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Old 26th September 2019, 06:55 AM   #11
EUVL is offline EUVL  Europe
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Your plot shows that at 0 of the signal, the residual is at something like -80 phase.
Not ?


Patrick
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Old 26th September 2019, 07:07 AM   #12
indra1 is online now indra1  Indonesia
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~180 compared to J2 residual.

Quote:
Originally Posted by Nelson Pass in Art_H2.pdf
The red fundamental goes up and down at a 1 KHz rate, and we see that the blue wave goes up and down as well at twice the frequency, but aligned with the red wave in a particular way - the blue goes down when the red goes up and the blue also goes down when the red goes down. I refer to this as negative phase 2nd harmonic. Positive phase 2nd harmonic is the opposite.
Please observe the alignment negative peaks of residual compared to both positive and negative peaks of the fundamental.
Attached Images
File Type: gif J2 residual.gif (2.3 KB, 1410 views)

Last edited by indra1; 26th September 2019 at 07:29 AM.
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Old 26th September 2019, 09:35 AM   #13
Morde is offline Morde  Finland
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Thanks Patrick for another intriguing design! I'm definately interested in building this. I hope the gerbers will match to the UMS specification.
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Old 26th September 2019, 10:08 AM   #14
EUVL is offline EUVL  Europe
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PCB layout is done to suit the circuit.
I don't follow DIYA standards.




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Old 26th September 2019, 05:47 PM   #15
EUVL is offline EUVL  Europe
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I am pleased to say that someone (I trust) has agreed to be Alpha tester.
So he will get the prototype built and tested first.
Any necessary changes will then be implemented before releasing the Gerber files to the public.

It will thus take a little longer.


Hopefully before Christmas,
Patrick
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Old 27th September 2019, 05:00 AM   #16
EUVL is offline EUVL  Europe
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Here a glimse of the PCB draft design.

Very similar to the SJJ, but not 1:1 compatible due to extra space required for the servo.
(FET mounting holes have to be shifted down by 2mm.)


Patrick

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File Type: png UDNeSS PCB V1 Public.png (21.9 KB, 1352 views)
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Old 27th September 2019, 06:15 AM   #17
jwjarch is offline jwjarch  United States
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Hi Patrick. Following this thread and very excited about this project. Does the servo require a separate power supply? Hard to tell what might be happening on the underside of the board. Thanks for developing this Obtanium J2!
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Old 27th September 2019, 07:04 AM   #18
EUVL is offline EUVL  Europe
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Servo uses the same power supply but have additional RC decoupling.
Too early to show everything till properly tested.

Good things take time. No point to rush.


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Old 27th September 2019, 10:33 AM   #19
mbrennwa is offline mbrennwa  Switzerland
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Quote:
Originally Posted by EUVL View Post
I am quite surprised myself that it came out so well, even if only in simulation.
Thanks for this, very interesting!

I have zero experience with SPICE, but I keep reading that SPICE simulations are not very reliable for predicting harmonic distortion. I guess the only way to really know if the harmonic distortion levels from the IRFP parts work out as nice as with the Semi South parts is to actually build the amp with both parts and then compare their measured performance.

What do you think?
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Old 27th September 2019, 10:33 AM   #20
EUVL is offline EUVL  Europe
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Default FET Matching

People asked about matching.

For best results, you always want to match.
Especially important for Q2,3.
Q1 is not important, as it is only current source and you can trim with Rdg.

Q4, 5 do not have to be matched to each other.
But if you want identical channels, you should match Q5 between channels.
Same for Q4.

Here are some simple matching circuits.

Note that rail voltage is limited by the opamp, as well as some other components in the opamp.
It is also limited by power device dissipation.


Patrick

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Attached Files
File Type: asc J113 Match.asc (911 Bytes, 105 views)
File Type: asc IRFP9240 Match.asc (1.2 KB, 91 views)
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