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Old 26th August 2012, 09:35 PM   #291
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If you can't get the parts, find a good IC.
For the record, I did a simple Google search for two complementary jfets, the J113 and the J175. I found both of them for sale under $0.50 each. You just have to buy a bunch of them and select them out. If you cannot invest $100 for this, then buy an IC. It will give you better performance.
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Old 26th August 2012, 09:43 PM   #292
coluke is offline coluke  Italy
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Quote:
Originally Posted by ChocoHolic View Post
In fact I appreciate much more to see a sim and measurements on a real set up of with average components, (...)
Agree - then I think you're going to appreciate the open-loop CF amp I'm talking about in this post: Marsh headphone amp from Linear Audio
Too many bjts to be mentioned here, but it works really fine with pretty standard and cheap * unselected * devices, and this was exactly what I was looking for.

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Old 26th August 2012, 09:43 PM   #293
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Now why did I choose these devices? They are representative of still available devices that can still be purchased, that Levinson used in the early days. OF COURSE, the Toshiba devices are easier to match, lower noise, and higher Gm. But if you can't get ANYTHING (Toshiba jfet), then alternatives should be chosen.

Last edited by john curl; 26th August 2012 at 09:56 PM.
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Old 26th August 2012, 09:49 PM   #294
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I would also point out that complementary differential works best when complementary jfets are used. Perhaps a different, single jfet pair, circuit would be best.
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Old 26th August 2012, 10:06 PM   #295
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Originally Posted by Johnloudb View Post
That's the spirit! ... Just kidding ya Nice circuit.

A DC servo addition would be nice. If not would probably want a cap at the output. DC can be dangerous to speakers as I'm sure you know.
I think the spec was for less than 2mV of DC offset, wasn't it? I can't remember.

This isn't my show, I just wanted to make a contribution, however small it may be.
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Old 26th August 2012, 10:07 PM   #296
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This is a recommended alternative to a complementary differential fet design. This design was used in several professional mixers as well as in three 30ips master analog recorders.
sorry about the bad copy, the original schematic goes back to about 1977.
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Old 26th August 2012, 10:07 PM   #297
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Quote:
Originally Posted by john curl View Post
If you can't get the parts, find a good IC.
For the record, I did a simple Google search for two complementary jfets, the J113 and the J175. I found both of them for sale under $0.50 each. You just have to buy a bunch of them and select them out. If you cannot invest $100 for this, then buy an IC. It will give you better performance.
These can be considered ' complementary ' ?
http://www.fairchildsemi.com/ds/MM/MMBFJ177.pdf
http://www.fairchildsemi.com/ds/J1/J111.pdf
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Old 26th August 2012, 10:20 PM   #298
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Yes, these are the devices. Many manufacturers still make them. However, they have a LARGE Idss spread, so only dumb luck will match the P's to the N's, but that is not very important, within limits. Just good N to N, and P to P is the most critical.
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Old 26th August 2012, 10:21 PM   #299
EUVL is offline EUVL  Europe
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The J17x series are rather noisy parts.


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Old 26th August 2012, 10:22 PM   #300
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To cite an old saying: 'You can't afford 2mV offset!' '-)
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