Which Pass amps scale?


2002-08-27 1:27 am
Im looking for an amp design that can be scaled to higher power output without changing gain and sensitivity characteristics. I need 6 channels in the 30-50 watt range and 2 in the 60-100 watt range. Does anybody know of Pass circuits that scale this way?
I have a ZenV4 underway so big brothers of this would be ideal.

Also any ideas on reducing the total heat output on something like this would be useful. Im not sure 1000+ watts of room heat will be much fun, may have to actively cool it and vent to the window.


Choose the alephs 3 for the 6 blocks,
and some Alephs 4 for the 2 left.

Gain and sensivity are mostly the
same,let's say 20 dB.Or 26 dB.
you can adjust gain by feedback

1000 W are quite a lot for heat to be
rejected in a single listening room.

I suggest you have a separate room
for amplifiers and drill walls to achieve
speaker connections and other wiring.
And seriously think about a proper
ventilation for "the engine's room".
Don't forget to restrict acces to this
particular area
:att'n: :hot: :hot:


2002-08-27 1:27 am
Apparently Nelson is considering posting an AB design. Does he have any AB designs already? Does anybody do boards based on the Adcom sponsored designs? I know some of the Alephs transition to AB but didnt think he had published any ABs.
A friend referred me to the elliot sound labs amps so I may start there if I go AB.
I do think the heat from the class A is too much at 1KW, not to mention a power draw like a floor sander.

I'm not sure whether the core question was ever answered clearly, so I'll take a whack at it.
All the Alephs (including the Volksamp versions) will scale quite nicely. The Aleph-X will also scale to any reasonable power.
What I'm not quite clear on is why you need to scale the circuit. There are already 30, 60, and 100W versions of the circuit readily available. Just build as many channels as you need.
People tend to get glassy-eyed when you talk about a few hundred watts of heat; as though the paint will melt off the walls or the carpet catch on fire. Ain't so. For perspective, go look at the wattage rating on a hair dryer--most of them are 1000 to 1500W. Ever tried to heat a room with one? Yes, it can be done, but it's hardly enough to turn a normal sized listening room into an oven. Class A amps do create more heat than AB or B amps, but they also sound better.
It's worth it.
Oh, and if you want to reduce the heat...drop back on the bias. Easy. Just make sure you've got enough to drive your intended load.


Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
moses said:
Fritz: All of the X amps operate AB Class once they pass a certain point in power.

Not necessarily. XSOZ for example or versions operating
with constant current sources will not operate AB no matter
how you load them or drive them.

With a push pull follower output stage, as with X600's and
so on, this is the case.

With an Aleph current source, you can run the stages into
shutoff, but they become nonlinear enough that we don't
spec that as valid operation.
Greenie Perspective...

"For perspective, go look at the wattage rating on a hair dryer--most of them are 1000 to 1500W. Ever tried to heat a room with one? Yes, it can be done, but it's hardly enough to turn a normal sized listening room into an oven. Class A amps do create more heat than AB or B amps, but they also sound better.
It's worth it."

Electricity here costs AUS13.94c per kWh - I do not leave 1000W (not even 40W) of lamps on if not needed.
These amounts add up, not to mention Greenhouse gases.


Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
I think it's a matter of what you are willing to pay for
entertainment. I won't take any criticism for a 200 watt
Class A amp from anybody who takes his 70,00 watt
car for a spin.

Particularly if he leaves it idling for several weeks to get
the acceleration character just right.



2002-08-27 1:27 am
I have a feeling that when my ZenV4 is done I will also say its worth it. The reason I want a scalable amp is because Im considering building the Linkwitz Orion Speaker. It uses four channels per stereo side and the active crossover circuitry requires matching gain and sensitivity. The bass channels would probably do well with more than 50 watts while the others could have 50 or less.
I realize 1000-1500w wont imediately cook me out of the room but my 1200 watt room heater definitely cooks me out of the bedroom in about 4 hours on a cold night. With 100 plus summers its something to consider. I guess it would probably take about 2500W to get that heat back out of the room. But Im thinking the amps might look nice in the unused fireplace and all the heat could go straight up the chimney.
My Chevy Suburban gets 9 MPG (for sale) at 65 MPH I think it takes about 20 HP to do this and thats about 15000 watts continuous by electric standards. So a one hour trip is 15 kilowatt hours and costs about 9 dollars in gas( I think thats about 10% thermal efficiency). The same 15 KWHs in the amp would cost about 2 dollars and would take me several days. Thats fairly cheap entertainment if I can stay comfortable in the room. Figure half of the year its doing what I want by heating the room and that doubles its efficiency!
Im very anxious to hear the class A and Id imagine at that point the decision will be based on pleasure as are most decisions in our not so green world.
I think if I bias down 3 of 4 pair I could keep it to 1KW total.
Here's how I see it.
Really good class A solid state is roughly equivalent to better-than-average class AB tube in sound quality. There are a few really oddball solid state circuits that manage--in spite of their maculate origins--to sound pretty close to tubes. The old Electrocompaniet 50W (solid state) comes to mind as an example. Damned fine sounding amp. No, I never heard the Krell KMA/KSA50s on a system that I was familiar with (only on Martin Logan CLSs...yuk...that upper midrange glare was something I couldn't bear), so no opinion there. The Aleph 2s I've got here (homebrew, not production units) manage the same feat, albeit without imaging quite as well as my ohmigod tube amps that I built a few years ago, and without <i>quite</i> the detail. That one's closer, though. (There's also an oddity in that the Aleph's image is offset about a foot behind my tube amps--I tossed this at Nelson and the consensus was that no one knows what goes on to make an image.)
I can't stand that Nelson's nipping at my heels on this. Changes are pending to the tube amps. Possibly a return to class A--something I tried for a while...loved...but wasn't willing to live with that little power (about 40W instead of 130W or so). But am I willing to buy new output transformers, etc. to build a bigger class A tube circuit? The jury is still out. Money don't grow on trees and it's been a rough year. We'll see what happens.
(An X tube amp? Sure...why not? My circuit's pretty much there anyway, even without knowing that I was getting "X-ness" at the time. Just one little change to tune it up a smidgen and incorporate a few things I've thought of in the interrim...)
Class A tube gear? Now that's something that solid state has yet to even approach. Can it be done?
He's about the only guy I know who can do it.

Yep. 6922/6DJ8 and 6SN7 versions already pretty much done. I'm going to get the solid state versions together before I do a writeup. That, in turn, will be after I get some other stuff done. There's only one of me and (unlike, say, Nelson) no employees to help.
I've got enough ideas floating around for quite a few writeups, but I'm afraid to mention anything more than I already have, since I don't have the resources to bring them to fruition quickly and people get frustrated. Witness the fuss over whether Nelson should publish El Pipe-o, The Claw, a crossover (I've already got a slow-motion thread on that topic that I should update), or a monster amp first. And he's got help. (Not to mention more resources to draw upon.) I'm in the semi-final stages of building a pair of 11' transmission lines, but don't have any immediate plans to write it up--there are plenty of TL designs out there and Nelson's should be out soon.