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Old 11th May 2004, 01:23 PM   #11
roibm is offline roibm  Romania
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what is a kit?
one channel bridged? or two channels bridged?
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Old 11th May 2004, 01:55 PM   #12
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Something that's crept in to later versions of this layout - the connection between pin 7, R1 and the output. I'm not happy about the noding here. The connection on the other half of the chip is a perfect textbook example of how to do it, but the "T"ing of the output connection worries me slightly. I can see the space constraints that have caused you to shape the track in the way you have, but could you not run a track on the red (top?) plane from pin 7 to R1, and then take the output from R1? The via shouldn't cause a problem here, as it will have the wire and solder from R1 to "beef up" the connection.

I also agree with peranders about the track linking the earth planes - it doesn't need to be so long, and would be better connected to the middle of the earth plane. I also think that the OG would be better if you moved it to be between OUT and SG - the symmetry would definitely improve performance - easily measured (if not necessarily audible). However, this is only an issue if you're not bridging a pair of boards, so I don't feel that strongly about it.

Have you considered moving R6 and R7 around to the right of the IC, behind the cap? It would reduce the length of the input traces, and these are at a higher impedance than the input node, so slightly more susceptible to pickup. You might even be able to make the board slightly smaller as a result. (Although, is the spacing of the caps chosen so that you can easily get to the screws holding the IC to the heatsink?). Also, the trace from R6 looks very close to the R9 output node, and as this is a non-inverting amplifier, the chances of positive feedback are very real.

Another small thing - the spacing of the resistors R3 to R7 looks to be non-uniform - is this the case in reality, or a screen-draw issue? Moving them all closer together so the spacing matches R6 and R7 will make it look a bit neater, and you will be able to tidy up the blue SG trace slightly (and the trace to R3, which looks as if it "misses" the centre of the pad).

Sorry if all of this seems unduly critical, but these are the sorts of details that I ask myself when I'm nearly ready to declare my designs "finished". I normally find that the critical analysis can take longer than the basic layout. But, I'm a perfectionist, which isn't always easy

Finally, is it an option to purchase the resistors along with the PCBs?

Best regards,

Mark
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Old 11th May 2004, 01:56 PM   #13
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2 channel paralleled or one channel bridged.
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Old 11th May 2004, 02:03 PM   #14
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I would be much more concerned with via than a T. There is no problem running this trace directly between pads, without the need for a T. I wouldn't recommend mixing 2 layers for that.

As to the output ground 200mill won't make a difference in performance, but it will make big difference in how easy it is to run the connection wire. I don't care for perfect symetry. I care much more for convenience.
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Old 11th May 2004, 02:08 PM   #15
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Quote:
Originally posted by mhennessy


Another small thing - the spacing of the resistors R3 to R7 looks to be non-uniform - is this the case in reality, or a screen-draw issue? Moving them all closer together so the spacing matches R6 and R7 will make it look a bit neater, and you will be able to tidy up the blue SG trace slightly (and the trace to R3, which looks as if it "misses" the centre of the pad).

The spacing it's done here on purpose. Those are not Krell (or Kristian's boards for that matter) where everything is lined up and spaced perfectly. Looks were not considered to be the goal, but performance. The board accomodates Caddocks, but I have strong feeling that Rikens will be better here, so this extra space allows to mount Rikens as well (in vertcal position). You wouldn't mind putting them this way? After all those extras on the leads are part of 3-D layout, (popularasied by Jonathan Carr)
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Old 11th May 2004, 02:11 PM   #16
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Quote:
Originally posted by mhennessy

Have you considered moving R6 and R7 around to the right of the IC, behind the cap? It would reduce the length of the input traces, and these are at a higher impedance than the input node, so slightly more susceptible to pickup. You might even be able to make the board slightly smaller as a result. (Although, is the spacing of the caps chosen so that you can easily get to the screws holding the IC to the heatsink?). Also, the trace from R6 looks very close to the R9 output node, and as this is a non-inverting amplifier, the chances of positive feedback are very real.
Even if you place those resistors closer to the chip, you still have to run the connection wires around the board (this makes those wires longer) so I don't see much difference here. And anyway, there is no space to place those resistors there. Again having conveniently placed input access points on the board was major deciding point.

I would rather modify the traces (less square) and this would further reduced their length.

Regarding the "trace from R6 looks very close to the R9", look how close those are on IC pins
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Old 11th May 2004, 02:15 PM   #17
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Quote:
Originally posted by mhennessy
Sorry if all of this seems unduly critical, but these are the sorts of details that I ask myself when I'm nearly ready to declare my designs "finished". I normally find that the critical analysis can take longer than the basic layout. But, I'm a perfectionist, which isn't always easy

It took at least 5 days and countless hand drawings to finalize that layout.

I'm still working on a DAC (for almost a month) before committing to final layout.

So be asured that a lot of thought went into those amp boards. Also, we ride on experience gained with a previous version, which tested by hundreds brought only positive feedback
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Old 11th May 2004, 02:16 PM   #18
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Quote:
Originally posted by roibm
what is a kit?
one channel bridged? or two channels bridged?
A kit will consist of the components for 2 amplifier boards and 1 power supply board. Additional components will be available for the bridging board, and the extra power supply board at additional cost.

My estimate on the kit price for the basic kit will be $40-45, and the premium kit will be $70-75.

Here is a list of components for the kit to contain:
2 - LM4780 chips
1 - PCB set
6 - 22k resistors
4 - 1k resistors
4 - 680 ohm resistors
4 - 0.22 ohm 3w resistors
2 - SMD resistors for mute
4 - 1500uF 50v Panasonic FC capacitors
2 - 4.7uF capacitors for power supply pcb
8 - MUR860 diodes for power supply pcb

The difference between the premium and basic kits is the choice of components. The premium kit will use Caddock MK132 resistors and 4.7uF BlackGate N capacitors for the power supply board. The 1500uF 50v Panasonic FC capacitors will be used for both kits for now. I am considering offering BG 1000uF STD capacitors in the future, but they are rather expensive costing $12.50 each (with quantity discount), making the price $50 for the capacitors needed fo a kit.

As for the upgrades to the kit, it will cost $5 to add the components for an extra power supply for the basic kit and $10 for the premium kit. I haven't determined the pricing for the bridging board components yet, as the design is being finalized.

I will post more details when everything is finalized.

--
Brian
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Old 11th May 2004, 02:17 PM   #19
joensd is offline joensd  Germany
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roibm,
would you mind ordering 2 additional sets of PCBs and send them to me. Just to save a bit of shipping cost.
Your email adress is not available through the forum, can you drop me a mail?

Regards
Jens
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Old 11th May 2004, 02:38 PM   #20
roibm is offline roibm  Romania
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Quote:
Originally posted by joensd
roibm,
would you mind ordering 2 additional sets of PCBs and send them to me. Just to save a bit of shipping cost.
Your email adress is not available through the forum, can you drop me a mail?
Neither is your email address. And this is not normal, as it has worked just fine previously.
I could do just that, even for other people if interested(as long as the quantity is not that high, otherwise we will have to pay customs + our lovely mwst)


If there is someone from romania that wants to order I could take the order for you as well. You will have to send the money to a romanian bank account so this way you will save some money. For more details contact me when the email contact function gets back.
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