[Elecraft] Yamaha CM500

[Joe Subich, W4TV]

>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.

0.047 uF was common for "mild presence" in high impedance (50 K)
mic circuits with tube radios.  0.001 uF was the "contester/DXer"
trick - similar to the Heil HC 4 element today.

The legacy of selecting capacitors to shape microphone response can
still be seen in the response switches in Yaesu microphones like
the Yaesu MH-1, MH-31 and MD-1.  The series capacitor values are
typically 10 times greater than those used with "high impedance"
mics ... e.g. 1 to 5 uF = "flat", .33 to .47 uF for modest boost
("HC-5") and .1 uF for "DX" ("HC-4") but they perform the same
function.

The series capacitor is particularly useful to counteract the
proximity effect (base boost) when a mic is used close to the
mouth.

73,

    ... Joe, W4TV


On 11/20/2010 1:30 PM, Ron D'Eau Claire wrote:
> 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
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