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In Reply to: Thanks Jim ... posted by KIS on March 4, 2006 at 20:17:54:
Just think about this for a minute - I believe it is one of the keys to why the Cit II works so well...In an amp without very wideband open loop response, the gain drops at high frequencies. As well, OPTs without wide bandwidth further attentuate high frequencies.
What this means in an amp with NFB is that the amp literally runs out of feedback at high frequencies. There simply isn't enough voltage available to feed back. The lack of NFB at high frequencies (while there is still adequate NFB at lower frequencies) means there will be differences in how the amp performs across the frequency range.
The very extended bandwidth of the Citation's video pentode front end produces lots of gain up to very high frequencies (> 1 MHz). The OPTs have excellent high frequency response, essentially dead flat to multiple octaves above the audible range. This means there is plenty of voltage at the highest frequencies to ensure the feedback is effective across the entire audible range and beyond. Some amps simply run out of feedback at high frequencies, and lose the benefits of it while retaining the drawbacks. The ability of the Cit II to benefit from NFB essentially equally across the entire audio range (and at least a few octaves beyond) makes it a unique amp.
Also keep in mind that the Cit II OPTs have a resonant frequency of about 450KHz, well outside the audio range, and therefore it won't cause any disturbances.
Just FYI - A Cit II produces a beautiful square wave at 20 Hz - at power levels the 300B can't begin to approach. In fact, a healthy production Cit II is essentially dead flat from 18 to above 40KHz at 60 watts output! At 20 watts, it's flat from 12 to above 80Khz, and at normal listening levels (1 watt) it's flat from 2 to 150Khz.
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Follow Ups
- Re: Thanks Jim ... - Jim McShane 20:59:05 03/04/06 (1)
- I would add... - Tre' 23:30:49 03/04/06 (0)