Just to clarify, for those who want to know...
The
transformers are from Jensen Transformers, extremely permeable 80% magnetic core.
Frequency Response is -3dB at 0.27Hz - 15MHz
THD @-5dBu with 100kOhm load is <0.0001%
Phase flat 20Hz - 20kHz
This is more transparent than most opamps and all caps. A slight sweetening is probably more appropriate description of how it affects the sound rather than warming, the numbers speak for themselves.
The Legato 3 can be trimmed to eliminate the DC offset on the output, both for balanced output and the SE output. Legato SE output circuit uses the devil's spawn LM4562 opamp so it remains unpopulated, only the BAL circuit is built, no SE, no buffers, no J5,6 jumpers. The devil is on ice. The transformer provides BAL/SE conversion. If Carl chooses, he could connect his transformer balanced output to his Mac amp bal input, bypassing the tube preamp.
Another option is to eliminate the transformers because the Legato 3 can trim out any DC offset, but that would require rewiring the Legato balanced output directly to the XLRs, and would require waking up the surface mounted devil for SE output into Carl's preamp.
The regulators on the DAC board are from Belleson. They perform better than any other regulator, very small and make very little heat. Highly recommended.
The power supply for the Legato3 is Twisted Pear's Placid HD bipolar. I chose to use Placid for mine instead of Belleson regulators because I bought the whole active Buffalo kit including Placids before I knew about Belleson, a long time ago. Carl liked the sound of my DAC with the old Legato1/Placid, so he bought the same thing with the newer versions. Placid is a complete PS with rectifier and storage caps, not just a regulator, so it is simpler to use than Belleson. The shunt regulators on Placid could be replaced with Belleson regulators if desired, but I don't think it would provide any advantage, since Legato (balanced part) is a class A amplifier. The 30VA 30VCT toroid Carl spoke of is for the Placid PS. As a side note, the original Placid PS that I used failed. I had another unbuilt kit of the old style placid on hand so I just replaced it with another old version. Carl has the newer Placid HD version. The Legato uses all discreet class A amplifiers, so the power to run it is a very easy, constant load, so any well designed regulated PS would work fine. I forget what the current requirement is, but I think the Belleson high current model (2A) can handle it. The Placid shunt supply gets good and hot but touchable during use, so venting the big heatsinks is important. I was able to place them directly in the airstream of the side vents of the Par Metal box.
Rod, the Buffalo 8 is the multichannel version of the Buffalo3. For stereo use, you would want the BuffaloIIIse, which parallels the internal DACs within 9018, 4 each side to make 2 channels. This makes enough voltage and current to drive most loads passively, which is originally why I tried transformers only, to fix the DACs 1V voltage offset. Transformer cannot load the DAC into current mode, so it's not ideal, imo.
A Buffalo8 can be used with 4 separate Legatos to make a multichannel DAC. I'm thinking about doing that as a source for my active speakers. But the cost of building that in this manner with regulators and transformer upgrades would be 2/3 the price of buying a new exasound e28. If one was found used, it would be the same price as Buffalo8/Legato. If the exasound has discreet amplifiers I'd go that way and have better resale. But I am confident that the Buffalo would at least keep up with it.
