Steve,
I've used a super simple approach for an outboard CW filter with older
Ten-Tecs: an 88mH telephone toroid in series with a 0.47uF+/- Mylar etc.
non-polarized cap, with a low-value pot or selected resistor across them.
Adjust the cap value to set the desired center frequency (or compensate for
component tolerances) and the pot/resistor to adjust the Q for your preferred
a balance of bandwidth and ringing. (Yes, the combination can ring a bit
without some resistance across it.) This circuit has the added benefit of
knocking the level down to "just about right" for low-Z headphones and is
surprisingly effective for as simple as it is. The values aren't critical:
I've seen 77mH pot cores mentioned as another option. Just choose a cap value
to resonate the circuit at your preferred pitch.
73, Al
On Fri April 29 2016 6:28:50 am Steve Ireland wrote:
> G’day
>
> I was interested to read the recent posts about the nice audio of a Ten Tec
> Corsair and how make it sound better. Barr N1EU’s clever replacement of
> the old hissy op amps in the Corsair is one way to go, but I recently found
> an even simpler of making a Corsair sound glorious if you are a CW
> operator.
>
> I recently acquired one of the passive audio filters that Ed Wetherhold
> W3NQN builds and sells, which is based on an Arithmetic Symmetry design by
> Jim Tonne W4ENE. Mine has a 3-dB bandwidth of around 190Hz and is designed
> for a centre frequency/pitch of around 490 Hz, as this suits my ears. The
> mono filter has an eight ohm input and output impedance, so you can run it
> out of the extension speaker socket of the Corsair and either use an 8-ohm
> speaker or a pair of 8-ohm headphones (such as the Kenwood HS-5).
>
> The mono passive audio filter totally kills the Corsair op amp hiss and
> pure-sounding CW signals just pop out of the band noise. I also use it on
> my Orion 2, using the mono extension speaker output, with the O2 filter
> bandwidth set to either 500 Hz or 200 Hz, depending on the level of band
> activity.
>
> I’d never used a passive audio filter until now – wish I had got one one
> years ago. No hum, no hiss, no artifacts, just fabulous sound. I love my
> Corsair even more now.
>
> Vy 73
>
> Steve, VK6VZ
>
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