symmetrical supply PLH amp

hi everyone..Nelson says that a PLH amp can be made output capacitorless..how can it be ? i dont wanna use an output or input coupling capacitor..please help..if it comes true the plh amp will sound one of the best amp..

best wishes
 

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Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
Such impatience...

The easiest way to DC couple the PLH is to turn it back into
the later versions of the JLH. This you can do with a P type
JFET or Mosfet on the input to do the level shifting and take
the feedback.

It becomes a different amplifier, however.

You can bridge two of these, operating them balanced, but that
only eliminates the output capacitor.

Other ways start getting complicated, and I don't really have
the time right now to work the issues out. Perhaps someone
else has a suggestion.

My other thought is that you are perhaps putting too much
emphasis on capacitors. They are not the only problems in
these circuits.
 
Historically, the split load phase splitter (Q1 in the PLH) was developed first as a tube circuit. Like most tube circuits, it was usually capacitor-coupled to the outputs, which were then transformer-coupled to the speaker.
In spite of capacitors and transformers, tube amps are still regarded by many as being superior to solid state. That's not the same thing as saying that capacitors and transformers are good for the sound. You can say either that tube stuff is so good that, even though it's not direct coupled, it still beats the competition, or you might simply come to the conclusion that caps aren't quite as evil as they're made out to be. Or both. Take your pick.
I've done tube circuits and solid state circuits. And I've done cap-coupled versions of both. Cap quality matters, as does the amount of current available to drive the signal through the cap. There are formulas for calculating how much current it takes to slew a signal of a particular frequency to a certain voltage through X amount of capacitance, but I generally give it more than the formula suggests.
The PLH, as Nelson published it, works. To get rid of the coupling caps is another matter. Given where I am at the moment in terms of audio philosophy, I'd probably go with Nelson's second suggestion--to bridge the amp. This time next year I might give a different answer, but these days I like bridged circuits, in part because they tend to make life easier for the power supply and a lot of what people complain about when they complain about amplifier sound quality is actually power supply sound quality.
If you bridge the circuit as it stands, you'll need a balanced input signal for the two halves.
You could cap-couple one phase splitter to two sets of outputs internally and do most anything you want with the output stages. Yes, it could be contrived so as to get rid of the output caps.
Incidentally, I know you're excited about the idea, but e-mailing me, then posting here, then posting again three hours later complaining because no one has answered you yet is poor manners. I've got three children to take care of during the day and I work at night. When I get home I like to try to get at least four or five hours sleep before I get up and do it all again. I try to respond to as many peoples' questions as possible, but I can't guarantee that I'll do it according to your schedule. It might have to be according to my schedule...which happens to be somewhat haphazard these days.

Grey

P.S.: While I'm on this topic...SRMcGee, if you're out there somewhere, I tried to answer your questions about the Aleph-X, but my e-mail bounced back. The short version of my answer is for you to read the 100W Aleph-X thread and the Aleph builders' thread. Between those two and the original thread, you should be able to build any size amp you want. There are other Aleph-X threads here that may or may not be of interest. Or you could always ask questions here--there are enough people who've built Aleph-Xs that you'll probably be able to get answers to most any question you care to ask.
Eventually.