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API 1608 Mix Buss - Op Amp Blind Listening Test - API 2520, 990C, Rogue 5, GAR 2520, VF600, Red Dot
Old 1 week ago | Show parent
Gear Maniac
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1 Review written
🎧 5 years
Originally Posted by johannburkard ➡️
I'm not sure I understand the context of that test. Pass does power amps doesn't he? He might be talking about very large voltages.

A slew rate is a function of frequency and voltage. You can convert a peak voltage + frequency into a slew rate required to faithfully reproduce it.

Its just 2pifV = slew rate.

To reproduce a 55V peak signal at 20 kHz you need a slew rate of just under 7V / uS.

2V / uS gives you 100kHz at +4 dBu.

As I said, I don't see the practical benefit.

This is well worth a read, if you haven't read it before.

Walt set out long ago that you want 0.5 to 1 V/uS slew rate per peak output volt to minimize slew rate induced distortion.
Old 1 week ago
One benefit of a high slew rate along with high open loop gain at 10k hz is no increase in THD at higher frequencies. Examine most opamps at 1k hz and they look great. Test at 20k hz and they drop off, even some of the better audio IC opamps also do this.

If an opamp can pass 20k hz at full power without any errors everything below that frequency will be equally clear. Run CCIF twin tone IMD tests and you will see "the rest of the story" along with fft's.
Old 1 week ago | Show parent
Originally Posted by Jim Williams ➡️
Run CCIF twin tone IMD tests and you will see "the rest of the story" along with fft's.
That is 19 kHz and 20 kHz, equal amplitude?
Old 6 days ago
A 1k hz spacing is typical but the AP allows for 80, 100, 120, 200, 250, 500 and 1k spacing. Sweep ranges go from 4K hz to 20k hz. DIM tests include a fixed 3.15K square wave. These are punishing twin tone IMD tests, closer to actual musical waveforms than a simple sine wave test, the easiest to reproduce. Analyzer residuals are around 1.2 ppm as the noise floor included in traditional THD + noise tests are factored out of the measurements.
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