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Old 23rd April 2016, 12:26 AM   #1
wall is offline wall  Portugal
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Default adding buffer to opa2132 cmoy

I'm about to build an OPA2132 cmoy from tangent's schematic and I still have 2 BUF634T left, how can add them as buffers?
This is the power supply I plan building powered by 2x 9v:
Click the image to open in full size.
And what opamp should I use for the power supply? I have some spare LT1028, LT1128, LT1124, LT1057, LT1365 and soic8 OPA827.
Thanks in advance.
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Old 23rd April 2016, 12:52 AM   #2
DPH is offline DPH  United States
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Just as described in that schematic-fit inside the 2132's feedback loop. There's also this exact information in the buf634 data sheet (page 13).

I assume you're going for a gain of one? No need for a opamp in the power supply, especially if that's the circuit you're using.
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Last edited by DPH; 23rd April 2016 at 12:55 AM.
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Old 23rd April 2016, 01:06 AM   #3
wall is offline wall  Portugal
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I don't know what gain it's set to, I'm following tangent's schematic.
So how do I build the power supply?
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Old 23rd April 2016, 01:06 AM   #4
wall is offline wall  Portugal
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I'll be using it with low impedance headphones.
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Old 23rd April 2016, 01:20 AM   #5
DPH is offline DPH  United States
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Well, the cmoy above has a gain of 11, and there is nothing crazy fancy going on here.

I unfortunately think you're at a point where you need a bit of the absolute basics of electronics before you move forward, just enough to at least understand these circuits. Tangent has a pretty good section describing how this circuit works.
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Old 23rd April 2016, 01:38 AM   #6
wall is offline wall  Portugal
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Are you saying a TLE2426 is enough? Even if I add the buffers to the amp?
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Old 23rd April 2016, 01:51 AM   #7
DPH is offline DPH  United States
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The linked circuit PDF is entirely passive. The "driven" ground is less than ideal. If the two sides are balanced and the drive currents low (which headphones?) then the tle2426 should be pretty okay.

Why not go with the dual battery schematic in the PDF?
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Old 23rd April 2016, 10:25 AM   #8
wwenze is offline wwenze  Singapore
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Nothing is stopping you from your plan. However it won't do much if the bottleneck isn't there. You would probably get better performance by putting the buffer at the output of your virtual ground, which incidentally results in the same topology used in mini3.

The current from the amplifier output needs to go somewhere after travelling through your headphone. In this case it goes into the virtual ground. So your virtual ground needs to be handle the combined current of both channels. TLE2426 handles 10 to 20mA while most opamps can do over 10mA each, so the TLE2426 is the bottleneck for current.

Some designs, instead of using TLE2426 to generate the virtual ground, they use an opamp instead.
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Old 23rd April 2016, 05:05 PM   #9
wall is offline wall  Portugal
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for the power supply I'll use this and just replace the voltage divider with a tle2426
Click the image to open in full size.
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Old 23rd April 2016, 06:35 PM   #10
DPH is offline DPH  United States
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Unless your headphones are incredibly low efficiency, then hearing damage will be the limiter long before the rail splitter. The buffers in respective locations are for transients. Likewise, I think a few of these opamps are marginal stability at unity, so be sure to double check data sheets, as that's a pretty trying usage. Might need to hf noise gain the opamp/buffer composite.

Again, which headphones? All of this might be irrelevant if your headphones are sensitive and current demand is low (also why I asked about gain)
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