JFet vs bipolar

[jewilson]

Ricardo,

What do these numbers mean? What type of test did you run, what was the point of the test and what does it prove. In addition, let us in on you test configurations so we can be enlighten.

[millwood]

Originally posted by jewilson
Well If there were only 709's, 741, uA739, 540's, available in this world then I might think that a 5534 was some kind of marvel. Having said that, na I would use tubes.

I used to use 324s and thought they were great, until I used the TL0xxs. Well, the 324s aren't bad with a light load. But under heavy load (I were bootstraping them in a power amp), they didn't do too well.

Originally posted by jewilson
Tim, sorry you can here the difference, but where did you do this research. You must have been in bad environment maybe faulty towers.

it must have been the power cords,

[dimitri]

John, I have a hardcopy, but sorry it is on the other side of the Earth. I can send it to you not earlier than a New Year. If you are in a hurry you could order through AES for $5:

http://www.aes.org/publications/preprints/search.html

Alternately, you can download Wurcer US patent 5,166,637

http://patft.uspto.gov/netacgi/nph-P...r&RS=IN/Wurcer

[johnferrier]

Originally posted by dimitri
I can send it to you not earlier than a New Year.

The other sources you provided are fine. Thanks!



JF

[peranders]

Originally posted by rickpt
the null test results

What is the file type? I don't get any .??? at the end.

[TimA]

Ricardo,

Thankyou for the op-amp null test figures....interesting!

Tim.

[rickpt]

setup: non-inverting amplifier with a(I chose this gains figure to use the OPA637 and the resistors were handy at that time) gain of five times and a 50k pot at the front end.a typical single opamp Pre-Amplifier
distortion could be a little lower if I used lower gain settings... as the setup was equal to all opamps,this cannot be blamed

about the null test like I said before, there is a lot of input about this test made by my friend Tube Dude in this forum, just search...

in short terms, it's a differential test that directly compares the input with the output leaving only the thing that cant be nulled, all nonlinearities created by the amplifying stage! lower the value, more the output resembles the input! one thing great about the test is that the distortion of the generator isn’t a problem like the typical distortion tests and that severely limits resolution of those tests

about the file, it's a word file

cheers

Ricardo

[sonnya]

??

First of all.. It can be blamed.

Design you circuit to match the opamps you are using.

1. A good example is the OP275GS/GP from analog. On page 9 in the datasheet there is a section called "Attention to source impedance Minimizes distortion"
There is descriped how a source impedance of more than 2Kohm and unballanced will affect its distortion performance alot.

That is because of capacitance modulation.

2. The AD797 outperforms the NE5534. There was an article in EW about capacitance distortion. The author have made a very pure sine wave oscillator. The distortion dropped below the NE5534 when he added a series resistor of 100R to the Cf. Reason .. Because of the very low rbb of the input diff. pair it needed a series resistor to dampen the capacitive interactions.

Look at page 10 in the datasheet.

So when it all sums up. The tests have to take there working conditions into account before comparing the specs and sound quality.

Sonny

[rickpt]

Design you circuit to match the opamps you are using.

whit a 50k pot that gives you about 10k of output inpedance at mid point position, fet amplifiers should be at home, and bipolar amplifiers should perform much worse... that wasn’t the case!

2. The AD797 outperforms the NE5534. There was an article in EW about capacitance distortion. The author have made a very pure sine wave oscillator. The distortion dropped below the NE5534 when he added a series resistor of 100R to the Cf. Reason .. Because of the very low rbb of the input diff. pair it needed a series resistor to dampen the capacitive interactions.

did you verify this with a null test? remember that the null test isn’t a typical thd test! all non linearity’s are measured.

about that resistor I don’t believe that was the case... I believe that Mr. Bateman had a parasitic oscillation when he inserted the AD797 on the circuit, and that resistor dampened that oscillation, and off course, distortion was lower, so nothing more than a base stopper...

now look at the typical diy'er, normally the topology is the same and only opamps are swapped...that was what I did but instead of listening, I was measuring

it's fairly easy to do a null test , so do it yourself and find your results...

cheers

Ricardo

[johnferrier]

Originally posted by peranders

What is the file type? I don't get any .??? at the end.

It's a zip file with a MS-Word doc inside. I just redownloaded, it works fine here.



JF