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Old 15th August 2015, 10:56 AM   #1
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Default parallel opamp amplifier

Currently i'm building my latest headphone amplifier.

It uses 2 dual opamps per side. 1 opamp channel for voltage amplification and 3 opamp channels as buffer in parallel. Global feedback is used.

Very small, only 50x100mm including mains powersupply.


It is my first design with SMD components. First test are good. Very quiet, and more then enough drive for low impedance headphone.
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Old 15th August 2015, 10:57 AM   #2
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Circuit diagram?
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Old 15th August 2015, 11:00 AM   #3
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Bit small , will try to post a bigger one later.

By the way, I'm stll waiting for SMD voltage regulators, that's why I have temporary used TO-92 parts.
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Old 15th August 2015, 12:51 PM   #4
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You should better use a buffer ic like BB BUF634 or LME49990.

As input ic you should a modern BJT or DIFET OPAMP.

Last edited by Keruskerfuerst; 15th August 2015 at 12:57 PM.
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Old 16th August 2015, 08:04 AM   #5
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Could do that, but as this was my first ever SMD layout i decided to use cheap commonly available parts. PCB including all components is only around 15 Euro



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Originally Posted by Keruskerfuerst View Post
You should better use a buffer ic like BB BUF634 or LME49990.

As input ic you should a modern BJT or DIFET OPAMP.
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Old 16th August 2015, 08:32 AM   #6
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Neat looking PCB. Mooly did a test recently comparing arrays of 5 different opamps. It was virtually impossible to hear any differences at all, and those who said they did had preferences all over the map. The one thing it proved is that preconceived notions are stronger than reality. In other words, your choice for ne5532 is an excellent one.
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Old 16th August 2015, 10:11 AM   #7
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Thanks, I'm very pleased with the result untill now. Sounds great. Just waiting for the SMD voltage regulators. I temporarily used TO-92 parts to test the board.


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Originally Posted by vacuphile View Post
Neat looking PCB. Mooly did a test recently comparing arrays of 5 different opamps. It was virtually impossible to hear any differences at all, and those who said they did had preferences all over the map. The one thing it proved is that preconceived notions are stronger than reality. In other words, your choice for ne5532 is an excellent one.
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Old 16th August 2015, 10:15 AM   #8
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Btw, I see you use 100Ohm resistors after the paralleled opamps. 1 Ohm might be better.
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Old 16th August 2015, 04:04 PM   #9
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That low? Doesn't this give too much imbalance between the parallel opamps?


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Btw, I see you use 100Ohm resistors after the paralleled opamps. 1 Ohm might be better.
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Old 16th August 2015, 04:44 PM   #10
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Originally Posted by sevenup2278 View Post
That low? Doesn't this give too much imbalance between the parallel opamps?
I agree that 100 Ohms here is excessive and will result in needlessly wasted output current capability. The determining factors for output balancing resistors is the maximum output offset voltage differential divided by output current. The 5532 has a maximum input offset voltage of 5mV (worst case) and a maximum output current of 60mA (short circuit.) Since the output buffers are unity gain, maximum output differential between them is 10mV. So doing the math, 10mV divided by 60mA gives 17 mOhms. Using the "rule of ten" the balancing resistors should be at least 1.7 Ohms, but any value up to around 10 Ohms should work just fine.

Mike

Last edited by Michael Bean; 16th August 2015 at 04:46 PM.
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