Audio Attenuator

Why A Audio Attenuator:
If you are into ESSB audio, or your just using some type of outboard audio equipment you may need a attenuator so that you do not over drive the front end of your transceiver. This attenuator is used to set down the audio going into  your radio by about 23db. I could have bought one. I decide to build my. And beside I like the idea of building so of my own gear and having some of the parts in my junk box it all work out. I built two of these attenuator but each one was a little different. The first one I built was a little more involve with more parts. The two one I built was very simple and only require a few parts that you may fine in your parts box. I will start with the simpler one first. Both of these attenuator were design by W2IHY Julius. These audio attenuator seem to have two name's for them. One being a Ibox and the other Murf Box.

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Second Attenuator I Built:
Parts needed for this project.
Resistors R1 2.2k -  R2 10k - R3 820 ohm.
2 1/4 phone plug. Or you can use RCA plugs if you like.
1 Audio transformer Stancor TTPC-2 or TTPC-8 telephone coupling transformer from Allied Electronic
1 Plastic or metal enclosure box. I use a small plastic box from Radio Shack.
As you can see from the picture of Fig 1 there is not much to this unit at all. Very easy to build. Fig 2 is a picture of the
schematic. This was my first attempt using a program to draw this schematic.
Fig 1
R2 can be replace with a variable 10k or 100k resistor if you like. I used a fix resistor in mine and works great. All resistor are 1/4 watt.

This Is The First Audio Attenuator I Built:
This unit is a little more involved and has more components in it.
Credit for his circuit design is by Julius W2IHY

Parts List..

C4-C6 - .001 uf Mylar
C7 - 100 uf radial electrolytic
C8 - .1 uf monolithic ceramic capacitors
R1,R3.R4 - 1K ohm watt resistor
R2 - fixed resistor or variable potentiometer
RFC1,RFC2 - put a piece of wire in place of the RF choke
RFC3,RFC4 - 470 uh miniature r.f. Choke
T1 - 1:1 600 ohm Audio Transformer
Other Parts Used :
(1) 1/4 phone plug   (2) 8 pin mini din connectors. I built this one to accommodate two radios. (1) DPDT switch used to switch between the two radios. You can used what ever type of connector that will work best for you.

Click image to view the Finish Product...

Page Created May 19, 2009
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