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In the Forum: Audio Discussions
In the Thread: Initial thoughts about new/old Lamm ML2s
Post Subject: How feedback is implementedPosted by Paul S on: 10/5/2007
Brad, I heard a KR years ago, only remember it was not the typical "no-feedback sound", which I think of as clear but flaccid and no push. I agree that "feedback" can eventually ruin bass, and more, as I mentioned earlier in connection with the original Music Reference RM9, where the least worked best. The ML2 PST and OPT are huge, heavy and silent. That's a lot of iron for an 18 watt amp, and like I said, I don't hear anything I have identified as saturation, not to say it does not happen as I abuse the amps. The bass I get from the ML2 is the best musical bass I have ever heard, as far as it goes with my system.
Yes, the second 6C33C for voltage regulation is interesting, and it appears that much thought went into the ML2's power supply. It is certainly much more powerful than other amps with its RMS rating. I have not experimented with the effects of this V regulation tube in mind, but changing them out ealry on had less effect than any tube I changed except the 5651A. I can't say, however, if this is merely because these tubes were still in relatively good shape when I replaced them as a matter of course. Following Romy's lead, I have just used old output tubes as voltage regulators. If the OPs keep drifting at their recent pace I will spring for some new tubes. Now that it's adjusted it still sounds great with the old tubes, BTW.
I am thinking now that the ML2's 6AK5 is somehow involved in tracking and correcting power supply (modulation) relative to the [input] signal, which would certainly be feedback to my way of thinking. Since the PS (rather than the signal) is what drives the speaker load, this would be one way to limit ultimate distortion, versus global feedback in the signal loop itself. I do not know whether the ML2 also uses signal path feedback, but my thinking is that what is being done works to good effect at the listener's seat. But then, I am just speculating design from sound; I have not even had the bottoms off the amps yet, as this is stuff is of secondary interest to me.
Thinking about KR and Lamm, I wonder if Lamm knew Kron? Both of these guys seem(ed) big on "proprietary" stuff.
Best regards,
Paul S
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