Saturday, December 5, 2015

Junkbox eardrum saver

Volume control for my volume control

So my lovely 1977 Ten-Tec Century/21 transceiver has not-so-lovely CW sidetone.  The sidetone has a pronounced thump or pop on the first key-down of each letter. When listening through the external speaker it's not too noticeable but when wearing headphones it becomes really obnoxious and even painful during a long ragchew.

There is a variable resistor on the C21's audio board for the side-tone but it doesn't eliminate the pop, in fact it makes it more pronounced as the sidetone volume is reduced and it is least pronounced when the volume is increased but then the sidetone is really, really loud, especially when using headphones.

Besides that, the headphone AF output is quite hot anyway even at the lowest AF level with my comfy Sennheiser headphones so I figured I could benefit from an in-line volume control.  

I looked at ordering one but I've used in-line volume controls built-into headphones before and they always seem to go bad within a year so I scrounged around in my junkbox and found some variable resistors and volume pots.  I tested them and found one that goes from 10 ohm - 475 ohm so it seemed to fit the bill.  I fished around some more and found a 1970s era Switchcraft 1/4" phono plug and some more old lamp cord and I was in business.

I used the end cap from an old USB thumb drive to lend some mechanical strength to the attachment of the variable resistor to the cord.  Wallah, in-line volume control with a hip see-through enclosure.

Junkbox, in-line headphone volume control
It works great.  Now I can tone down the killer sidetone audio at the headphone jack from my old beauty and as a bonus, the old Switchcraft plug is a historical match for the C21. The variable resistor let's me tailor it to my ear fatigue.  I know this is a simple little 5 minute project but sometimes those are the ones that you appreciate the most.

Free in-line volume control
might buy me a couple of months of hearing in the future
That's all for now.

So lower your volume and raise your hearing longevity

Richard - N4PBQ

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