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Valve DAC from Linear Audio volume 13
Valve DAC from Linear Audio volume 13
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Old 3rd November 2019, 07:47 PM   #351
MarcelvdG is offline MarcelvdG  Netherlands
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With 1500 pF + 1500 pF, as suggested in post 322, you don't get the 20 pF error.
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Old 3rd November 2019, 07:58 PM   #352
MarcelvdG is offline MarcelvdG  Netherlands
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Quote:
Originally Posted by Zoran View Post
Maybe there is mistake on the schematic? How iti is seems like MCK and BCK outputs from USB-I2S/DSD interface are shorted? Cut out the line/connection after RS8 and RS9 at the input of the circuit?
cheers.
Considering the length of the thread, I can imagine you haven't read all of it, but the idea is to place at most one of the 0 ohm resistors R58 and R59 and definitely not both. See post 301 for details.
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Old 4th November 2019, 06:21 PM   #353
nautibuoy is offline nautibuoy  United Kingdom
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I had another delivery today so now I can finalise my reconstruction filter PCB. The inductors are from Don Audio, custom wound to Marcel's spec (3rd order filter).

Click the image to open in full size.
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Old 5th November 2019, 10:43 AM   #354
merlin el mago is offline merlin el mago  Catalonia
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Looks nice Ray.
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Old 16th November 2019, 06:37 PM   #355
nautibuoy is offline nautibuoy  United Kingdom
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and now I have some PCBs on which to mount the inductors and output transformers.

Click the image to open in full size.

Tomorrow I hope to start drilling some metalwork so I can start assembling and testing...
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Old 16th November 2019, 06:47 PM   #356
nautibuoy is offline nautibuoy  United Kingdom
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I designed the PCBs to slot into channels in the rear panel of my chassis. It doesn't look like it in the picture but there's plenty of space behind the board so the soldered board won't make contact with the chassis.

Click the image to open in full size.
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Old 16th November 2019, 08:54 PM   #357
MarcelvdG is offline MarcelvdG  Netherlands
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Looks good!

Do you mean testing the filter board standalone or testing the whole DAC?

Last edited by MarcelvdG; 16th November 2019 at 09:02 PM.
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Old 16th November 2019, 09:44 PM   #358
nautibuoy is offline nautibuoy  United Kingdom
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Quote:
Originally Posted by MarcelvdG View Post
Looks good!

Do you mean testing the filter board standalone or testing the whole DAC?
Thanks Marcel.

I plan to test a step at a time as far as possible. First will be the power supplies, which I hope to start assembling tomorrow.

I wouldn't know how to test the filter boards in isolation though?
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Old 17th November 2019, 05:38 AM   #359
MarcelvdG is offline MarcelvdG  Netherlands
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One thing you definitely should not do is to test audio line level transformers with DC, for example with the resistance function of a multimeter, especially the lowest resistance ranges. When you temporarily saturate the core, its remanence will increase the transformer's even-order distortion from that moment onward until someone demagnetizes it.

If you have a balanced audio source and a couple of resistors and capacitors at your disposal, I can come up with a way to test the filter boards in isolation, but considering their simplicity, I doubt if it will be worth the effort.
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Old 17th November 2019, 06:33 AM   #360
nautibuoy is offline nautibuoy  United Kingdom
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Quote:
Originally Posted by MarcelvdG View Post
One thing you definitely should not do is to test audio line level transformers with DC, for example with the resistance function of a multimeter, especially the lowest resistance ranges. When you temporarily saturate the core, its remanence will increase the transformer's even-order distortion from that moment onward until someone demagnetizes it.

If you have a balanced audio source and a couple of resistors and capacitors at your disposal, I can come up with a way to test the filter boards in isolation, but considering their simplicity, I doubt if it will be worth the effort.
Thanks Marcel. I know it's a definite no-no to put DC into the transformers so I have no plans in that respect and, as you say, they're simple so I'm confident that with a suitable input signal the reconstruction boards will 'work' - what they sound like, on the output of your DAC, time will tell.

That said, I have still to test the isolator/reclocker board that sits on my Beaglebone - it was discussed a while back - I plan to test it with a very simple low-pass filter and DC blocking cap 'No DAC' arrangement once I get the BBB and its power supply assembled and I'm wondering if this might offer an opportunity to 'run' the reconstruction filter boards?
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