[TenTec] Binaural (Stereo) CW Redux!

[Jerry Volpe]

Here is a replay of the essential info I placed on this reflector or 
sent to individuals who asked for more information (If you don't find 
what you are thinking about here look a few weeks back in this 
reflector's archive):

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1. Last time I posted info on this project I got a number of emails 
indicating problems with the link I had provided to Harry's (SM0VPO) 
Project Site

Try here:

http://sm0vpo.8m.com/

And select his ' Projects' page. Then at the top of that page click on 
'Projects' and from the resultant menu bar across the top select 'Morse 
Code' and from the resultant left-side menu select 'Stereo CW.'

If you run into problems remember Google is your friend. Just do a 
Google Search on Harry's callsign SM0VPO and you will get there.

(I noticed that his ISP has a pop up going on so if you have trouble 
with site see if you are blocking pop ups.)


________

2. Text from my first message to reflector on Binaural CW:

I imagine many in the club have transceivers that have this 
functionality built in, but for those whose rig's don't and you like to 
operate CW then you might want to consider whipping together this little 
goodie. I completed mine earlier this evening and I am most seriously 
impressed.

The design is from Harry Lythall - SM0VPO
http://sm0vpo.8m.com/

... I love the floating sound of shortwave signals, however sometimes 
punching down  a whole lot of filtering to isolate a signal distorts the 
tone enough to be a rather unpleasant experience. The whole filtering 
down thing got me to thinking about a series of articles on Binaural CW 
in HR magazine many years ago. So after a bit of a Google search I came 
up with the notion that this was something to try. I didn't find too 
many actual circuits and only one very expensive add-on DSP unit 
providing a commercial alternative (and perhaps too much delay to make 
it practical for QSK)... I settled on Harry Lythall's circuit. Last 
night and this evening I put it together using basically Radio Shack 
Parts (well I had to dig a bit for the 39K resistors). The finished 
filter works great and I'm having a lot of fun listening to 'wide 
bandpass' cw.

BASIC CONCEPT:  Two OP amp filters, one low pass, the other high pass, 
split the incoming audio out to the headphone jack where esentially 
everything below 700-800 hz is heard in one earphone and everything 
above in the other. In practice you will hear the low frequency 'noise' 
in one earphone and the high frequency noise clearly in the other and 
the cw stations you are listening to more or less spread out across the 
inside of your head. This separation gives our brain more to deal with 
in identifying a particular sound which in turn makes it easy to 'hear' 
it. You actually don't really need or want to use the narrowist receiver 
filter settings when usining this Binaural external filter. You can of 
course, but it sounds far better and less constrained when you don't.

Of course you can take the output of the Binaural filter into a small 
stereo amplifier and then into two speakers one on either side of you 
and experience the spacial placements this way, but headphones are 
easier. Now, of course you have to have stereo headphones. I use Kenwood 
HS05 headphones which are normally Monaural, but I moved two wires and 
changed the plug and now they are stereo.

One last IMPORTANT point. In Harry Lythall's article he mentions that 
with some OP-AMPS his basic circuit may suffer from 'Crossover 
distortion problems. He suggests if this happens to place certain value 
resistors between the OP-AMP stage outputs to the +12 volt supply rail. 
As it turned out mine was horribly distorted. With a few tests I fixed 
the problem entirely by placing a 10k resistor from pins 1 to +12 volts, 
another 10k resistor from pin 7 to +12 volts, a 560 ohm resistor from 
pin 8 to +12 volts and another 560 ohm resistor from pin 14 to +12 
volts. I imagine you will have to do the same.

If you enjoy CW you should try this out.

___________

3. Parts list (mostly from Radio Shack):


1 ea    276-1650   Multipurpose PC board   $1.76
1 ea    276-1999   14-pin IC socket   $1.19
1 ea   276-1711   LM324 Quad Op Amp   $1.49
1 ea    272-1068   2 pk 0.047 uf PV-mount metal film capacitor   $1.29
1 ea    272-1066   2 pk 0.022 uf PV-mount metal film capacitor   $1.29
2 ea   272-135   2 pk 0.1 pf ceramic disk capacitor   $1.29
1 ea   272-1030   470 uf radial-lead electrolytic capacitor   $1.29
1 ea    272-1025   10 uf radial-lead electrolytic capacitor   $.99
2 ea   271-1347   5 pk 100k 1/4 watt resistor   $.99
1 ea   271-1335   5 pk 10k 1/4 watt resistor   $.99
1 ea   271-1321   5 pk 1k 1/4 watt resistor   $.99 (for power on LED)
3 ea                     39k 1/4 watt resistor (only in bulk at Radio Shack
1 ea                     LED with holder (many to choose from) about $2
1 ea                     SPST swithc (many to choose from) about $3
1ea   274-252   1/4 inch stereo panel-mount jack   $2.99

I will leave how you get audio and power in connections to your 
imagination. The box might best be aluminum in a high rf environment but 
I used plastic with no problems noticed in my environment.

______________

OK, there it is.... Binaural CW Redux! If it is useful in notion give it 
a try.

73,
Jerry, KG6TT
Albany, CA