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In Reply to: Driver Tube in Atma-Sphere MA1 MKII.2 posted by David M. on July 31, 2005 at 15:46:34:
What I intended to ask is if this is the only tube in the signal path...Thanks
Follow Ups:
No, the driver tube is NOT the only tube in the signal path. The tubes that comprise the dual-differential cascode circuit at the input of the amplifier are very much in the signal path, and in fact have a lot more to do with sonic qualities of the amp than does the driver tube. Four tube sections are required to construct the input topology, so two dual-section triodes are used, the 6SN7s. The input stage does all the voltage amplification; the driver stage does not supply additional gain. It converts the voltage output of the gain stage to a low-impedance current output to "drive" the output tube section. The dual-differential cascode is subserved by a constant current source (CCS), which greatly improves its performance, reduces distortion, etc. One might say that the CCS is "not in the signal path", but in my experience everything matters. The CCS is constructed using another 6SN7 in the MA1.
The output tubes are also in the signal path.
Thanks Jim - I guess the question was obviously a bit incomplete. Seems like I read that the only tube in the MA1 in the signal path other than the output tubes was the driver. Which position does the driver tube occupy? I am pretty sure it is the last one in line in front of the output tubes? Thanks...David
Sorry I did not respond to that part of your question. It's because I do not own an MA1. However, since the driver tube is the link between the input stage and all those output tubes (which of course are also in the signal path), I think it is a safe assumption that it would be mounted physically nearest to the output tubes. That's the way it's done on all other Atma-sphere amps in my experience. Does not the Owner's Manual help you to answer this question?
On an MA-1 Mk.II, the driver tube is closest to the edge of the chassis, on the same side as the power tubes. On an M-60 Mk.II.3, it is the tube furthest from the front of the amp.While this tube *is* in the signal path, it's generally known that it tends to have less effect on sonics than other tubes in the circuit. I have heard a report (from an MA-2 owner) that at least one version of Tung-Sol tubes do not work correctly in this location; that they make the amplifier sound 'broken'. While this is curious and questionable, I thought I would pass it along - so that others can draw their own conclusions.
The CCS tube (constant current source) sources current for the voltage amplifier. Again, it is not directly in the signal path, but the quality and stability of the tube do affect the nature of the DC power fed to the voltage amp. A lower-priority tube, but significant in its own way.
Thank you for the info...David
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