John Curl's Blowtorch preamplifier part II

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#80,342
scott wurcer said:
The second has been reduced to insignificance (<-130dB) in many op-amps.
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I guess if you are designing test gear that is resolving around -120 dBV on a good day then you would want to start considering non- linearity contributions at -130 dBV. That said, for audio, thermal modulation is a non issue in opamps. In discrete circuits you have thermal gradients contributing more LF noise . . .

For those that are interested, see James Solomons 'Operational Amplifiers: A Tutorial Study' for a description of the problem and the solution. IIRC the paper was published in 1970.
 
#80,343
Bonsai said:
I guess if you are designing test gear that is resolving around -120 dBV on a good day then you would want to start considering non- linearity contributions at -130 dBV. That said, for audio, thermal modulation is a non issue in opamps. In discrete circuits you have thermal gradients contributing more LF noise . . .

For those that are interested, see James Solomons 'Operational Amplifiers: A Tutorial Study' for a description of the problem and the solution. IIRC the paper was published in 1970.
Click to expand...

It is also frequency dependent and at >1kHz even more attenuated.
 
#80,344
My two PS go to 30vdc. Not enough for some opamps..... higher voltage PS coming;

But 2-30vdc is enough for the AD797. I got some brand new ones. They do fine up to +/- 26 vdc then start to distress themselves by showing sudden high thd. Running for days at extremely low thd at +/- 24vdc. So far the 50v or more that Walt Jung said was typical for opamps is holding up well.

THx-RNMarsh
 
#80,345
RNMarsh said:
My two PS go to 30vdc. Not enough for some opamps..... higher voltage PS coming;

But 2-30vdc is enough for the AD797. I got some brand new ones. They do fine up to +/- 26 vdc then start to distress themselves by showing sudden high thd. Running for days at extremely low thd at +/- 24vdc. So far the 50v or more that Walt Jung said was typical for opamps is holding up well.

THx-RNMarsh
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You have variable supplies.....have you noted any sonic changes wrt supply voltages ?.

Dan.
 
#80,346
RNMarsh said:
My two PS go to 30vdc. Not enough for some opamps..... higher voltage PS coming;

But 2-30vdc is enough for the AD797. I got some brand new ones. They do fine up to +/- 26 vdc then start to distress themselves by showing sudden high thd. Running for days at extremely low thd at +/- 24vdc. So far the 50v or more that Walt Jung said was typical for opamps is holding up well.

THx-RNMarsh
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1.) What do you need to do that's so high in voltage?
2.) Bootstrap the supply instead?
 
#80,347
The level Bruce was looking at was another -10db or greater in residual.

"When properly designed, the dual op-amp architecture can deliver amazingly low residual THD, typically below -140 dB! Indeed, it is the design approach I took when developing many of the analog circuits in the Audio Precision APx555."

not insignificant.

but, how to measure?

Alan
 
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#80,348
Max Headroom said:
You have variable supplies.....have you noted any sonic changes wrt supply voltages ?.

Dan.
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I havent listened.... only curious that the Absolute Max rating is so conservative. I've only monitored thd/thd+n and it doesnt change.
I havent blown any up yet.... maybe with the new PS?

I have no application for higher output levels than I could get with +/-15vdc PS. Maybe for someone who needs greater dynamic range.... Pro app levels ?

THx-RNMarsh
 
#80,352
Dunno if posting a link to a diagram from another thread works but here goes.

http://www.diyaudio.com/forums/atta...ulus-86-r2.1_-multi-tone-test-40-w-8-ohm-.png

Now whilst this will be of no interest to those who think that their amplifier should dump kW into sub ohmic loads, but in terms of being low enough distortion that it challenges the test equipment and needs Bruce's cleverness it's certainly there. That's my version of glorious excess in audio 🙂

(and I'm pretty sure the efforts of a few others on this forum are knocking on the door of this sort of level of cleanliness.)
 
#80,353
Certainly I have cleansed transformer ringing waveforms from (small) to (zero), without pausing to consider whether (small) was, or was not, negligible or near-negligible. Why live with (small) when (zero) is easily achievable, at the cost of two 20% capacitors and one 5% resistor? Easy decision, to me.
 
#80,354
jneutron said:
All the particle beam machines need levels of precision in the micron range around the entire structure. Synchrotron machine beamline users, some are sensitive to the nanometer range. We are about 10 miles from the south shore, and some of the users have issues with the periodicity of the waves on the beach. They see the deflection of the beam as a result of the waves, especially if the surf is a foot or two. Being two miles from the nearest expressway, we also have problems with rush hour traffic, specifically trucks taking things east in the morning rush.

These two things are the reason the International Linear Collider can't be built here, they need beam stability down in the 2 to 3 nanometer range.
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Good lord, I don't know how we even frame a house around these parts! Here in Nova Scotia we have the world's highest tides. Twice a day the Bay of Fundy fills with water, and twice a day it empties, and the entire peninsula that is our province tilts half an inch each cycle.
 
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