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One Last Attempt at Discrete Opamp in DIP8 Footprint
One Last Attempt at Discrete Opamp in DIP8 Footprint
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Old 11th May 2019, 05:43 AM   #31
dreamth is offline dreamth  Romania
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Pro Discrete Op Amp SS2590 - SparkoS Labs Inc.
Hypex NC500 Buffer Upgrade
https://sparkoslabs.com/wp-content/u.../03/SS2590.pdf
looking at the datasheet i can only be amused...it's only the power and the power supply that's better than any modern audio op-amp, nothing else...

Last edited by dreamth; 11th May 2019 at 05:50 AM.
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Old 11th May 2019, 01:24 PM   #32
Mark Tillotson is offline Mark Tillotson
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Originally Posted by dreamth View Post
https://sparkoslabs.com/wp-content/u.../03/SS2590.pdf
looking at the datasheet i can only be amused...it's only the power and the power supply that's better than any modern audio op-amp, nothing else...
But surely the profit margin ($/unit) is massively higher? A very important performance criterion for many! And the self-congratulation coefficient is pretty high too

Obviously lacking is the current noise density, so there's no way to judge its noise figure in most small signal circuitry. Its apparently optimized for voltage noise with the paralleled input devices, which suggests it is not optimized for current noise (more important in reality for most uses, since typical circuitry is at 1k to 20k impedance, not 10 to 300 ohms!) The (uncorrelated?) input bias current cancellation circuitry doesn't bode well for this either.

The circuit looks good, the high gain, EF VAS and two-pole compensation should give great THD, but they never actually state the THD or graph it, which comes across as suspicious - it ought to perform well but why keep schtum in that case? The class AB output should give an interesting compromise in performance for heavy loads - which will cause an increase in output stage distortion without affecting the performance at low currents. Its basically a good BJT power amp with the feedback network and output stage chopped off AFAICT. The lack of THD measurements is immediately curious - perhaps something goes badly wrong with the output biasing?

Googling didn't seem to throw up anything about the current noise or measured THD or IM.
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Old 11th May 2019, 02:56 PM   #33
dreamth is offline dreamth  Romania
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A simple power buffer added to OPA454 (6 euros each for 1 pcs)and there's no competition in that voltage range...
http://www.ti.com/lit/ds/symlink/opa454.pdf
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Old 11th May 2019, 03:16 PM   #34
scott wurcer is offline scott wurcer  United States
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Quote:
Originally Posted by dreamth View Post
looking at the datasheet i can only be amused...it's only the power and the power supply that's better than any modern audio op-amp, nothing else...
The technical description contains plenty of nonsense.
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Old 11th May 2019, 04:49 PM   #35
Lingwendil is online now Lingwendil  United States
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Originally Posted by scott wurcer View Post
The technical description contains plenty of nonsense.
"Cascode structures inside of the device will begin to debias when the outupt swing approaches 3.5V
away from either supply rail. This is non destructive, and the output will not visibly clip, however
there will be a ~25dB reduction in open loop gain, resulting in higher THD."

This is terrible.
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Old 11th May 2019, 08:57 PM   #36
Mark Tillotson is offline Mark Tillotson
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But you have +/-24V rails instead of +/-17, thats affordable, you're still 3dB up on standard opamps. As I said its a power amplifier with the output stage chopped off.
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Old 11th May 2019, 09:12 PM   #37
Mark Tillotson is offline Mark Tillotson
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Originally Posted by dreamth View Post
A simple power buffer added to OPA454 (6 euros each for 1 pcs)and there's no competition in that voltage range...
http://www.ti.com/lit/ds/symlink/opa454.pdf
Voltage noise density 35nV, 300nV at 10Hz. But its FET inputs so current noise not a problem. The compromises made for high voltage are costly - the dynamic range is much less than a standard part due to the voltage noise. Flicker noise knee seems to be somewhere between 1kHz and 10kHz.

The THD at x10 gain is about 25 times more than at unity gain, and rises precipitously above 1kHz to 0.035%

The GBW product is 3MHz, explaining the bad HF distortion at gain rather well.


So doesn't stack up at all against regular parts at +/-17V since all of the extra headroom is pissed away on noise, and the basic bandwidth is missing.
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Old 11th May 2019, 09:23 PM   #38
Monte McGuire is offline Monte McGuire
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One Last Attempt at Discrete Opamp in DIP8 Footprint
It's not a single pole amplifier, so the effective feedback isn't as simple as determining the 0dB gain frequency (3MHz) and counting backward at 6dB per octave. For example, the amplifier open loop gain shown on the graph is about 85dB at 10kHz, not possible with a 3MHz single pole amplifier.

I guess this also means that there are circuits you can put it in that it will not be stable, but it'll probably work over some sort of gain range - have not explored this amp in detail.

Last edited by Monte McGuire; 11th May 2019 at 09:26 PM.
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Old 11th May 2019, 09:39 PM   #39
dreamth is offline dreamth  Romania
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Mark...I still see no competition in that discrete op-amp...
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Old 12th May 2019, 05:22 PM   #40
Lingwendil is online now Lingwendil  United States
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Quote:
Originally Posted by Mark Tillotson View Post
But you have +/-24V rails instead of +/-17, thats affordable, you're still 3dB up on standard opamps. As I said its a power amplifier with the output stage chopped off.
For the majority of applications where you're working with the "usual" rail voltages that's pretty poor headroom.

Overall there are better, cheaper choices that would offer better performance, even at higher rail voltages.
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