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Old 20th September 2004, 06:28 PM   #1
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Default Help with my 4780 board?

Hey.... I've been working on a NI 4780 board for the last several weeks and just wanted to share what I've done. I'm looking for feedback and suggestions for improvement.

This is an Express PCB file so you have to use their software to view it. If anyone knows of a simple way to save these as JPGs let me know.

Couple notes: This is straight from National's tech notes with a couple changes.

#1. The zobel is left off the PCB. Wire it to the speaker post if desired.

#2. The capacitor bank is for standard Panasonic FC 1000uF. You obviously have the option of adding up to four in parallel. I went this way to lower ESR while allowing flexibility to experiment with different amounts of capacitance.

#3. The caps C3, C4, C5 & C6 all mount on the bottom. Didn't have room on top for everything I wanted. These are optional bypass caps. C5 & C6 are a non-inductive MKP as I couldn't bring myself to use ceramics.

#4. Ci1 & Ci2 are optional but recommended if you want little to no DC offset issues. Optionally you can use a large MKP film cap under the board rather than an electrolytic.

#5. PCB accepts both DACT CT2 volume control or RK16 motorized Alps pots.

#6. Should work in stereo, parallel or bridged with a couple jumpers and component changes.

Express PCB 4780 Layout
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Old 20th September 2004, 07:02 PM   #2
BrianGT is offline BrianGT  United States
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gif of the layout:

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Old 20th September 2004, 07:03 PM   #3
BrianGT is offline BrianGT  United States
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pdf of files:

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Old 20th September 2004, 07:28 PM   #4
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Thanks Brian!..... that helps. The PDF shows more detail with top/bottom layers.


Couple more notes: The RM1, RM2 & CM are for slow-start with the mute as per the National tech notes. I have yet to try this but you should be able to change the slow-start time by varying the capacitor size.

The outline on the upper right of the board is for the optional input caps which would mount under the board. I sized these for some ICW MKP 1.5uF caps that I stock.

The schematic is almost exactly like the one used by National in the tech notes with the exception of all the parallel caps, zobel & a few other minor details. Resistors are all Dale/Vishay RN series and caps are all Panasonic FC series (except the film caps).
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