Linkwitz LM4780 PCB Proposal: Comments Wanted! - diyAudio
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Old 1st April 2006, 11:50 PM   #1
dfdye is offline dfdye  United States
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Default Linkwitz LM4780 PCB Proposal: Comments Wanted!

After building a set of LM3886 amps based on the Linkwitz circuit (which I really like!), I figured I would try an amp using the LM4780 based on the same circuit layout. Since I haven't used this chip before, I figured I would ask:

1) If anyone has used the Linkwitz circuit ( http://www.linkwitzlab.com/images/graphics/3886amp.gif ) using the LM4780 as two LM3886's. I know other amps (Brian and Peter's come to the front of my mind) use this chip in a similar manner, but I was specifically interested to see if anyone has used the Linkwitz topology. It should be fine, but there is no since in re-inventing the wheel if there is someone who has already found out any issues. (Searching the forum didnít show much, but I figured someone has to have done this!!!)

And 2) Attached is a proposed PCB that fell together rather nicely, but I figured I would run it past more experienced designers first. Particularly, I am concerned about the V+ section coming from the input pin header to C+ and the input signal traces running along the top right edge of the board. If anyone has any comments either way as to whether my concerns are justified, or if I am in good shape, I would appreciate the feedback. Any suggestions or comments about the rest of the board are welcomed as well!

Thanks!
David


As a side note, I started off trying to make this a single sided PCB. That idea got trashed rather quickly, but I was wondering if anyone has used a single sided LM4780 PCB?
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Old 3rd April 2006, 10:52 PM   #2
dfdye is offline dfdye  United States
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Well, I hope nobody finds anything! I just dropped in a prototype order (with a bunch of other stuff too . . . ) so I guess we will see how it comes out!

David
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Old 5th April 2006, 01:47 PM   #3
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just letting you know that someone is reading your thread with interest...

-Dwight
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Old 5th April 2006, 02:30 PM   #4
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do you mean to use additional opamps, or use the LM4780 itself as one of the components in a filter network?
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Old 5th April 2006, 05:54 PM   #5
dfdye is offline dfdye  United States
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Quote:
Originally posted by jackinnj
do you mean to use additional opamps, or use the LM4780 itself as one of the components in a filter network?
I am not sure I understand you question. I am using the LM4780 as the amplifier, not a filter.

(If I misunderstand your question, please forgive the basics. . . .)

I am treating the LM4780 as two LM3886's. If any additional filtering is required, I will indeed use external components. I am currently planning on using these as part of a multichanel amp that will drive actively filtered speakers, so yes, I will be using additional opamps as a filter network, but I am not considering the LM3886's to be part of that filter network. The exception is if I use the two 220uf electrolytics in CGA/B instead of a 10uf film cap. This effectively filters most of the high end response if you are using these amps for woofers. This amp layout is pulled right from linkwitzlab.com, but I guess a copy of the schematic might be helpful. The Ci* cap does add a filtering, but again, that is not really the point of this circuit.

If this is not what you were asking, sorry for the tangent.

David
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Old 5th April 2006, 05:56 PM   #6
dfdye is offline dfdye  United States
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Quote:
Originally posted by morgandc
just letting you know that someone is reading your thread with interest...

-Dwight
Thanks! I'll let you know when I get the amps built and tested.

David
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Old 5th April 2006, 07:11 PM   #7
alexcd is offline alexcd  United States
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Looks pretty good. I'm having a hard time keeping the output stable in a bridged configuration. Make sure you use small bypass caps very close to the chip and keep leads short and neat. Ballast resistors are required if you plan to bridge channels.
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Old 5th April 2006, 07:32 PM   #8
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Rail lines are too slim, David. Image it in real size and imagine, that there should " flow " 10 A....
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Old 5th April 2006, 08:58 PM   #9
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Quote:
Originally posted by dfdye
I am not sure I understand you question. I am using the LM4780 as the amplifier, not a filter.
Using the overture series chips as part of an active filter has been tried -- not by me -- I haven't heard (or seen) any results published so I wonder if it is stable in this app.

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Old 5th April 2006, 09:03 PM   #10
dfdye is offline dfdye  United States
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Quote:
Originally posted by jackinnj
I haven't heard (or seen) any results published so I wonder if it is stable in this app.
Ah, now your question makes more sense. I am not sure, but I have not tried it in that configuration.

David
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