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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 21st October 2017, 07:37 PM   #11
phase is offline phase  United States
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Id like to try a headphone amp made with several jrc muse02 op amps, they do some things really well.
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Old 21st October 2017, 07:45 PM   #12
jcx is offline jcx  United States
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Default I'd recommend higher current, power DSL drivers

parrallel and wrap in a multiloop with good audio input op amp
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Originally Posted by jcx View Post
6x TPA6120 dual op amps, rated 400 mA each op amp - parallel pairs biased against each other for Class A push-pull output (a little over 200 mA Class A bias for the headphone amp)

this is sized as a headphone amp so the outputs are cascaded for higher drive V (600 Ohm cans or the insanely low sensitivity AKG K1000)

TPA has exposed Cu power pad meant to be soldered to board for several W dissipation, by soldering "belly up" I contact them to the Cu slug of a pc cooler - running ~ 30 W quiescent total without fan

re arranging the I,V by flat paralleling you could get 2.4A, 15 V peak each channel for ~ 14 Wrms into 8 Ohms Class AB stereo

all up, both channels paralleled as a monoblock the shown components, heatsink should drive down to ~3 Ohms

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Old 21st October 2017, 09:03 PM   #13
CharlieLaub is offline CharlieLaub  United States
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Building a massively parallel op amp power amplifier
I designed and built a 16-amp-per-channel stereo 5532 headphone amp inspired by Self's Op-Amplifier. In the end I think it is a stupid idea for a power amp unless 10W is enough power including peaks. This is because the rail voltage is very limited, and that will be the same no matter what small-signal op-amp you choose. The 5532 is good because it is cheap, has very good performance, is well-characterized by Self, and has a low GBW so layout is not so critical, etc. Also, the 5532 generates a bit of heat per IC and this adds up to quite a bit of quiescent dissipation. That would of course be different for other op-amps (e.g. JFET input). For a headphone amp, it actually worked out well because typical drive levels top out around 1Vrms or so, and the rail voltages can be a more reasonable +/-12V. Self really had to push up the rails to the edge of IC reliability to squeeze out as much voltage headroom as possible from the 5532. I learned a good lesson in noise of paralleled amplifiers, and as I increased the number of 5532 amp channels in parallel from 1 to 16 the noise and THD all fell by a good amount, although at the moment can't recall exactly how much. The project is documented on the headphone forum here and was done about 3 years ago IIRC.

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.
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Old 21st October 2017, 10:44 PM   #14
Idiosyncrasy is offline Idiosyncrasy  Netherlands
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Building a massively parallel op amp power amplifier
Quote:
Originally Posted by jcx View Post
I'd recommend higher current, power DSL drivers
parrallel and wrap in a multiloop with good audio input op amp
Nice amp, I came across it in the other threads. I've a built a few composite amps for my headphones now and they're really fine. I could do something like OPC did with his LPUHP amp, but I chose this approach simply because it puts a smile on my face.
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Old 21st October 2017, 10:56 PM   #15
Idiosyncrasy is offline Idiosyncrasy  Netherlands
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Building a massively parallel op amp power amplifier
Quote:
Originally Posted by xrk971 View Post
Btw, parallel output devices can never sound as resolving or coherent as a single output device (or opamps). The analogy is the sound of a choir vs a soloist. It's just the limitations of being able to match perfectly.
Hey xrk, interesting observation. Is this based on your experience with parallelling the BF862?
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Old 22nd October 2017, 12:06 AM   #16
CharlieLaub is offline CharlieLaub  United States
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Building a massively parallel op amp power amplifier
Quote:
Originally Posted by xrk971 View Post
With parallel discrete output transistors we need to spend time matching them. I wonder if the same is true for parallel opamps? Btw, parallel output devices can never sound as resolving or coherent as a single output device (or opamps). The analogy is the sound of a choir vs a soloist. It's just the limitations of being able to match perfectly.
This really sounds like BS to me. Got any data to back that up?

Maybe when you are trying to reproduce signals in the 10s or 100s of MHz range... for the audio band the devices themselves are so much faster it should not make a difference.
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Old 22nd October 2017, 12:14 AM   #17
scottjoplin is offline scottjoplin  Wales
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Certainly when opamps are paralleled distortion decreases
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Old 22nd October 2017, 12:23 AM   #18
DPH is offline DPH  United States
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Quote:
Originally Posted by xrk971 View Post
With parallel discrete output transistors we need to spend time matching them. I wonder if the same is true for parallel opamps? Btw, parallel output devices can never sound as resolving or coherent as a single output device (or opamps). The analogy is the sound of a choir vs a soloist. It's just the limitations of being able to match perfectly.
Or you don't match them and maintain decent emitter resistance. Then the different transistors dither the crossover region.

Applying the same, you of course want output resistors to balance the load. No need to sweat it.
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Old 22nd October 2017, 12:24 AM   #19
CharlieLaub is offline CharlieLaub  United States
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Building a massively parallel op amp power amplifier
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Certainly when opamps are paralleled distortion decreases
NO! That is absolutely NOT correct. It's possible to get reduction in both noise and distortion with many op-amps in parallel. Self has described the noise benefits of parallelization, and you are welcome to check out this post of my measurements, and other posts in that thread:
My LM5532 Headphone Amplifier project - 16 amp stages in parallel per channel (measurements)
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Last edited by CharlieLaub; 22nd October 2017 at 12:29 AM.
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Old 22nd October 2017, 12:27 AM   #20
scottjoplin is offline scottjoplin  Wales
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No, can't be bothered, I choose to believe Doug Self
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