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Pizzicato, a 200W low distortion CFA amplifier
Pizzicato, a 200W low distortion CFA amplifier
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Old 1st September 2019, 10:14 PM   #391
tcpip is offline tcpip  India
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Quote:
Originally Posted by Mark Tillotson View Post
Indeed, but those are high on-resistances compared to low voltage MOSFETs. If you want to switch 10A without heatsinking you'd like 5 milliohms or so, 15A then 2 or 3 milliohms, all feasible at lower voltage.
Ya, if you want to stay below 10 mOhm, there are few choices. But then if we're talking about 10A continuous (or almost continuous), that's not a domestic amp, that's a sound reinforcement pro amp, right? And if 10A is just peaks, then we can get there with just PCB copper as heatsink, can't we?
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Old 8th September 2019, 09:56 AM   #392
Tournesol is offline Tournesol  Belgium
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... Of course, with the same printed board, changing some components values, it will always be possible to build a CFA amp with a more conventional OLG.(See attached)
As it is the opposite of the purpose of this project, I let the self-proclaimed gurus of this forum the task of demonstrating their mastery and proposing their optimized version in this direction.
Attached Images
File Type: gif olg2.gif (97.2 KB, 557 views)
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Old 8th September 2019, 12:17 PM   #393
voltwide is offline voltwide  Ireland
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Originally Posted by Tournesol View Post
I let the self-proclaimed gurus of this forum the task of demonstrating their mastery and proposing their optimized version in this direction.
Could you pls be a bit more specific and list the persons you want to attack?
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Old 8th September 2019, 03:57 PM   #394
tcpip is offline tcpip  India
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Originally Posted by Krisfr View Post
If you don't agree with something, move on and go start your own thread. At least that is my thought. But if you can help, please do it and don't say "I know how" but I want you to show me if YOU can.
Very well put. I know what you mean.

In another thread, I asked one of the posters to please explain one of his comments, and he responded with: "Search for the word "because" and then read that paragraph two or three times." I feel sorry for people who get their jollies from responding this way.
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Old 9th September 2019, 01:51 PM   #395
Mooly is offline Mooly  United Kingdom
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Pizzicato, a 200W low distortion CFA amplifier


New Kicad thread here:
KiCad Fusion360 Python for PCBs
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Old 10th September 2019, 12:09 PM   #396
Tournesol is offline Tournesol  Belgium
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Krisfr, may-be it should be a good idea add those two resistances and two caps to the input stage ? The purpose is to reduce the collector voltage (power dissipation) of the first emitter follower.

A good practice should be to set the R values to match the collector voltages to the ones of the collectors of second stage amplifier transistors, when it is set with the casode.

If the cascode do not provide obvious benefits on AC results, it helps to give more latitude (power margins) on input stages currents, hence more choices of input transistors.

BTW, I'm on the same learning tracks than you, trying to switch from LTSPICE to MICROCAP ;-)

PS: To voltwide: I wonder how you can know better than me what *i* think by inferring intentions that I do not had.

Anyway, your ad hominem post, not really friendly as most of your previous ones, was both out of topic and an invitation to violate the forum's rules, reason why i did not answered as I will not answer to any other of the same kind.


I wanted to try the Dadod OITPC compensation. The occasion to set a more traditional version of this amp for a CFA: IE extended flat OLG up to 10KHz.
Here the results.

For OITPC, as I had not found a clear explanation of how to make calculations, I did-it by trying and groping.

it uses, apart the compensation, exactly the same schematic, only some resistances and caps values changed.

Krisfr, you can use this schematic for the paths as it is populated with all the options. Distortion is without "Error correction" (Amp alone).
Attached Images
File Type: gif mod.gif (24.9 KB, 439 views)
File Type: gif Pizzicato-high-olg-bdw.gif (79.4 KB, 405 views)
File Type: gif Pizzicato-caf-hbw-loops.gif (208.8 KB, 393 views)
File Type: gif pizzicato-h_olg-hd.gif (103.7 KB, 375 views)
File Type: gif Pizzicato-caf-SR.gif (33.7 KB, 49 views)
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Old 17th September 2019, 12:47 AM   #397
Mark Johnson is offline Mark Johnson  United States
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Pizzicato, a 200W low distortion CFA amplifier
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Originally Posted by Tournesol View Post
The pack won. I unsubscribe and leave this place too badly attended.

Quote:
Originally Posted by Mark Johnson View Post
Is your decision irreversible?
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Old 18th September 2019, 07:21 PM   #398
Tournesol is offline Tournesol  Belgium
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The two versions comparison.
The V one, VFA like (blue), offer more gain at low frequencies (Less distortion up to iKhz, more damping factor ). The C version, traditional CFA like) a flat open loop gain up to 10 KHz, faster slew rate. The two versions will use the same printed board, sharing most of the components.

Just a little change of 8 resistances values and 3caps. I suggest them to be in through holes for an easier swap.

As previously said, the purpose is to can figure out what matters more and how each version will impact listening results. And if the 10dB distortion reduction provided by the optional error correction will modify-it. Simulated results promize both versions to be in the top league. I will publish soon the two sim files, after everything deeply verified.

Comparison of HD with error correction.
Mistake with the colors, I inverted the colors with the previous image.
I apologize.

The last version V (Vfa like)
10Khz, 100V P.P.:
Without error correction: Total Harmonic Distortion: 0.000695%(0.000697%)
With the error correction: Total Harmonic Distortion: 0.000323%(0.000305%)
See (attached) the loop gain curves of the two options, with and without EC.

Krisfr, you can use this one as definitive for your printed board in progress :-).
The schematic is not going to change any more. In red, the values that gonna be different between the two versions.
Attached Images
File Type: gif compar.gif (136.2 KB, 74 views)
File Type: gif comp-HD.gif (73.9 KB, 67 views)
File Type: gif compar-err-corr.gif (127.8 KB, 43 views)
File Type: gif Pizzicato-V.gif (110.3 KB, 101 views)
Attached Files
File Type: asc pizzicato-v.asc (42.6 KB, 10 views)
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Old 20th September 2019, 02:20 PM   #399
Tournesol is offline Tournesol  Belgium
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And, to conclude, the C version (CFA-like).
Pros: Flat OLG up to 10 KHz, very high slew rate.
Con: Increased distortion in low frequencies, little less damping factor.

That's all, folks.
Attached Images
File Type: gif Pizzicato-C compare HD.gif (79.2 KB, 99 views)
File Type: gif Pizzicato-C.gif (100.1 KB, 111 views)
File Type: gif Compar-errcor-C.gif (109.6 KB, 102 views)
Attached Files
File Type: asc pizzicato-c.asc (42.6 KB, 11 views)
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Old 20th September 2019, 07:58 PM   #400
arpagon is offline arpagon  Bulgaria
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So many RC frequency correction groups which actually just hamper schematic's performance.
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