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Old 24th April 2003, 05:03 AM   #11
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I use the LM353 and NE5532 still to fool around with....they are cheap and output noise is half decent in non crucial demands..just my 1/2 a canadian cent LOL
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Old 24th April 2003, 11:19 PM   #12
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5532/34 is stil a fine amp...although I think TI is the only one who does it justice.
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Old 26th April 2003, 04:13 PM   #13
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Your standard op amp can be bade to operate at higher Rail voltages by a method called bootstraping. see the AN-211 from ADI http://www.analog.com/UploadedFiles/...17334AN211.pdf
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Old 26th April 2003, 04:38 PM   #14
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this is a basic bootstraped op amp. you must be sure your chosen device is free from phase reversal if the Input is overdriven as this will cause seriose damage to this circuit is that happens. Most modern op amps meet this requirement however some older FET input Op amps are prone to this. check data sheet.
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Old 26th April 2003, 05:44 PM   #15
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Current feedback by a patented design could be something? This Mark Alexander amp is not very well regarded here but I think it's quite intersting. I help a friend many years ago with this amp and it worked alright. I have tried this concept myself with excellent results. Check here
Original, but I have a better copy of the scanned document. Send me a message if you want the better one.
http://www.analog.com/library/applic...udio/AN211.pdf
http://homepages.strath.ac.uk/~cnbp111/amp1.html
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Old 26th April 2003, 05:50 PM   #16
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during the tube days, people would put a small (and high wattage) resistor between the speaker and the ground and use that for negative feedback. I have seen some SS amps with that design and tried one myself. Not much sonic improvement other than for a subwoofer.

Anyone remember those designs?
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Old 26th April 2003, 11:30 PM   #17
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millwood> Ah... Yes i do Remember those days and also alot of old Kenwood Tube Amps and receivers had a switch that allow different damping factors using a similar technique.

peranders> Hi glad you droped in. The alxender circuit was intended only as an illistration of the Bootstraped Technique i talked about. I was not intending to indicate it was any Kind of sonic marval.

I have used Just plain BUF-634 Buffers Bootstraped to High Voltage transistors to follow a tube output stage in a topology similar to my posted op amp schematic above with splendid results. sure true Tube-O-Files could detect the solid state eliment in the sound But over all no one complained about the sound and alot of local Tube Equipment owners have since adopted this technique into there equipment in order to gain low impedance drive for stuff like Headphones.
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Old 28th April 2003, 02:31 PM   #18
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Default Re: op amp recommendations

Quote:
Originally posted by millwood

I like to get about 100w out of this amp so I am looking for an op amp with slew rate roughtly in the 35-40v/us range.

Any suggestions? thanks in advance.

Use an output stage with gain, and you will not need a high-slew op-amp.
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Old 29th April 2003, 01:49 PM   #19
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Thumbs up ...to continue...

The hypothetical op-amp., G1, (see attached), with a slew rate of 40V/uS, is connected to an output stage, G2, with a gain of 10, and the whole is enclosed in global feedback loop, giving an overall closed loop gain of 40.

It is straightfowardly demonstrated that the output slews at approx. 400V/us. This obviously assumes that the output stage possess a slew rate well in excess of this figure, otherwise the overall slew rate is then determined by the output stage.

This is almost invariably the case, and should therefore not be a concern.
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