32 opamps in 50mm square buffer - diyAudio
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Old 30th December 2014, 05:32 PM   #1
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Default 32 opamps in 50mm square buffer

It says NE5532s, but any SO8. It might get warm... I don't have the time and energy to build and test this. It's all there, the schematic/layout is in Proteus7

What it looks like:

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I haven't done any mounting holes.

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Schematic:

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CAD files:

Attachment 456369

Schematics and layout files:

Attachment 456375

Power:

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Input:

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Output:

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Top pour:

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Bottom pour:

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I have retained decoupling to ground at each chip, rather than rail-to-rail.
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Old 30th December 2014, 11:48 PM   #2
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I don't get it.

edit: is this suppose to be a power amp to drive speakers?
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Old 31st December 2014, 12:15 AM   #3
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No, but it'll drive 16 ohms +. Not many headphones under 16 ohms.

Somebody asked about a low OP impedance buffer.

O/P impedance <0.4 ohms. If I've got the layout right, it'll have very low noise and distortion. 2 off will drive a speaker. As for input impedance, depends which opamps you use.
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Old 31st December 2014, 04:15 AM   #4
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Originally Posted by counter culture View Post
No, but it'll drive 16 ohms +. Not many headphones under 16 ohms.

Somebody asked about a low OP impedance buffer.

O/P impedance <0.4 ohms. If I've got the layout right, it'll have very low noise and distortion. 2 off will drive a speaker. As for input impedance, depends which opamps you use.
if its not intended to drive a speaker, why do you need low impedance?
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Old 31st December 2014, 08:00 AM   #5
andynax is offline andynax  Hong Kong
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LME49720 is better than NE5532 and the pirce just x4 only.

Try add Rin and Rf resister (750ohm) in each buffer circuit for further high-speed opamp upgrade ~AD827

Anyway, single opamp is better than dual opamp in one chip !!
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Old 31st December 2014, 08:39 AM   #6
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Why don't you use LME49600, LME49610 from TI?!
Everythings is more simple...
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Old 1st January 2015, 09:39 PM   #7
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Yes, but output impedance is 5~10 ohms. You need to include LME49600 in feedback loop with opamp to get low OP impedance. Output impedance here is <0.4 ohms. Of course this is entirely possible, but somebody asked about a low OP impedance buffer. This is a way of building one which is uncomplicated in principle and comparatively cheap. I have lots of headphone amplifiers of many varieties. They say it's the spice of life.
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Old 1st January 2015, 11:59 PM   #8
HotIce is offline HotIce  United States
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What's wrong with the 49600 in the feedback loop?
I have used many times in the typical configuration with an opamp VAS followed by the 49600 buffer.
I use to feedback both from the opamp output and and 49600 output, such that if the overall (with both feedback sources wired) gain is N, the opamp VAS stage itself (with the 49600 feedback line open, and the opamp one wired) has a gain of about 6..8 * N.
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Old 2nd January 2015, 12:39 AM   #9
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What's wrong with the 49600 in the feedback loop?
Nothing. It wasn't what the guy wanted though. Somebody suggested a beefed-up diamond buffer, with high bias current. I thought, 'How can I do this without thinking much?'

You'll get at least twice the current of a 49600, more depending on opamp.
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Old 2nd January 2015, 12:41 AM   #10
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Quote:
Originally Posted by counter culture View Post
No, but it'll drive 16 ohms +. Not many headphones under 16 ohms.

Somebody asked about a low OP impedance buffer.

O/P impedance <0.4 ohms. If I've got the layout right, it'll have very low noise and distortion. 2 off will drive a speaker. As for input impedance, depends which opamps you use.
I have done something similar recently with DIP packages and onboard regulated power supply for a headphone amp within 100mmx100mm. I put 5532 packages and bypass caps on both sides and packed everything into the available space. Works great and could also be used as a buffer as you have mentioned. See: My LM5532 Headphone Amplifier project

I think that your design has one potentially serious flaw. The inputs for all of your 5532s are in parallel. The input impedance can be as low as 35k ohm per amplifier from the datasheet with 100k-300k more typical. But still, with so many buffers in parallel you need to feed some real current to the input. You almost need another buffer upstream to drive the input to this board! Also, have you calculated the quiescent current that all those 5532s need even if there is no input signal? PS requirements may be getting a bit high and at some point additional 5532s in parallel are not gaining you anything really.

I used 16 amplifiers (8 dual amp 5532 packages) per channel and drove the 5532s using a LME49720. This also allowed me to have a sane input impedance to my board but still have several 5532s in parallel for the output.

My suggestions are to reduce the number of 5532s acting as buffers and convert the space that you free up to a proper input stage with the required parts for DC blocking and RF filtering. Keep an eye on the input impedance, or distortion will climb. This would likely make the board more practical and better performing in real world use.
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