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Old 26th November 2003, 08:47 PM   #11
Bricolo is offline Bricolo  France
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Default Re: kilometers Per hour

Quote:
Originally posted by Fred Dieckmann
Here's some Gain Bandwith products for some of the most popular op amps among
the DIY builders:

OPA627 16MHz

OPA604 20MHz

AD8610 25MHz

AD825 41MHz

OPA627 >50MHz

I think Per is probably in the neighborhood of a reasonable bandwidth. It sounds like a good idea to me.........
Fred, there's 2 OPA627. The 16MHz one is correct, but the other... maybe an OPA637?
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Old 26th November 2003, 08:51 PM   #12
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Default Re: Peranders

Quote:
Originally posted by ACD
This is serious!
Please explain to me the advantages of having audio gear that are able to reproduce 20MGHz and up.....
The harmonics are "long gone" at that frequency!!!!!
Sorry, Jan, I can't. First of all it's a thrill technically to scream out 20 MHz with gain from plain BC-transistors.

Hugh (and his many customers) on the other hand thinks that his rather slow AKSA amp is sounding good so there you have the opposites. I will come back later and tell you if 20 megagigaherts(!) is good or bad soundwise.
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Old 26th November 2003, 08:55 PM   #13
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Default Peranders

Thanks for your reply....
I was worried that you have gone "fanatic"
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Old 26th November 2003, 08:55 PM   #14
PMA is offline PMA  Europe
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Default Re: Re: Speed

Quote:
Originally posted by peranders

Maybe so, but I (or anyone else) can adjust that. Faster isn't automaticly better but building the prototype will give us the answers but I have a hunch about linearity and high speed. Normally this is positive.

Pcb's are ordered in case any wonders...
Yes, inherently fast and stable is good, but impulse response unfortunatelly tells nothing about intermodulation with D/A HF residuals. We have compared "unlimited" buffer-preamp (about 6MHz/-3dB) with filtered version (about 140 kHz/-3dB) and the final judge was clear - everyone of 10 listeners preferred the bandwidth limited version. Cleaner, less agresive, non-harsh, more details, more natural sound.
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Old 26th November 2003, 09:21 PM   #15
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Per, it is all about " fine tuning " of final product - I hope that you will inform us about this hearing experiences . Last arbiter is human ear, but it must be ears of guys, which have not " glass head " .
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Old 26th November 2003, 09:33 PM   #16
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I was one of this ten listeners - results was quite convincing, but I must say, that I have not " glass head " - for this guys are all frequencys over 20 kHz " dangerous " - for me it start over about 500 kHz .
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Old 26th November 2003, 10:38 PM   #17
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Default Some is paying attention....

"Fred, there's 2 OPA627. The 16MHz one is correct, but the other... maybe an OPA637?"

Yes indeed. thanks for the heads up.
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Old 27th November 2003, 01:46 AM   #18
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Default Even if it does work to 20 MHz.........

You still need to limit out-of-band signals!!!!! Nothng magical about that, just plain common sense engineering.

Jocko
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Old 27th November 2003, 05:41 AM   #19
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I would say, that this is one nice CFP amp.

The bandwidth is just fine.

Of course you need to limit the bandwidth with a LF filter in the input. ... lets say to 200KHz, but with this large bandwidth his amp has nearly the same distortion spectrum at 20k as at 1k. I think this is one parameter we all would like to get....

The ear is very sensitive to harmonics in its "window"....

Sonny
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Old 27th November 2003, 08:29 AM   #20
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Default Re: Re: Re: Speed

Quote:
Originally posted by PMA


Yes, inherently fast and stable is good, but impulse response unfortunatelly tells nothing about intermodulation with D/A HF residuals.
Listen up guys which remove the output filter of DAC's! The garbage from a DAC _can_ be audiable. If you happen to have a unit which produces unwanted (out of band) signals you should block these signals instread of creating circuits which can make them pass further in the chain.

Quote:
Originally posted by PMA
We have compared "unlimited" buffer-preamp (about 6MHz/-3dB) with filtered version (about 140 kHz/-3dB) and the final judge was clear - everyone of 10 listeners preferred the bandwidth limited version. Cleaner, less agresive, non-harsh, more details, more natural sound.
The reasons for this "bad" sound can be that high frequency residuals produces audiable "garbage".

My theory is to have a fast circuit BUT limit the incomning signal with a plain LP-filter at a sufficiently high frequency.

The amp we talk about here has also a input filter as every amp have which I have designed. This is just common pratice I think.

The design is very easy to adjust when in comes to speed and current consumption.
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