A week or so ago, KS4L asked for info on powering the CM500 from his K2. He tried the instructions I gave, but it didn't work. Bear in mind here that several variations of output stages are used for the FET impedance converter in electret mics, and not all mfrs wire them the same way to their plugs. For this reason, a single powering method doesn't work for all electret mics. We learned this two decades ago in the pro audio world when we started using lavalier (clip-on) mics with wireless mic transmitters, and every mfr of both mics and wireless systems published lots of info about how to hook their stuff up.
The CM500 works directly with the K3, so I looked at what the K3 does for power. It's 5.6K to the tip only. The K3 makes no connection to the ring. Randy tried that and it works fine. So -- revised advice. From the CM500 mic plug, wire the tip to the mic input, add a 5.6K resistor between +DC on the K2 mic jack and the mic input. The resistor value is not critical, 4.7K to 8.2K should work fine. There is very little current, so very small resistors are fine. The sleeve (common) of the plug goes to common at the mic jack. The same wiring should work with this mic for nearly all other ham rigs. I would expect the CM500 to work really well with the K2. One of the few shortcomings of the K2 is that since it was originally designed as a QRP CW rig, the support for SSB is not a strong point. One way this shows up is in relatively low audio gain and not enough LF rolloff. The CM500 helps this situation, first because it's a pretty "hot" mic (that is, higher than average output level) and because the low end is rolled off internally. There are several published mods to improve the gain of the SSB signal chain, some of which go all the way to the RF end of the chain. I took the simpler approach, modifying my K2s by changing a few resistors and capacitors in the mic stages to provide rolloff around 500 Hz and increase the gain by about 7dB. This allows the mic to hit the compressor harder (and the rolloff prevents low frequency sounds from hitting the compressor), making the audio more competitive. The CM500 should provide the same improvements but without the mods. 73, Jim Brown 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
