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Old 20th July 2007, 02:05 AM   #1
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Default Best OP Amplifier in the World!! Look Amp Circuit

Hi,

This is the absolute best OP amplifier circuit that I have ever heard! It can be used in amplifiers or preamps alike.

In amplifiers, this dual jfet input stage would be followed by a bipolar voltage stage and a mosfet output. (2sk134 and 2sj49)

The amplifier could have an extremely high frequency bandwidth and high slew rate, i.e. DC-500kHz at +/- 1dB.

I've been an audio engineer for over 11 years now and can tell you guys that nothing compares!

http://i189.photobucket.com/albums/z...s005/OPAmp.jpg

Norbert
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Old 20th July 2007, 11:16 AM   #2
Gordy is offline Gordy  United Kingdom
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Hello Nagys,

Thanks for sharing your interesting idea.

For info, some people have found advantage in the following:

1. Add a capacitor from the junction of the cascode resistors (51k, 33k) to ground, to reduce power supply influence on the bias voltage.

2. Replace the 75r resistors with a potentiometer (with the wiper connected to the "tail" of the differential), so that the off-set of the final circuit can be tweaked towards zero.

3. Use a LED to bias the "tail" constant current source instead of the zener diode, to increase CCS temperature stability.


Good luck.
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Old 21st July 2007, 01:48 AM   #3
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Hi, NagysAudio,

Nice one . Do you have a more complete schematic? The one in post #1 is the input differential, right?
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Old 21st July 2007, 02:12 AM   #4
anatech is offline anatech  Canada
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Hi Norbert,
It's a pretty standard circuit. Nothing surprising really. I do agree though.

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Old 21st July 2007, 03:29 AM   #5
Leolabs is offline Leolabs  Malaysia
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Yes.Standard circuit but sounds good because of accurate operating point of the components?????
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Old 21st July 2007, 06:26 AM   #6
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Hey Chris,

Hmmm I agree it's a fairly standard circuit. But do you know of any amplifiers or preamps that use something similar? I would love to audition them!

Norbert
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Old 21st July 2007, 06:26 AM   #7
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Hi everyone,

Here are 2 pictures of the entire amplifier schematic (monoblock). Please let me know what you all think. The only thing not shown is a part of the power supply.

Basically, there are 2 toroidal transformers, one for the positive rail and one for the negative. And a bridge rectifier. The rest is shown in the scans!

http://i189.photobucket.com/albums/z...5/scan0002.jpg

http://i189.photobucket.com/albums/z...5/scan0001.jpg

Norbert
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Old 21st July 2007, 09:44 AM   #8
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Look at this, Norbert...
Attached Files
File Type: pdf dpa386se_1.pdf (51.0 KB, 777 views)
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Old 21st July 2007, 09:45 AM   #9
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Part two...
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File Type: pdf dpa386se_2.pdf (94.3 KB, 442 views)
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Old 21st July 2007, 10:20 AM   #10
AndrewT is offline AndrewT  Scotland
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Quote:
2. Replace the 75r resistors with a potentiometer (with the wiper connected to the "tail" of the differential), so that the off-set of the final circuit can be tweaked towards zero.
Hi,
do not deliberately unbalance the inherently balanced input stage.

Apply a correction elsewhere to zero out any DC output offset.

A discrete cascode Jfet input stage sounds quite normal, although the BJT version is a bit more common.
This type of circuit powers most competent power amp front ends.
Some builders even use part of a Jfet opamp input stage feeding the power amp to gain the advantage of the matched pairs (and laser trimmed) inside the IC.
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