Steve,
I hope you leave the pictures on the web site until I get around to
building it.
Jerry W5JH
"building something without experimenting is just solder practice"
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Steve Hunt
Sent: Friday, March 15, 2013 3:37 PM
To: Discussion of Ten-Tec Equipment
Subject: [TenTec] CorsairII sidetone modification
I finally decided I needed to do something about the "raspy" sidetone on my
CorsairII. Being a lazy guy I was looking for a simple and easy modification
that made a significant improvement with minimal alterations to the radio.
This is what I came up with - not sure if it's original?
Audio waveform before the modification:
http://www.karinya.net/g3txq/corsair_sidetone/before.jpg
Audio waveform after the modification:
http://www.karinya.net/g3txq/corsair_sidetone/after.jpg
I simply added two components to form a high-Q tuned circuit across the
Sidetone Level control. Here's the schematic:
http://www.karinya.net/g3txq/corsair_sidetone/schematic.png
Lmod and Cmod are the two new components - they resonate at 650Hz.
This was the implementation:
I took a small piece of PCB material and scored a gap along the centre - one
side for ground and one side for the connection to R96,R97,C65. I bent a
solder tag and soldered it to the ground side of the board:
http://www.karinya.net/g3txq/corsair_sidetone/board.jpg
I wound 122 turns of ecw on a high permeability toroid (I got tired at that
stage) and measured the inductance as 40mH. I calculated I would need 1.5uF
for resonance at 650Hz. Mounted the toroid on the board with a hot glue gun,
and soldered a 1uF and a 0.47uF capacitor in parallel:
http://www.karinya.net/g3txq/corsair_sidetone/circuit.jpg
Then mounted the board at the front of the IF/AF board using the existing
mounting screw between the AF Gain and Notch controls.
Connected a short lead (yellow lead in the photo) between the board and the
exposed end of R96; the board gets its ground through the mounting
screw:
http://www.karinya.net/g3txq/corsair_sidetone/installation.jpg
Adjustment simply consists of adjusting the sidetone pitch to place it at
the centre of the new filter - it peaks noticeably as you adjust it.
Result: much nicer sounding sidetone; minimal changes to the radio; Sidetone
Pitch and Level controls still work as normal.
If you decide to replicate the mod, be aware that the inductor needs to be
pretty high Q otherwise the output level drops considerably - I measured the
Q of mine as 330. Initially I tried one of the small Toko inductors, but its
Q was less than 10!
The inductance is not critical - I tried values of 20mH to 100mH when I was
experimenting - simply choose the matching capacitance value to resonate at
your preferred sidetone frequency.
Hope that may be of interest to some. In slower time I'll write it up as a
page on my web site.
73,
Steve G3TXQ
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