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Old 29th November 2012, 06:09 PM   #1
dmaumau is offline dmaumau  Brazil
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Default Op Amp Stacking - Sharp LA6520

Hello guys.

I have and OLD cd player based entirelly on a Sharp design, including the transport.

Just for fun I connected it on a several thousand dollars stereo system (Cary Audio, Dali, Audiopax and Audia Flight gear) and was completelly astounded when it sounded REALLY good. Let's say almost 9K US good.

Just for fun, you may buy one for 30 bucks online.

Well, it uses the Sanyo LA6520 as the output op amp and I tryed to stack another to see what would happen.

With the +VCC condered, no sound. With + Vcc disconnected it works fine for about 2-3 minutes then starts overheating.

I thought about adding an alluminum radiator like used on a poer transistor, but it would not be practical.

Could you guys gelp me with some ideas ?

BTW, obviously I could not make a serious audition, but the first biased impression is that the sound was even smoother with this stacking, so I would not like to abandon the idea.

I'm attaching the LA6520 datasheet so you guys may take a look.

Thanks.

Mauricio
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File Type: pdf LA6520.pdf (39.5 KB, 48 views)
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Old 29th November 2012, 06:28 PM   #2
DUG is offline DUG  Canada
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The amps probably have different Vos (input offset) and are fighting each other for control.

Paralleling opamps is not as simple as just putting them in parallel.

Let each have its own feedback resistor set for same gain and then measure the DC output from each.

If it is close then combine the two outputs through a couple of 47R resistors.

This way they probably won't blow up.
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Old 29th November 2012, 06:45 PM   #3
Mooly is online now Mooly  United Kingdom
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The LA6520 is a high power device more likely used as a motor/pickup coil driver. It won't be used for the audio stages.
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Old 29th November 2012, 07:19 PM   #4
dmaumau is offline dmaumau  Brazil
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Dear Moderator you might be right about that. Because what happened after 2 or 3 minutes was exactly that the motor sounded like skipping.

Darn

In my defense, I have an electronics degree, but haven't worked with since 1989, so it might have escaped me... LOL

Thanks for you insight.
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Old 29th November 2012, 07:42 PM   #5
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Both the 0.15V/uS slewrate and the PSRR are quite pathetic. So don't even consider using for audio purpose.
Maybe good for guitar distortion tough.
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Old 29th November 2012, 07:55 PM   #6
Mooly is online now Mooly  United Kingdom
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Your welcome
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Old 30th November 2012, 03:03 AM   #7
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I can confirm that the LA6520 is STRICTLY used as a motor & focus/tracking coil driver. I would fully expect it to get angry having another paralleled onto it.
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Old 30th November 2012, 11:18 AM   #8
dmaumau is offline dmaumau  Brazil
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hehehe, indeed he did...
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