12dB attenuation cable

apa

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I was looking though the manual for an Elextrix Repeater and toward the
end it has a diagram for building a 12dB attenuation cable for plugging
it into a guitar amp. It's three resistors arranged like this:


tip-------------3.9k----------tip
| |
2.2k 2.2k
| |
sleeve------------------------sleeve


>From my math, this gives about -8.9dB, not -12dB.
My math's not very good though. Could someone just confirm that I'm
wrong so I can go back and look for my mistake(s)?

Thanks
 

apa

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Sorry about that. It's PI shaped. The 3.9k is in series tip to tip.
One 2.k to ground before it and one 2.2k to ground after it.

I ran it for 1M ohm and 10M ohm input impedance and got the same
answer, but I didn't figure in the output impedance. The output
impedance is 1K ohm. The way I was looking at it, the output impedance
didn't seem to matter as far as the amount of attenuation. Guess I need
to look again.

Jim Gregory wrote:
> Need to know source and load nominal impedances to work it out.
> Is the r/h 2k2 supposed to be to the right of the 3k9 resistor? In
OE6 it
> does not look right.
>
> "apa" <tacoma57@hotmail.com> wrote in message
> news:1112479535.082263.286180@g14g2000cwa.googlegroups.com...
> >I was looking though the manual for an Elextrix Repeater and toward
the
> > end it has a diagram for building a 12dB attenuation cable for
plugging
> > it into a guitar amp. It's three resistors arranged like this:
> >
> >
> > tip-------------3.9k----------tip
> > | |
> > 2.2k 2.2k
> > | |
> > sleeve------------------------sleeve
> >
> >
> >>From my math, this gives about -8.9dB, not -12dB.
> > My math's not very good though. Could someone just confirm that I'm
> > wrong so I can go back and look for my mistake(s)?
> >
> > Thanks
> >
 

apa

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It's supposed to be regular guitar amp, so I figured for 10M ohm and 1M
ohm - got the same answer each time in terms of attenuation.

The manual list the output impedance of the Repeater as 1K ohm.
 
G

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I don't know. I get the same answer. What's the input impedance of the
device it's padding, though? If it's a regular guitar amp, you'd think
the input impedance would be high enough to not matter. Or what if the
output impedance of the Elextrix Repeater is low enough to cause an
additional loss of 3.1 dB with this 8.9 dB attenuator? If my math is
correct, a 700 ohm output impedance would do the trick....very close to
your traditional 600 ohm output impedance for devices back in the day.

Cheers,
Trevor de Clercq

apa wrote:
> I was looking though the manual for an Elextrix Repeater and toward the
> end it has a diagram for building a 12dB attenuation cable for plugging
> it into a guitar amp. It's three resistors arranged like this:
>
>
> tip-------------3.9k----------tip
> | |
> 2.2k 2.2k
> | |
> sleeve------------------------sleeve
>
>
>>From my math, this gives about -8.9dB, not -12dB.
> My math's not very good though. Could someone just confirm that I'm
> wrong so I can go back and look for my mistake(s)?
>
> Thanks
>
 

apa

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Mike,
That clears things up.
Thanks, Andy

Mike Rivers wrote:
> In article <1112479535.082263.286180@g14g2000cwa.googlegroups.com>
tacoma57@hotmail.com writes:
>
> > I was looking though the manual for an Elextrix Repeater and toward
the
> > end it has a diagram for building a 12dB attenuation cable for
plugging
> > it into a guitar amp. It's three resistors arranged like this:
> >
> >
> > tip-------------3.9k----------tip
> > | |
> > 2.2k 2.2k
> > | |
> > sleeve------------------------sleeve
> >
> >
> > >From my math, this gives about -8.9dB, not -12dB.
>
> Your math is fine as far as the voltage divider between the 3.9K and
> the 2.2K resistor on the ouptut (right) side. The couple of megohms
> input impedance of the guitar amplifier in parallel with the 2.2K on
> the output won't make a measurable difference.
>
> There's another voltage divider that we don't know about, though, and
> that's the one formed by the source impedance of the Repeater and the
> 2.2K resistor on the input (left) side. If the intent is to drop the
> output of the Repeater by 12 dB, that divider would need to have an
> attenuation of about 3 dB. That would make the source impedance about
> 900 ohms, higher than I would have expected but not unreasonable,
> considering the application.
>
> Or maybe they just assumed the output impedance of the Repeater was
> 1K, used easily obtainable resistor values, and hoped that some
> smartass kid wouldn't try to check their math or even measure the
> actual attenuation.
>
>
>
> --
> I'm really Mike Rivers (mrivers@d-and-d.com)
> However, until the spam goes away or Hell freezes over,
> lots of IP addresses are blocked from this system. If
> you e-mail me and it bounces, use your secret decoder ring
> and reach me here: double-m-eleven-double-zero at yahoo
 
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In article <1112479535.082263.286180@g14g2000cwa.googlegroups.com> tacoma57@hotmail.com writes:

> I was looking though the manual for an Elextrix Repeater and toward the
> end it has a diagram for building a 12dB attenuation cable for plugging
> it into a guitar amp. It's three resistors arranged like this:
>
>
> tip-------------3.9k----------tip
> | |
> 2.2k 2.2k
> | |
> sleeve------------------------sleeve
>
>
> >From my math, this gives about -8.9dB, not -12dB.

Your math is fine as far as the voltage divider between the 3.9K and
the 2.2K resistor on the ouptut (right) side. The couple of megohms
input impedance of the guitar amplifier in parallel with the 2.2K on
the output won't make a measurable difference.

There's another voltage divider that we don't know about, though, and
that's the one formed by the source impedance of the Repeater and the
2.2K resistor on the input (left) side. If the intent is to drop the
output of the Repeater by 12 dB, that divider would need to have an
attenuation of about 3 dB. That would make the source impedance about
900 ohms, higher than I would have expected but not unreasonable,
considering the application.

Or maybe they just assumed the output impedance of the Repeater was
1K, used easily obtainable resistor values, and hoped that some
smartass kid wouldn't try to check their math or even measure the
actual attenuation.



--
I'm really Mike Rivers (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo
 
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Need to know source and load nominal impedances to work it out.
Is the r/h 2k2 supposed to be to the right of the 3k9 resistor? In OE6 it
does not look right.

"apa" <tacoma57@hotmail.com> wrote in message
news:1112479535.082263.286180@g14g2000cwa.googlegroups.com...
>I was looking though the manual for an Elextrix Repeater and toward the
> end it has a diagram for building a 12dB attenuation cable for plugging
> it into a guitar amp. It's three resistors arranged like this:
>
>
> tip-------------3.9k----------tip
> | |
> 2.2k 2.2k
> | |
> sleeve------------------------sleeve
>
>
>>From my math, this gives about -8.9dB, not -12dB.
> My math's not very good though. Could someone just confirm that I'm
> wrong so I can go back and look for my mistake(s)?
>
> Thanks
>
 

Tony

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It all depends on the source and load impedances. Coming from a 100k
plate load resistor it could well attenuate a LOT more than 12dB. IOW,
it's designed for a specific application.

On 2 Apr 2005 14:05:35 -0800, "apa" <tacoma57@hotmail.com> wrote:

>I was looking though the manual for an Elextrix Repeater and toward the
>end it has a diagram for building a 12dB attenuation cable for plugging
>it into a guitar amp. It's three resistors arranged like this:
>
>
>tip-------------3.9k----------tip
> | |
> 2.2k 2.2k
> | |
>sleeve------------------------sleeve
>
>
>>From my math, this gives about -8.9dB, not -12dB.
>My math's not very good though. Could someone just confirm that I'm
>wrong so I can go back and look for my mistake(s)?
>
>Thanks

Tony (remove the "_" to reply by email)
 
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"apa"
>
>
> tip-------------3.9k----------tip
> | |
> 2.2k 2.2k
> | |
> sleeve------------------------sleeve
>
>
>>From my math, this gives about -8.9dB, not -12dB.



** If you put the two 2.2 kohms in parallel at the output end, that creates
13 dB of attenuation with 5 kohms input impedance.




........... Phil
 
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In article <3b8to4F6g8mi6U1@individual.net> philallison@tpg.com.au writes:

> ** If you put the two 2.2 kohms in parallel at the output end, that creates
> 13 dB of attenuation with 5 kohms input impedance.

Yeah, and if you put ice cream under it, and chocolate sauce and
whipped cream on top, that creates a chocolate sundae. The schematic
doesn't show the two 2.2K resistors in parallel at the output end.

Reading is FUNdamental. Apparently so is making irrelevant
observations.

--
I'm really Mike Rivers (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo
 
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Mike Rivers wrote:

> The schematic doesn't show the two 2.2K resistors in parallel at the
> output end.
>

Correct. I think Phil is losing it. ;)
 
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"Joe Sensor" <crabcakes@emagic.net> wrote in message
news:3bagp5F6j0aaiU1@individual.net
> Mike Rivers wrote:
>
>> The schematic doesn't show the two 2.2K resistors in parallel at
the
>> output end.
>>
>
> Correct. I think Phil is losing it. ;)

*it* was lost by Phil, long ago. ;-)
 
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In article <3bagp5F6j0aaiU1@individual.net> crabcakes@emagic.net writes:

> > The schematic doesn't show the two 2.2K resistors in parallel at the
> > output end.

> Correct. I think Phil is losing it. ;)

No, he's just up to his usual trick of dismissing the stated facts
without considering that they could be correct, then changing the
question to one he can answer.

--
I'm really Mike Rivers (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo
 
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Mike Rivers wrote:

> No, he's just up to his usual trick of dismissing the stated facts
> without considering that they could be correct, then changing the
> question to one he can answer.


Wow! Sounds like Phil went to the same school as my wife. <eek>
 
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On 2 Apr 2005 15:32:20 -0800, "apa" <tacoma57@hotmail.com> wrote:

>It's supposed to be regular guitar amp, so I figured for 10M ohm and 1M
>ohm - got the same answer each time in terms of attenuation.
>
>The manual list the output impedance of the Repeater as 1K ohm.

Put that 1k between the left Tip connection and the left 2.2k, and
calculate the attentuation from that. Note that to get the
attentuation ratio at the left 2.2k, you have a 1k in series with the
parallel combination of 2.2k and 3.9k+2.2k. I suspect the result will
be very close to the claimed 12dB.

-----
http://mindspring.com/~benbradley
 
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"Mike Rivers"
>Phil Allison
>
>> ** If you put the two 2.2 kohms in parallel at the output end, that
>> creates
>> 13 dB of attenuation with 5 kohms input impedance.
>
> Yeah, and if you put ice cream under it, and chocolate sauce and
> whipped cream on top, that creates a chocolate sundae.

** Yum.


> The schematic
> doesn't show the two 2.2K resistors in parallel at the output end.


** The schematic posed by the OP makes no sense at all.


> Reading is FUNdamental.


** Taking everything you see utterly literally is *AUTISTIC* !!!


>Apparently so is making irrelevant observations.



** Nothing irrelevant about some lateral thinking that produces the right
answer.





............. Phil
 
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In article <3ba1j8F6dkaqvU1@individual.net> philallison@tpg.com.au writes:

> > The schematic
> > doesn't show the two 2.2K resistors in parallel at the output end.
>
>
> ** The schematic posed by the OP makes no sense at all.

Sure it does. Didn't you read my explanation?

> ** Taking everything you see utterly literally is *AUTISTIC* !!!

You mean like reading a schematic provided by the equipment
manufacturer is autistic? It's simple enough so that it's unlikely
that the original poster made an error copying it. And it has a
perfectly reasonable explanation.

> ** Nothing irrelevant about some lateral thinking that produces the right
> answer.

We call that "thinking inside the box."



--
I'm really Mike Rivers (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo
 

David

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In article <3ba1j8F6dkaqvU1@individual.net>, Phil Allison
<philallison@tpg.com.au> wrote:

> ** Taking everything you see utterly literally is *AUTISTIC* !!!



Naa. Autism is considerably more interesting than that.





David Correia
Celebration Sound
Warren, Rhode Island

CelebrationSound@aol.com
www.CelebrationSound.com
 
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