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One of the Top Solid-State CFA amp design
One of the Top Solid-State CFA amp design
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Old 16th July 2018, 06:26 PM   #811
AndriyOL is offline AndriyOL  Ukraine
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Do you mean external series resistor 1R at output or input? And 8R dummy load with 47nF in parallel?
Perhaps better would be to perform these tests with new optimized pcb? Do you think the schematic is complete for new layout? The doubts left only in compensation values.
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Old 16th July 2018, 07:34 PM   #812
mjona is offline mjona  New Zealand
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External series resistor at the output and 8R in parallel with 47nF. You should try first a 50kHz square wave into the 8R dummy load alone with the amplifier as it stands with a range of low level input signals.
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Old 17th July 2018, 10:52 PM   #813
AndriyOL is offline AndriyOL  Ukraine
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I've made a layout for this sim file. I added 10R GND resistor as per original schematic. There are two gnd planes, at IPS section and as output zone. One thing I'm not sure with gnd planes, as this is not visible in the layout, is how opposite layer components go through these gnd planes.
Comments and offers are welcomed.
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File Type: jpg PCB.jpg (395.2 KB, 65 views)
Attached Files
File Type: asc SSAHP kplus siggen sim5C-R.asc (25.5 KB, 4 views)
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Old 18th July 2018, 01:17 AM   #814
mjona is offline mjona  New Zealand
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Douglas Self made repeated comments earlier that a ground plane is not necessary.
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Old 18th July 2018, 04:56 AM   #815
kct is offline kct  Canada
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One of the Top Solid-State CFA amp design
Sadly, Douglas is very mistaken in his believe.
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Old 18th July 2018, 05:59 AM   #816
AndriyOL is offline AndriyOL  Ukraine
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I may believe that it can be true, but using gnd plane turns out with much compact and easier layout than if I route gnd tracks separately. It's beneficial in two points: simplicity and noise immunity.
In fact Douglas agreed as well gnd plane can be beneficial in post 115, as I understood.
Sorry, previous image was without GND plane, I thought I uploaded the correct one. Chris, please replace the image with this one. Thanks.
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File Type: jpg PCB.jpg (524.5 KB, 61 views)
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Old 18th July 2018, 07:23 AM   #817
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Do you ever sleep :-)
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Old 18th July 2018, 07:30 AM   #818
AndriyOL is offline AndriyOL  Ukraine
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Of course)
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Old Today, 05:50 PM   #819
AndriyOL is offline AndriyOL  Ukraine
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Quote:
Originally Posted by IanHegglun View Post
if you still have motivation, OITPC appears to offer up to a factor of ten lower THD at 20kHz but in practice there are likely issues hidden from us using our inadequate simulations so it may take a lot of effort to succeed with OITPC. But it would be nice if OITPC works well first try!
I tried this compensation but I left C13 as 320uF, forgot to replace it. The results are worse than with previous compensation. The amplifier is a bit unstable, I can only bias the input only to 3mA, likewise too much noise from the speaker. Here are the scope screenshots without input signal (first start up and couple of minutes run) and two with input signal.
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File Type: jpg 20180720_020837.jpg (817.1 KB, 21 views)
File Type: jpg 20180720_021756.jpg (905.3 KB, 19 views)
File Type: jpg 20180720_203827.jpg (726.7 KB, 19 views)
File Type: jpg 20180720_203859.jpg (907.0 KB, 4 views)
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Old Today, 06:09 PM   #820
keantoken is offline keantoken  United States
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Ian, have you checked that compensation for overshoot?

The phase margin is increased by the means of a resonance after the unity gain frequency. Are you sure the Q of this resonance will remain stable under dynamic conditions considering the Ft of the output transistors may vary 5x or more?

Furthermore this compensation provides a path for frontend rail noise to be injected directly into the VAS input. The simulation does not include modulation of the frontend rails. To fix this the compensation would need to be split into two sections, one for the positive VAS and one for the negative VAS. R44 will be split into two resistors going to their respective rails rather than to ground.

The VAS uses the rail as it's reference node, therefore referencing the OITPC to ground through R44 causes a reference conflict.
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File Type: png OITPC Overshoot.png (19.2 KB, 8 views)
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