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Valve DAC from Linear Audio volume 13
Valve DAC from Linear Audio volume 13
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Old 29th March 2021, 08:38 AM   #1541
acg is offline acg  Australia
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Join Date: Oct 2013
Location: Sunshine State
No worries Marcel, I've not managed to get to turning it on just yet. Am struggling to get all my work complete before the Easter holiday...may not be for a little while yet.

Thanks for letting me know.

Anthony
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Old 5th April 2021, 03:55 PM   #1542
Tix88 is offline Tix88  Italy
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Join Date: Jan 2015
Hi, anyone interested I have a pcb kit available for sale.
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Old 21st April 2021, 11:44 AM   #1543
SonnyMarrow is offline SonnyMarrow  United States
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What is the best point to attach to chassis ground? I'm using a ground loop breaker and connecting to the chassis at a single point.
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Old 21st April 2021, 01:26 PM   #1544
MarcelvdG is offline MarcelvdG  Netherlands
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Join Date: Mar 2003
Location: Haarlem, the Netherlands
I didn't have that issue with my wooden enclosure, but it's probably at the analogue output.

That is, I would tend to connect all balanced in- and outputs according to AES48: XLR pin 1 straight to the chassis and one point of the chassis to the circuit ground. For that last connection I'd take a point close to the analogue outputs and connect it to the ground pins of the output connector of the filter board.

Do you have any unbalanced inputs, such as S/PDIF? I think I kept my S/PDIF inputs completely insulated with an insulated cinch connector and a transformer right behind the connector, but I can't check if I remember that correctly right now..

Last edited by MarcelvdG; 21st April 2021 at 01:38 PM.
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Old 21st April 2021, 02:12 PM   #1545
SonnyMarrow is offline SonnyMarrow  United States
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Join Date: Dec 2016
My initial plan was to wire pin one of the output XLRs to the ground of the filter PCB, then from the filter PCB to the ground loop breaker. Can the jacks be connected to the chassis directly and not the star ground? I had a concern with this method because my case will likely be powder coated.

Last edited by SonnyMarrow; 21st April 2021 at 02:14 PM.
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Old 21st April 2021, 02:39 PM   #1546
MarcelvdG is offline MarcelvdG  Netherlands
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Join Date: Mar 2003
Location: Haarlem, the Netherlands
I think your initial plan should also work. How do you want to make contact with your powder-coated case?

The idea behind AES48 is to let the shields and chassis form one big Faraday's cage, to take for granted that there may be ground loops, but to ensure that the current in those ground loops doesn't flow through any internal circuitry (which is often unbalanced, even in professional equipment). It's an approach that only works with balanced inputs and outputs, but it results in better RF shielding than pure star grounding.
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Old 21st April 2021, 03:15 PM   #1547
SonnyMarrow is offline SonnyMarrow  United States
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Join Date: Dec 2016
Ok I think I'm almost ready to turn on the DAC for the first time. Right now I only have optical input setup. Before I flip the switch, I had a question about using a DC power supply for the 6.3v. Do I just connect the positive and negative to pins 3 and 4 of the power terminal? I was going to connect the positive to 3, where I jumped the THT.
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Old 21st April 2021, 03:41 PM   #1548
SonnyMarrow is offline SonnyMarrow  United States
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Join Date: Dec 2016
Well, first test boot was unsuccessful so I quickly turned it off.

All PSUs, including the on-board 5V supply, are working properly. When I turn on the DAC, the tubes begin to light/heat up, but the clipping light is on and none of the other indicator lights work. I have switch 3/C on the FPGA set to on, so the lights should be on even if not using surprise. I also quickly tried surprise to see if that would change anything and it did not.

Could it be that I flashed the FPGA before shorting the resistor pad on it?

Last edited by SonnyMarrow; 21st April 2021 at 04:07 PM.
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Old 21st April 2021, 04:20 PM   #1549
MarcelvdG is offline MarcelvdG  Netherlands
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Join Date: Mar 2003
Location: Haarlem, the Netherlands
Does the 85A2 light up and if so, immediately or after a few seconds? When does the clipping lamp turn on?

It shouldn't make any difference whether you programmed the FPGA module before or after shorting the R102 pads.
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Old 21st April 2021, 04:23 PM   #1550
SonnyMarrow is offline SonnyMarrow  United States
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Join Date: Dec 2016
I will double check the 85A2, but it seemed to light up immediately. The clipping lamp (using an LED) turns on immediately and stays on. I have no inputs or outputs connected, though the filter board is connected to the DAC.

Last edited by SonnyMarrow; 21st April 2021 at 04:26 PM.
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