Benchmark DAC1 Pre - anybody heard a mod?

Thank you all for your suggestions. I took the plunge...bought a MHTD Labs Havana DAC. The Havana is a NOS non-upsampling DAC with a tube buffer. The unit arrived today and I am running it through the analogue inputs of the Benchamrk Pre. So far so good! The DAC still needs to be run in but the 'harshness' of the Benchmark is gone. The sound is 'fuller' and the clarity and resolution of the Benchmark is still there. The bass sounded a little muddled at fist but this is clearting up as well.

I could have possible gotten the same outcome from a tube pre but there are not that many good deals in the Singapore market.

So now I have 2 DACs. Will probably sell the Benchmark in the near future and get a proper pre-amp once the Havana is run in. The question would be tube or solid-state. The journey goes on...

I have just bought the DAC1 USB to replace my XDACV3. The XDAC has a sweeter treble but not quite as much resolution. I agree that the DAC1 does sound a bit tipped up in the high mids and treble. I suspect that some of this is due to the LM4562 output op-amps which do have a pronounced 'presence' but I also feel that the power supply caps are largely responsible. I have some experience with the 4562 op-amps and have found that bypassing with Elna Silmic or Cerafine mosly eliminates the glare and the result is much nicer and sweeter mids and treble. There are also a couple of 5532 op-amps used for I > V from the DAC. The XDAC also used these devices and I ended up substituting them with OPA2134 amd the result was less grain + smoother and sweeter as well as a much fuller bass. I will probably do a full range of mods to the DAC1 USB in the very near future and will report back here.

I have confirmed that the DAC1 USB uses 4562 op-amps for the output buffer which is an upgrade from the standard DAC1 which uses 5532's.

The newest 'DAC1 Pre' uses LM4562 op-amps throughout. These are very superior op-amps so the Pre version should sound better than previous versions - and measure better too. Upgrading an existing DAC1 USB is possible but requires the replacement of the +/- rail regulators to reduce the rail voltage to +/- 17V.

I just finished the power line conditioner. It uses a 240V primary and a 36V secondary which is in series (opposing) with the 'active' on the load side. This is a neat way of reducing the mains voltage by 20%. There are ferrite beads on both sides to reduce EMI. I measured the DC voltages inside the DAC1 PRE and the input to the 18V regulators has dropped from 31 to 25. There is still > 5V between input and output all all regulators (3.3V, 5V, +/-18V).
After an hours use the unit is now barely warm. Out of interest I tried several transformers - for different output voltages. From a SQ POV this voltage seems to be the sweet spot. The treble seems to be slightly more 'analogue' - smoother and sweeter.

Please e-mail me if you want details on this mod.