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Old 22nd March 2010, 06:20 PM   #11
Beftus is offline Beftus  Netherlands
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Originally Posted by Jack Tupp View Post
Thanks Beftus, you're helping me a lot. I don't understand what "my" R value is or should be. What is a good all around set up here with these resistors that's going to produce acceptable power supply results?
The value of R in the CRC setup should be chosen with the value of C to give the cut-off frequency you want. Choose your frequency low, 30-40Hz.

Suppose you want a cut-off frequency of ~20Hz. With a 10000uF final cap you're looking at a value for R of about 0.825 ohm (4x 3.3 ohm). Make sure the resistors can handle the heat! Chosing a larger final cap results in a lower value for R meaning less heat to dissipate. Try to divide the load accross multiple resistors, five 3Watt resistors in parallel can dissipate a total of 15Watts.

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So I am assuming that if we fill the resistor slots then this line from the original BOM is not necessary
That's right.

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Do those values look like it will make an indicator light and not a flashlight?
Some people prefer a very bright LED, some don't. And with all those different LED colours it's hard to give a single advice regarding LEDs. Mine has a blue LED with a 22K resistor. It's blue but not very bright.
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Old 22nd March 2010, 10:30 PM   #12
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The value of R in the CRC setup should be chosen with the value of C to give the cut-off frequency you want. Choose your frequency low, 30-40Hz.
The board seems to offer the flexibility to do all kinds of different setups. I am only interested in running 2 standard mini alephs off it.

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Suppose you want a cut-off frequency of ~20Hz. With a 10000uF final cap you're looking at a value for R of about 0.825 ohm (4x 3.3 ohm). Make sure the resistors can handle the heat!
Yes I'm using 10,000uF caps and I want to use 5 3 Watt resistors to dissipate heat and have a low cut off frequency. What is the value of the 5 resistors?

Last but not least the C1-C2 capacitors. What are they for and what type/value do I need there?
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Old 23rd March 2010, 12:05 PM   #13
jtktam is offline jtktam  Canada
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Originally Posted by Beftus View Post
No. Capacitance is in Farads, so 15000uF = 0.015F

Equation becomes: 1 / (2*Pi* 0.094 * 0.015) = 112.88 Hz
wow, so my cut off is too high then..

the mini-a bom says to use jumpers.. i figure jumpers would make the above equation approach infinity (i assume jumper = 0 ohm)

-joe
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Old 23rd March 2010, 05:53 PM   #14
Beftus is offline Beftus  Netherlands
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Originally Posted by Jack Tupp View Post
Yes I'm using 10,000uF caps and I want to use 5 3 Watt resistors to dissipate heat and have a low cut off frequency. What is the value of the 5 resistors?
Pick your preferred cut off frequency and do the math yourself. Not because I don't want to help you but because it will make you understand the underlying principle.


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Last but not least the C1-C2 capacitors. What are they for and what type/value do I need there?
Additional decoupling caps, a low value film cap would do, say 0.1uF.
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Old 23rd March 2010, 05:56 PM   #15
Beftus is offline Beftus  Netherlands
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wow, so my cut off is too high then..

the mini-a bom says to use jumpers.. i figure jumpers would make the above equation approach infinity (i assume jumper = 0 ohm)

-joe
With jumpers you don't have a low-pass filter and no attenuation of mains related hum.
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Old 23rd March 2010, 07:21 PM   #16
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I pulled up the list of available resistors in the pretty, baby blue line of Panasonic 3 w metal film resistors and picked the one in the middle.

How about 4.7 ohms 4.7 / 5 = .94

2 * 3.1415 * .94 * .01 = .0590

Seems like a nice number but it means absolutely nothing to me. Is this an acceptable resistor to use in R3-R12?

Also could I use the same resistors in R1-R2 to simplify things?
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Old 23rd March 2010, 08:32 PM   #17
Beftus is offline Beftus  Netherlands
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Seems like a nice number but it means absolutely nothing to me.
Stop. Learn some basics first. Read a lot of relevant stuff on the forum first. Try to grasp what it means. Building an amp is more than connect the dots. Ignorance and electricity are a deadly combination.
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Old 25th March 2010, 03:27 AM   #18
jleaman is offline jleaman  Belgium
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in the psu board, just stuff ALL the holes for the crc with 0.47 P0.47W-3BK-ND's it will work perfect for the mini a's.


Jase
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Old 31st January 2011, 04:54 AM   #19
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Default Cut-off Freq ?

Hello everyone. I to am thinking of possibly building a Mini-A. Though still having alot to learn, how does the psu cut-off frequency effect the amplifier please explain ? I plan on using the wonderful pcb's form chipamp.com and the power supply board is set-up for CRCC I think !
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Old 31st January 2011, 07:44 AM   #20
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