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Building a massively parallel op amp power amplifier
Building a massively parallel op amp power amplifier
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Old 22nd October 2017, 01:29 AM   #21
DPH is offline DPH  United States
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Or Charlie it's sitting in the errors of your measurements.
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Old 22nd October 2017, 01:38 AM   #22
CharlieLaub is offline CharlieLaub  United States
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Quote:
Originally Posted by DPH View Post
Or Charlie it's sitting in the errors of your measurements.
What's sitting in the error?
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Old 22nd October 2017, 01:46 AM   #23
DPH is offline DPH  United States
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Your parallel experiments are showing errors down in the >-110 dB range. Worse or better at that level from a sound card without a good distortion amplifier is at or below the resolution the test can deliver.

Especially if the distortion is already low, a very marginal improvement is easily lost in error bars of a test.

Reading your edit, I think we might be driving at the same point.
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Old 22nd October 2017, 01:57 AM   #24
CharlieLaub is offline CharlieLaub  United States
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Quote:
Originally Posted by DPH View Post
Your parallel experiments are showing errors down in the >-110 dB range. Worse or better at that level from a sound card without a good distortion amplifier is at or below the resolution the test can deliver.

Especially if the distortion is already low, a very marginal improvement is easily lost in error bars of a test.

Reading your edit, I think we might be driving at the same point.
You only need to read the two or three posts above the one I linked to to find answers to your questions about sensitivity limits, noise and distortion improvements, etc.
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Old 22nd October 2017, 08:34 AM   #25
Idiosyncrasy is offline Idiosyncrasy  Netherlands
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Originally Posted by CharlieLaub View Post
I designed and built a 16-amp-per-channel stereo 5532 headphone amp inspired by Self's Op-Amplifier.
Charlie, I had a look at your project thread; the quiescent current is indeed something to keep in mind. The quiescent dissipation of the LME49720 is comparable to that of the 5532 ICs, so keeping the supply voltage as low as possible will be important. As I wrote before, my preferred listening level doesn't require heaps of output power.

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Instead of doing this work of folly, build a decent class-A amp of 20W a la FirstWatt, or a quiet single ended amp like the MR7-MKIV. These will be a much better use of your time and money.
I like a good class A amp as much as the next guy on this board. I really want to do something akin to this peculiar amp by Self though for this project.

Edit: the application note from Analog Devices that jcx linked to in that thread provides some solid info for op amp decoupling in various configurations, for example, when bridging amplifiers.

Last edited by Idiosyncrasy; 22nd October 2017 at 08:39 AM.
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Old 22nd October 2017, 06:35 PM   #26
xrk971 is offline xrk971  United States
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Building a massively parallel op amp power amplifier
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Originally Posted by jcx View Post
parrallel and wrap in a multiloop with good audio input op amp
This is a cool looking design with big PC cooler. 200mA is huge - nice.

Click the image to open in full size.
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Old 22nd October 2017, 08:47 PM   #27
Idiosyncrasy is offline Idiosyncrasy  Netherlands
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A sneak peek at the circuit board layout (work in progress -- ignore the color scheme if you will; the preview has been configured to resemble OSH Park boards ):

Building a massively parallel op amp power amplifier-20171022-pcb-layout-progress-png

I've also been optimizing some of the resistor values to further reduce the input stage noise without sacrificing distortion performance (in the sim, at least). Plus, a couple of jumpers have been added here and there for testing and verification of isolated parts on the board.
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Old 22nd October 2017, 09:51 PM   #28
DPH is offline DPH  United States
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Originally Posted by CharlieLaub View Post
You only need to read the two or three posts above the one I linked to to find answers to your questions about sensitivity limits, noise and distortion improvements, etc.
There's a difference between what the software says and your limits of detection. I did not read anywhere that really characterizes your measurement setup, just load conditions etc. Long ffts aren't enough (and may cause other issues). But I'm not trying to be adversarial, just to state that any improvement or not in your setup could easily be lost in the limits of the test. But it's also a low enough error as to be essentially meaningless for audio purposes.

Anyhow, in any case you're results are fine, please don't worry or let it dilute the discussion here.
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Old 22nd October 2017, 09:55 PM   #29
DPH is offline DPH  United States
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OP, given the design and differential input, would it make sense to drop the voltage further and go bridged?
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Old 22nd October 2017, 10:05 PM   #30
flyingfishtw is offline flyingfishtw  Taiwan
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Default Did you buy the op?

Good news everyone, if you haven't buy op amp, you should consider LME49860 for 2 reasons,

1. it's the same as LME49720 just with better voltage tolerance, 22V
2. I think it's end of product life, so on LME49860MA/NOPB - TEXAS INSTRUMENTS - AUDIO AMPLIFIER, CLASS AB, SOIC-8 | e络盟 台湾 it cost 1.5 dollar, half price compare to LME49720

If you know how to dissipate the heat, it will be a good choice, provides more power, +- 21V output voltage.

Heat is your enemy, quiescent current is around 10mA each, @JA 145C/W. Just the idle temperature will be 42*0.01A*145 = 60 degree, and you have to add signal power dissipate as well, I don't know how to calculate that.

Maybe a copper sheet on top of the SOIC top??
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