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Old 5th October 2012, 02:47 AM   #1531
bcarso is offline bcarso  United States
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Quote:
Originally Posted by fas42 View Post
Just tried something else in my version of SW-OPA, looking at PSRR. At 20kHz, only a bit over 15dB on the -ve supply, 30dB on the +ve when working at a gain of 20. So an extremely well regulated supply will be necessary for the circuit as is ...

Frank
Not to knee-jerk defend, but are you measuring this based on your closed-loop gain of 101?
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Old 5th October 2012, 02:55 AM   #1532
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anyway isnt it time to put the new Jung shunt superreg to the test? anyone built that yet?
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Old 5th October 2012, 03:17 AM   #1533
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Quote:
Originally Posted by bcarso View Post
Not to knee-jerk defend, but are you measuring this based on your closed-loop gain of 101?
????? ...

Quote:
At 20kHz, only a bit over 15dB on the -ve supply, 30dB on the +ve when working at a gain of 20.
Feedback resistors of 2k, 40K. Tried also 2k, 10k, so gain of 6, that improved performance by about 10dB ...

Frank
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Old 5th October 2012, 03:53 AM   #1534
bcarso is offline bcarso  United States
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Originally Posted by fas42 View Post
????? ...

Feedback resistors of 2k, 40K. Tried also 2k, 10k, so gain of 6, that improved performance by about 10dB ...

Frank
Sorry, my overlook.
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Old 5th October 2012, 05:35 AM   #1535
fas42 is online now fas42  Australia
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And of further interest, a member PM'ed me about a breadboard he's already knocked up, and his PSRR figures, measured at lower frequencies, correlate beautifully with what the sim predicts ...

Frank
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Old 5th October 2012, 06:22 AM   #1536
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Frank,

dadod's version sims at about ~-25db at 20KHz on the negative side with your 20K/2K feedback values. Switching to K170/J74 models for the front end @ 7mA, everything else otherwise the same, brought it up around ~-31db at 20KHz. Low frequency is about -89db for the LSK389/J109 with the knee at about 65Hz. The K170/J74 was in the -96db range with the knee around 70Hz. High side PSRR is better.

All based on the LTSpice sim of course… Anybody else get similar numbers from it? It would be nice to know it works the same in multiple locations, even if just in the sim at this point.

Dave
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Old 5th October 2012, 01:33 PM   #1537
BFNY is offline BFNY  United States
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Originally Posted by qusp View Post
anyway isnt it time to put the new Jung shunt superreg to the test? anyone built that yet?
This circuit is shown here, and discussed close to the end of the Audio Xpress interview with Walt Jung

WaltsBlog

Probably off topic here, but worth a new thread in the right place...
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Old 5th October 2012, 03:21 PM   #1538
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Quote:
Originally Posted by fas42 View Post
And of further interest, a member PM'ed me about a breadboard he's already knocked up, and his PSRR figures, measured at lower frequencies, correlate beautifully with what the sim predicts ...

Frank
PSRR is something to look at and there could be some tweaks. I would expect non-cascoded inputs to be fairly sensitive to source impedance mis-match. Welcome to the design process.

EDIT- OK we need to track down the discrepancy, the very first circuit (all N flavor FET's but input cascoded) shows me flat -100dB RTI on both supplies out to 20K.
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Last edited by scott wurcer; 5th October 2012 at 03:35 PM.
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Old 5th October 2012, 04:43 PM   #1539
bcarso is offline bcarso  United States
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General appeal: could people please reference a post # when referring to a design? It would burden things unduly to attach the schematic each time, but at least we can use the number and go back and confirm what we're talking about.
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Old 5th October 2012, 06:04 PM   #1540
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PSRR

This is what I'm getting when simulating Scott's BF862 circuit with the buffer.
I have also attached the schematic I'm using, showing how I do the PSRR simulation. Maybe I'm doing it wrong?

Stein
Attached Files
File Type: pdf NEG PSRR.pdf (35.8 KB, 54 views)
File Type: pdf POS PSRR.pdf (37.8 KB, 36 views)
File Type: pdf SW BF862 with buffer.pdf (34.6 KB, 125 views)
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