Rise time

Tweakers' Asylum

Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ.

In Reply to: Slew Rate posted by AudioTweaker on February 10, 2001 at 19:41:08:

The slew rate needed is related to rise time and voltage.A square wave is a sine wave with all its odd harmonics added.In theory all the odd harmonics out to infinity.In reality after the 25th harmonic it doesn't look much squarer.20khz plus its odd harmonics out to the 25th means 500khz.This translates to a 2ÂµS rise time.Now comes voltage.A CD player puts out roughly 2 volts.If the signal can rise 2 volts in 2ÂµS then it has a slew rate of 1 volt per ÂµS.This means we need a slew rate of .5 volts per ÂµS per peak volt of output.100 watts at 8 ohms with 3dB of headroom is 56 volts peak.Therefore a slew rate of 28 volts per ÂµS is adequate.This is where john came up with his figure.A SET with a 2A3 puts out 3 watts.If it has 3dB of headroom it can put out 10 volts on peaks at 8 ohms.If this amp could slew at 5 volts per ÂµS it would have a small signal bandwidth of 500khz.As regards your original question about op-amps I don't recommend going much faster than 20 V/ÂµS.As you can see from the pevious discussion the speed is not really needed.High speed circuit design requires very carefull circuit board layout and power supply de-coupling.Just dropping a high speed op-amp into a non-optimum layout generally sounds quite different.After a time you may notice it is noisy and the high-end sounds like an electric shaver.

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Follow Ups Full Thread

Topic - Slew Rate - AudioTweaker 19:41:08 02/10/01 (9)

Rise time - djk 02/11/0121:42:33 02/11/01 (7)

Re: Rise time - GM 02:15:28 02/12/01 (4)

Re: Rise time - djk 04:16:51 02/12/01 (3)

Re: Rise time - GM 17:38:53 02/12/01 (2)

Re: Rise time - john curl 20:01:00 02/12/01 (1)

Bingo! - Jon Risch 22:07:51 02/13/01 (0)

Re: Rise time - john curl 00:02:23 02/12/01 (1)

Thank You ! - djk 02:19:23 02/12/01 (0)

Re: Slew Rate - john curl 20:10:09 02/10/01 (0)

Follow Ups

Rise time - djk 02/11/0121:42:33 02/11/01 (7)

Re: Rise time - GM 02:15:28 02/12/01 (4)

Re: Rise time - djk 04:16:51 02/12/01 (3)

Re: Rise time - GM 17:38:53 02/12/01 (2)

Re: Rise time - john curl 20:01:00 02/12/01 (1)

Bingo! - Jon Risch 22:07:51 02/13/01 (0)

Re: Rise time - john curl 00:02:23 02/12/01 (1)

Thank You ! - djk 02:19:23 02/12/01 (0)

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