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 ______________________________________________________________ ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
