LM3386: point to point or PCB? - diyAudio
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Old 5th November 2012, 01:03 AM   #1
tbj is offline tbj  United Kingdom
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Default LM3386: point to point or PCB?

I am building an LM3386 based stereo chip amp and I am trying to decide whether to wire point to point or use PCB.

I can etch PCBs but I hate doing it, and so far I can see that the only advantage to PCBing this amp, due to its simplicity, is for looks, with point to point even offering some advantages if done well due to keeping lead lengths nice and short and minimising stray capaticance.

What are your thoughts? Is it just a matter of personal taste?
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Old 5th November 2012, 03:50 AM   #2
DUG is offline DUG  Canada
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Think about why you are building it in the first place.

That will give you more information about what you should do than our opinions (or facts)

I have seen (pix in diyaudio) both done very well, and both give good results.

my $.02 CAD worth

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Old 5th November 2012, 03:57 AM   #3
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Its a matter of personal taste. Point to point is easier to tweak the SQ of - I find grounding/decoupling schemes have a big influence on sound and tweaking that on a PCB is less convenient.

Myself I use a kind of hybrid between PCB and point-to-point. I buy a standard assembled PCB and hack it around because there's a fair amount of time to be saved in getting a functional amp module to begin with. The end result looks much worse than either of the two methods you mentioned though - its 'quick and dirty'
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Old 5th November 2012, 04:09 AM   #4
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Quote:
Originally Posted by abraxalito View Post
Point to point is easier to tweak the SQ of - I find grounding/decoupling schemes have a big influence on sound and tweaking that on a PCB is less convenient.
+1 ...

Frank
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Old 5th November 2012, 11:05 AM   #5
KSTR is offline KSTR  Germany
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P2P is perfect for small amp project like single 3886 in standard config.

Just make sure the the chip's leads are not stressed and bent to avoid any shorts between them. This I find most easily done by supporting the passive components with isolated stand-off eylet strips or turret boards like have been used in tube gear for decades (hint for purchasing). I often use a small central solid copper ground plane and buss bar. For quick prototyping I just solder everything together based on a piece of copper sheet, though.

With short, properly twisted and shielded cabling of critical connections the electrical properties of a P2P build can be outstanding. One might need shielded overall metal case for lowest hum and highest noise immunity.
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Old 5th November 2012, 11:52 AM   #6
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I took short signal paths to the extreme with my P2P 3886. Just make sure you don't want to change anything later if you go to that extreme.

I'd love to reduce the gain on mine but the thought of trying to replace the gain setting resistors has stopped me from doing it (If you have seen the pictures on my blog you will know why )

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Old 5th November 2012, 12:17 PM   #7
AndrewT is online now AndrewT  Scotland
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I'm going to disagree.
The 5pin chipamps really do suit P2P.
But only if you have already decided exactly which components are needed and what values each of them need to be. P2P is quite difficult to swap out later.
With the 3886 there are many extra pins that need extra components and there always seems to be less space than you want/need for the last component.

The 11pin chip makes even more important that you know exactly what components are needed.

I would suggest developing the final schematic on plug boards and/or on ready made PCBs, BEFORE you adopt the final P2P.
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Old 5th November 2012, 03:27 PM   #8
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I have made LM4780's as well with p2p, also using SMD resistors, so LM3886 seems really easy, I've found that with p2p I never get hum problems, with wrong PCB design I do.
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Old 5th November 2012, 08:50 PM   #9
KSTR is offline KSTR  Germany
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Andrew is partly right, I would say.

With P2P one still should decide whether you just prototype things in a temporary build, just soldering up things one some GND plane, or whether you go build "production quality units" -- or at least something that is nice and sturdy. But once you gonna make more than 3 units a PCB seems to be less effort (or effort shifted to the layout stage).

With P2P, the bypass and local supply capacitors tend to get in the way. One can extend the wiring to supply/bypass caps, though. I regularily use up to 10cm (4in.) of coaxial cable (75R satellite antenna cable) wired to blank double sided copper PCB strips with rows of capacitors soldered along the edges. This is as low inductance as it gets for the frequencies of interest (<20Mhz).
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Old 5th November 2012, 09:05 PM   #10
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As I said earlier I went to extremes. Bypass and local supply caps are right on the chip pins, BUT it makes it very difficult to fit everything else in, and there is zero chace of changing anything later if so desired

I was a bit worried about temps for the feedback cap (the one on top of the chip) but I used a large heatsink and it only gets warm.

Tony.
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Last edited by wintermute; 5th November 2012 at 09:06 PM. Reason: add comment on feedback cap
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