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Old 8th October 2014, 10:05 PM   #1
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Default Looking for the Über Buffer

Well guys,

I'm looking for an audio signal buffer that can output 2v pp into a 100R load. The reason? It's the inverting input node of my amp schematic; it's run in inverting modus. The reason for this is partially the elimination of the CM voltage, but primarily to control sources and returns in order to get the global grounding right and have zero 'dirty' returns. In a simulation I verified that the chosen grounding topology does not distort the speaker output.

In order to make this work, I need to buffer the inverting input of the amp, so this buffer will be the source going through the feedback network, rather than the signal drive coming from the preamp board. The non-inverting input is already high-impedance and doesn't need to be buffered. Instead it is connected to the DC servo sense, which also needs to be grounded. These two connections go off-board through a wire to the global star point.

This way, the output signal of the preamp will be relative to the star ground; the input of the poweramp will also be references to that same starground ( and NOT the ground of the board itself!). The fun bit is, that because of the inverting modus, the virtual ground created should exactly be at the starpoint potential. This means, that the Rfb connects the starpoint potential to the output node, which means immunity to dirty currents from various sources. This setup gets me a groundloop free config while still be able to use two power amps on a shared supply and preamp.

With a test rig I was able to simulate that the grounding scheme did not increase THD, eventough I had given resistances to all the various supply power leads and so on.

But! Back to the beginning. To make this grounding scheme work as designed, the power amp must have a capable, distortion free buffer that can drive 100R with like 0.00morezeroes% low THD

It would be a shame if my prototype's supposed specs were squandered by a lousy grounding scheme and or sub optimal buffers.


So... what'd you guys recommend me to use as a unitygain buffer that can drive 2Vpp into 100R at amazingly low distortions?
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Last edited by MagicBox; 8th October 2014 at 10:11 PM.
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Old 8th October 2014, 10:16 PM   #2
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Use four 5532 amplifiers (two DIP packages) in parallel, each configured as a buffer and with 1R series output. A single 5532 amplifier can drive 600R to much higher voltages at about 0.0005% distortion, rising only above 10kHz to about 0.001%. That should be a sufficient number of zeros... You mush drive the quartet lot with a low source impedance, e.g. below 1k ohm.
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Old 9th October 2014, 02:06 AM   #3
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Maybe Kean's? The Kuartlotron
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Old 9th October 2014, 05:50 AM   #4
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Quote:
Originally Posted by CharlieLaub View Post
Use four 5532 amplifiers (two DIP packages) in parallel, each configured as a buffer and with 1R series output. A single 5532 amplifier can drive 600R to much higher voltages at about 0.0005% distortion, rising only above 10kHz to about 0.001%. That should be a sufficient number of zeros... You mush drive the quartet lot with a low source impedance, e.g. below 1k ohm.
I've tried to do this with 4x LT1115 (LT's 5532-like opamp), . They don't alter THD when one is loaded by 10K. However, using 4 of them, each driving up to 2.5mA 2Vpp still leaves a lot to be desired at 20KHz
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Old 9th October 2014, 06:03 AM   #5
BV is offline BV  Slovakia
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Quote:
So... what'd you guys recommend me to use as a unitygain buffer that can drive 2Vpp into 100R at amazingly low distortions?
LM6171
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