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Old 10th March 2011, 03:23 AM   #1
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Join Date: Feb 2007
Location: HICKSVILLE TN
Default Balanced Line driver help.. noisy

I have attached 2 schematics ( one borrowed , one done by an old acquaintance) for a balanced line driver. I need two things. What can I do to improve them for noise performance? We built the BLD REV.pdf as shown on a PCB layed out at the local tech skool. The sucker was ok, but I got lots of hiss and noise in my car amp and some buzzing(grounding?) It was also very noisy when just driven from my home preamp ( no dc coupling in car)

The second circuit I do not understand where the +/- legs are for the output..
Which circuit would you use and what improvements can we make?

I'll bread board the next unit and then have a professional board done when I'm happy.

The criteria is super low Thd and noise. I intend to use this line drive in both my car and home( I got a long cable runs in both and my gear will accept balanced inputs). I've searched the forums but I must be looking in the wrong place I guess. I want to isolated I/O to eliminate as much noise as possible and ground contamination and a minimum gain of 12 db.. my pres only put out between 1-2 V.

Thanks for time in advance.
BUBBA the electrified gearhead.


PS I have samples of AD8599, LM4562, OPA1642, TLE2072 and 1 set of OPA627 and opa1612 I assume a 10K input impedance would be "normal and 600ohm on the outputs?
Everything I've read and from some previous circuit swapping has me favoring the 8599 but I may be totally clueless here.
Attached Files
File Type: pdf BLD REV .PDF (50.5 KB, 58 views)
File Type: pdf BLD REV 2.PDF (21.0 KB, 39 views)

Last edited by IMSTOOPID; 10th March 2011 at 03:37 AM.
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Old 11th March 2011, 12:41 AM   #2
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Join Date: Feb 2007
Location: HICKSVILLE TN
Default oops

ok been studying this and I need help..I;m not sure what would constitute the best balanced circuit, but I realized one of my circuit scans sucked so I'm reposting it. really just need some general guidance.. I'm not a circuti designer but I can do good board layout, understand the basics of decoupling and filter caps and general stuff but actually making the circuits work..I'M LOST..thanks
Attached Images
File Type: jpg BLD REV2.JPG (858.8 KB, 119 views)
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Old 11th March 2011, 10:50 AM   #3
AndrewT is offline AndrewT  Scotland
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read Walt Jung, ESP, Jensen, Pass diy, D.Self for information about why balanced impedance connections are used, how to achieve them and what to avoid.
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regards Andrew T.
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Old 11th March 2011, 03:01 PM   #4
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Join Date: Nov 2008
Your second circuit is not balanced , but single ended out.
Your first circuit is OK but not a true balanced but a differential output. It will do unfunny things when an output is grounded.
Check the Analog Devices SSM-2142 (or sim. parts) and their app notes on it.
E
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Old 11th March 2011, 03:14 PM   #5
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Join Date: Feb 2007
Location: HICKSVILLE TN
I DID PROBLEM SOLVED..THANKS LUKUS!!!!

YES I DO PRO GEAR..A I undertstand the need for balanced impedence, THAT'S WHY THE FIRST CIRCUIT HAD ME KINDA BAFFLED.

yes I posted the wrong circuit on the 2nd one.. one output would mean single ended right>>LOL thanks for the ref to the AD-SSM too..I'll read that.!
thanks guys.
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