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Sat, 02 May 2009 20:30:07 +0000
The first iteration of my AF amp. A basic Class A amp for some voltage gain feeding a Class AB power amplifier. I should not need a bunch of gain at AF, since I expect to get most of it in the IF. LTSpice predicted some crossover distortion, which my scope confirmed. However, the distortion was negligible when listened to. I suspect that I will do some refinements on the circuit, but it is at least in a working state for now. - Jason, NT7S 26 Nov 2006 Already made some changes. Increased C5 to improve low frequency response and added C7 to roll off higher frequencies. LTSpice shows a much nicer frequency response with these changes. Peak gain is almost 20 dB at CW frequencies. This amp isn`t going to win any awards for audio fidelity yet, but the audio from my IC-718 into it is starting to sound acceptable. - Jason, NT7S 26 Nov 2006 I was wrong about distortion. Listening to a 600 Hz tone sounded good on the previous version, but connecting my MP3 player to the amp showed me a whole new world of pain. In order to eliminate the distortion as much as reasonably possible, I made the R6-R7 leg of the amp much ``stiffer``. The additional current improved crossover distortion in the Class AB amp greatly. Now high fidelity music sounds reasonably OK, and HF radio sounds just great. Another added bonus was bump in the gain to about 27 dB. - Jason, NT7S 27 Nov 2006
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