[TenTec] Adding headset boom mic to headphones

[Frank]

Jim Brown wrote:

>On 10/28/2011 6:49 AM, W8KZW wrote:
>  
>
>>I recently elisted a computer-type headset for ham use.
>>    
>>
>
>I've had similar great results with some Plantronics miniature 
>headset/mics that I bought several years ago at the Milwaukee hamfest. 
>Made adapters to use them with all my rigs, which at that time included 
>an Omni V, k2, TS850, and IC746.  All of the mics worked fine and 
>sounded really good with all of the rigs.
>
>  
>
>>  They use an
>>electeret element, so you need to apply about 8 volts DC through a dropping
>>resistor (2,200 ohms or so, value isn't critical)to protect against the
>>short to ground that occurs upon insertion and removal of the plug.
>>    
>>
>
>That's NOT why you need the dropping resistor (but you DO need it) -- 
>the resistor prevents low impedance of the 8VDC power supply from 
>shorting out the audio.  I'd use a higher value, more like 4.7K.
>  
>

Apparently there is more than one reason for using a resistor in series 
with the power supply.

>  
>
>>  You
>>also need to keep the DC off the mic line to the rig with a capacitor
>>    
>>
>
>I've never seen the need for this.  Most rigs are designed to accept 
>electret mics that are biased in this manner.
>  
>
Yes, MOST rigs have DC isolation in the mic line.  That also implies 
that ALL rigs don't have isolation.  Why take a chance?

>  
>
>>  Very inexpensive and great results.
>>    
>>
>
>Yes.
>
>Bob Heil has done lots of advertising in the ham world and sells his 
>very cheaply mics for a lot of money.  They are no better than the Shure 
>mics designed for communications use, like the 444 (look for it used for 
>$25), or the mic in the Yamaha CM500 (about $45 new from many online 
>sources).  The CM500 is so good that it doesn't make sense to try to add 
>a boom mic to another good set of headphones. I have two pairs of 
>MDR7506s, both of which now sit on the shelf. All you need to do to use 
>a CM500 (or other good headset designed for use with computers) on your 
>Ten Tec rig is a simple connector adapter for the mic, and a 1/8-inch to 
>1/4-inch adapter for the phones.
>
>See the Solving Problems in the Shack chapter of 
>http://audiosystemsgroup.com/RFI-Ham.pdf  and also the appendix on audio 
>for details on how to hook up the mic, and sources for good connectors 
>from a good US online source.  The same info is in a power point of a 
>presentation I've done to a bunch of ham clubs.
>
>http://audiosystemsgroup.com/HamInterfacing.pdf
>  
>


I have to admit that spending serious money on an interface box is not 
just unecessary but also silly.  Almost as silly as directly connecting 
a computer to a radio.  While transformer isolation of audio inputs and 
outputs along with opto isolated PTT lines might seem like overkill, 
they do avoid possible problems caused by ground loops and electrical 
incompatibilities.