attenuating patch cord

attenuating patch cord

Post by Robert W. St. G. Fisher, I » Tue, 20 Jun 2000 04:00:00

Can anyone tell me how to make an attenuating patch cord?  I need to tie
my radio into a VOX tape recorder and right now I get a really bad hum.
It has been suggested that this may be due to overloading the mic input
on the recorder, hence the patch cord....

I know I can get one at RS, but if I can make one....

Thanks
Robert F

 
 
 

attenuating patch cord

Post by Who Did you Expec » Tue, 20 Jun 2000 04:00:00



Quote:

>Can anyone tell me how to make an attenuating patch cord?  I need to tie
>my radio into a VOX tape recorder and right now I get a really bad hum.
>It has been suggested that this may be due to overloading the mic input
>on the recorder, hence the patch cord....

>I know I can get one at RS, but if I can make one....

>Thanks
>Robert F

Since it is very hard to fit even 1/8 watt resistors in a 1/8"[3.5mm] jack,
might I suggest that you:
1]get a small metal box. Altoids mint boxes are great.
2]get 2 female 1/8" conectors,
3]get a 10k and a 1k resitor,
4]get another 1/8" to 1/8" patch cable{you can skip the jacks and just
cut your present patch cable in half, but if you do, in 5 minutes you will
need another patch cable for something, trust me I know!!}
Drill 2 holes in the Altoids box to hold the female connectors, even though
you should have a good ground via the connectors, run a wire from each shell
to a common point, scrape and solder to the case.
From the hot[center concuctor on the input connector]run the 10K resistor
to the hot on the out put connector., on the out put connector run a 1k
resistor from its hot to either the shell or the common ground.
You might consisder adding yet another female jack to allow a
speaker/earphones to be used at the same time. Wire the shell to the common
ground, and run a piece of wire from it's hot to the input jack "hot".
Be SURE to LABEL each jack.
For a step up, use the same general case and use a 5k resistor and a 5K pot
[volume control] for an attenuator that you can adjust.
For even more fun, use a transformer to isolate the grounds between the
radio and the recorder. Some groudn loops can only be broekne with this
trick. Get a RatShack[sm] 600:600 telephone matching transformer, wire as
above, ececpt make the output[to recorder] isolated from the case.
Connect one side of the primary to to junction of the 10K and 1K and
the other side of the primary to case ground/junction of the 1K and case.
Connect on side of the secondary to the output hot and the other to the
outpus shell. It really does not make any difference which winding you use
as primary or secondary. And yes there is one heck of a msimatch, but for
recording scanner, sw, non-HiFi, it will work great.
A better solution is to use 10K to 10K transformers, but they are much harder
to come by and the ratsahck[sm] telephone jobbers work great!
good luck and I hope this made sense.
I have given up on ascci diagrams. even I can not decypher what I am trying
to explain after a week or so.