Dual Buffer Op Amp PCB

Frequent asked about building blocks: gain stages, buffers, clipping configurations, ...
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astrobass
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Post by astrobass »

Hi!

Recently I had cause to build an effect that utilized an op amp buffer for input and output buffers. I'll be doing a post in the DIY effects forum in a few days to showcase that once I have proper samples recorded. But here's a teaser, and possibly a useful thing for those of you with etching capabilities but who haven't looked into buffer design yet.

This board assumes you're using any op amp with the "standard" (in reality, conventional) pin-out, such as the *4558, TL072, LM833, etc. Personally I recommend using the TL072 for this as it has huge input impedance and when used in this fashion to provide unity gain, really doesn't introduce any noise into the circuit that you'll ever be able to observe. It's also dirt cheap, you can buy 20 for $6 CAD with free shipping on eBay.

This design is willing to take 18V in place of the 9V pads indicated, so if you're designing something like a Tube Screamer with op amp buffers and caps rated to accept 18V safely (NOT THAT I'D EVER DO SUCH A THING), you can connect this to the 9V/18V rail, and regardless of whether you connect a 9V or 18V power supply, you'll be in good shape.

Assuming of course, that you use 50V caps. As someone who has actually had a 16V cap explode in his face on a regulated 9V supply (good thing I have shitty eyes and wear glasses), I do recommend going over double on your voltage ratings for caps. It barely costs more anyways.

The obnoxious thing about it being modular is that it takes up extra space. The nice thing is, you can easily add it to any design that lacks buffers (many, many boutique designs and older fuzz circuits), making it easy to see which benefit from buffers. Buffers make a difference. This makes it easy to prove that out.

NOTE: I Somehow fucked up my settings in Eagle and the pads on op amps are a bit big. I usually tidy up my etching masks in photoshop before etching. I also usually fill in the areas that can afford a wider trace. YMMV. If you're good at transfers, you should be fine either way. I'm sure the layout could be tighter, especially if you go to standing resistors, but I don't like to exchange width for height.
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Dual Buffer.png
Dual Buffer.png (9.64 KiB) Viewed 981 times
This is the etching mask.  Invert the colours, and if your etching skills aren't great, clean the pads a bit.
This is the etching mask. Invert the colours, and if your etching skills aren't great, clean the pads a bit.
Dual Buffer PCB Etch.png (2.26 KiB) Viewed 982 times

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atreidesheir
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Post by atreidesheir »

Is this buffer verified?
thanks for the design.
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astrobass
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Post by astrobass »

Yeah I used it. It's simple enough to reverse and verify vs. the datasheet example of a unity gain buffer, too.

(Though I am the guy who posted it. I don't know if anyone else has used it)

There's a mild inefficiency in that Vref is set twice. Actually. I don't know if that's dividing the voltage a second time. It might be. I should fix that just to save two resistors regardless.

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Post by astrobass »

This version is cleaned up. Nothing but the bare essentials, and it fits in 0.75" x 1.00". Nothing to clean-up in the realm of overly large pads. Much simpler. Haven't verified this one yet, but you can easily trace it vs the schematic, so if the schematic is good (and I do believe it is), it'll be fine.
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The schematic.  All junctions labelled.
The schematic. All junctions labelled.
Dual Op Amp Buffer Schem.png (8.58 KiB) Viewed 902 times
Cross-ref the values vs. the schematic via component names.
Cross-ref the values vs. the schematic via component names.
Dual Op Amp Buffer Layout.png (4.88 KiB) Viewed 902 times
Just invert colours and print.  Since I used the "top" trace like a dummy, you don't want to mirror this before printing.  You want to let this get mirrored by the ironing on process.  When in doubt, remember that you want pin 1 to go into the squared off hole from the other side of the board.
Just invert colours and print. Since I used the "top" trace like a dummy, you don't want to mirror this before printing. You want to let this get mirrored by the ironing on process. When in doubt, remember that you want pin 1 to go into the squared off hole from the other side of the board.
Dual Op Amp Buffer Etch.png (1.26 KiB) Viewed 902 times

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Post by copachino »

seem good, i will try it out with a TL072 op amp

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Post by copachino »

astrobass wrote:This version is cleaned up. Nothing but the bare essentials, and it fits in 0.75" x 1.00". Nothing to clean-up in the realm of overly large pads. Much simpler. Haven't verified this one yet, but you can easily trace it vs the schematic, so if the schematic is good (and I do believe it is), it'll be fine.

confirm it as verified, at last have the chance to build it, was a great help to have it in possitive for my possitive pcbs

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Post by astrobass »

Awesome. Glad it was helpful!

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