CFA Topology Audio Amplifiers

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#5,041
ostripper said:
Oh , you like it simple. I didn't "kill anything" ??

I like it a' drippin' with parts ... 😀

Build the VSSA 😀 ...

check out below , 14 devices.

Let me explain ....

Q5/6 and 1/2's Vbe cancel each other. This happens pretty well
on the "simple version", but with the Q13/14 "new cascode"
All these devices can be the same (ksa1015/c1815).

Use ksa992/c1845 for both the "new cascode" and the CCS's
these will also cancel. Hawksford has almost 0 co-efficient.
All is set for polar to tropics 🙂 .

PS - just 4 .37c$ mouser devices... why the drama ?
I know this will work ... because it already does (in the real world)...

Edit - your image didn't post.

That one , based on the VSSA .... has really lame LF performance. ASK NAF
he says ... " built VSSA , bass is lacking ... NAD-S has the best bass by far".
VSSA 20hz thd is 100's of PPM. And the offset floats all around at LF , as well.

OS
Click to expand...

Quite ridiculous comparison, takeaway pre/drivers from NAD and bass will lack the same way. Do compare apples and then make assumptions. :yes:
 
#5,043
Lazy Cat ...

I'm just going on simulated performance.
Those who built are most likely comparing these circuits to OEM's
or Ebay kits.

ALL of this borders on the subjective. Your response borders on
the economics , I suspect.

I did not start this ... all you CFA "guys" subjectively discredit
good VFA designs saying a CFA sounds more "musical". 😡

OS
 
#5,045
Bob Cordell said:
I get very annoyed by Doug renaming terms to his own use. His ditching TMC in favor of his own term, just because someone else (Edmond) came up with it is a good example.
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Mr. Cordell, one may argue that your habit of conveniently missing citations (and the TMC origins are a good example), snubbing alternative views (because you mentioned it, again TMC is a good example), and choosing width over depth in discussing audio power amplifiers, are also rather annoying.

Both books are valuable resources. IMO, yours is more of a compendium (when I quickly need a reminder, I know it's in there), while Mr. Self's is a book that is worth studying in depth. Your book is targeted more towards the enthusiastic DIYer, Mr. Self's book was originally targeted more towards the professionals.

One thing that annoys me in Mr. Self's book is carrying over, edition over edition, a number of errors and, subjectively on purpose, missing or mishandling very important topics (for example mosfet OPSs, CFAs, etc...).

You both are masters of not consistently citing each other 😀.
 
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#5,046
ostripper said:
My VFA "leach" was only able to reach 200V/us by the careful addition
of lead compensation. Without it , a higher value Cdom was needed
to prevent ringing on SW tests. The "leach" also simulated at 4X the
GD , (as compared to the typical CFA).
That extra phase delay requires the lead comp. to retain adequate
margin at UG.
The CFA "bypasses" all this with its utter simplicity.

In the end , I did get the leach and NAD/NX to nearly match each
other's performance .... it "blurred" the basic CFA/VFA differences.
OS
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Which version Leach, the LTIM or the SUPERAMP (DOUBLE BARRELLED) V4.5. I built both of these amps for my system and would be very interested in your custom modifications or subsequent literature to reach the fugures you are posting. GRH
 
#5,047
grhughes said:
Which version Leach, the LTIM or the SUPERAMP (DOUBLE BARRELLED) V4.5. I built both of these amps for my system and would be very interested in your custom modifications or subsequent literature to reach the fugures you are posting. GRH
Click to expand...

I know this is OT (an evil VFA amp) ... but it does have many
CFA attributes. Its 55db open loop gain extends nearly to 20K (like a CFA) , hence
my symmetry comment.

http://www.diyaudio.com/forums/solid-state/248105-slewmaster-cfa-vs-vfa-rumble.html


Post #803 .. you can even build it.

I am now even "chasing" it (the leach) with CFA tech ... as it is # uno. 😀
Subjectively , most have preferred the CFA front ends. But , a good VFA
can "blur the gap" (post 878 in the above thread).
We are actually building/listening ... this thread is the "hatching ground". 😀

OS
 
#5,048
CFA-simplicity

Does under 0.05% at 20KHz/50V.
 

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#5,050
ostripper said:
I get yer' drift ...

Mirror the hawksford .. 🙂

This DID bring something to the "table". In fact , exactly what I wanted.

Lower LF and HF THD at 120V p-p/ 3R loads. That's what i'm optimizing
my IPS's for these days .... as that is what is wanted. 😀 (below 1)

I can't really find any fault with (below 2) ... who would hear 28ppm
at this "ungodly" power level ? All "hail the "NX" ... very robust
design/topology - scales real nice! (82V rails) 😱

PS - I'm going through all the OPAxxx CFA IC topologies - I want
a KV/us amp !! 😀😀

OS
Click to expand...

Now some one really did get it! 🙂

I have told it a couple of times, but no no it is to complex.

It is so simple, adds stable idle current (which D.self complained about In his book) and improve overall .
 
#5,051
A symmetrical vfa will also benefit from it.

Folded cascode will also need ccs and Then again it makes the VAS idle current stable.

Folded cascode is also a true single stage gainstage like cfa In its simple form.

Regarding current on demand.... The leach is nonlinear compared to the cfa. If i remember right the leach design needs to overcome a certain level before delivering more current than a Classic LTP stage.
 
#5,053
ostripper said:
What should we describe it as ?
Doug wrote the book first .. I found one 8 years ago.
OS
Click to expand...

Good point. Its always nice to have a simple name for a topology. I seem to recall it being called a "Lin" circuit back in the 70's, but I'm not sure that is accurate. One of its progenitors was the HK citation 12. That had no degeneration in the LTP, no current mirror, I think a real current source VAS load (others of the time used a capacitor bootstrap for the load), and a quasi-comp output. That design quickly evolved to use complementary EF in the output and emitter degeneration in the LTP and a current source VAS load. The usual good engineering had the 2 TR VAS and the current mirror load well before the end of the 70s. Most of these features were found in some of the op amps at the time, especially the current mirror load.

Cheers,
Bob
 
#5,056
Hi Bob,

Did you ever get a copy to look at - #42? Shows better modeling just for the CFA, also.

And, #44 is a good point .... another 'partial' or contributor on how CFA topology contributes to its low distortion and high speed and low noise.

THx-RNMarsh
 
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#5,057
Waly said:
Mr. Cordell, one may argue that your habit of conveniently missing citations (and the TMC origins are a good example), snubbing alternative views (because you mentioned it, again TMC is a good example), and choosing width over depth in discussing audio power amplifiers, are also rather annoying.

Both books are valuable resources. IMO, yours is more of a compendium (when I quickly need a reminder, I know it's in there), while Mr. Self's is a book that is worth studying in depth. Your book is targeted more towards the enthusiastic DIYer, Mr. Self's book was originally targeted more towards the professionals.

One thing that annoys me in Mr. Self's book is carrying over, edition over edition, a number of errors and, subjectively on purpose, missing or mishandling very important topics (for example mosfet OPSs, CFAs, etc...).

You both are masters of not consistently citing each other 😀.
Click to expand...

Brutal. I see that you are honest in your beliefs and feelings and opinions.... I share much of your descriptions above. I just wouldnt say it that way. However, you and others keep me on my toes. I thought about this obsuficating thing along with another who said I spoke in riddles. I am trying not to give direct answers as much as possible. But point to something of importance on the topic which is close to my heart. I, personally, dont do the details of design anymore..... just conceptual sketches, usually. Experts are for that. Experts in SIM or experts in analog, digital, DSP, SW, RF or what have you. As I have moved away from R&D, tech/EE and into projects managing people, I just point out direction and subjects/topics to the smart guys and to use my experience to get the job done thru their best efforts. Its up to the others to take it and use it or run or not. Its just a different approach.... which keeps me from spending too much time on the Internet and too many details that others know or can figure out or read/study about.


Thx-RNMarsh
 
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