 12:42 PM   #3
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In the pic, you are looking at the roundish side of the transistor w/ the ztx printed on it. The flat side doesn't have anything printed on it. Seems to me this is correct. Email me and i'll send you the real pic.

-Matthew K. Olson
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Old 18th February 2005, 12:47 PM   #4
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Mattyo5,

For the ZTX450 it seams to me they are OK.

Refer to the picture...

Regards.

Alain.
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Old 18th February 2005, 01:44 PM   #5
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i've seen the pic, the "back" is the curved part and is where ZTX 450 is printed and is the face that is facing us in the pic I posted. i think its correct

-Matthew K. Olson
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Old 18th February 2005, 02:01 PM   #6
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Adjustment of Aleph current source can be found here .
Read on page 3: "In any case, to achieve this 50%..."

Also, look at the WIKI -> AlephX for a more practical example.

/Hugo
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Old 18th February 2005, 03:07 PM   #7
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Ok, very cool. THATS the link i was looking for. Lets see if i get this straight.

i measure voltages across resistors

voltage across one source resistor VRS

voltage across output resistors VRO

and in the case of aleph 2, i adjust r21 to get proper ac current gain....

so the math

VRO/ (output resistance) = x amount of current
VRS/ (source resistance) = y amount of current

[1 - (y/x)] x 100 = ac current gain percentage

an example w/ my numbers might be:

.05v / .07 ohms = .71A
.05v/ (16 fets total, and 1 ohm source resistors = .0625 ohms) = .8A

.8A/.71A = 110% ac current gain ...yikes ...hope i don't measure .05 v across all those resistors!

is this math theoretically correct though, assuming i measured .05v across those resistors...which i didn't

??

thanks guys, just trying to clarify things for the morons like me

-Matthew K. Olson
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Old 18th February 2005, 03:14 PM   #8
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Hi,

thatīs right although in this case you get more current out than you put in

Donīt forget to measure AC-Current.

William
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Old 18th February 2005, 03:55 PM   #9
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Ok, right, i gotta have my multimeter set to ac volts. Also, do I have a signal playing , like 1khz sine when i do this?

-Matthew K. Olson
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Old 18th February 2005, 04:26 PM   #10
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Quote:
Originally posted by Mattyo5
Also, do I have a signal playing , like 1khz sine when i do this?

-Matthew K. Olson
Your math seems OK but you didn't read the book carefully.
Yes 1K will do. Only, it's such an annoying tune. I prefer lower like 100Hz.

/Hugo
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