Hmmm, it might be.

I haven't had any problem with 3.1 though.

I would check all connections and solder points first. And check the power supply. Are you feeding +-15v ?

Edited by user Sunday, August 28, 2011 6:42:23 AM(UTC)  | Reason: Not specified

And keep an eye on those resistors. I changed almost the whole board on the old Legato before hitting the nail - the resistors.

Possibly, but all I did is replace a Legato 2 with the new 3.1. The Sympatico amp was working perfectly, and still is - as if I swap leads the problem moves to the other channel.

The DAC is off, and the bipolar analog power supply is working perfectly for the other Legato 2 and 3.1 boards.

That doesn't leave much except for the interconnect cable....

Actually, the interconnect is OK (or is at least not the root cause)

There seems to be instability causing high frequency nasties now that I have 2 Legato 3.

In my mult-amp setup it jumps from amp to amp and channel to channel after startup.

I am guessing this is because the Legato 3 doesn't have output caps and somehow this is causing it.

I had similar problems, but i have have kind of found a solution to it. Here is my setup:

- Buffalo II with tridents
- Legato 3.1 (SE stage completely omitted)
- 2x Placid BP (~70ma shunted per rail, ~160ma CCS)
- 1x Placid
- Arduino based control through I2C
- Balanced output only

Amp:
- 2x Hypex UcD400 HG HxR
- 2x Hypex SMPS 400@400
- XLR input

What i have experienced is that if I connect the amp everything power them on, and start listening to music, i'll get this hissing+crackling problem on one or both channels after a while. Believe me, i have checked and double checked everything, re-soldered everything, cleaned the Legato with isopropanol, checked if the i2c connection is the cause, checked cabling, and what not.

BUT when both devices turned off and music stopped, if I
1) disconnect the XLR cables on the dac
2) power on the dac and let the arduino do it's thing (takes a few seconds with OSD animations and stuff :d/ ) (in my case by plugging the power cable, i got no on/off button)
3) connect the XLR cables
4) power on the amp (in my case by plugging the power cable, i got no on/off button)

No hiss, no crackling and i've been tuning the Legato like this numerous times already and the trick always works. And i've been running the combination with no problems for couple of days now, with +-15V and +-12V and everything between. Every other "power on" sequence fails. The disconnecting and re-connecting the XLR cables in that exact order is the crucial part.

I don't know for sure, but I suspect this has something to do with common mode voltage on the XLR outputs, or somehow bad grounding between the devices. Possibly just a unlucky combination of output stage and amp. There was no problems like this with IVY III or my Benchmark DAC1. I don't mind, if i have to reconnect the cables once in a while. Unless i am tuning something the Hifi is always turned on anyways.

Edited by user Tuesday, August 30, 2011 7:46:19 AM(UTC)  | Reason: Not specified

I added coupling caps (by going back to the Legato 2). The problem persisted.

I added an independant earth shield to my balanced interconnects (i.e. signal ground is lifted from earth, and is not used for shielding). This mitigated the problem to a great extent. The severe crackling is gone and only a faint whistling remains.

The problem therefore seems to be RFI-related.

So I have to burn my Legato in for a month before I can use it ?

I have added 2,2 ohm Carbon Composite between the Dac and the Legato 3.1. The same between the opamp and the Buffer.

Problems like this could easily be a burnt transistor for even a cold solder joint etc.

The MOSFETs need to be handled with care regarding ESD.

Well there is no problem other than you well get somewhat degraded performance in terms of THD and Dynamic range.