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Old 5th September 2009, 10:55 PM   #41
cbdb is offline cbdb  Canada
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Just a couple of notes. Most opamps have lots of gain at low freq but usually start to drop (6db/oct) at as low as 10 hz (60 db down by 8Khz). Most opamps cant handle the voltages in power amps. Most designs need the gain stages to run near the same voltage as the outputs. Most opamps cant handle more than +- 20 volts. The number of opamps avialable today is unbelivable, and they have a lot more parameters than gain and noise to consider. There's an excellent resource on this site; someone tested the distortions of 35? opamps and posted a 250 page PDF of the results Its called opamp distortion.
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Old 5th September 2009, 11:16 PM   #42
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Originally Posted by Borat View Post
Is using a high-end op amp for gain stage an acceptable practice in an ultra-high-end amplifier ?

is the practice mostly avoided out of snobbery or are there actual downsides ?

if there are downsides are these subjective or measured ?

also if ther are downsides how can we explain what causes them ?
Are you talking about a gain stage inside the amplifier feedback loop? You want to be careful with that because the loop gain will be the opamp's gain added to the subsequent follower gains, and unfortunately their phase shifts also add up as well. The phase margin at unity gain might very well disappear as a result, so you could have a lovely hundred watt RF oscillator - until the output devices melt.

http://en.wikipedia.org/wiki/Phase_margin
http://en.wikipedia.org/wiki/Nyquist...lity_criterion
http://en.wikipedia.org/wiki/Bode_pl...d_phase_margin
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Old 7th September 2009, 02:12 PM   #43
Bigun is offline Bigun  Canada
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I would imagine (having not used any before) that Opamps would make perfectly acceptable components in some amplifiers - it depends on the goals of the builder.

Perhaps, a factor that some might not admit, is that DIY amp building is one of the last bastions of electronics where we can build something that is still relatively simple, using parts and circuits that we can (almost) fully understand, see, measure and tinker with. Where for the most part we can build circuits without tweezers and a microscope (SMT). An OpAmp takes that enjoyment away by burying it's secrets inside a 'black box'. It isn't a big jump from that to finding reasons to avoid them.

All of the music you listen to has very likely passed through several OpAmps in it's journey from the originator to your amplifier.
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Old 7th September 2009, 03:05 PM   #44
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All of the music you listen to has very likely passed through several OpAmps in it's journey from the originator to your amplifier.
Yes, I've heard this argument a number of times. IMO it's the monotony that bothers us, not that record X has a sound that's made up by microphones and electronics as long as record Y or record Z has a totally different sound.

I think monotony is one of the reasons why people constantly roll opamps, or change any other part in their sound system or strive for the perfect sound without coloration. They get tired of hearing a certain coloration.

If all records sounded like Associates "Sulk", The Cure's "Charlotte sometimes" or Simple minds "Sparkle in the rain", it would be unbearable. Still those are great recordings with a "perfect" sound.
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Old 7th September 2009, 03:23 PM   #45
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Originally Posted by nelsonvandal View Post
Yes, I've heard this argument a number of times. IMO it's the monotony that bothers us, not that record X has a sound that's made up by microphones and electronics as long as record Y or record Z has a totally different sound.

I think monotony is one of the reasons why people constantly roll opamps, or change any other part in their sound system or strive for the perfect sound without coloration. They get tired of hearing a certain coloration.

If all records sounded like Associates "Sulk", The Cure's "Charlotte sometimes" or Simple minds "Sparkle in the rain", it would be unbearable. Still those are great recordings with a "perfect" sound.
Exactly!
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