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Old 23rd January 2013, 10:27 PM   #11
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by portreathbeach View Post
I'm still thinking of having a go at building something like this and the
NE5532s are way cheaper than the OPA2134, but are they as good?
Hi,

A handful of chips are better than the 5532 for audio but way more expensive.

The way Self uses them in the 5532 power amplifier probably means
you'll get very little benefit using way more expensive chips in a
different topology, or trying using them in the same topology.

If you have enough op-amps and overdrive the amplifier it will clip
near the rail voltages. If you don't have enough op-amps for the
current it will clip at lower voltage swings somewhat differently.

I'm not sure why such low value current sharing resistors are used.
Pretty sure anything up to 10R or so would work just fine.

rgds, sreten.
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Old 23rd January 2013, 10:40 PM   #12
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Cheers Sreten. Is something like this worth building in your opinion. It sure would look cool with stacks of boards populated with OpAmps, but would it sound any good? It would be nice if it sounded as good as my headphone amp I built that uses a single OpAmp. I spose I need to design and build it....... I'm still working on my DAC/Pre Amp, will be finished eventually if I don't keep getting distracted with other projects
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Old 23rd January 2013, 11:02 PM   #13
sreten is offline sreten  United Kingdom
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Hi,

I'm one of those people that thinks that basically only badly designed
amplifiers don't sound good, and the merits of decent designs hard
to judge. For sure the 5332 amplifier will have low distortion, but
as to sounding good I don't know, I've never heard one.

Seems to me more a case of it can be done, so here it is.
As usual with Self everything seems to be done properly

Certainly more practical than the "Beast with a thousand J-Fets".

rgds, sreten.
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Last edited by sreten; 23rd January 2013 at 11:06 PM.
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Old 23rd January 2013, 11:08 PM   #14
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Did you see the link I posted at the start of the thread:

SoundStageXtreme.com | UltraAudio.com | Blue Circle Audio NSL Stereo Amplifier

Looks like each channel has 6 boards of 16 OpAmp packages, that's 192 per channel! It's loads, but as you said, no where near as many as the 'Beast with a thousand J-Fets'
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Old 23rd January 2013, 11:57 PM   #15
jcx is offline jcx  United States
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you can ease the task by using higher current op amp, packaged with heatsinking in mind

the 6x TPA6120 (duals) clamped to the CPU heat sink Cu slug could be rearranged to be in parallel Opamp based Amps - Question
Click the image to open in full size.

Last edited by jcx; 23rd January 2013 at 11:59 PM.
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Old 24th January 2013, 03:33 AM   #16
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I presume the series resistors at the ouput of each opamp is to keep the opamps from dragging each other around, ie. isolation.

They do the same sort of thing with the LM3886 parallel designs, I presume others as well...

Btw, Gilbert also made some amps into womens shoes some years back for CES...

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Old 24th January 2013, 03:48 AM   #17
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by bear View Post
I presume the series resistors at the output of each opamp is to
keep the opamps from dragging each other around, ie. isolation.
_-_-
Hi,

I know what they are for, and why they are needed, but
cannot make much sense of the chosen value, seems low.

rgds, sreten.
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Old 24th January 2013, 04:36 AM   #18
jcx is offline jcx  United States
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I used 1 Ohm, the calculation is what max gain and Vos error will cause how much Vout difference between paralleld amps - and how much current output capability you're willing to "waste"
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Old 24th January 2013, 04:53 AM   #19
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I was looking at this circuit a couple of months ago. I have been trying out a few headphone amp circuits on a breadboard (gonna build one or three when I make my mind up) and I tried a 5532 in a master/slave buffer circuit with equal currents (10 ohm resistors in the prototype; could be tweaked). I was surprised at how well it worked into generic 32 ohm phones. It sounded very clear and dynamic, with good lows and highs. I will try 3x2 (6 opamps) master/slaves in parallel.
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Old 24th January 2013, 07:50 AM   #20
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The reason I originally was looking at using high resistors, 560R, was that it would limit the current the opamp could put out.

Anyway jcx, nice looking heat sink on that amp! How does it sound? I didn't really want to go down the heat sink route if I were to build this, that's the reason for using lots of OpAmps and running them 'cooler'. Do OpAmps generally have built in thermal trip?
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