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Valve DAC from Linear Audio volume 13
Valve DAC from Linear Audio volume 13
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Old 26th January 2021, 10:11 PM   #1391
MarcelvdG is online now MarcelvdG  Netherlands
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Join Date: Mar 2003
Location: Haarlem, the Netherlands
The one I wrote about in post #1383. I think it's a good idea to put a resistor between the buffer and the cable to the main board, probably of the order of 82 ohm, to prevent cable resonances. Neither the buffer nor the resistor is needed when the optical receiver is just a few centimetres from the DIX4192, as is probably assumed in the DIX4192 datasheet.

Last edited by MarcelvdG; 26th January 2021 at 10:13 PM.
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Old 27th January 2021, 02:44 AM   #1392
SonnyMarrow is offline SonnyMarrow  United States
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Incorporated the 82 ohm resistor, re-added the buffer, put the optical input back to RX4P, and moved the other inputs accordingly so there isn't a "gap." I'll leave RX1 unpopulated.
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File Type: png myschematic.png (21.0 KB, 114 views)
File Type: png input board.png (44.3 KB, 117 views)
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Old 28th January 2021, 11:49 PM   #1393
acg is offline acg  Australia
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PCB's have arrived today! 7 sets of ValveDac and 8 sets of the Reconstruction Filter boards so between Leadbelly and myself there is scope for several more ValveDacs out in the wild.

Will start populating one tonight.
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File Type: jpg 20210129_103642 (Custom).jpg (351.7 KB, 92 views)
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Old 29th January 2021, 12:18 AM   #1394
SonnyMarrow is offline SonnyMarrow  United States
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Awesome! Glad to see there will be more out in the wild.
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Old 29th January 2021, 02:29 AM   #1395
acg is offline acg  Australia
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Not looking forward to the fine pitch smd soldering...might have to do that first and get it out of the way...
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Old 29th January 2021, 02:34 AM   #1396
SonnyMarrow is offline SonnyMarrow  United States
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I did the small pitch chips and those awful FPGA connectors first. The rest of the SMD stuff wasn't bad, there's enough room around them. FPGA connectors were stressful because the little pins are so frail.
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Old 29th January 2021, 05:28 AM   #1397
acg is offline acg  Australia
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It's friday night here...might have to do the fine pitch stuff first then pour a wee dram of whiskey afterwards, rather than the other way around...haha.
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Old 29th January 2021, 06:18 AM   #1398
MarcelvdG is online now MarcelvdG  Netherlands
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That sounds like a good plan... At least you have spare boards if the SMD soldering should go wrong.
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Old 29th January 2021, 03:07 PM   #1399
SonnyMarrow is offline SonnyMarrow  United States
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I think I'm done revising my input PCB. Now to find a case to put this all in.
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File Type: png input board.png (62.3 KB, 79 views)
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Old 31st January 2021, 09:43 PM   #1400
acg is offline acg  Australia
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Two days of soldering and everything is populated apart from a handful of power supply caps that are yet to arrive. Went a bit stupid ordering resistors but in the pre and power amps I've built any resistor or capacitor on the grid/anode/cathode of the valve makes a difference to the sound and I have no reason to believe it would be any different in the ValveDAC.

Have put any of the taller through-hole components underneath the pcb so I can maximise the height of the valves protruding from the top of the case. Basically started with the necessary parts such as the trimpots and anything taller had to go down below.

Even managed to wind 24 inductors for two filter boards for 6th order "0.05deg Linear Phase" and "Gaussian to 6dB"...except I dropped one and shattered a ferrite core half so will have to reorder that part. Was going to solder everything to the filter pcb's but was struck by how little metal there is around the holes. Is this normal? Can someone with leadbelly pcb's please have a look and let me know, that would be great. Might have to give the fab house a phonecall to get them re-done if necessary. No issues at all with the pcb for the dac.
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File Type: jpg 20210201_073002 (Custom).jpg (460.4 KB, 59 views)
File Type: jpg 20210201_072943 (Custom).jpg (385.4 KB, 45 views)
File Type: jpg 20210201_074325 (Custom).jpg (203.5 KB, 43 views)

Last edited by acg; 31st January 2021 at 09:44 PM. Reason: spelling
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