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Old 10th June 2018, 07:25 PM   #81
Russ White is offline Russ White  United States
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Hmm - you could have some DC on your mains - an isolation transformer can help for that. Otherwise you might just need better shielding. Large ground bounces can wreak havoc on your gear.

Also - you can detect when a reset occurs and then respond by re-initializing to your desired state.
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Old 29th June 2018, 06:21 PM   #82
francolargo is offline francolargo  United States
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Hmm - you could have some DC on your mains - an isolation transformer can help for that. Otherwise you might just need better shielding. Large ground bounces can wreak havoc on your gear.

Also - you can detect when a reset occurs and then respond by re-initializing to your desired state.
Been away traveling but now back on this issue. Two things:

1. I added (what I hope is) a decent multi-stage power filter to the BBB/DAC plus the switching power supply for the external chassis fans. I also put the amps on a better surge suppressor. Still gathering data. I don't claim to know everything that could go wrong.

2. I've been studying my Python, and have now modified the control program for the system so that it runs in multiprocessing mode. This allowed me to add a 'police' function that checks one register in each of the 9028s at fixed time intervals (trying 0.3 seconds). The question is, what is the best register to monitor in this situation? The ultimate problem is DC going to the speakers. I don't really know if that has been caused by a full DAC reset or just some registers being disturbed. For various reasons I suspect the latter. Otherwise, why would only one of two tweeters fry? So I'm wondering if there is one register in particular to blame, because that would be the one to monitor. My guess would be register 15 somehow being knocked out of 'stereo mode'. It might be feasible to monitor two registers - I haven't tried. Any and all thoughts on this question would be appreciated. Pure speculation welcome!

Cheers,

Frank
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Old 30th June 2018, 12:23 PM   #83
francolargo is offline francolargo  United States
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The question is, what is the best register to monitor in this situation?
Reflecting further on this, I would like to know the mapping of the 9028's 8 channels by Buffalo. Specifically, to the plus and minus sides of each differential output. I saw problems when I tried to tweak the relative volume of the left vs. the right channel using registers 16-23. If that were done incorrectly, could it 'unbalance' the output of a channel?
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Old 28th August 2018, 09:02 PM   #84
francolargo is offline francolargo  United States
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Sporadic work on the problem of 9028 register stability is yielding some progress.

Unintended alterations of 9028 registers is still occurring. How? Still no clue. The 3 DAC boards are housed together in a rack chassis and the BBB is housed in a smaller chassis - the two are attached by a multi-function cable with 2X5v power and I2C connections. All the chassis casing is shielded to the same ground, with the 4 ft. power cable being completely surrounded by copper braid. I2S signals travel through separate cat6 cables via teleporters. I placed a power conditioner on the power plugs to the DAC chassis - 10A Two Outlet Power Conditioner | Furman Power | Purifying power for over 40 years. That made an improvement - now it seems that the main source of interference is the power switches to the 6 amp channels. They have large power supplies, and they are protected by their own separate surge suppressor - 6 Outlet, 2x3 Pro Surge Suppressor Strip | Furman Power | Purifying power for over 40 years.

I have been tweaking the Python program that controls the system's core functions. To prevent damage to the drivers, I've been monitoring register 15 of each 9028 three times per second to assure stereo mode is maintained. If that register becomes corrupted I reset all of the important registers. It worked pretty well until once the I2C function quit and then some heat damage occurred - but not to expensive drivers. Now I also monitor for proper I2C function, and if that is lost then the BBB immediately kills the process running whatever player is producing I2S. So far, so good... However, amps must be turned off before hard resetting the DACs to prevent major thumps!

We're getting there... Next step is to incorporate diagnostic logging into the Python control program. Then data can be collected without real-time monitoring from the command line. That will allow me to gain sufficient confidence before risking damage to 'good drivers'. But even with the temporary setup, the sound is SO GOOD! It will be truly worth the effort to overcome these thorny issues.

Ideas, thoughts, comments? Please speak up. Especially any of you engineers!

Frank
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