[Elecraft] K3 Audio Low Pass Filter

[Gregg W6IZT]

What are the values of the components for filter?

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Mike Scott
Sent: Saturday, July 04, 2009 1:21 PM
To: Elecraft at mailman.qth.net
Subject: Re: [Elecraft] K3 Audio Low Pass Filter

>G'day,
>What about - how did it perform?
>...does it in any way respond to the "pink" vs. "white" noise thread of a
few weeks ago.
>Mike VP8NO

Mike,
I am still evaluating but I believe the LP filter took the harshness out of
my audio. I had been one of people with a complaint about harsh audio and so
far I like it. I seem to have distortion products above the intended audio
passband that this filter cuts out. That extra stuff made it fatiguing for
me; other people don't hear it. I understand that some people can be
fatigued by odd order harmonic distortion even when the distortion is way
down.

I am not set up to compare with another radio and I can't do an A-B test as
the filter is hardwired in. I plan to live with this set up for a while and
maybe put in larger coupling caps to bring up the audio warmth. Perhaps I
will replace with 100 uF SMD devices like the current production caps.

The filter is a 4th order Chebyshev low pass filter with a -6dB shoulder
somewhere around 4.5 KHz judging by looking at a plot. It is flat below 3.2
KHz and low ripple, so, nothing to do with pink noise. Maybe Wayne will get
around to putting a pink noise filter into the DSP.

I am experimenting with the following Rx EQ settings from another post to
simulate a pink noise filter:
1 +0
2 +8
3 +2
4 -1
5 -1
6 -3
7 -5
8 -10



Mike Scott - AE6WA
Tarzana, CA (DM04 / near LA)
NAQCC 3535
K3-100 #508 / KX1  #1311





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