Au Revoir NE5534

[Craig Sawyers]

Originally Posted by Radio Wrangler

Thermal and semiconductor noise is random, and therefore unpredictable.... So he was after something that Douglas Adams' philosophers demanded: "We demand rigidly defined areas of doubt and uncertainty!"

Any measurement of the averaged power of noise over a finite time leaves you with the uncertainty of whether you happened to hit a loud patch or a quiet patch and repetitions of the measurement will show scatter which diminishes as the averaging time is increased. Certainty takes infinite time, and once you've made one of those measurements, there is no time left in which to use the result

David

Indeed. The fact that the noise spectral density plots for the OPA210 go down to 0.1Hz is impressive. There is serious difficulty in going down that far. Jim Williams describes a system for measuring noise in the 0.1Hz to 10Hz range in his Linear Technology apps note 124 https://www.analog.com/media/en/tech...tes/an124f.pdf . He calls for a 1300uF 30V wet slug tantalum (currently £400), necessary for leakage reasons (less than 5nA), guard rings all over, dual FETs etc etc

Craig

[Radio Wrangler]

In the final analysis, there is no certainty. Everything we can have in finite time has to be processed noise. If we're lucky enough and foxy enough, we might still get something sufficiently well processed for our purposes.

Deep thoughts, to chuck in another Adams reference. As a mere oily rag-carrying engineer, I'd like to know what the specified tolerance on that '42' is.

David

[G.Castle]

Originally Posted by Radio Wrangler

In the final analysis, there is no certainty. Everything we can have in finite time has to be processed noise. If we're lucky enough and foxy enough, we might still get something sufficiently well processed for our purposes.

Deep thoughts, to chuck in another Adams reference. As a mere oily rag-carrying engineer, I'd like to know what the specified tolerance on that '42' is.

David

I'll calculate it:

Ask again in 7.5 million years, I should have your answer by then.

[Craig Sawyers]

I got around to running the numbers comparing the late great NE5534 with the OPA1611 (surface mount only).

NE5534, -78.1dB SNR, 2.3db worse than a noiseless amp.
OPA1611 - -75.8dB SNR, 4.6dB worse than a noiseless amp

Ref 5mV and Shure 75ED cartridge model at the input (610 ohms and 470mH), and full RIAA correction. My spreadsheet model does not take care of 1/f noise, which is much better on the 1611 as compared with the 5534, nor does it take account of any weighting (such as A-weighting).

So the closest equivalent is 2.3dB worse SNR than the NE5534. That is actually quite close, possibly closer as a result of lower 1/f noise.

Craig