Can I use the 2N5484 jfet diff pair in an audio amplifier front end? - Page 3 - diyAudio
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Old 27th March 2009, 01:19 AM   #21
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Quote:
Originally posted by carpenter
Thanks for the input, JJ. I'll check that part out, too.

For the moment, I'm pretty much sold on the J310. I can't quite get over the 7 cents per piece price tag...
Go for it, these parts are way better than people give them credit for. You might need to select for noise, but the yield is high.

I'm glad you folks got some mileage out of that BF862 recommendation.
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Old 27th March 2009, 01:26 AM   #22
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Thanks, Scott, how do you select for noise?
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Old 27th March 2009, 01:48 AM   #23
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Quote:
Originally posted by carpenter
Thanks, Scott, how do you select for noise?
Just make a generic high gain stage and listen. If you gain it up enough there will always be some hiss and the bad ones will stand out.
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Old 27th March 2009, 02:00 AM   #24
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So, if I have low gain--say 2 to 3, which I do in my particular design, then noise is automatically mitigated?
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Old 27th March 2009, 12:04 PM   #25
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Quote:
Originally posted by carpenter
So, if I have low gain--say 2 to 3, which I do in my particular design, then noise is automatically mitigated?
At that low of a gain I wouldn't expect noise to be an issue.
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Old 27th March 2009, 06:02 PM   #26
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Quote:
Originally posted by scott wurcer


At that low of a gain I wouldn't expect noise to be an issue.


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Old 28th March 2009, 12:35 AM   #27
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I certainly hope the J310's work well -- I've used them in my 7 channel preamp, which might be finished in a month or two. The price of J105's skyrocketed, but you might be able to get them at a reasonable price from Fairchild. I think most people would consider the J105 a big, slow, stupid Jfet -- but they made a great sounding preamp. Maybe you will want to get a few of the other garden variety Vishay and Fairchild Jfets and compare the sound.

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Old 28th March 2009, 12:55 AM   #28
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Big, slow, stupid.... for a second, I thought you were talking about me...

I'll look the J105 up, see what's cooking.

I've just made a major discovery with my amplifier. I don't know how it happened, but it's so cool. I've been designing a power buffer amp--built one to test it's capabilities--and it sounds very nice, sweet, strong. This is the best thing I've every fabricated. I owe so much to Nelson and you guys for setting me straight.

Anyway, back to the cool discovery: My choke loaded follower output has been forever lock into a low voltage mode. If I tried to raise the voltage to the power mosfets the output set point would raise and there'd be no way to take advantage of the addition voltage for increased signal output.

I tried simming a buffer between the middle gain stage and the power buffer output (this amp has a gain of 1 jfet diff in front to split the signal, which feeds a differential middle stage which used to feed the power buffer output). I disconnected the biasing network to the power buffer mosfets and fed them directly from the buffer network following the middle stage. I was able to lower the set point of the power buffer to 2 volts. It held that position while I added voltage to the power buffer. I was able to raise the voltage from 7 volt up to 12 volts without moving the power mosfets from their set-point. Now, I can get gain without resorting to lowering the speaker impedance.

My amp used to deliver 5 watts to an 8 ohm load, now it delivers 26 watts. It will drive a 2 ohm load and deliver 100 watts or so. I'm thrilled.

Just wanted to pass this little trick on...
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