DipTrace

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simon
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#1 DipTrace

Post by simon »

Rather than pollute the MoFo thread I thought I'd start another - I'm having a go at trying to draft an op amp gain stage PCB using DipTrace.

This is the simple circuit:
20221103_174705.jpg
20221103_174705.jpg (121.35 KiB) Viewed 6680 times
And after I'd got it working on a breadboard Nick made some suggestions:
Nick wrote: Mon Nov 07, 2022 8:47 pm
simon wrote: Mon Nov 07, 2022 5:58 pm Mmmmmm. Just taken the op amp gain stage out and the sound is immediately better without it. More shine and sparkle, more detail, more space, more realism. More music. Interesting experiment.
I would suggest trying with better metal film or carbon resistors, maybe tackman. Also try a simple 9v battery (or two if its split rail) I don't trust that SMPS and certainly don't if you have made a dummy split rail. Also if that ceramic cap in the feedback path? of so, replace with a polystyrene. Most ceramic (not so much C0G) introduce a shocking amount of distortion. Also need power rail decoupling, electrolytic and ceramic.
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#2 Re: DipTrace

Post by Nick »

Still, decoupling on the -ve supply also.
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#3 Re: DipTrace

Post by simon »

So here's my first attempt, very simple, just the op amp circuit to start. The orange copper pour on the bottom obscures things a little and I haven't worked out how to move the component labels yet but to explain my thinking:

DC input is at the bottom of the board, notionally +15V 0V -15V
Signal input is at the top of the board, each channel with a common ground pad
The signal grounds, DC 0V, V+ and V- cap bypasses negatives, and R2 ground pads are all connected to the copper "ground" pour on the bottom (I think!)
I've left the trace width at the default 0.013" (0.33mm) width. This seems pretty skinny but there's very little current involved but maybe they should be made wider?

Any thoughts, comments, suggestions?
Op Amp Gain Stage v1.PNG
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#4 Re: DipTrace

Post by simon »

Nick wrote: Tue Nov 08, 2022 5:06 pm Still, decoupling on the -ve supply also.
Yep, I've got it in the circuit but hadn't bothered to update the original sketch. You're right to mention it.
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#5 Re: DipTrace

Post by simon »

And here's one without the copper pour if it's clearer
Op Amp Gain Stage v1 no copper pour.PNG
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#6 Re: DipTrace

Post by Nick »

You could be picky and suggest the electrolytic's closer to the input header to prevent supply noise current from using the traces from the supply input to the first cap as antenna, but its all, as I say, a bit picky.

But yep, arn't PCB's easy.
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#7 Re: DipTrace

Post by simon »

Cool, that will be rev 2. I'm thinking of all sorts of things I could build :-D.

I've just run the Design Rules Check and there are errors with all the connections to the copper pour - it's specifying a negative gap, which is therefore less than the minimum. Odd. I've obviously not done it properly somehow.

How important is a ground plane? I could just have a wide net to connect them all up.
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#8 Re: DipTrace

Post by Nick »

I don't know the tool so cant help, but a ground plane is rarely a bad idea. You could also make the traces wider, not important but no reason why not.

Google make me think it may be how you have drawn the traces. The error suggests things touching that shouldn't. Did you draw the traces by hand instead of maybe this:

"To avoid DRC errors you shouldn't connect pads in Pattern editor. Do it in PCB Layout using traces or copper pour instead shapes."

https://diptrace.com/forum/viewtopic.php?t=10244
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#9 Re: DipTrace

Post by simon »

Yeah I used PCB Layout and added traces. I think I probably just need to understand the correct way to do it, I'll have another play tomorrow.
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#10 Re: DipTrace

Post by Nick »

Normally you start with drawing the schematic and layout the parts from that then it knows what should be connected to what.
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#11 Re: DipTrace

Post by simon »

I tried drawing the schematic up first previously but couldnt work out how to use relays. Perhaps I'll have another go with something simpler, like an op amp.
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#12 Re: DipTrace

Post by Nick »

Relays often come in multiple parts with the coil and the contacts that need expressing individually.
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#13 Re: DipTrace

Post by simon »

Yep, that's what confused me! Running before I could walk...
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#14 Re: DipTrace

Post by ed »

does diptrace work with library loader?

if so, a suggestion would be to download library loader(samacsys?) and read the get started stuff.....
this will allow you to put the required part number(from a choice of suppliers) on your pcb image and it will assign the footprint

I'm fairly certain all the other pcb designers work with library loader or other library managers. It's a must if you are going to be using a pcb designer for more projects..imo
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#15 Re: DipTrace

Post by simon »

Umm, I've no idea ed. Thanks for the pointer, I'll do some research.

(DipTrace does have a lot of components in its internal library, is this kind of what you mean? There's no LME49720 or OPA2134 though so I had to find something with the same number of legs.)
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