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Lateral CFA 120W - BSA
Lateral CFA 120W - BSA
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Old 6th June 2019, 08:41 AM   #1
dadod is offline dadod  Croatia
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Default Lateral CFA 120W - BSA

This is simplified version of my lateral mosfet amplifier here: 200W MOSFET CFA amp
I think that to make it more simple would degrade this amp sound. Original amp is quite simple and sounds wonderfully, and I just replaced input stage CCS with resistor. THD increased a bit but not significantly.
Attached schematic, layout, some simulated plots and the gerber files.

I called it BSA, "Beautifully Simple Amplifier" or maybe "Best Sounding Amplifier".

Have a nice bulding.
Damir
Attached Images
File Type: jpg 120W-LMOSFET-VAS-OITPC-simple-sch.jpg (293.3 KB, 941 views)
File Type: jpg 120W CFA lateral-simple-layout photo.jpg (470.0 KB, 931 views)
File Type: jpg 120W-LMOSFET-VAS-OITPC-simple-LG.jpg (301.2 KB, 842 views)
File Type: jpg 120W-LMOSFET-VAS-OITPC-simple-CLG.jpg (303.8 KB, 778 views)
File Type: jpg 120W-LMOSFET-VAS-OITPC-simple-FFT.jpg (181.8 KB, 825 views)
Attached Files
File Type: zip 120W-OITPC-LMOS-gerbers simple.zip (88.2 KB, 71 views)
File Type: txt BOM 120W CFA lateral simple.txt (1.6 KB, 61 views)
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Old 6th June 2019, 09:21 AM   #2
AKSA is offline AKSA  Australia
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Good move Damir, an excellent simplification!!
Your son would approve - Birmingham Small Arms, a weapon manufacturer in Britain, who until about 1975 also produced some very nice motorcycles. I had one, a BSA 650, in the early seventies. Appalling distortion, but wonderful sound........ kept burning its exhaust valves.

HD
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Old 6th June 2019, 09:26 AM   #3
dadod is offline dadod  Croatia
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Quote:
Originally Posted by AKSA View Post
Good move Damir, an excellent simplification!!
Your son would approve - Birmingham Small Arms, a weapon manufacturer in Britain, who until about 1975 also produced some very nice motorcycles. I had one, a BSA 650, in the early seventies. Appalling distortion, but wonderful sound........ kept burning its exhaust valves.

HD
Thanks Hugh.
My son still likes motorcycle, last one BMW, not sure what model. I am not very happy with this.
Best wishes,
Damir
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Old 6th June 2019, 02:27 PM   #4
dadod is offline dadod  Croatia
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This is FFT at 20kHz, and it shows second harmonic on the same level as FFT for 1kHz at the same output power. This is result of flat Loop Gain up to 20kHz.
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File Type: jpg 120W-LMOSFET-VAS-OITPC-simple-FFT20k.jpg (174.9 KB, 239 views)
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Old 6th June 2019, 02:56 PM   #5
nigelwright7557 is offline nigelwright7557  United Kingdom
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Quote:
Originally Posted by dadod View Post
This is FFT at 20kHz, and it shows second harmonic on the same level as FFT for 1kHz at the same output power. This is result of flat Loop Gain up to 20kHz.
Might be to do with bias current not being enough ?
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Old 6th June 2019, 03:20 PM   #6
dadod is offline dadod  Croatia
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Originally Posted by nigelwright7557 View Post
Might be to do with bias current not being enough ?
I don't get what you want to say? Bias current was set to 130mA per output pair.
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Old 6th June 2019, 04:29 PM   #7
nigelwright7557 is offline nigelwright7557  United Kingdom
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Quote:
Originally Posted by dadod View Post
This is FFT at 20kHz, and it shows second harmonic on the same level as FFT for 1kHz at the same output power. This is result of flat Loop Gain up to 20kHz.
Looks about 80db down to me, or am I missing something ?
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Old 6th June 2019, 11:08 PM   #8
AKSA is offline AKSA  Australia
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Nigel,
I make it 66dB + 28dB = 94dB down for H2.
I have to say that this is exceptional. I normally see around 70dB down at 20Khz for H2. Bravo, Damir!
HD
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Old 7th June 2019, 04:39 AM   #9
dadod is offline dadod  Croatia
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Quote:
Originally Posted by AKSA View Post
Nigel,
I make it 66dB + 28dB = 94dB down for H2.
I have to say that this is exceptional. I normally see around 70dB down at 20Khz for H2. Bravo, Damir!
HD
And what is important too, it follows decreasing harmonic pattern similar to 1kHz FFT.
Here is clipping behavior.
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File Type: jpg 120W-LMOSFET-VAS-OITPC-clipping.jpg (110.5 KB, 161 views)
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Old 7th June 2019, 09:35 AM   #10
johnego is offline johnego  Indonesia
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Originally Posted by dadod View Post
This is FFT at 20kHz, and it shows second harmonic on the same level as FFT for 1kHz at the same output power. This is result of flat Loop Gain up to 20kHz.
It's interesting how the loop gain is flat up to almost 20kHz (where my best CFA is only up to 1k). I looked at the cct to find out why it is so. I think it is from the extra 1 gain stage i don't have? But surprising to me is, my amp has better thd 1kHz AND 20kHz (at lower power, due to 36v supply), so I'm not quite sure if the 20kHz loop gain plays an important rule here?

Somebody mentioned that he is using compensation to tailor the harmonic spectrum of his amps. So i'm trying to figure out, what is the benefit of this extra complex compensation? Mine is stable with only one cap across Rfb. Your amp is more stable of course, but i predict that it is simply caused by the 47pf connected directly to the output.
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