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Old 13th April 2013, 04:07 AM   #21
rsavas is offline rsavas  Canada
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MMBFJ310LT1G & BF862 for SOT-23, drain and source are marked differently, but NXP says that they are interchangeable.
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Old 13th April 2013, 11:22 AM   #22
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Yup saw that. Makes life easier... :-)
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Old 14th April 2013, 07:15 AM   #23
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Done, made a few other improvements, like the option to use multiple power supplies, popped a few caps in around the place for psu decoupling, and included in pads for the surface mount fets if used.

Those bf862's aren't overly expensive either...

As before the part names are incorrect as I haven't bothered to create the appropriate parts in eagle - I've just used equivalent pinout/profile parts already there.
Attached Images
File Type: png PSU v2.png (143.5 KB, 97 views)
File Type: png PSU Board v2.png (162.8 KB, 89 views)
File Type: png V2Board.png (270.2 KB, 84 views)
File Type: png Schematic v2.png (200.4 KB, 81 views)
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Old 29th December 2013, 09:34 AM   #24
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Default Belated Progress

And here's where I'm at with it now. I've put a slow start on the board, so the turn on thump should be mitigated. Otherwise I hope I've designed a sensible layout...

I bought a bunch of bf862's, J109's and J111's and I've a stash of J310's so perhaps I'll build a few of these to see what the differing jfets sound like (if indeed there's a difference I can pick). So that's an idea to pursue if I fancy it.

Anywho I'll etch I few of these soonish (or seeed them) and see how I go.
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File Type: png SSTART SCH.png (174.1 KB, 56 views)
File Type: png SSTART BRD.png (250.7 KB, 32 views)
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Old 30th December 2013, 02:14 PM   #25
rsavas is offline rsavas  Canada
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Grado Labs | Reference1 & Master1
Spec Input=47K,
no need for a R20 as R19 is 47K.
It is a low o/p at 0.5mV, but this is a MC pre so it should be fine stock values, R15, use a jumper. Would not worry about C15, test to see what it is like. $1500 cartridge, must have fine record collection to go along with it :-)
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Old 1st January 2014, 08:30 PM   #26
BigE is offline BigE  Canada
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has anyone played around with LTspice on this circuit? I'd like to compare results if possible....

Thanks!

I tried 16 pieces of J310, with 200R bias resistor and 1K drain. 60V power for 0.095 % thd at 1K. Climbs to 0.45 at 20K.

Last edited by BigE; 1st January 2014 at 08:32 PM.
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Old 1st January 2014, 09:03 PM   #27
BigE is offline BigE  Canada
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Forgot to mention, the big mosfet is IRFP240.

woops, just noticed max gate source voltage is exceeded.... why does LTspice not flag this error???

Last edited by BigE; 1st January 2014 at 09:06 PM.
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Old 1st January 2014, 10:32 PM   #28
BigE is offline BigE  Canada
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Found error.... wire drawing problem!


Still, awful thd figures...

Last edited by BigE; 1st January 2014 at 10:47 PM.
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Old 2nd January 2014, 12:45 AM   #29
BigE is offline BigE  Canada
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replaced IRF610 with IRF510 (possible model issue) and changed 22.1K resistor to 40 Ohm.

Now, thd is below .1 percent for unity gain with 2V input at frequency of 1K.
Attached Images
File Type: gif sstart.GIF (60.1 KB, 24 views)
Attached Files
File Type: txt Analyzer_Controls.txt (10.5 KB, 3 views)
File Type: asc sstart.asc (4.1 KB, 1 views)

Last edited by BigE; 2nd January 2014 at 12:57 AM.
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Old 2nd January 2014, 01:35 AM   #30
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I did a version with a little bit of feedback and got (from memory), um, 0.4% THD? at 10k?

I'll dig it up and post shortly... <edit> included some data that was bad - will repost </edit>

Last edited by aspringv; 2nd January 2014 at 01:52 AM.
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