pavlo_y0l0s
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This is a study of whether changing op-amps in a DAC makes a measurable difference. Taking a lead form "rolling" tubes in tube products, a trend has started in replacing op-amps -- sometimes with much difficulty -- to improve performance of solid state products like DACs. A few months ago I tested the Topping D10 DAC and since it has a socketed op-amp, members asked if I could experiment with changing it to other pin-compatible parts. A couple of kind members supplied me with a good inventory of op-amps to test all the way up to esoteric discrete ones.
Here is the overall circuit diagram:
You can see how the ESS DAC drives the OPA2134 op-amps that are soldered, providing current (I) to voltage (V) conversion. Their outputs in turn drive a pair of op-amps in the socketed Op-amp (circled) which are our output buffer/op-amps. That is the part we will be replacing.
EDIT: an earlier version of this review mentioned that we were changing the I/V op-amp due to misunderstanding of a statement from Topping. It is now corrected above.
The op-amps I had on hand were:
- OPA-2134 (shipped in the Topping D10)
- Muse 8820
- Muse 8920
- LME49720
- OPA-1612a (SMD part mounted to through-hole socket)
- 994Enh-Ticha Dual Matched Discrete Operational Amplifier. This one is quite fancy: http://www.sonicimagerylabs.com/products/Model994DiscreteOpAmp-Ticha.html
View attachment 15684
It retails for a whopping $94 each! The OPA2134 in contrast costs $4.79 in single units.
Measurements
For this testing, I thought any important difference would show up in THD+N (distortion + noise) versus frequency as this is what the data sheet for op-amps emphasizes a lot. We will see the effects of both noise and distortion in one measurement.
Here are the results:
View attachment 15683
This chart is hugely amplified (vertical axis) relative to what I normally show. Despite that, the differences are tiny. Assuming you want to go by that difference anyway, the best performance was achieved using the op-amp shipped with the unit, the TI OPA2134!!! In other words, the designer knows best.
I also looked at SINAD differences (not shown) and there was no difference to speak of there. The unit itself varied in performance by 1 dB there and that was what I observed as I changed op-amps.
Conclusions
With respect to Topping D10 DAC at least, rolling opamps is of no value at all. Fortunately nothing bad happens but nothing good either. I suggest leaving it alone as is.
I will try the same exercise with a different DAC in the future to see how consistent the results are.
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As always, questions, comments, recommendations, etc. are welcome.
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What you got here is the distortion profile of the OPA2134 that has been used as I/V converter. Anything you put after it will have those distortions just passed down the chain. What might really change the sound - is swapping those SMD soldered opamps. They are not socketed and require soldering which sucks.
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