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Old 11th May 2004, 04:35 PM   #31
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Quote:
Originally posted by Peter Daniel


The spacing between those resistor should be according to that scetch. Only than installing Rikens present's no problem. This spacing is deliberate. It seems like Brian didn't do it quite accurately though.

OK - I take your point, although it looks to me like that spacing was to accomodate the blue ground traces - something that isn't an issue with the latest layout.

Also, can I compliment you on your perfect output noding

I'm looking forward to seeing (and eventually hearing) the finished product. Thanks to you and BrianGT for all your work!

Cheers,

Mark
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Old 11th May 2004, 04:49 PM   #32
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As of now, I'm already working on improving layout based on your suggestions.

Spacing of those resistors is not really desirable (as blue ground trace would be easier to run) but I need that space.

I never seen vias on well implemented audio boards, you can see them in digital a lot though. Aleph X group purchase board was designed with vias, but it was questioned initially, and whwnever I look at that, I think to myself that it could be done differently. To me, via connection is a waek point in a signal path and I never even consider it from pure audiophile POV. Using it is conveneient though.

Regarding vertical resistors, this is not really standard option for that board, Caddocks can be easily used here, but I think that Rikens will sound better (they do on 3875 board) and I wanted to allow placing them here, even at the cost of vertical arrangement. I personally also don't like that way to mount resistor, but inn some cases it is a calculated compromise. In this particualr layout, using Caddocks, leaves more space for running uninterupted ground plane, so I opted for Caddocks (or Vishays) as it looks good and it's a small package. But in my personal amp, I wil be probably using Rikens here. Doen't treat it as inproperly mounted resistor, treated as a resistor with additional trace attached in 3-D space. To me it doesn't make any difference. Running extra trace in air is worth of widening the ground plane.

Regarding the other two resistors (the series input connection), it would be nice to place them closer to the chip, but then the ground returne path is getting longer, (as you can't move all resistors from lack of space) so I don't know if anything is gained by that.

I reply fast, because I already have al lthe answers ready. I asked those questions myself many time when doing that layout.

However I agree that there is a room for improvement here, and whatever possible, it will be done (this ones for real)
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Old 11th May 2004, 05:24 PM   #33
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Quote:
Originally posted by Peter Daniel
Regarding the other two resistors (the series input connection), it would be nice to place them closer to the chip, but then the ground returne path is getting longer, (as you can't move all resistors from lack of space) so I don't know if anything is gained by that.
Thanks for the reply. It had never occurred to me that vias could be a week point, because they are no worse than a standard thermal relief in a ground plane, but I would agree that it's normally good plactice to keep signals on one side of the board...

Anyway, I'm not sure if I explained the two-resistors thing clearly enough, so I've modified the .gif (I don't have access to PCB CAD here) - the image is messy, but you'll hopefully get the idea. Perhaps putting them there causes physical problems (if they're vertically mounted, for example)? Note that I also took the liberty of following this through to the logical conclusion - I moved R4 to occupy the space left by R6/7, improving the earth trace that I mentioned earlier.

Having said all of that, I prefer the aesthetics of 5 little resistors in a neat row
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Old 11th May 2004, 05:32 PM   #34
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But do you see how input trace extended? So nothing is really gained except for unning shorter 2 traces and longer a single trace. Also the SG node is chanched and I don't think if for better.

I modified resistors spacing a bit and some traces, addressing T connection and trying to simplify input traces (they are shorter now). I still didn't do adjust polygon but connected SG and OG with a single blue trace.
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Old 11th May 2004, 05:37 PM   #35
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With regards to have OG centrally positioned, I think it could be swaped with SG pad for more central placement.
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Old 11th May 2004, 05:45 PM   #36
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Quote:
Originally posted by Peter Daniel
But do you see how input trace extended? So nothing is really gained except for unning shorter 2 traces and longer a single trace.
Yes, but the point you're missing is the traces between the resistors and IC are the vulnerable ones! Sure, the input trace is perhaps slightly longer, but remember that this trace is just an extension of the input wiring from the rear panel (or DRV134 PCB). This trace is at low impedance, and less prone to interferrence.

Quote:
Originally posted by Peter Daniel
Also the SG node is chanched and I don't think if for better.
The earthing is actually better with this, but as it's the signal earth and no currents are flowing here, this is a mute point.


Quote:
Originally posted by Peter Daniel
I modified resistors spacing a bit and some traces, addressing T connection and trying to simplify input traces (they are shorter now). I still didn't do adjust polygon and forgot to connect SG and OG with a single blue trace.
Yes, this is much better, and addresses most of my concerns.

The biggest problem with my input resistor move is the uncomfortable aesthetic of those two resistors all out on their own (although you did say that you prefered sound to aesthetics )... While I was playing, I couldn't resist improving the signal earthing further (possible alternative route shown in green, although I prefer the blue)
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Old 11th May 2004, 05:45 PM   #37
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Like this, but I'm not sure if it's really better. I'd rather prefer to have input signal and input ground side by side, and moving OG by 200mil won't make any observable difference, IMO.

Another issue is running the connections wire. Going away from the board I would also prefer to have them spaced, and this arrangement doesn't relly allow it (if you know what I mean).
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Old 11th May 2004, 05:50 PM   #38
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Quote:
Originally posted by Peter Daniel
With regards to have OG centrally positioned, I think it could be swaped with SG pad for more central placement.
Yes, I'd agree with this

Although the two wires from the input signal "straddle" the OG, which might be uncomfortable. But, these amps are capable of passing a lot of current, and every mil is important - so it's a compromise I'd seriously consider. But, I'm using these in bridged mode, so as I said before, I don't personally feel that strongly about it.

Hometime now - look forward to seeing the updates tomorrow morning

Best regards,

Mark
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Old 11th May 2004, 05:51 PM   #39
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Quote:
Originally posted by mhennessy

although I prefer the blue)
If you check pin out on the chip, the pin where you connected blue trace is NC. The best connection point for ground path would be your left, green trace.

Regarding long traces from input resistors to the chip, I might be concerned with them, but obviously it wasn't a concern of National design team when they made evaluation board. Those traces are even longer on their board.
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Old 11th May 2004, 07:42 PM   #40
joensd is offline joensd  Germany
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roibm,
You can now click my profile to drop me a mail.
Speak to you soon.

Regards
Jens
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