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I have been running a BuffPro9038 with Mercury fed by Cronus/Amanero without issue. I recently received a 9028 and tried setting it up with an old legato but can't get any sound. I am trying to use balanced out. I removed the power jumpers and am powering it dual mono. Everything appears to be measuring properly, lock light is on and not muting. I've zerod differential-mode DC bias at the outputs and measure about 8.5v of common-mode DC as expected. What should I check next? The attached picture shows the current set up. I get no sound with or without the output caps. https://drive.google.com...fUfxKxl/view?usp=sharingEdited by user Monday, October 19, 2020 3:01:08 PM(UTC)
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As a follow-up, I swapped the legato for the mercury and am not getting sound so it seems it's something to figure out with the 9028 DAC board. I tried swapping the AVCC regulators for the trident as well and am not getting sound.
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Just replied on another thread before looking at this one...
How is ground connected to your AVCC? I see what looks like two V+ feeds tot he regs, but no GND.
I would try connecting your output caps directly to the Buffalo outputs with the Legato removed to see if you are getting output there. That would shift focus to either the DAC or the Legato. I suspect the Legato as the DAC is tested before shipping.
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Thanks Brian. I'll try it with the caps directly. GND is soldered directly to the backside of the regulators. I'm trying everything with the tridents now pulling power from the board for testing.
If the 9028 was producing sound shouldn't I get sound when using the mercury even with resistors set for the 9038 output level (albeit much quieter)?
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Brian, I just measured the GND/OUT of the stock AVCC trident and am measuring 0v on both sides, so this seems to be the issue. Is there anything else I can check here? I also tried another AVCC trident that I wired for external power. I measured 3.6v when powered externally but do not get sound. I'm using an external clock with no XO regulator, but measure about 1.2v between GND and MCK on the DAC. The VDD and DVCC tridents measure normally. Edited by user Tuesday, October 20, 2020 8:14:31 PM(UTC)
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Originally Posted by: stewart  Thanks Brian. I'll try it with the caps directly. GND is soldered directly to the backside of the regulators. I'm trying everything with the tridents now pulling power from the board for testing.
If the 9028 was producing sound shouldn't I get sound when using the mercury even with resistors set for the 9038 output level (albeit much quieter)? Yes
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I would try to keep it simple (onboard XO, etc) to get it working, then change one thing at a time until it stops (hopefully doesn't :) ).
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In my rush to wire it up, I only soldered one pin of each AVCC header and I now get sound which also explains the 0v measurement on the AVCC trident when powering locally. I will try with legato now. Volume levels seem normal when using the mercury with resistors set for the 9038. Do resistors only impact volume level on the mercury? One strange thing that happened is that bass is better and back to where I have been trying to get the 9038. I would have expected the 9038 to be more impactful. Somewhere along the way swapping power supplies and local regulators hurt the 9038 bass from where it was when I started. Swapping the 9028 with everything else the same has brought it back. One other odd thing is that when I try powering the AVCC trident module with an external supply, the power supply will not power up when connected to the right side. If it's only connected to the left AVCC it works, but connected to the right side only it will not power up and if connected to both it will not power up. Any thoughts? I will start implementing each change from stock and see what happens. I am also using 2.2uf caps on the balanced outputs as my balanced amp will block DC offset on the positive side but can't accept large negative DC offset. After playing for a while I'm still measure about 100mv of dc offset between x/- and gnd. When I hold the multimeter on the contact points this drops eventually and after an hour or so of running it's down to 0 on one side and 15mv on the other. I think the caps may need time to settle in and warm up. The DAC is also uncased and the IEC gnd isn't connected. GND is connected from XLR chassis to the legato which may have something to do with it. Edited by user Wednesday, October 21, 2020 4:20:12 PM(UTC)
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I wanted to follow-up here. After a few weeks of settling in, I'm getting about 300ma of DC offset between +/- and gnd on the balanced outputs. Everything sounds fine, but I was under the impression with 2.2uf caps dc offset should be almost nothing. I am using Mundorf 2.2uf aluminum oil caps.
Thanks.
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Bump. Things sound good and have settled in but I'm still measuring about 170mv of DC between GND and + / - of the balanced outputs. Is this normal?
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To measure offset, you need to short the +/- inputs to GND (disconnected from DAC), then measure. This isolated the measurement to the local circuit.
I don't think what you are measure is unusual.
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Thanks. When you say disconnected from DAC, are you referring to disconnecting the XLR cables running to the amp so I'm measuring the offset with the cables disconnected?
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No, I mean disconnect the Legato from the DAC, short it's inputs to GND, then measure offset at the outputs (also disconnected).
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