ANY AMPLIFIER WITH SLEW RATE GREATER THAN 50V/ýs? - diyAudio
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Old 9th July 2008, 10:14 AM   #1
fotios is offline fotios  Greece
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Default ANY AMPLIFIER WITH SLEW RATE GREATER THAN 50V/ýs?

Is there any amplifier with voltage slew rate bigger than 50V/ýs? Please not words, only documents like this one quoted below. Also the calculation should be the same as that made by G. Kleinsmidth in below curve. Glen estimated that the slew rate of an amplifier it is 30V/ýs from this curve. Please use the same method.

Click the image to open in full size.
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Old 9th July 2008, 01:54 PM   #2
sreten is online now sreten  United Kingdom
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Hi,

There are amplifiers with > 50V/uS slew rate, and the way it is
measured does not matter as long as the method is accurate.

Your post seems pointless .....

/sreten.
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Old 9th July 2008, 04:55 PM   #3
fotios is offline fotios  Greece
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Quote:
Originally posted by sreten
Hi,

There are amplifiers with > 50V/uS slew rate, and the way it is
measured does not matter as long as the method is accurate.

Your post seems pointless .....

/sreten.
Instead of a vague answer, can you post a curve of output rise time, of an amplifier of those you refer, obtained from a DSO?
So as to be able to calculate the slew rate as did Glen Kleinsmidth? My post it is not so pointless as you suppose, sreten, as it has a specific objective which will see then.
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Old 9th July 2008, 05:02 PM   #4
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Fotios, you are mixing and confusing slew rate with rise time limiting. One adds harmonics, while the other filters out harmonics. This is the source of your problem. Most of us usually deliberately rise time limit our designs to remove RF passthrough, noise, and to make the design 'slew rate proof'. You must REMOVE the bandwidth limitation or increase the drive voltage to really measure the slew rate.
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Old 9th July 2008, 05:07 PM   #5
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Fotios, I assume you are talking discrete power amps, since you can easily get op amps with several thousand V/us for a few dollars. Then you must also take the output power into consideration when comparing power amps.
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Old 9th July 2008, 06:11 PM   #6
fotios is offline fotios  Greece
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Quote:
Originally posted by john curl
Fotios, you are mixing and confusing slew rate with rise time limiting. One adds harmonics, while the other filters out harmonics. This is the source of your problem. Most of us usually deliberately rise time limit our designs to remove RF passthrough, noise, and to make the design 'slew rate proof'. You must REMOVE the bandwidth limitation or increase the drive voltage to really measure the slew rate.
Mr. Curl thanks for your reply which is picking up the meaning of my post with the curve quoted. Without wanting to sound selfish (that i know everything) i know well the difference between them. But these, you must tell to Glen Kleinsmidth, and not to me. He was which made the calculation of slew rate by this curve intended exclusively for measuring the rise time of an amplifier at full power loaded with 8┘, with feedback closed, with Cdom in place, as well input-output filters in action. As for me, never i tried to measure slew rate. I am only interested for measuring the rise time, and i have as target values between 1,5 to 1,8ýs without load in full output swing, and as much 2,1 to 2,2ýs with 8┘ load in full output swing. And i know that this value it is same for any frequency from 20Hz to 100KHz. During this, i compromise with the value in which the amplifier it is stable (without any overshoot or noise). Moreover the only instruments that i have for measurements are one DSO 50MHZ and one function generator 10MHz both of Hameg. That is my budget.

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Old 10th July 2008, 03:14 AM   #7
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one reliable way of measuring slew rate is to apply a sine wave and increase the frequency until slew rate limiting makes the output triangular. the slew rate can then be calculated from the resulting oscope trace. also positive going and negative slew rates may be different. this method doesn't need a pulse generator or a square wave generator with high rise and fall times, once the sine wave is triangularized, the amp no longer swings rail to rail, and the amp doesn't need to be driven to high output swings to see this effect (at lower input voltages, the frequency where slew rate limiting begins will be higher than when the amp is driven rail to rail).
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Old 10th July 2008, 06:05 AM   #8
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I prefer a Heathkit, sine-square generator for my slew rate measurements. It is very fast.
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Old 10th July 2008, 06:35 AM   #9
Eva is offline Eva  Spain
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Are you trying to drive 80Khz ultrasound transducers?

Both digital and analog recordings are inherently slew rate limited. For example, a 200W@8ohm amplifier connected to a standard 44Khz digital source and playing full volume will never be asked for more than 8V/us. In practice, a music signal will hardly ask for more than half that.

BTW: The required s.r. for a sine wave is 2*pi*V_ampl*freq
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Old 10th July 2008, 07:28 AM   #10
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198 V/uS. This is a headphone amp, but it can be used to drive speakers as well. Amb is a very clever guy, well known in the DIY headphone world, and he's very generous sharing his knowledge. We're lucky to have such people at our discussion forums.
http://www.amb.org/audio/beta22/
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