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-   -   The Kuartlotron - keantoken's simple error-correction superbuffer (https://www.diyaudio.com/forums/analog-line-level/251413-kuartlotron-keantokens-simple-error-correction-superbuffer.html)

keantoken 7th March 2014 05:34 AM

Your transistors measure close to equal Vbe whereas mine measured close to 60mV different - so it wouldn't be a good idea to try and copy my results.

danielwritesbac 9th March 2014 04:51 PM

How to arrange the Kuartlotron input to buffer a dac that has a differential output?

keantoken 9th March 2014 08:29 PM

For one thing I don't know about DACs. I don't know whether current mode or voltage mode is better or for what reasons. I'd appreciate links to app notes on this topic.

Most of the time it's not a good idea to try to force an unbalanced circuit to use balanced input. You usually don't get much of the benefits and end up having worse performance.

So for a balanced circuit you would want to use 2 kuartlotrons.

The Kuartlotron doesn't have any very useful internal nodes like you would expect in a feedback circuit. This is because every node in the Kuartlotron is already used for distortion cancellation and disturbing that will lead to reduced performance.

Trileru 9th March 2014 08:47 PM

I was hoping in using this buffer for my DAC's balanced output.
I have no idea how to use 2 kuartlotrons for my application. Could you make a drawing?
Thank you

Ken Newton 9th March 2014 08:58 PM

Quote:

Originally Posted by Trileru (https://www.diyaudio.com/forums/analog-line-level/251413-kuartlotron-keantokens-simple-error-correction-superbuffer-post3848652.html#post3848652)
I was hoping in using this buffer for my DAC's balanced output.
I have no idea how to use 2 kuartlotrons for my application. Could you make a drawing?
Thank you

This will depend on your DAC. The kuartlotron is a buffer, so it does not provide voltage gain. Therefore, your DAC would need to already produce the full desired signal voltage amplitude. Does your DAC produce a voltage output?

Trileru 9th March 2014 09:11 PM

1 Attachment(s)
Oh yes. In fact here's the schematic. It currently uses an op-amp with unity gain on the output, and I wish to bypass that with the kuartlotron buffer. The differential voltage output is about 2.5V.
The schematic is for AK4393 and my DAC uses AK4396 but it's the same schematic for both.

keantoken 9th March 2014 09:20 PM

Is your DAC output at ground or is it at some other voltage?

Trileru 9th March 2014 09:24 PM

I need to measure that. But I guess it's 2.5V between the balanced pins of the chip on each channel, not relative to ground. But I can measure each pin vs ground.

Ken Newton 9th March 2014 10:47 PM

Quote:

Originally Posted by Trileru (https://www.diyaudio.com/forums/analog-line-level/251413-kuartlotron-keantokens-simple-error-correction-superbuffer-post3848696.html#post3848696)
I need to measure that. But I guess it's 2.5V between the balanced pins of the chip on each channel, not relative to ground...

Okay, here's my brief assessment. If you place a kuartlotron after the op-amp you will retain the full signal output amplitude of about 2VRMS. However, the purpose of the op-amp is to convert the differential DAC outputs to a single-ended output. Which means that each phase of the DAC outputs is only half the amplitude of the single-ended op-amp output. Therefore, should you want to eliminate the op-amp, you would be limited to using only a single kuartlotron that's connected to one of the DAC's two output phases (per channel, of course). The end result would be a single-ended signal of only half the amplitude than if using the op-amp, or about 1VRMS. In addition, that 2.5VDC common-mode bias offset will need to be blocked with a capacitor, which would be most conveniently located at the output of the kuartlotron.

keantoken 9th March 2014 11:30 PM

It is possible to make the negative DAC output a virtual ground for the Kuartlotron (which would run on an isolated trafo winding), creating a full-voltage unbalanced output, but in practice I don't like PSU bootstrapping like this because it sends ground noise into the circuitry. It could be worth trying with a CM choke in a strategic position though.


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