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I am thinking that I have a ground loop between my B-II and a SOtM async USB board (XMOS). The only thing I changed was providing materclock to the B-II from the SOtM over I2S-synchronous clocking. I have left the local Crystek on the B-II board, and just removed the Trident to keep it unpowered. The level of the noise is very low at the speaker, but still, there was none previously, so I want to get rid of the loop.
Unplugging the USB cable makes no difference, so the loop is not caused by the computer. Powering down the USB board, with the DAC still powered, and all is quiet.
The USB board and the B-II get power from separate shunts, each getting AC from a single secondary of a dual secondary transformer. I2S wiring has 4 ground leads, all terminated at the ground input on the B-II board, the only change is running a single lead for masterclock to the B-II (R17 pad) and removing the clock Trident-seems weird to me???
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Rank: Member
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Joined: 7/21/2010(UTC)
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Location: Colorado
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OK, for anyone experiencing anything similar, here is what I found. Apparently the problem was not caused by a ground loop, but by radiated fields from the AC input wiring/transformers being picked up by the Master Clock wiring from the SOtM async USB card to the-II board. Becasue my I2S lines were longer than desireable anyway (~20 cm), I re-arranged my layout, locating the SOtM USB card so it just overlapped the input side of the B-II. I used 3M silver plated copper/teflon ribbon cable for the I2S lines, except for the Masterclock. For the masterclock I added a SMD micro BNC to the undersind of the SOtM card, and ran a U.FL coax cable from the SOtM card to the R17 pad on the B-II. Now all the lines are ~6 cm, and the noise pickup has dissappeared into the (very, very low) noise floor of the system.
I would suggest to one who has a low jitter I2S source give synchronous clocking a listen; I find it gives a slightly more natural sound, while retaining all the details and dynamics the B-II is capable of.
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Joined: 8/25/2010(UTC) Posts: 42  Location: south of
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As soon as i figure out where to connect my masterclock, from I2S-WaveI/O, to where it has to go on the I2S-B-II, ,i will relay my observation if sound signature changes .
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Rank: Member
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Joined: 7/21/2010(UTC)
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Location: Colorado
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Regis: You can connect the MC in at the R17 pad on the B-II. Use your ohmeter to confirm. If you are using Tridents, just unplug the VXO Trident to unpower the onboard clock, and you are good to go for synchronous clocking. Try and get the Wave IO as close to B-II as you can, and keep the leads short.
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