The Aleph-X

[GRollins]

Tempting, but no.
The output grounding resistors will see a lot of DC when the amp isn't tuned properly (watch your heat dissipation on the 30 ohm resistors...), and a 10VDC offset isn't going to provide a good ground reference. At that point the bias (which is depending on a solid frame of reference between the front & back) is going to go completely haywire and could easily destroy the output devices. Even once the DC has been tuned, it will drift a bit, again, not optimal for hooking the two together.
Note that I'm still running a bipolar supply. I reserve the right to fine-tune these ideas as I move back into the power supply region.

Grey

[HarryHaller]

So we are in agreement on one plus and minus supply for this amp?

H.H.

[GRollins]

Harry,
You posted as I was still writing.
As I start diddling with power supply things, I'll be going for regulated rails (that ML-2 fixation I've got)--just normal bipolar stuff at first. I like the idea of separate rails for the front end and back end, but will only try it if both are regulated. At least here, my rails are <i>far</i> too floppy (not yet regulated and not enough capacitance) to try to separate the two now.
If bipolar for the front and monopolar for the back doesn't work, I'll try bipolar front and back (both regulated), sharing a common ground. If that drifts too much (it'll be easy to see--the DC offset will serve as a nice indicator), I'll go back to the original plan with standard bipolar rails shared between front and back.

Grey

[Peter Daniel]

This is taken from "The return of Zen" article by Nelson Pass which appeared in AA 3/94:

"The most objectionable flaw I found was the noise, specifically about 5mV of hum at the output, which made it sound more like a tube single-ended amp. I easily cured this by cleaning up the supply, which I approached from two directions. First, I ran the amplifier from a regulated supply, which, I can report, takes care of the problem perfectly well.

Second, I made a pi filter in the existing supply using an additional 10kuF of supply capacitance an a 1 or 2mH air-coil separating them. This circuit in the power supply portion reduces the hum by about 26dB, making it generally inaudible.

I prefer the sound of the pi filter over the regulated supply, although I can't imagine why."

Which brings the question: Maybe regulated power supply isn't such a good idea after all?

[Brett]

<b>Maybe regulated power supply isn't such a good idea after all?</b>

In my experience, that depends on whether the active reg is a series or shunt. A series reg I've never found to do anything but mess up the sound, especially on dynamics. I've tried shunts a couple of times recently in tube gear, and found it to be a worthwhile improvement, with none of the negative sonic characterictics I've heard from series. Add in a Pi and it gets better yet. The PSU for my tube pre is CLCRC-shunt reg. A pair of shunts would be easy to apply to the front end of the Aleph-X, as that doesn't consume too much power, with a pi fpr the whole circuit?

I've been following this thread with interest, as this might be an SS amp I could live with. Just too overcommited with other projects for the moment, so living vicariously through others. I think I'll build mine p2p.

[sonnya]

Hi grollins why have you put R2,R3,R42 and R43 in series with the speakers? protection?

Only a suggestion.

If you put the feedback point behind those resistors you could get some improvement on driving capacitive load.
Those resistors together with a capacitive load will perform a phaseshift wich could make you amp unstable with extreme capacitive loads (10uF).

Have you tried?

[GRollins]

The two biggest factors I've found for sonic problems with regulation are:
1) People use a dinky little cap (sometimes none at all) after the regulator. The 'sound' of the regulator circuit dominates because most if not all of the current comes directly from the regulator. Generally speaking, a decent quality cap will sound better than even a high quality gain device, so let the cap apply its 'signature' to the juice, not the regulator.
2) AC behavior of regulators (like anything else) is imperfect. They just don't respond quickly enough to sudden demands for current--hence my recommendation for a decent amount of capacitance after the regulator. However, this circuit has a little trick working for it...the current draw sums to 0VDC when taken across either the front end differential or the output stage. When one side is going up, the other side is going down. At all times the draw will balance to a DC draw on the power supply, subject to small imbalances between the sides. (Another reason I suggested to match components across the amp back at the beginning of the thread.)
And if there's something a transistor can do well, it's DC...
This is one of the first things that attracted me to this circuit idea; the sound of the power supply--whether regulated or not--will be minimized.

Grey

[GRollins]

Sonny,
The resistors you refer to are the current sensing array for the Aleph current source. They're part of the deal. If you start rearranging the output, it won't be an Aleph any more. That's not to say that it wouldn't work, and I'm sure it would sound good...but it wouldn't be an Aleph-X. Perhaps it would be better to disable the Aleph portion of the circuit entirely (R2, 3, 11, 12, 33, 34, 42, 43, V1 & 3, and C1 & C6) and proceed with it as a direct-coupled Zen. Then you'd have a Zen-X. Might be worth trying as a variation.
Brett,
Sorry, forgot to catch you in the previous post. I see no reason why a shunt regulator wouldn't work. Jam loves 'em. Perhaps the two of you could get together and work one up. For the reasons I mentioned above, you could keep the waste heat down, since the load will be pretty near constant.

Grey

[sonnya]

Should i try run some sims on both the Aleph-X and a Zen-X. Like openloop gain, frequency response and so on? I can do this next week.

Then i sould upload some pictures with those datas. If ou are interrested?

Sonny

[Kilentra]

Hi everyone, I'm new here and I am considering this as an amplifier project. I was going to build this using budget components to drive my 4 ohm speakers with a modest amount of power (50W would be fine). I just have a few quick questions about the implementation I was considering.

I was going to use 15V rails and double up on the output transistors to accomodate my 4 ohm load. However, the largest transformer I could find with 12V secondaries was a 225VA Plitron. Does anyone know where I could find a transformer in the 300-400VA range with a 12V output? Or will it be acceptable to use the 225VA with quite large capacitance like 141,000uf and good filtering?

Per Grey's 'rule of thumb' calculations, using 15V rails, I'll bias each side with 2.34 amps and have source resistors of .213 ohms. This results in a dissipation of 140 W and 88W of output (a little much is fine with me, and I don't mind the 2 pairs of transistors for each side plus major heatsinking). But 140 W is dangerously close to the 160 W a 225VA transformer would put out. How close is too close?

Thanks to Grey and everyone else for creating and discussing this new circuit and so graciously answering questions. I am learning a lot from it.