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Old 5th June 2004, 03:17 AM   #1
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Default unbal-balanced driver with opamp

What is the best possible unbalance-balance converter using opamp? In RodE's site he's using a cross feedback between 2 opamps (like C). Is this giving better performance than stand alone (B)?
I saw (A) in here. Is (A) possible to make unbalance-balance converter?
Maybe I draw (C) wrongly. RodE using 3 opamp. I saw these kind of configuration with 2 opamps, in PDF somewhere in here, but forgot how it looks like, feedback crossing with only 2 opamps. Anyone can help, which opamp pdf datasheet have drawings like (C)?
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Old 5th June 2004, 04:04 AM   #2
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A has positive feedback, so i'd say not to use it.
B has a lot of resistors. they must be chosen such that the resistors on the bottom opamp are 2x the resistors on the top.
C doens't look like it works.
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Old 5th June 2004, 04:43 AM   #3
jleaman is offline jleaman  Belgium
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What about just useing a balanced chip ? I ordered a few samples they go from rca to balanced and there pretty cheap.
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Old 5th June 2004, 05:22 AM   #4
mandat is offline mandat  Poland
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Look at Texas Instrument home page and search Burr-Brown's OPA1632.
The OPA1632 is a fully-differential amplifier from input stage to output stage. It is dedicated to driving high-performance ADCs.
FEATURES:
Distortion: 0.000022%, Noise: 1.3nV/SQRT Hz, SR: 50V/s, GBW: 180MHz
Supply: 2.5V to 16V, Power Shutdown option.

The OPA1632 is available in an SO-8 package and a MSOP-8 PowerPAD package.
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Old 5th June 2004, 07:26 AM   #5
mikeks is offline mikeks  United Kingdom
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try this

http://diyaudio.com/forums/showthrea...726&highlight=
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Old 5th June 2004, 02:46 PM   #6
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This circuit is best:

http://focus.ti.com/lit/ds/symlink/drv135.pdf

It mimics a transformer.
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Old 5th June 2004, 03:38 PM   #7
mandat is offline mandat  Poland
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This a copy from a THS4130 datasheet, an older brother of OPA1632. In this case you use one opamp, only.
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Old 5th June 2004, 09:56 PM   #8
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To the unwashed, the 1632 circuit looks similar to the 135 circuit, but close examination shows that it is not.

If you actually intend to send audio any distance down a balanced line, the circuit must mimic a transformer.

If you actually intend to receive audio any distance down a balanced line, the receiver must be a transformer. The receiver chips, despite their 0.001% matching of resistors, are up to 50dB worse than a transformer.

Those that have been to the balanced line seminar at CEDIA will be familiar with these ideas.
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Old 5th June 2004, 10:07 PM   #9
markp is offline markp  United States
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Take a look at these http://www.analog.com/Analog_Root/pr...2142%2C00.html
They work really well in everything I've used them for. Low noise and the ability to drive very long cables. Its an easy one chip solution.
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Old 6th June 2004, 02:50 AM   #10
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While the SSM2142 mimics the performance of fully balanced
transformer-based solution for line driving, the previously linked to TI/BB DRV135 is an IMPROVED REPLACEMENT FOR SSM2142.

The SSM2142/2141 is the SPECIFIC CHIP SET used in the CEDIA seminar showing that this solution can be up to 50dB worse than using a transformer for the receiver.
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