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Topic: slew rate for op amps (Read 5623 times) previous topic - next topic
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slew rate for op amps

Hi. Lately I have been looking into slew rate specs for op amps, particularly for RCA output of CD players. For example my pioneer CD player and my marantz CD player have roughly 4v/ms and 6v/ms (microsecond) slew rate respectively. The marantz player definitely has better transient performance(at least to my ears). I've been to a web site that calculates the amount of slew rate needed for a particular voltage output and highest frequency to be encountered by which both of these CD players exceed this.  Does the slew rate have to be considered also for the width (the time taken) of the main lobe of the impulse response as well? Thank you so much.

slew rate for op amps

Reply #1 –
Quote from: cool n hot on
Hi. Lately I have been looking into slew rate specs for op amps, particularly for RCA output of CD players. For example my pioneer CD player and my marantz CD player have roughly 4v/ms and 6v/ms (microsecond) slew rate respectively. The marantz player definitely has better transient performance(at least to my ears). I've been to a web site that calculates the amount of slew rate needed for a particular voltage output and highest frequency to be encountered by which both of these CD players exceed this.  Does the slew rate have to be considered also for the width (the time taken) of the main lobe of the impulse response as well? Thank you so much.


The slew rate goes both ways, for rising as well as falling slopes. It is possible for an amplifier to have different slew rates for rising and falling edge, but that would be poor design.

However, you won't be able to measure the slew rate of an op amp used as a buffer amplifier after the DAC chip and reconstruction filter in a CD-Player, because the bandwidth limitation afforded by the DAC/filter combination will limit the slew rate before the signal hits the op amp. The response of the whole signal chain to a single non-zero sample will tell you something about the filters, but not about the op amp's slew rate.

Good design practice would demand an op amp whose slew rate is better than what's indicated by the bandwidth and maximal signal level of the preceding stages in the signal chain. Improving slew rate beyond that does not serve any useful purpose, and wouldn't have a noticeable effect on the impulse response.

slew rate for op amps

Reply #2 –
Quote
The marantz player definitely has better transient performance(at least to my ears).
In a blind, level-matched, listening test? 

....Typically, you won't hear "transient response" directly...    If there's a transient response issue, you'll probably hear frequency response variations.  In the case of "too slow" transients, an attenuation of high frequencies.  And in severe cases of "too fast" transient response, ringing.  But, the ear & brain don't have very good transient response so the ringing has to be severe before it's perceived as ringing.

I'm NOT an expert on slew rate, but from what I understand it limits the voltage-swing at high frequencies, so high-level high-frequency signals would be attenuated and lower-level high-frequency signals would be unattenuated or less-attenuated.  That would cause dynamic compression of the high frequencies.  It would also mean that high-level frequency response is worse than low-level frequency response.    A low slew rate would also distort the waveform, but since this is happening at the highest-audio frequencies, the distortion components should be supersonic.

Slew rate "damage" should also be limited by the fact that there isn't much high-amplitude high-frequency information in normal music.

slew rate for op amps

Reply #4 –
Quote from: cool n hot on
Hi. Lately I have been looking into slew rate specs for op amps, particularly for RCA output of CD players. For example my pioneer CD player and my marantz CD player have roughly 4v/ms and 6v/ms (microsecond) slew rate respectively. The marantz player definitely has better transient performance(at least to my ears). I've been to a web site that calculates the amount of slew rate needed for a particular voltage output and highest frequency to be encountered by which both of these CD players exceed this.  Does the slew rate have to be considered also for the width (the time taken) of the main lobe of the impulse response as well? Thank you so much.


Total waste of time.  The peak slew rate that a digital player can possible contrive to make is ridiculously low.

The maximum slew rate at the output of a DAC's reconstruction filter is given by:

2 x ? x F x V

where  ? is pi or 3.14159

F is the frequency in Hz

V is the peak-to-peak voltage which is 2.828 times the RMS voltage

So for a 96 KHz signal (192 KHz sample rate) that is 2 volts RMS, max slew rate is 1.7058 volts per microsecond.

For 44.1, max slew rate is about a quarter of that or under 0.5 v/ uSec.  Your existing op amps are already vast overkill.

As others have pointed out, a reasonable diagnosis of what you believe you hear is audio nervosa stimulated by sighted listening evaluations.

slew rate for op amps

Reply #5 –
So it's Myth Busted then.  Thank you all for replies.