That's an interesting point. Some of those old amps could be adjusted for positive or negative DF, with an intermediate setting that yields theoretically infinite damping. Negative DF causes the amp to actively drive the woofer cone in the direction opposite to its current motion.I have seen some old tube amps that have adjustable feed back, or damping factor, one in particular is the old Fishers.
Current VTL amps like the current version of mine offer variable NFB.I have seen some old tube amps that have adjustable feed back, or damping factor, one in particular is the old Fishers.
Same with my 980BX, rated 1000. Really takes hold of my 2235H and makes them behave.My Rotel RB-990BX supposedly has a damping factor of 1000.
Easy now. Science has no place here!The only reason to strive for a high damping factor – which can, after all, do no harm – is the
usual numbers game of impressing potential customers with specification figures. It is as certain
as anything can be that the subjective difference between two amplifiers, one with a DF of 100 and
the other boasting 2000, is undetectable by human perception. Nonetheless, the specifications look
very different in the brochure, so means of maximizing the DF may be of some interest.
"Audio Power Amplifier Design Handbook, Fifth Edition, Douglas Self"
My Dad's old Bogen RR550 had adjustable damping factor. Don't recall where he set it, but I experimented with it when it was passed to me (50 years ago.
As I recall, lower damping factor resulted in more (although mushier) bass.
I think you mean to say that DF is measured at the amplifier output terminals, not at the speaker terminals, right?Once again, don't forget that DF is measured at the speaker terminals. Once you add a length of wire, the DF drops dramatically, like divided by 10 ! The thickest wire would be best for tube amps because of the low DF.
My Dad's old Bogen RR550 had adjustable damping factor. Don't recall where he set it, but I experimented with it when it was passed to me (50 years ago.
As I recall, lower damping factor resulted in more (although mushier) bass.
That's a great idea! And you are right, I meant the amp. speaker terminals.I think you mean to say that DF is measured at the amplifier output terminals, not at the speaker terminals, right?
An elegant solution to this problem would be to drive the speaker through one pair of wires while taking feedback to the amplifier through a separate pair attached to the same speaker terminals. Lab power supplies often provide the necessary four-terminal hookup to guarantee excellent voltage regulation at the load, regardless of cable losses. Every hi-fi amplifier I've seen takes feedback from its output terminals instead, which is the reason that DF can be cable-limited. If I live long enough, I'm going to design and build myself a tube amp with four-terminal load connections.
I think Kenwood did something similar in the early 80’s with their sigma drive. Then Onkyo with their super servo.I think you mean to say that DF is measured at the amplifier output terminals, not at the speaker terminals, right?
An elegant solution to this problem would be to drive the speaker through one pair of wires while taking feedback to the amplifier through a separate pair attached to the same speaker terminals. Lab power supplies often provide the necessary four-terminal hookup to guarantee excellent voltage regulation at the load, regardless of cable losses. Every hi-fi amplifier I've seen takes feedback from its output terminals instead, which is the reason that DF can be cable-limited. If I live long enough, I'm going to design and build myself a tube amp with four-terminal load connections.