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In Reply to: Re: Input impedance posted by Jim Womble on March 26, 2007 at 06:35:47:
Just to reinforce Jim's point, I have an LL1676 configured 2:1+1 with 5K series resistors and a 100K variable shunt control. The noise added by the line stage is not audible over the residual amplifier hum and noise, which in itself is less than 2mVrms (noise bandwidth 10Hz to 50KHz) at the speaker terminals. The noise from a properly constructed differential tube preamp and 3 stage differential tube power amp, all with AC filaments can be readily made to be plenty good enough for use with speakers having sensitivities in the mid-90sdB. It's not a concern for speakers like the Ariel or ME2 at all.On the subject of 3 stage differential power amps, you don't need a 45 driver stage to have a wonderful sounding amp. There are a host of lower Rp tubes that can and have been used successfully. I have an affinity for the 6BX7GT and the 6BL7GT, both of which I have used in the Art Audio Vivo and in my own amp. Others have used triode-connected 6V6GTs, 6CK4s, the low Rp half of 6EM7s, etc. They are all viable choices.
Kevin Carter
K&K Audio
www.kandkaudio.com
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