I’m glad someone else tried swapping the OP amps and got results similar to mine. Earlier I mentioned that replacing the stock single‑ended, unlabeled OP with an OPA2134 worked out really well. one month Later I experimented with changing the two IV‑stage, unlabeled OPs to MUSES OPs — the sound signature shifted quite a bit, but honestly I didn’t like it. I quickly reverted to the original setup, and the sound went back to how it was before the mod. Of course, this could all just be placebo since I didn’t run any measurements, so take it with a grain of salt.
Nevertheless, I believe SMSL must have had solid technical reasons for replacing the unlabeled stock OP amp with an OPA1612, developing the D200, and positioning it as a high‑priced model. At the very least, it’s reasonable to assume they conducted proper measurements and validation. Haha.
As long as people don't use genuine blind tests with identical original devices and/or meaningful measurements to verify modifications, they're deceiving themselves in 99% of cases and wasting a lot of time on nonsense.
That's precisely why I started working with a second, identical device without any modifications for comparison 25 years ago. It's much cheaper than wasting so much time.
Disguised components, including op-amps, primarily serve to conceal the fact that they've found a well-functioning and inexpensive op-amp, sometimes not even from the audio sector, thus securing this competitive advantage. Standard NE5532 op-amps were never disguised in the past by SMSL, Topping, or any other manufacturer.
The D200 also features two unidentified op-amps in the I/V stage directly after the DAC chip, in addition to the six OPA1612 op-amps.
SMSL typically uses the circuit diagrams and evaluation boards of the chip manufacturers as templates for its devices and modifies them to achieve good measured values, as can be clearly seen in the D1 and D300. Unlike other manufacturers, SMSL is not very innovative in its circuitry and usually limits itself to specific components with which it has experience.
The D200 is quite different. This device appears to have been developed by an external designer, as it is built completely differently than what is typical for SMSL, with different components and circuit solutions, and is significantly more complex in many areas.
For example, it features a true analog balanced preamplifier function with one NJU72315 per channel for volume control. This makes the D200 a DAC with an analog preamplifier section after the DAC chip. It's a shame SMSL missed the opportunity to add analog inputs.
The D200 also contains two unidentified op-amps in the I/V conversion stage. Since there are no coupling capacitors, the subsequent OPA1612s are presumably part of a DC coupling circuit.
The use of a toroidal transformer for the power supply is also unusual these days. The elaborate generation of numerous dedicated voltages for the various sections is also noteworthy.
The digital section appears to be divided into several areas, and a total of five crystals are used.
