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In the Forum: Analog Playback
In the Thread: 7788 tube mic pre design
Post Subject: Too much gainPosted by hagtech on: 1/17/2008
Maybe I was a little hard on these tubes. I have this habit of listening to noise floor at extra high gains. Maybe 20dB above loud. It is part of the design process for me. I like to hear all of the hiss, whine, buzz, hum, shimmer, and ping of everything going on. I tap on all parts of the chassis and tubes. This is much more effective than running measurements.
Anyway, I finally had the chance to listen to the tube. The hum was not so noticable at normal playback levels. And the tube microphonics were also much less than I had eluded to. I could still hear the 5kHz tuning fork between songs. However, then one channel went very bad. The sound was like a hair stuck under a stylus while playing LP. Huge distortions, most notably on the louder passages. Funny, it took me awhile to cath on, as the other channel was crystal clear, and the brain was trying to sort things out and run real time corrections. A quick swap of tubes from left to right and the problem went with it. So I have a very baaad tube. Sadly, the one with the 5kHz resonance is the good sounding one.
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