Howard, W1WF wrote: I was listening to 40 meters late last night (virtually no one there so I had some time to fool around with the rig) and noticed the level of audio hiss in the K2. With RF gain off completely and AF gain fully advanced, there is a fair amount of hiss. This is also noticeable at operating levels and is a distraction from listening to weak signals. (obviously the operating af gain is set much lower and the hiss is also less obvious. Since I usually use a very good set of in ear buds, I normally have the AF gain way down)
All audio amps will create hiss at some gain level because you are amplifying noise that is inherent in the components. But I'm wondering if anyone has tried to mod the K2 to create a quieter audio amp? This appears to be an areas where some improvement is possible and it would make the K2 more pleasurable to use and weak signals more easily heard. I seem to recall from way back that we used to mod Dynaco stereo preamps by replacing carbon resistors with low noise equivalents (usually wire wound at the time) replacing potentiometers with gang switched low noise resistors, etc. Some semiconductors and ICs also have low noise equivalents. ------------------------------ My K2 makes a fair bit of noise with the AF gain all the way up too. I never thought much about it because that's how all the receivers I've used functioned. I frequently do not use AGC. That's how I learned to tune in CW since, until the more modern exotic AGC systems used today were developed, the BFO in a receiver would trigger the AGC system. Hence, AGC was used only on AM signals. Operating a receiver in CW mode involved turning down the RF gain, then advancing the AF gain to the point where the background noise was just audible. The reason for that was, as you observed, any higher and the background noise would become objectionable on weak signals. The AF gain is kept below that point. Then the RF gain is advanced and used to control the level of signals. Operated that way, my K2 behaves like any other good CW receiver I've had. There's plenty of gain, even with the AF gain backed down so the internal noise isn't noticeable. The receiver is capable of rattling my phones with band noise on even the narrowest filter settings. Another reason for not running the K2 audio gain full up is that the K2's "RF GAIN" is not really an RF gain control. It adjusts the gain of the Intermediate Frequency (I.F.) amplifier instead. The K2's RF amplifier is either switched in or out fixed at full gain to raise or lower the RF gain, or an optional attenuator may be selected to reduce the RF gain below that of the K2 with the RF amplifier (Preamplifier) switched out. The range of level control of the K2's the so-called RF GAIN is rather limited, with significant signal leakage through even at minimum. That's typical for those integrated circuit amplifiers. Keeping the AF Gain below maximum helps keep the signal leakage at minimum RF Gain setting from being objectionable. Something else that's come up here often over the past several years is that there's apparently a fair bit of variation in the gain provided by the audio amplifier in the K2. That's sure to make the apparent background level higher in some K2's compared to others. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
