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Old 29th November 2007, 04:16 PM   #301
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Quote:
Why not ask Nelson?
Well, partly because there are so many knowledgable people who post here, it is nice to hear everyones input rather than immediately direct all questions to Papa. And in part, because I thought if Papa does have some spiffed up current source, he might be saving it for the "20th Anniversary Edition" of the Aleph.

Nelson--is there some way to succinctly increase the Aleph current source linearity at high frequency and high output, without doing something like adding a P-channel follower?

JJ
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Old 29th November 2007, 04:40 PM   #302
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Quote:
Originally posted by jupiterjune


Well, partly because there are so many knowledgable people who post here, it is nice to hear everyones input rather than immediately direct all questions to Papa. And in part, because I thought if Papa does have some spiffed up current source, he might be saving it for the "20th Anniversary Edition" of the Aleph.

Nelson--is there some way to succinctly increase the Aleph current source linearity at high frequency and high output, without doing something like adding a P-channel follower?

JJ

that's easy - just place faster and better control element in Aleph CCS ;

now that's just one sole bjt.........

place darlington there , and give him enough juice to drive that hungry gate .........

and there is still issue ............ should that be better , for ears ...... ?
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Old 29th November 2007, 06:29 PM   #303
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I am widely renowned as having the IQ of an onion, so as a favor to this humble one of limited intellect, can someone explain from whence commeth this obsessive idea that the Aleph current source is in dire need of revision? Please use words of ten syllables or less and limit the reply to something less than 5000 words.
It's pretty much a given that circuits will increase in distortion as the frequency increases. This is not limited to the Aleph current source. I can't think of a reason why the Aleph current source deserves to be insulted in this manner (the poor thing came to me in tears an hour ago...used a whole box of tissues in the process of getting it calmed down).
The Alephs came out over ten years ago. I don't seem to recall a bunch of reviewers lambasting the amps for their distorted highs--but maybe I wasn't reading the right magazine. The schematics were made available to us DIY critters six or eight years ago, and although there's been quite a bit of talk about trying to improve them in one way or another since, I can't remember that any of it centered around high frequency distortion. Maybe I wasn't reading the right posts.
I think I missed something. Maybe just my brain. I asked my wife if she'd seen it. Her reply was that there were little bits and pieces of it scattered about the house; it wasn't all in one place. Figures.
Can the Aleph current source be improved? Sure. So can everything. Show me a perfect...or even improved...gain device and I'll show you an improved Aleph current source. In principle it can be done with any device--even tubes--so if anyone feels that bipolars or tubes or JFETs or whatever are more linear, then feel free to build one with other devices.
I once toyed with a variant on the Aleph current source. I don't remember the particulars, but I don't remember that it was an improvement, either. That's not to say that something can't be done, but I think it would be better if the problem was outlined a little more clearly. That might suggest a line of attack.

Grey
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Old 29th November 2007, 07:03 PM   #304
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Actually most of the fault is in the main gain transistor itself, not
in the current source. I have tried a lot of variations on the
current source, and as long as they have gain (50% being the
popular figure) you will get the distortion character that you
see in the stock version.

There is no requirement for gain in the current source, and as I
have pointed out, it works fine, but the amplifier will have more
distortion, enough to help swamp the high frequency distortion
and make it look more spectrally consistent.

The argument that the current source is not fast enough is
likely not correct - reports that the circuit sounds better with
no gain tend to validate the bandwidth of the current source,
since it is the same circuit with a resistor removed.

You will find that if you compare the distortion of the current
source with no gain against a high value / high voltage resistive
bias, you will find similar results.

If you like that sound, no problem by me, and if you can improve
the measurements of the original, have at it.

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Old 29th November 2007, 09:12 PM   #305
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hmm, much to consider is this....

JJ
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Old 29th November 2007, 10:22 PM   #306
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Quote:
Originally posted by GRollins
I am widely renowned as having the IQ of an onion, so as a favor to this humble one of limited intellect, can someone explain from whence commeth this obsessive idea that the Aleph current source is in dire need of revision?
Grey, give me a break "an onion"? "humble one"? "obsession"? "dire need"?
Quote:
Please use words of ten syllables or less and limit the reply to something less than 5000 words...
Grey
Well, I thought you would have said something about all the tolerances of componets and temperature stability. And you would go on to suggest both BJT and MOSFET have high gain in there necessary operating range, wich I suppoose you would have suggested was also in there most linear operating area. You might note something regarding capacitance, ft, etc. of the gain devices effecting bandwidth. I suppose you wouln't forget explaining a little about properly compensating this high freq creation? You might eve say a few words about possible "boutique" components being a good bang for the buck here or there
I beleive you yourself have said it is possible to enjoy the sound of resistive loading more than the CCS?
I believe jupiterjune needs a little help prying all this knowledge from people like you, Yes, you
You obviously know more than your telling
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Old 30th November 2007, 02:07 AM   #307
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Quote:
can someone explain from whence commeth this obsessive idea that the Aleph current source is in dire need of revision?
This theory comes from many posts in many threads discussing the funny asymmetrical distortion in the alephs at high output and high frequency. The current source seemed to be the usual suspect as the cause, but Nelson's reply suggests the current source may have been framed! I was definitely not ready to declare the current source guilty, just very curious as to the true nature and cause of the distortion. I have never seen anything that seemed to be a concrete explanation for the behavior. (possibly it is out there somewhere, and I just missed it!)
Papa's comments definitely shed some light on the nature and cause of the distortion.

Anyway, if I look at the Aleph in certain light from a certain angle, "the problem" seems to be the asymmetrical distortion seen in many DIY Alephs at high output and high frequency, and also the observation that the X-amps are a bit clearer in the top end compared to an Aleph. (I believe Chef mentioned this when comparing the sound of his Aleph-X to his latest masterpiece.) My personal theory was that the asymmetrical distortion was caused by a slight phase variation in the current source, compared to the gain device output.
Viewed from another angle, the asymmetrical distortion might simply be clipping, which is inherent to all amps. The upper frequency clarity issue might be in the front end, not the output stage, and it might be part of what makes the Aleph so sweet sounding. I just would like to know 'for sure'!


JJ
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Old 30th November 2007, 03:02 PM   #308
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The asymmetry you refer to is more likely explained by the fact that the Alephs don't like to be driven into class B. If you look at how the Aleph current source derives its signal, you'll see that it takes a sample of the output. In normal class B or class AB circuits when one side shuts off (i.e. when it leaves class A operation), the opposing side continues to conduct. In the Aleph circuit, when the bottom MOSFET--the gain device--leaves class A and shuts off, the Aleph current source is deprived of its signal--it can't continue on its own.
Slowing down or speeding up the Aleph current source will not alter this one simple principle--if there's no signal at the output, the current source gets lonely and shuts down, too. Given that it has a different topology, it will inevitably and necessarily shut down differently from the gain device and the distortion will necessarily be asymmetrical.
Boutique parts will not alter this. Nor is it related to parts tolerances or thermal properties. It is an inherent characteristic of the Aleph current source topology.
Using a resistor is always an option, but then you're back to a normal gain situation as opposed to the Aleph current source. The characteristics will then be determined entirely by the gain MOSFET on the bottom and will be (assuming that the circuit is properly designed) more symmetrical. Of course the circuit will be much less efficient and the damping factor will effectively cease to exist, but at least such a circuit would be easy enough to design.
It's not a question of 'prying knowledge' out of me--it's a question of trying to identify the problem. In this case, I suspect that there's actually nothing wrong at all; that the whole thing is s tempest in a teapot. It's just a question of pointing out the normal behavior of the Aleph current source. If it's a hard-running amp you want, I'm not sure I'd recommend an Aleph. Build something more along the lines of an X amp--biased class A if you wish. You'll find that it has much more predictable behavior when pushed hard.

Grey
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Old 30th November 2007, 03:17 PM   #309
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there is old rule - at least as I'm told by one old PA geek :

"if you want louder - use bigger amp
if you want even louder , use more bigger amps
if you still want more , use all amps and use horn speakers

if that's not enough , go **** yourself"

end of cite .


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Old 1st December 2007, 01:53 AM   #310
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Thank you Grey and Nelson--

As I read Grey's last post, I remembered the turning off of the current source was mentioned previously. I didn't understand the mechanism behind it, though. It is clear now, although this doesn't explain why it doesn't seem to happen at lower frequencies for the same output voltage.

But at least I can quit obsessing about it!

JJ
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