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alidav

25 db cable attenuator scheme trs - trs

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I want to build a TRS TRS cable to wire a Tascam dr100 line out to a canon 5d MK III mic in.  can anyone suggest me a detailed scheme that helps?

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1 hour ago, alidav said:

I want to build a TRS TRS cable to wire a Tascam dr100 line out to a canon 5d MK III mic in.  can anyone suggest me a detailed scheme that helps?

 

Once you know the input and output impedances of your devices, use a calculator like http://www.nu9n.com/tpad-calculator.html to determine your resistor values. You'll need to build two T pads, one for each unbalanced channel.

 

You might be able to build the pads inside a 1/4" TRS connector, but it'd be a lot easier to use a small project box.

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Your call. For the hours it would take me to figure it out, build it, screw up, re-build it I’d rather just buy it and move on in life. I make most of my own cables but this kind of thing I usually buy off the shelf. 

 

But go for it if you have the time. 

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1 hour ago, Allen Rowand said:

 

Once you know the input and output impedances of your devices, use a calculator like http://www.nu9n.com/tpad-calculator.html to determine your resistor values. You'll need to build two T pads, one for each unbalanced channel.

 

You might be able to build the pads inside a 1/4" TRS connector, but it'd be a lot easier to use a small project box.

assuming that Tascam dr 100 line out is 200 ohm and the mic input on any reflex is 10 Kohm the result give resistors of 21 ohms 4952 ohm, quite hard to find. 
do I make something wrong? I have to wire a Tascam stereo line out into the canon 5d stereo mic input.

on the specs of tascam line out is 200 ohm, but cannot find any info about mic in

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1 hour ago, alidav said:

 

assuming that Tascam dr 100 line out is 200 ohm and the mic input on any reflex is 10 Kohm the result give resistors of 21 ohms 4952 ohm, quite hard to find. 
do I make something wrong? I have to wire a Tascam stereo line out into the canon 5d stereo mic input.

on the specs of tascam line out is 200 ohm, but cannot find any info about mic in

 

You're looking at the H pad values, you need a T pad. If your impedances are correct, the resistor values are:
(R1) 9904 Ohms
(R3) 42 Ohms
(R2) 160 Ohms

 

If I had to build this pad out of what I have in the garage, I'd use:

(R1) 10k ohms

(R3) 47 ohms

(R2) 100 ohms + 47 ohms.

 

If the pad wasn't enough I'd add another 20 ohms to R2.

 

But yeah, I'd probably just buy the Sescom cable. Even if I had all the parts on-hand to build the pad, the value of my time is more than the cost of that cable.

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15 hours ago, Allen Rowand said:

 

You're looking at the H pad values, you need a T pad. If your impedances are correct, the resistor values are:
(R1) 9904 Ohms
(R3) 42 Ohms
(R2) 160 Ohms

 

If I had to build this pad out of what I have in the garage, I'd use:

(R1) 10k ohms

(R3) 47 ohms

(R2) 100 ohms + 47 ohms.

 

If the pad wasn't enough I'd add another 20 ohms to R2.

 

But yeah, I'd probably just buy the Sescom cable. Even if I had all the parts on-hand to build the pad, the value of my time is more than the cost of that cable.

 Ditto to what Allen said. You can be fairly loose with the component values. Even if it changes the impedance slightly, you’ll still be fine. You can build these in TA3 connectors with 1/8 W resistors. They’re quite small. But you need to have good eyes, and a steady hand. 

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Based on the specs, this is likely how the Sescom pad is wired (or very close to it):

 

 

              5 K. ohms
IN >——-\/\/\/\/\/\/\——|—————> OUT
                                      |  
                                      |
                                      |
                                      /
                                      \
                                      /   100 ohms
                                      \
                                      /
                                     |
                                     |
                                 __|__

 

 

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This L pad as recommended by John, has about 34 dB of attenuation. The previously recommended H pads and T pads require an additional resistor and are only necessary if you are trying to match input AND output impedances. Generally this is not necessary when going from a lower impedance output (most audio outs) to a high impedance input (most inputs). The L pad is easier to build as it only requires two resistors and is just as effective and much easier to build in a connector.

Best Regards,

Larry Fisher

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21 minutes ago, LarryF said:

This L pad as recommended by John, has about 34 dB of attenuation. The previously recommended H pads and T pads require an additional resistor and are only necessary if you are trying to match input AND output impedances. Generally this is not necessary when going from a lower impedance output (most audio outs) to a high impedance input (most inputs). The L pad is easier to build as it only requires two resistors and is just as effective and much easier to build in a connector.

Best Regards,

Larry Fisher

being an unbalanced stereo cable,  line to the mic input, I have to build 2 of them obviously 

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FWIW,

 When I recommended the H-pad in another thread on this subject, I assumed the context was a balanced line out to a balanced mic in. I did not recognize that the use of the term "reflex" as referring to a digital single lens reflex camera and I hadn't guessed that the recorder had unbalanced outputs.

 

 A pair of L-pads does seem like the better choice in the intended scenario.

 

 

 

 

 

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I need a solution to attenuate the signal from a recorder to feed a DSLR, no matter if a box with 2 trs females or a cable, a box maybe is more easy to build for me. anyway this UK guy makes this nice tool very convenient. https://www.ebay.it/itm/ATT40-STEREO-AUDIO-ATTENUATOR-40dB-REDUCE-LINE-LEVEL-TO-MICROPHONE-LEVEL/112899580191?hash=item1a4956e11f:g:THUAAOSwE0JY-nza

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I built an xlr cable with a pad in the xlr to take line level feeds from a console into a trx742 (mic level only).  Probably took me half an hour total.  It's a handy tool to have in the kit, especially since I personally dislike barrel adapters.

If this is something you will use a lot, building it into a cable is an elegant and very doable solution.

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For this particular case i think i would buy the cable, it seems more handy that handling all the extra boxes and stuff, but if you enjoy doing this projects go for it is very simple to build and it would cost you a third of the price.

Have you decided yet?

 

 

 

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