John Curl's Blowtorch preamplifier part II - Page 3330 - diyAudio
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Old 22nd January 2013, 01:44 PM   #33291
PMA is offline PMA  Europe
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If there is anyone interested, here is the complete measurement of opamps + schematics.
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File Type: zip opamp_measurement_pma.zip (914.2 KB, 77 views)
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Old 22nd January 2013, 01:46 PM   #33292
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Quote:
Originally Posted by simon7000 View Post
Very true

Now lets try a simple question. If my PSSR at 120 Hz is 90 dB, There is .1 V P-P ripple (120 Hz.) on my negative supply, none on the positive supply and my gain is 60 dB. Can you predict from the data sheet what the output ripple will be?

Can you offer a value based on experience?



ES
Never looked at anything that bad. I don't see the point in discussing something no one would ever do unless they are learning for the first time.
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Old 22nd January 2013, 02:00 PM   #33293
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Originally Posted by SY View Post
I guess it's suitable for mid-fi. The only way it could work for High End is to hide it inside some mysterious box and tell a good story.
I haven't seen preamps where line stage has 40dB of gain lately.
What happens when you reduce the gain to 20 or 10dB? Still no 7th?
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Old 22nd January 2013, 02:00 PM   #33294
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Originally Posted by PMA View Post
If there is anyone interested, here is the complete measurement of opamps + schematics.
Thank you .
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Old 22nd January 2013, 02:01 PM   #33295
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Originally Posted by PMA View Post
Low noise but high distortion and higher order distortion. The last one in my test
Too bad this is the last one in this test, was hoping you had some opa211 laying around.
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Old 22nd January 2013, 02:05 PM   #33296
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I am sorry I wrote OPA627 in the 1st chart in the zip file, it was OPA637 as correctly stated at the measurement page.

vacuphile - I do not have OPA211, sorry.

elektroj - if I reduce gain to 20dB or 0dB, there is already no 7th, but I am unable to measure distortion and noise then, for it goes below sound card threshold.
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Old 22nd January 2013, 02:05 PM   #33297
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I don't know if this is an appropriate time, but a great deal of confusion has been generated about: not only my designs, but low noise design as well.
I personally have been working on low noise design of phono stages since 1966. I really hoped to make a solid state pre-preamp to replace the Ortofon transformer that I was using. When I read that I could PARALLEL devices, I realized that I could get almost any voltage noise floor that I was willing to invest in. However, I needed more understanding of solid state tradeoffs, before I could advance.
In 1967, I visited Ortofon, in Copenhagen while on a tour of Europe, and asked them for the specifications of the transformer that they originally included, that was mounted directly BEHIND the cartridge body. This added MASS to the phono cartridge, and the transformer was necessarily very small, (compromised) as well, at the time.
I was shown that future transformers would be mounted OUTBOARD so the 'mass' problem was fixed. Then I mentioned that I was still thinking of building a solid state 'transformer eliminator' and they 'showed me the door' literally, claiming that their best engineers had claimed it impossible, and therefore I was just some 'nut' wasting their time.
Well time passed, and within a few months, I got use of a QuanTech noise analyzer, and I got busy. It took years to make a 'truly unique' ultra low noise design, but I had the problem solved in 1968, by using 4 paralleled 2N4403 or even better, 2N4405 (to-5) transistors in parallel, to get an equivalent noise of about 10 ohms or so. The problem then, was HOW to follow the input stage with something elegant, rather than just an add-on circuit. That took much longer. Ultimately the Levinson JC-1 appeared with a rated noise of 0.4nV/rt Hz noise at the NY AES in 1973. Of course, nobody believed it, just like today. However, it was a VERY SUCCESSFUL, if limited design (dynamic range wise) and held its own for several years, almost a decade.
I could go on, but here is the point: Low noise design has been known about (what to do) for many decades. The problems are: Which devices, both affordable and available are REALLY LOW NOISE for the application they are to be used?
Second: Can you make the rest of the design both well performing, and even elegant?
Third: Can you avoid 'problematic' parts like input caps and biasing diodes that only add to the distortion/noise of the unit?
If you can do all three, you have a good chance of making a low noise, successful audio design.

Last edited by john curl; 22nd January 2013 at 02:19 PM.
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Old 22nd January 2013, 02:06 PM   #33298
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Originally Posted by Esperado View Post
Time to confess, now.
In 70s, our boss was putting much pressure on us (r&d office) to offer some quadraphonic feature to our market (hype at this time, while no quadraphonic records were available) .
So we added in one of our amplifiers some resistances to feed 2 extra loudspeakers to be situated back to the listener's place, with the difference signal of the main amplifier (each added loudspeaker in phase opposition).
L, R, (L-R),( R-L).
As we were very shamed with it, the resistances where hidden in resin. Of course, we let the marketing department free to compose the marvelous story and benefits of our mysterious black box.
I hope this will be forgotten or forgiven the day i will do a job ask at the Paradise's door.
It entertained the mass, and did no harm in epoxy it MAGIC . The buyer saw it as value no harm to them you will be forgiven.
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Old 22nd January 2013, 02:13 PM   #33299
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Originally Posted by scott wurcer View Post
Never looked at anything that bad. I don't see the point in discussing something no one would ever do unless they are learning for the first time.
Would you be happier with 300 uV?
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Old 22nd January 2013, 02:14 PM   #33300
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Originally Posted by PMA View Post
Hi Mogens,

already replied here:
http://www.diyaudio.com/forums/analo...ml#post3337110

I bought a new software to get reliable results in SNR and NL. It also generates clean signals (ref. Fs and FFT length) and uses rectangle window, more in the manual.
Hi Pavel,

Thanks

Better get those eyes checked.

Mogens
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