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GreenAmp ++ modulated Class G output
GreenAmp ++ modulated Class G output
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Old 19th January 2019, 02:31 PM   #21
ostripper is offline ostripper  United States
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Quote:
Originally Posted by Veysel View Post
Hi os you must try parallel capacitor on r25 , 100nf..10uf
IPS or OPS ?
Wait till I re-lable the OPS ( R101 /C101 / Q101) , that is the finished "standard".
OS
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Old 19th January 2019, 02:39 PM   #22
ostripper is offline ostripper  United States
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Originally Posted by sajti View Post
So the class G solution comes form Crest CC1800 amplifier:
On the Crest -

2 schottky's in parallel for low rail ? Is this advantageous ?
But .... no R/C to mitigate the switching ?

OS
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Old 19th January 2019, 05:44 PM   #23
Veysel is online now Veysel  Turkey
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Quote:
Originally Posted by ostripper View Post
IPS or OPS ?
Wait till I re-lable the OPS ( R101 /C101 / Q101) , that is the finished "standard".
OS
Ips (68k)
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Old 19th January 2019, 05:58 PM   #24
padamiecki is offline padamiecki  Poland
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Originally Posted by ostripper View Post
I have simulated successfully , but more THD and "glitches" beyond 10k.
strange, I almost do not see hf harmonics... this is the first time in gnfb amp I can see hf harmonics are descending so quickly
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Old 19th January 2019, 07:19 PM   #25
sajti is online now sajti  Hungary
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Quote:
Originally Posted by ostripper View Post
On the Crest -

2 schottky's in parallel for low rail ? Is this advantageous ?
But .... no R/C to mitigate the switching ?

OS
The 6CWQ10FN is double diode in a single package. This is the reason of the paralelling.
I don't know the reason why the snubber is missing...

Sajti
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Old 19th January 2019, 07:30 PM   #26
ostripper is offline ostripper  United States
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Originally Posted by padamiecki View Post
strange, I almost do not see hf harmonics... this is the first time in gnfb amp I can see hf harmonics are descending so quickly

That was before I fixed a reversed driver in the OPS. Now (below).

14ppm with class G - 20K , near full power /4R.
Look again below , there are some H7+ , 2nd is dominant.





Veysel - .1u to 10u parallel with R25 .... no effect - explain ?


So close , should I even add error correction or non-switching
to the OPS ??



OS
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File Type: jpg greenamp V1.1.jpg (402.4 KB, 349 views)
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Old 19th January 2019, 07:45 PM   #27
ostripper is offline ostripper  United States
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Quote:
Originally Posted by sajti View Post
The 6CWQ10FN is double diode in a single package. This is the reason of the paralelling.
I don't know the reason why the snubber is missing...

Sajti
6CWQ10FN - https://www.vishay.com/docs/93318/6cwq10fn.pdf


Better specs than most Schottky rectifiers , D-pac will be easy for

my first prototype PCB.


OS
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Old 20th January 2019, 05:40 AM   #28
sajti is online now sajti  Hungary
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This is the highest quality class G amplifier I ever seen:

Click the image to open in full size.

With the famous MT200 Sanken output devices...

Sajti
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Old 20th January 2019, 06:38 PM   #29
ostripper is offline ostripper  United States
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But have they gone to the next level ?


- Very few schema's show snubbering / switching considerations.
- Even as they can "belt out" the efficient high power , they do it with
less than audiophile quality.
Edit - they try to compensate through careful selection of semi's , at best.

My plain class G (EF) and your simulation (CFP) , even as they do better than the

OEM ones I have made (simulated) .... still fall short.


I have (almost succeeded) in making the (class B) steps non-switching.
POS/NEG step semi's idle at 20-30ma. The class G steps switch
mid - waveform when the inner pair are already heavily conducting ,
much more evident then the inner pair at crossover. 4 extra bigger xover
like distortions for NFB to hopefully negate (which it can't) - fully.


Emotiva and other audiophile class G OEM's have secret IP class G - ooh!!
They even produce the step controllers as potted modules or leave
the steps blank in the official schematics - JERKS !


I am going to make my steps into beta enhanced voltage controlled current sources.
This will at least negate the extra 4 class G switch points.
I could go further and just make all 4 OP devices non-switching.
I think I have read enough to do both.


OS
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Last edited by ostripper; 20th January 2019 at 06:42 PM.
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Old 20th January 2019, 07:14 PM   #30
wg_ski is offline wg_ski  United States
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Two things you can do with class G that help with the commutation noise. First, take a page from optimizing class B in general - which is to keep the drivers conducting well on either side of crossover. In normal class B, this means biasing the drivers relatively high. You’re probably going to do this anyway. Do the same with the rail switches - never let them turn off even when they don’t supply current to the load. Have a minimum load of 20, 50 mA or whatever it takes hanging off their emitters. Then they do not turn on abruptly when switching from the low rail to the high - it just starts increasing the current through the upper transistors, and the collector voltage of your outputs begins to rise. The other suggestion is to use schottky rectifiers, not regular ultra fast. Yeah, they are leaky and limited as to what kind of supply voltages you can use, but they do eliminate reverse recovery spikes. This will minimize the snubbering you need. Even a few mA of leakage is nothing if you “waste” 20mA or so biasing the slaves for faster turn on.
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