Aleph current source vs mu stage?

As Nelson Pass wrote, there are different ways to skin a current source. I am trying to improve my understanding about the pros and cons of the different types of active current sources used in single ended amps, such as in the Alephs, the ACA, or the J2.

In particular, the Aleph current source arrangement and the mu stage seem to be conceptually very similar. As far as I understand, their main difference is how they sense the AC current that needs to be provided to the loudspeaker. The Aleph uses a current sense resistor inserted at the amp output, in series with the loudspeaker. The mu stage uses two resistors inserted in between the transistors of the gain stage and the current source (as described here: https://www.diyaudio.com/forums/pass-labs/33100-aleph-circuit-single-sepp-srpp-post2610429.html ).

What are the pros and cons of the Aleph vs the mu stage? Why would one choose one over the other when designing an amp?
 
..... Why would one choose one over the other when designing an amp?

mood , perhaps ?

:clown:

if lazy and without decent measuring apparatus , use LTSpice and compare ...

for me , these two are similar enough to not think too much , except about fact that mu follower is easier to tweak with (ratio of resistances up and bellow output node) to invoke planned THD spectra

on second thought .... it's pretty much the same for me - tweaking with resistances ratio vs. playing with value of one resistor for Aleph CCS modulation ........

in the end , it'll be mood

:rofl:
 
There is a fundamental difference between the two.

The driving signal to the Mu-Follower is proportional to the dynamic current of the driver MOSFET alone.
That for the Alpeh CS is proportional to the total output dynamic current.
i.e. the difference between that of the driver MOSFETs and that of the CS MOSFET.

You can draw your own conclusion which one you prefer.


Patrick
 
The driving signal to the Mu-Follower is proportional to the dynamic current of the driver MOSFET alone.
That for the Alpeh CS is proportional to the total output dynamic current.
i.e. the difference between that of the driver MOSFETs and that of the CS MOSFET.

Does that mean that the Aleph tends to amplify it's own errors? Or does it compensate its errors?
 
How is the mu follower simpler? Parts count? Figuring out parts values?

take in account that I'm Old Geezer ( pleonasm there ?)

Pa is older enough that I'm harrasing him for years to adopt me ...... ( but not old enough to be so naive and agree)

so , do not expect Geezers having completely logical** reasons for everything they do

it's simpler to his brain , that's enough

:devily:

**at least logical to youngsters
 

res07njc

Member
2005-05-11 3:05 pm
FL
Its worth mentioning that the two most prominent Mu's that NP has laying out there are ACA and J2. ACA because it was simple, and J2, because the Aleph CCS in standard form makes difficult for doing the Vgs bias of a Semisouth active part.

I don't think that really encompasses the purpose of the OP's posited question however. I think he's seeking intellectual merits of one vs. the other. And of course, as ZM says to me... it's a black box. But... then why do different black boxes exist? And under which circumstance is one dis-advantageous? If such a thing exists.... It may be that there is no disadvantage... and that could be represented faithfully as well for the purpose of teaching others.
 

res07njc

Member
2005-05-11 3:05 pm
FL
I got to thinking about this today.. as being terminally in the 'others' camp lol. Can only learn.

The teachers can wax the merits when they feel the desire, but in reality its an empirical endevor, without measurements, for those like me.

Here goes... many things pass current (as a source)... resistor, bulb, mosfet, jfet, etc. What separates simple builders such as myself from those who nuance and tune, is the ability to shape. Let's be honest, any monkey can cobble a series of parts together, figuratively speaking.

So what's to shape? H2 and H3 of course. And the relationship between the current source and the driver. The Aleph is somewhat elaborate by most standards... offers a trick or two, Zen part 2 as 6L6 offers. But within its complexity it offers the ability to play with a single low wattage resistor to adjust the gain of the CS. In reading Nelson's white papers you get the best elaboration of this. And it's not just H2/H3, its open loop gain vis-à-vis feedback and all that good stuff.

Conversely, the Mu follower CS, it's more simple by parts count. But the difference here is that these relationships of gain, H2/H3... they work with bigger parts. 3 watt resistors at the least. And it's fully adjustable too, and dependent of the parts being used. It's complexity is literally couched within that simplicity. A most generous person recently elucidated over this... Babelfish ᄅſ....or FW J2 on Steroids .... or Not your Father's J2! Nugets of mathematical goodness there. But even by his measure and more important.. his ear... he never fully captured J2, when compared to a real J2. (correct my if I'm wrong Generg or anyone, that was read on baby Diy's many moons ago).

So even when we can adjust to our hearts content, it might not be content. That's us diyers vs. the masters. They measure, have decades of gifted ability in motion.

Nelson has said here, if Mu'ing.... he always starts high and then softly parallels more resistance between the devices downward. By ear and experience I'm certain. We can do this too. Maybe.

or we can build that Aleph thingy and twiddle a 1/4watt resistor, listening all the while. Working toward all of this myself, in time. :)

And please correct me anywhere too.
 
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Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
Since this topic remains interesting, I will point out that the Aleph follower has
one single advantage, which is the simple adjustment of its gain without alteration of
the bias figure. You can easily put a little pot on the resistor going from the
output to the Base of the bias control transistor and play with the waveform
there. Not as easily done with conventional mu follower.
 

res07njc

Member
2005-05-11 3:05 pm
FL
Thank you Nelson, for filling in the elephant left out about the Mu. We can get around bias changes by doing an array of Rs but its adjustment is only as 'fine' as the array itself, which might not be very fine at all. It would adjust the relationship between driver and source, But, what ability does it have to shape H2/H3? Slightly or significantly?
 
Since this topic remains interesting, I will point out that the Aleph follower has
one single advantage, which is the simple adjustment of its gain without alteration of
the bias figure. You can easily put a little pot on the resistor going from the
output to the Base of the bias control transistor and play with the waveform
there. Not as easily done with conventional mu follower.
The circuit on the left is the "ordinary" mu follower circuit using an opto coupler. The mu follower circuit shown on the right allows for independent adjustment of the CCS current and the mu follower gain.
 

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