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In Reply to: RE: "Low frequency ringing"... posted by Steve O on March 18, 2015 at 11:18:21
He said in Valve Amplifiers that it was a waste of power to have the amp slowly oscillating at 0.5Hz or so and firmed up the power supply to remove it. He said that most amps that he measured did oscillate at very low freq. It was a surprise to me.
Follow Ups:
While regulation is desirable, it's not practical in vintage designs. In new/DIY designs, regulation may be possible but it adds expense and size, esp at higher power levels. Real world implementation of regulation typically involves solid state devices that in my experience are not as reliable as the tube circuits they supply....kinda brute force too. I prefer circuit/component solutions if possible. As always YMMV.
I threw it out there because I do not regulate B+ at all times and was wondering what happened when you do. I have only regulated B+ on drivers not power tubes.
It's not all that practical in new designs either, unless you stay all class A, which sort of defeats the need in the first place.
The demands placed on such a regulator in a class ab amp are pretty nuts, but at the same time, a choke input filter will get you close.
Hello,
Can you elaborate on this?
My undertsanding might be wrong, but I always thought a class A amp was where there was the greatest benefits to have a regulated B+.
Since in class A the PS is in the signal loop, the lower Z it has, the better. Of course, as Steve posted below, the regulator's error amp is an other amp that follows the supplied stage's signal demand.
Thakns,
Joris
In a class A amp, provided the output transformer has sufficient inductance, you aren't going to see huge deviations in power supply demand.
If you have an AB push-pull amp, when you leave class A and move towards class B, the current draw from the power supply changes drastically. (Regulation helps here)
This isn't to say that a fully regulated class A amp is a bad thing, it's actually easier to do and will sound different, but it's not solving the obvious issue that class AB amps have.
I think a good case could be made that an active regulator is a feedback amp that has to operate down to DC with great stability compared to an audio amp that only has to run down to 10Hz or so. Regulating an amp's supply is sorta like cascading two amp systems.
that and I have yet to need more than 3 stages, including the linestage. usual practice is two stages, plus a linestage. just no need for even a 5-20 style 3-stage.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
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