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#21 |
diyAudio Member
Join Date: Dec 2002
Location: Calgary, Alberta
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Hi, just noticed this thread. This is very interesting to me, but the pcb prices seem so high compared to Chinese manufacture. Marcel, if you have Gerbers I can run a group buy. I ran one here quite a few years ago, but still remember the in's and out's.
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No one wants advice - only corroboration. John Steinbeck |
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#22 |
diyAudio Member
Join Date: Mar 2003
Location: Haarlem, the Netherlands
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It indeed uses sigma-delta (or delta-sigma, that's the same) modulation. In fact you can choose between three sigma-delta algorithms, a seventh-order chaotic sigma-delta and two fifth-order sigma-deltas with a kind of embedded pulse width modulator with randomly rotated pattern. These last two have the advantage that they are dithered according to dither theory, which eliminates the tonal behaviour that many sigma-delta modulators have. You can also do a blind ABX test, I've included a state machine for that.
The complete design database including Gerber files, KiCAD database and FPGA files (source code and synthesized + implemented) can be downloaded for free from the downloads section of the Linear Audio website, Downloads | Linear Audio. You have to scroll down to "Design data package for Marcel van de Gevel's Valve DAC from Vol 13". The article that explains the ideas behind the design can also be downloaded, but that will cost you almost half a euro, see Linear Audio | your tech audio resource I rather like buying things that are not made in China every now and then, but of course you can have the PCB manufactured in China or wherever you like. Some component values may have to be adapted when the prepreg thickness is very different from the 360 um that Eurocircuits uses, but that can be done. Last edited by MarcelvdG; 19th October 2017 at 09:41 PM. |
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#23 | |
diyAudio Member
Join Date: Dec 2002
Location: Calgary, Alberta
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Quote:
Even if you have made the package freely available, it would not be ethical for me to even start a group buy without your agreement. I would plan on Chinese manufacture of the boards, looking for best price and also previous experience on this forum. I would start by opening a thread in the group buy forum to gauge sufficient interest. Let me know your thoughts.
__________________
No one wants advice - only corroboration. John Steinbeck |
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#24 |
diyAudio Member
Join Date: Mar 2003
Location: Haarlem, the Netherlands
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Don't worry, I'd consider it an honour if you started a group buy for this. I would like to warn you, though, that the PCB is not the only expensive part, see also posts 8 and 9.
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#25 |
diyAudio Member
Join Date: Apr 2014
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But how does it sound?
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#26 |
diyAudio Member
Join Date: Dec 2002
Location: Calgary, Alberta
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Yes, of course. That is the beauty of a group buy, if there is enough interest even parts other than PCB's can be sourced at lower cost. It really just depends on interest more than anything else.
__________________
No one wants advice - only corroboration. John Steinbeck |
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#27 |
diyAudio Member
Join Date: Mar 2003
Location: Haarlem, the Netherlands
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#28 |
diyAudio Member
Join Date: Dec 2002
Location: Calgary, Alberta
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Marcel, I am starting to get some questions back from the PCB houses, and I have some of my own:
The filter PCB gerber files do not include silkscreen or solder mask. What about PCB specification itself: substrate, thickness, surface finish, etc.? What are they for your prototypes, can we use this, or do you have suggested improvements? You mentioned that there is a error with the transformer solder pads. Is this because the software library assumed a different Jensen form factor? This may be important if we seek a substitute supplier such as Cinemag. You mention that the transformer is optional. The schematics in the design package don't show that option. Is it to be found somewhere?
__________________
No one wants advice - only corroboration. John Steinbeck |
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#29 | ||||
diyAudio Member
Join Date: Mar 2003
Location: Haarlem, the Netherlands
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#30 | |
diyAudio Member
Join Date: Dec 2002
Location: Calgary, Alberta
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Quote:
I was surprised at 1.55mm thickness. With this large a board, 4 layers, and the need to survive multiple tube socket insertions and removals, I would have thought that thicker would have been the way to go. Any comment?
__________________
No one wants advice - only corroboration. John Steinbeck |
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