asus stxII with sparkos discrete opamps

In my experience, op amps even in the I/V position will affect the sonic signature.  However, the I/V op amps are placed right at the DAC chip output.  The DAC chip is outputting straight DC pulses.  These are essentially square waveforms.  The purpose of the I/V stage is to amplify these square waveforms and also provide some sort of smoothing to turn these into the curved analog waveforms of true sound.  The slow slew rate of the 8820 may be helping to smooth these straight line square waveform pulses.  On the buffer output stage, the waveform is already somewhat smoothed, so the slow slew rate is having even more of an effect to reduce the high frequency response.

Sorry, got a little lost, my knowledge is not as good as yours.

Are you saying that a slow slew rate may be advantageous in the i/v position and a fast slew rate may be advantageous in the buffer.
With the stock configuration of 8820 in the buffer and 8920's in the i/v the bass and mid are both excellent, the treble is reduced with poor detail.
With 8920 in the buffer and 8820 in the i/v the treble detail has returned, but the quality of the mid and bass has lowered, does not have that warm tube like sound of stock.
Am trying to undersand why this is happening, trying to get the best of both configurations but struggling.
Thanks!

Do you think a possible reason may be that slow slew rates result in poor treble in the buffer section, but may be advantageous to bass and midrange.
Thanks!

I was just indicating that a slow slew rate may not reduce as much treble clarity as much when in I/V because it's responding to straight line square waveforms.

That being said, yes, a slow slew rate will ultimately result in poor treble. It's slowing down the waveforms so the midrange will get thicker and bass will get thicker/warmer. However, if you slow it down too much, it gets too warm and messy. There's no clarity or "separation of instruments".



I think you still have to have a minimum slew rate in audio.  However, you don't want a fast slew rate for I/V position.  The buffer/output stage can have a high slew rate, though.  I think the OPA827 is an excellent I/V op amp.  You could also try OPA2132 if you wanted to for I/V op amp.  They are relatively cheap at about $12 each from digikey (get the OPA2132P model).  The OPA2132 is the most popular op amp to be used for I/V position.  Even my Krell S1200U home theater processor uses opa2132 for I/V, but it has it's own fully discrete Class A output stages.

For output, if you wanted more clarity you could try Burson V6 Vivid.  Slew rate is around 40V/us.  (somewhere between 36 and 49).

However, your new OPA827 probably need to be burned in some.

Hi Johnny,

Based on our conversation, I have gone back to try different opamps for I/V in my reference modified DAC. The OPA827 appears to be the best in this position due to the slower slew rate when compared to my other reference op amps. However, when I use OPA827 in the output buffer, the sound actually slows down some. It’s not as clean/clear and doesn’t have as much attach or high frequency resolution. I found putting Burson V6 Vivid in the output buffer really helped in this case. The V6 Vivid is definitely better than OPA827 for output buffer. It is much cleaner and clearer. Midrange and high frequencies are faster and better represented. I don’t know how you are liking your current sound, but you might try getting a couple V6 Vivid for your output stage on the STX.

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Just a thought.