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Gear / Technical Help => Cables => Topic started by: Nick's Picks on July 26, 2007, 09:59:20 AM
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Hey all....
I"m fixing a cable for someone here on the board. the cable has a built in resistor based attenuator inside.
when opening it up I saw 4 of them. one on each lead and two on the shield/ground.
I'd like to re-build it from scratch, but am not sure what resistors to use.
the ground ones had 4 stripes. the others only two (and I have since misplaced those !!!).
I really want to finish this up ASAP as the owner has been waiting a while...very patiently.
I'm not too proud to ask for help on this. I've google'd a ton, came up w/nothing for attenuators.
any insight? direction ?
thanks.
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You might want to check with Micheal Grace. We sent him one of our MR-1000s and he if figuring out the exact attenuation needed for a V3 analog out while simultaneous digital out (so the signals are the same level)... He knows all the right parts needed for the cables.
We need these cables too!
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If you can find out what level of attenuation the cable provided before, that would be helpful. Also, I can't tell from your write-up if this is a balanced/XLR attenuator cable or an unbalanced and perhaps stereo unbalanced (eg, 1/8" mini TRS with attenuation on both channels).
Anyway, this website is pretty helpful:
http://www.uneeda-audio.com/pads/
For balanced, you'd probably want to use the U configuration, or for unbalanced the L configuration. Use 1% metal film resistors and buy extras beyond what you'd need just for this cable. Then hand-match the resistors using your multimeter to measure the actual resistance for each resistor. Very important to get the two balanced sides of a balanced cable matched as closely as possible. Also good to match the resistance across left to right channels, but that isn't quite as important.
If you had all the resistors from the cable, you could use your multimeter to measure them, but at this point, just decide what level of attenuation you want and use the info from the uneeda website to decide on resistor values. Just remember the formula for getting resistor values uses gain as "k", but this is measured as a ratio.
The formula for gain/attenuation in db is gain = 20 * log (V1/V2), or gain = 20 * log (ratio)
So if you want 20db of attenuation, you've got 20db = 20 * log (k), so K=10 (or I guess really for attenuation, -20 = 20 * log (1/k), with k again = 10). Similarly, 40db attenuation = 20 log (1/k), so k=100.
Once you determine what level of attenuation you want, you can figure out k, and then use the info from uneeda to determine resistor values.
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0 Bad Black
1 Boys Brown
2 Rape Red
3 Our Orange
4 Young Yellow
5 Girls Green
6 But Blue
7 Violet Purple
8 Gives Grey
9 Willingly White
Resistance = [Color 1][Color 2] x 10 ^ [Color 3]
Example: Brown Black Red is 10 x 10 ^ 2 = 1000 ohms. Blue Grey Orange is 68k.
http://en.wikipedia.org/wiki/Electronic_color_code (http://en.wikipedia.org/wiki/Electronic_color_code)
-
0 Bad Black
1 Boys Brown
2 Rape Red
3 Our Orange
4 Young Yellow
5 Girls Green
6 But Blue
7 Violet Purple
8 Gives Grey
9 Willingly White
Resistance = [Color 1][Color 2] x 10 ^ [Color 3]
Example: Brown Black Red is 10 x 10 ^ 2 = 1000 ohms. Blue Grey Orange is 68k.
http://en.wikipedia.org/wiki/Electronic_color_code (http://en.wikipedia.org/wiki/Electronic_color_code)
I was taught In Catholic high school no less... ;)
0 Bad Black
1 Boys Brown
2 Rape Red
3 Our Orange
4 Young Yellow
5 Girls Green
6 But Blue
7 Virgins Purple
8 go Grey
9 Willingly White
-
0 Bad Black
1 Boys Brown
2 Rape Red
3 Our Orange
4 Young Yellow
5 Girls Green
6 But Blue
7 Violet Purple
8 Gives Grey
9 Willingly White
Resistance = [Color 1][Color 2] x 10 ^ [Color 3]
Example: Brown Black Red is 10 x 10 ^ 2 = 1000 ohms. Blue Grey Orange is 68k.
http://en.wikipedia.org/wiki/Electronic_color_code (http://en.wikipedia.org/wiki/Electronic_color_code)
I was taught In Catholic high school no less... ;)
0 Bad Black
1 Boys Brown
2 Rape Red
3 Our Orange
4 Young Yellow
5 Girls Green
6 But Blue
7 Virgins Purple
8 go Grey
9 Willingly White
;D ;D
That's how I was taught to remember them as well.
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thanks all...
i've got the resistor "layout" in terms of color and number...but have not quite made it "click" for me.
the cable is unbalanced, stereo.
looks like its coming from a VMS box (BNC, 75ohm coax...but its an analog cable) > stereo mini
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If you can find out what level of attenuation the cable provided before, that would be helpful. Also, I can't tell from your write-up if this is a balanced/XLR attenuator cable or an unbalanced and perhaps stereo unbalanced (eg, 1/8" mini TRS with attenuation on both channels).
Anyway, this website is pretty helpful:
http://www.uneeda-audio.com/pads/
For balanced, you'd probably want to use the U configuration, or for unbalanced the L configuration. Use 1% metal film resistors and buy extras beyond what you'd need just for this cable. Then hand-match the resistors using your multimeter to measure the actual resistance for each resistor. Very important to get the two balanced sides of a balanced cable matched as closely as possible. Also good to match the resistance across left to right channels, but that isn't quite as important.
If you had all the resistors from the cable, you could use your multimeter to measure them, but at this point, just decide what level of attenuation you want and use the info from the uneeda website to decide on resistor values. Just remember the formula for getting resistor values uses gain as "k", but this is measured as a ratio.
The formula for gain/attenuation in db is gain = 20 * log (V1/V2), or gain = 20 * log (ratio)
So if you want 20db of attenuation, you've got 20db = 20 * log (k), so K=10 (or I guess really for attenuation, -20 = 20 * log (1/k), with k again = 10). Similarly, 40db attenuation = 20 log (1/k), so k=100.
Once you determine what level of attenuation you want, you can figure out k, and then use the info from uneeda to determine resistor values.
In order to make an effective pad you also have to know the source impedance of the circuit its connecting too.
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oh?
the attenuator XLR types (male>female w/the circuitry inside) doesnt know what you're plugging them into....yet they still work.
I just want to cut the signal by 15 to 20db
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Anyway, this website is pretty helpful:
http://www.uneeda-audio.com/pads/
Sweet.
Thanks Todd. that makes sense to me ..., mostly.
I think I'll get it from here. If only I didn't loose those two little bastards!
then I could figure it out w/ease.
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oh?
the attenuator XLR types (male>female w/the circuitry inside) doesnt know what you're plugging them into....yet they still work.
I just want to cut the signal by 15 to 20db
Actually most attenuators that are "generic" are not designed properly and will not function exactly as they claim, because in order for a resistive pad to be effective one must know what the pad is being plugged into ( input impedance ) and what the pad is outputting to ( source impedance ) with out knowing these two things its impossible to make a pad that is accurate.
Chris
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I hear what your saying, and it was addressed on that link that Todd provided.
but a "ball park" is fine.
:)
-
0 Bad Black
1 Boys Brown
2 Rape Red
3 Our Orange
4 Young Yellow
5 Girls Green
6 But Blue
7 Violet Purple
8 Gives Grey
9 Willingly White
Resistance = [Color 1][Color 2] x 10 ^ [Color 3]
Example: Brown Black Red is 10 x 10 ^ 2 = 1000 ohms. Blue Grey Orange is 68k.
http://en.wikipedia.org/wiki/Electronic_color_code (http://en.wikipedia.org/wiki/Electronic_color_code)
I was taught In Catholic high school no less... ;)
0 Bad Black
1 Boys Brown
2 Rape Red
3 Our Orange
4 Young Yellow
5 Girls Green
6 But Blue
7 Virgins Purple
8 go Grey
9 Willingly White
Here's what I was taught when I took a few electronics courses.
0 Bad Black
1 Beer Brown
2 Rots Red
3 Our Orange
4 Young Yellow
5 Guts Green
6 But Blue
7 Vodka Purple
8 goes Grey
9 Well White