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flashgo  
#1 Posted : Saturday, May 26, 2012 5:37:43 AM(UTC)
flashgo

Rank: Member

Groups: Member
Joined: 9/8/2008(UTC)
Posts: 10
Location: Arizona

I've had a Buffalo II + Tridents running happily for over a year. I recently decided to rearrange the Buffalo II / Legato and MUX so that the I2S connections would be much shorter (down from ~14cm to ~4cm). This entailed some new wiring but no other changes. Now my Buffalo sounds like it's singing through a kazoo. Vocals and drums, in particular, sound like they're causing a paper membrane to vibrate – in both channels.

Measurements:
VD = 5.30V (from Placid HD with CCS = 460mA)
VDD = 1.18V
VDD_XO = 3.27V
DVCC = 3.28V

Narrowing:
Removed the MUX & wired a Toslink receiver directly to the Buffalo S/PDIF input
Swapped Toslink receivers
Dropped the output of the S/PDIF receiver from TTL to consumer level via 261-75R voltage divider (and flipped the switch on the Buffalo)
Replaced the wires connecting the Placid to the Buffalo

All to no avail.

What could be wrong, and is there anything else I can test? It's unlistenable as is.

UPDATE: I took the output directly off the Buffalo (no Legato in the path), and it sounds great, so the problem is with the Legato. Now over to that forum for some hints....

Edited by user Sunday, May 27, 2012 4:20:44 AM(UTC)  | Reason: further narrowed to Legato

flashgo  
#2 Posted : Sunday, May 27, 2012 5:10:05 PM(UTC)
flashgo

Rank: Member

Groups: Member
Joined: 9/8/2008(UTC)
Posts: 10
Location: Arizona

SOLVED: The actual problem was in the Placid HD-BP powering the Legato. I went through the complete set up for the Placid from scratch.

In the end, the Placid HD-BP ended up:
~±14.9V
120-130mA shunt at rest
~360mA CCS

Twiddling the pots on the Placid was an exercise in frustration. There is a lot of hysteresis (i.e., the value you get at a particular pot setting depends on whether you approach from below or above) and even non-monotonicity (i.e., turning the shunt pot continuously in one direction causes CCS to go up or down 10% in the short term, even though there is a greater trend in one direction).
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