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Old 17th October 2012, 07:53 PM   #1781
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Quote:
Originally Posted by kgrlee View Post
.

The simplified Wurcer 990 I post in #1692 has excellent performance. On fas42's more stringent 100x 20kHz 20Vpp 600R test in #1694, its actually better than Guru Wurcer's more complex supa dupa circuit.

2nd -101.7dB 3rd -102.8dB Simplified 990
2nd -89.9dB 3rd -89.3dB Wurcer SupaDupa

ricardo 'wannabe a SPICE guru' lee
Just stick a 1N914 in (an oversite). That circuit is a fine option since it can do the 75 Ohm drive. Samuel Groner bases a few on the JE990-ish circuit but this one does not need inductors.
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Old 17th October 2012, 11:31 PM   #1782
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Originally Posted by kgrlee View Post
The 0.28nV/rtHz version runs 3mA total with 2 of the Hitachi devices. More current doesn't help which tends to confirm the rbb. The 2 'commercial' versions didn't use more current cos there weren't any MC amps at that time that were quieter with real MC cartridges .. even with my non-optimal noise matching. Description is in README.doc[/edit]
That works. As an historical point Nordholt and Van Vierzen ran a custom IC for the same Ortophon cart in 1980 (rbb = 1.4 Ohm). I have probably the only two left in existance. Your complimentary version is far more satisfying and simple (they used a HUGE coupling cap) even though they might have shaved a few tenths of a nanovolt.
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Last edited by scott wurcer; 17th October 2012 at 11:40 PM.
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Old 18th October 2012, 01:32 AM   #1783
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Quote:
Originally Posted by scott wurcer View Post
With default values I found the worst case drift AFTER trimming the offset back to zero was about 20uV/C for both pairs of FET's having a 10% mismatch of Idss (combined in the worst way).
I'm getting somewhat worse figures: with perfect matching of 3 FETs and just one out by 10% on Idss the drift is over 50uV, if only the FETs are subject to temperature change. The rest of the circuit offsets the drift to some degree, with the bipolars I've got. If the single mismatch is 17% (the first one I tried) the drift is 100uV ...

Will be interesting to see what the real devices do ...

Frank
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Old 18th October 2012, 04:01 AM   #1784
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i'm all for the complex version myself, i'll try both, but its always good to have options and I want to offer my encouragement for the development of this fresh circuit.
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Old 18th October 2012, 10:36 AM   #1785
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Some good news, hopefully ... I mentioned on another thread about using an NTC thermistor for thermal feedback, so tried this as a simple alternative in the sim: the drift caused by a single mismatched FET in the previous post was compensated for, by including the thermistor in a balance of resistors of a current source and managed fairly easily to restrict drift to only 15mV at x100 gain in the range 27 to 57 degC. This equates to a drift of 5uV/degC ...

Frank

Last edited by fas42; 18th October 2012 at 10:43 AM.
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Old 18th October 2012, 01:41 PM   #1786
RNMarsh is offline RNMarsh  United States
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Default second the motion

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i'm all for the complex version myself, i'll try both, but its always good to have options and I want to offer my encouragement for the development of this fresh circuit.
I'll second that motion.
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Old 18th October 2012, 01:44 PM   #1787
RNMarsh is offline RNMarsh  United States
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Default Thermistor offsets drift

Quote:
Originally Posted by fas42 View Post
Some good news, hopefully ... I mentioned on another thread about using an NTC thermistor for thermal feedback, so tried this as a simple alternative in the sim: the drift caused by a single mismatched FET in the previous post was compensated for, by including the thermistor in a balance of resistors of a current source and managed fairly easily to restrict drift to only 15mV at x100 gain in the range 27 to 57 degC. This equates to a drift of 5uV/degC ...

Frank


Shouldnt we prototype the thing and learn the true story on what it 'really', actually does and then see if such is needed or other way? Especially with conflicting sim results...

git er done.

Last edited by RNMarsh; 18th October 2012 at 01:50 PM.
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Old 18th October 2012, 02:12 PM   #1788
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PLEASE let's get beyond SIM! We've talked it to death. How about a parts list with the latest additions for both the SWfetJE990 as well as the new SWOPA? It would be great to have a post with the most recent schematics in one post where we don't have to hunt through 179 pages. Thanks, Ray
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Old 18th October 2012, 02:17 PM   #1789
rsavas is offline rsavas  Canada
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Default PCB layout assistance?

Hello folks,

I am following this thread as a learning experience. Gives me a chance to learn some analog design techniques & LTSpice as well.
Since it is such a small PCB, I can offer my assistance to continue doing the PCB layout and provide the fab data when completed. No sense in duplicating a parallel effort, if someone else is doing it as well.
I did not get much feedback, when I posted my first attempt, maybe to early for this to be reviewed, that's okay. If you want me to continue, just let me know? If not, good luck with your design!!


Regards
Rick
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Old 18th October 2012, 02:49 PM   #1790
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Quote:
Originally Posted by scott wurcer View Post
Your complimentary version is far more satisfying and simple (they used a HUGE coupling cap) even though they might have shaved a few tenths of a nanovolt.
Thanks Scott!

I gotta confess I originally took someone else's circuit, threw bits out and changed others to get SOTA performance. Just focussing on what's required for good sound and ignoring all Golden Pinnae considerations.

ricardo "whose head is now too big to get through the door" lee
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