Single or dual differential?

[jcarr]

Hi Hugh:

>I stand corrected.<

No problem.

>I lean towards the single diff.<

You mean a single non-complementary input differential pair, with the second-stage being?

The terminology used in this thread has stayed arbitrary for so long that I would like to confirm where everyone stands and what everyone means.

For instance, I can state that I have previously used what I call a dual differential circuit in a commercial product, but I should clarify that this was _not_ a complementary differential circuit.

regards, jonathan carr

[AKSA]

Jonathon,

yes, precisely that, with ....a single ended voltage amplifier, some supplied from bootstrap, and some from a constant current source.

It is always tricky to use words to describe a topology. Different folks, different strokes.....

But nice pictures take longer to put on the forum, dammit......

Hugh

[jcarr]

Hi Hugh (again):

From your post:
http://www.diyaudio.com/forums/showt...958#post266958

>One valid, real-world approach is to have extremely fast devices and very short, non-inductive feedback and signal paths which minimize group delay and thus bring down overshoot and distortion to vanishingly low levels.<

I completely agree (some of my previous posts cover the same territory), but will add that the above should be accompanied by a low-pass input filter so that the circuit does not need to deal with HF signals that may possibly give it trouble.

IMHO, unless the designer is willing to implement the aforementioned attention to detail in the actual design (including the physical construction aspects), this thread discussion of what topology is best is a somewhat academic exercise.

regards, jonathan carr

[bocka]

Even though it LOOKS symmetrical, I think npn and pnp are not exact opposite in behavior. So if the behavior is not an exact opposite, would it be that the output like "have a shadow" or "blurry"?

Completely correct. A complementary design reduces even order distortion, not canceling it out. But again, the main mechanism of distortion is the output stage, if this stage produces even order distortion (and it will, because NPN and PNP are not completely complementary) we'll get overall even order distortion, regardless of a complementary input diff stage or not.

The complementary input stage has more sensitivity to the bias influence of VAS than a single LTP with a current source. A big disadvantage. To come out of this problem you need emitter degeneration of the VAS stage. On the other side a complementary design has lower distortion levels as john curl has pointed it out. So we've one advantage and one disadvantage and the freedom to design both topologies right...

BTW complementary designs have only slightly more components (about 10% or so) than asymmetrial designs.

[mcp]

This may help.

[hitsware]

>This may help.

Thanks ! I don't know if it's relevent or not, but something I've noticed is that A seems to have better recovery characteristics than C............. I.E. coming out of clipping there is not as much 'lag' or something (the little step off of the flat place going back down to the wave shape) .......... mike

[jcarr]

mcp:

Thanks for the figure. Most convenient.

A Japanese EE would call A "Single Differential", B "Dual Differential", and C "Complementary Differential". Don't know about elsewhere.

regards, jonathan carr

[Nelson Pass]

There's quite a few more, so I suggest you with stick with
pictures describing diff pairs after the first two.

[hitsware]

>A Japanese EE would call A "Single Differential", B "Dual Differential", and C "Complementary Differential". Don't know about elsewhere.

Makes sense. I tend to call A single and C dual, but your nomenclature is much more succint .......... mike

[PRR]

Yes, thanks, MCP.

If we actually keep talking about different diff-input stages, someone should probably paste that chart every few pages, so we all know what hook-up is being discussed.

jcarr> A Japanese EE would call A "Single Differential", B "Dual Differential", and C "Complementary Differential"...

MCP's image with Jcarr's "Japanese EE" terminology, tight layout:


I have a copy on my machine but the URL is ugly. Wrap the UBB URL tags around this tiny-URL: http://tinyurl.com/vuqt