Today I finished upgrading my Buffalo2 DAC by adding the Legato active output stage powered by the Placid-BP bipolar shunt power supply. These DIY kit modules are offered by Twisted Pear Audio to compliment the Buffalo DAC. I am using the earliest versions from several years ago. There are newer updated kit versions and newer user manuals available now.
Although it seemed to sound good in a few other systems, especially those with active preamps to buffer the DAC, I started to think that the DAC with only passive transformer output was sounding a bit thin in my system, and comparing it to my old Buffalo32 DAC with its built-in opamp buffers proved this to be true, although the Buff32 sounds a bit less open and refined than the passive transformers.
I assumed the thin sound was due to the lack of output buffer, but it could also have been due to the Buffalo32 running the DAC in current mode while the passive was voltage mode. The legato also runs the DAC chip in current mode by offering a very low load impedance, like 1 ohm. Then the current signal is converted into voltage signal and buffered. Legato has a true balanced signal path with discreet transistors, 5 per channel, running deep in class A and no caps in signal path.
There are a lot of happy Legato reviewers over the years since. But I've hear that song before... Audio hope is dope! But I already owned the Legato and Placid kits, so I'd might as well try them. But I was thinking that if it didn't work out I would throw in the DIY DAC towel and get a high value, high end commercial DAC like the new stereo exasound DAC, or Zodiac, etc.
By using the discreet active Legato in combination with the transformer outputs in place of the Legato's output caps I was hoping I could keep the refined, open and natural sound of the passive transformers plus gain the bass solidity and tonal fullness of the active buffer, while also avoiding the somewhat closed-in sound of the "IVY" output stage on the Buffalo32 DAC which uses all opamps for I/V and buffer. The LM4562 used as buffer on the Buff32 is one that I particularly dislike. Legato also optionally uses LM4562 as BAL/SE output buffer so I enjoyed leaving that part of the board unpopulated.
I used only the core of the Legato without the optional discreet balanced current buffers, and with no BAL/SE (balanced to single ended) conversion stage. I replaced the Legato's large electrolytic output coupling caps with the super-awesome 80% nickle core, ultra-low distortion, wide bandwidth, professional line-out transformers that I used before as passive outputs. They eliminate the DC offset on the Legato's output and provide choice of balanced or single ended output. I am just using SE output now, but Sol has designed a simple circuit that can switch between BAL and SE jacks that I will employ eventually.
Well it was a good gamble, the DAC sounds awesome! I couldn't be happier to hear it come to life and sound so good. There is great body and presence along with with excellent space and ambiance. No closed in sound at all, and excellent tone, every bit as good as the transformers alone, probably better. Time will tell.
Today Sol and I were playing the DAC with my I-15 amp and he put on a Telarc Fanfare for the Common Man. I think it was the best sounding recorded trumpet I have ever heard. Such subtle tonal details and the exquisite comb filtering acoustic effects of the two trumpets playing in unison in the large hall plus perfectly natural and biting brass edge was an eye opener for me. I can see why you hard core audiophile types fall hard for this... Sol's amps deserve credit for allowing that kind of detail and power to get to the speakers intact, but I'm sure that this is the best source I've owned so far.
Usually it's a bit of a let-down after a day like today because some of the great sounding gear usually goes home with its owners, but today the good stuff stayed behind because it's mine! I'm pretty happy with the way my new system is coming together!