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Old 13th February 2006, 12:34 AM   #1
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Default CF-Opamp

Hi,
what current-feedback opamp suitable for high quality audio with very low input offset do you know of?
Is the AD811 with the 3mV top notch?
Rüdiger
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Old 14th February 2006, 04:04 AM   #2
jcx is offline jcx  United States
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ad811 was simply early not best or even very good by today's standards

search for asl dsl reciver or driver op amps from ad, linear, ti, ...

TPA6120 has good audio specs but few cfa's will have really low Vos by today's precision op amp standards (<1mV) - servo, manual trim or ac couple
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Old 14th February 2006, 04:35 AM   #3
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Two-Stage Current-Feedback Amplifier
by Will Drachler
The AD8011's excellent performance (table) and power economy are due to a unique two-gain-stage current-feedback architecture (Figure A1) and fabrication on Analog Devices's bonded-wafer extra-fast complementary bipolar (XFCB) process.
Two-Stage Current-Feedback Amplifier

AD8011
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Old 18th February 2006, 04:09 PM   #4
testlab is offline testlab  United States
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Current FB amplifiers are attractive because they are typically very fast and circuit bandwidth is relatively independent of gain. They are typically used for video amplifiers.

The down side for audio use is that, due to their speed, layout and output impedence matching can be critical. These things will oscillate at the drop of a hat. Also, the output impedences are not typically suitable for audio circuits.
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Old 18th February 2006, 05:50 PM   #5
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Default Re: CF-Opamp

Quote:
Originally posted by Onvinyl
Hi,
what current-feedback opamp suitable for high quality audio with very low input offset do you know of?
Is the AD811 with the 3mV top notch?
I have a couple current feedback amps in my bag. One of them with discrete design had 0.00046% distortion. I recommend that you read some about current feedback because they won't simply work in some applications and the reason is the feedback. The feedback mechanism is different compared to voltage feedback. Walt Jung has a chapter about this in his 1000 pages book "Opamp Applications" which can download from Analog Devices.
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Old 18th February 2006, 11:04 PM   #6
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Old 3rd April 2006, 04:09 PM   #7
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Quote:
Originally posted by jcx
ad811 was simply early not best or even very good by today's standards

search for asl dsl reciver or driver op amps from ad, linear, ti, ...

TPA6120 has good audio specs but few cfa's will have really low Vos by today's precision op amp standards (<1mV) - servo, manual trim or ac couple
Yes, there are a couple of newer ones available. But, looking closer, i have not found any that has all the needed features the ad811 has:
- low voltage noise (mandatory)
- low input offset voltage (3mV max, however, I have 8 examples here, all measuring between 0.2 - 0.4mV) (mandatory)
- high slew rate (don't know how important that is at the end of the day, but the ad811 sounds good )

Due to bad PSSR of the ad811, one needs a good PSU, however.
any comments?
Rüdiger
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