[Elecraft] Yamaha CM500

[Ron D'Eau Claire]

Common Ham and general communications transmitter designs with vacuum tubes
also used very small coupling capacitors between the speech (audio)
amplifier stages for the same reason. 0.047 uF such as Joe noted was common
but sometimes as little as 0.001 uF, depending upon the impedances involved
and the amount of roll-off wanted. 

They also frequently employed smaller cathode bypass capacitors than normal,
which further reduced bass response and introduced some negative feedback to
help stage linearity, but the greatest frequency shaping in the pre-digital
age came from the microphone.  

What was widely accepted as the "ideal" communications speech characteristic
had a smooth rounded peak at 3kHz. Below 3 KHz it rolled off to about 10 dB
down at 1 KHz and another 5 dB down at 200 Hz (with a steep drop below 200
Hz). Above 3 KHz it rolled of smoothly to 10 dB down at 5 KHz and continued
to drop to about 30 dB down at 10 KHz. 

Many high-end communications microphone companies tried very hard to match
that characteristic in their products since nothing but general frequency
shaping with capacitors was done in the rigs. Astatic was successful in
doing that with the venerable D-104, which is why it was popular among Hams
for many decades  - and still has a strong following.   

Ron AC7AC

-----Original Message-----

On 11/19/2010 6:23 PM, Luis V. Romero wrote:
> These Orions are really bassy. 

I understand.  Makes you appreciate the K3 even more -- no need for the 
W2IHY unit, or for external EQ.

Take a look at the simple circuit that Joe, W4TV,  posted yesterday. 
It's a very old broadcast engineering technique that we both remembered. 
I've used the series capacitor when I wanted to use other pro mics with 
ham rigs that lacked mic EQ, and it worked quite well.  You'll see that 
in the Ham Interfacing tutorial that I posted to my website several 
years ago. The cap is for LF rolloff, not DC blocking (which is not 
needed).  The only trick is finding the small cap needed to fit inside 
the connector.

73, Jim K9YC
______________________________________________________________