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Relays that are "audiophile" grade

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starfly

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You're still not showing the signal grounds for inputs and outputs. I would keep the load resistors at something like 100K or greater since the inactivated contacts are going to be loading the signal lines for the input which is being used at the time. It is important that you place the grounds since if they are not on the schematic, they are not going to be generated when you make the Gerbers. Each component (even eyelets) must have an associated footprint so the proper holes and silk screen can be generated for each component. I don't know what layout program you are using (I use Altium), but you should get familiar with the protocols for making boards so that it goes smoothly in the future.

This is a very simple audio circuit schematic showing signal grounds.

View attachment 156460

Thanks, I'll revisit this tomorrow. I'm using KiCad to make my drawings and to do the PCB design. It's open source and thus free, but I'm sure not nearly as advanced as Altium.

Edit: Ah, I see what you mean now, duh. Each input should really be a 4 port terminal block, In/Out for L and In/Out for R. And same for the output. And then make sure the Out is also to ground.
 
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Colin James Wonfor

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I use Orcad, Proteus, Mentor Graphics, and PADS, the best and most simple to use is Proteus with ARES and ISIS.
The earth or 0v return should be a single point called star earthing and each 0v or earth track should have on one path back. This is often ignored when designing Digital Lies.
On the Analog Components site there was a great down load data file with tips on star earthing.
 
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starfly

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Ok, I updated the schematic with 4 pin terminals to more accurately reflect the actual Left and Right channel inputs. Does this look right?

1633100418714.png
 

antcollinet

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You have a serious problem here. You have joined unused pins together. That means when a relay is "OFF" it shorts the L/R output together.

EG in the state shown - K2 2 and 7 are joined together, and connected to output 1 and 3. Output 1 and 3 are therefore shorted, as are input 1, 1and 3. Same when the relays are switched.

If you are going to put the resistors in, you need a separate resistor for each pin AND consider they represent a load on your input signals, so they need to be large compared with the output impedance of your source. I'd also make them significantly bigger than the load impedance of your destination device, so probably in the region of 500Kohm. Personally I'd consider them un-necessary, since the pins are already driven at low impedance by the switched in source.
 
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starfly

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You have a serious problem here. You have joined unused pins together. That means when a relay is "OFF" it shorts the L/R output together.

EG in the state shown - K2 2 and 7 are joined together, and connected to output 1 and 3. Output 1 and 3 are therefore shorted, as are input 1, 1and 3. Same when the relays are switched.

If you are going to put the resistors in, you need a separate resistor for each pin AND consider they represent a load on your input signals, so they need to be large compared with the output impedance of your source. I'd also make them significantly bigger than the load impedance of your destination device, so probably in the region of 500Kohm. Personally I'd consider them un-necessary, since the pins are already driven at low impedance by the switched in source.
Ok I see what you're saying. It was suggested here that the unused pins on the relays need to go to ground via a load resistor, and this was my attempt to do that. And then have the ground signal from the inputs also go to the same ground location. But yeah, I see how it shorts everything out.

What's the best way to fix this?
 

JayGilb

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61QR34LKFRL._AC_SY240_.jpg


Or you could buy something like this on Amazon for $8 which comes with opto-isolators, selective active high/low relays. These are SPDT relays which would eliminate cross talk that might come with DPDT relays.

You are talking line level signals that may be be switched, at most, a few times a day. These relays are most likely audibly transparent.
 
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starfly

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View attachment 156570

Or you could buy something like this on Amazon for $8 which comes with opto-isolators, selective active high/low relays. These are SPDT relays which would eliminate cross talk that might come with DPDT relays.

You are talking line level signals that may be be switched, at most, a few times a day. These relays are most likely audibly transparent.
Ha, but where's the fun in that? :)
 

JayGilb

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starfly

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Either omit or use separate resistors for each pin. I would say omit.

So when you say omit, just leave the unused relay pins as is, don't connect them to anything? That would certainly simplify things :)
 
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starfly

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View attachment 156570

Or you could buy something like this on Amazon for $8 which comes with opto-isolators, selective active high/low relays. These are SPDT relays which would eliminate cross talk that might come with DPDT relays.

You are talking line level signals that may be be switched, at most, a few times a day. These relays are most likely audibly transparent.

I actually used one of these (or one similar to it) in my amp build last year, to provide trigger functionality to my amp from my AVR. I can always hear a high pitched whine sound (coil whine?) coming from it, and I don't even have to be that close to it.

I think that building this relay myself, it would be completely silent.
 

JayGilb

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I actually used one of these (or one similar to it) in my amp build last year, to provide trigger functionality to my amp from my AVR. I can always hear a high pitched whine sound (coil whine?) coming from it, and I don't even have to be that close to it.

I think that building this relay myself, it would be completely silent.

I have used these on a few projects and this model, at least in my design, did not produce any audible whine. I used a 13.6vdc wall wart to power them, but added a lm7812 and a cap downstream to reduce ripple.
 

antcollinet

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So when you say omit, just leave the unused relay pins as is, don't connect them to anything? That would certainly simplify things :)
That is what I would do. I can't see any benefit from grounding them.
 
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starfly

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Ok, how does this look now?

1633110247410.png


Edit: Ok, looking at this again, a question: I will need to have both the + and - signal of the L and R channels, per input, be routed to the output. That's 4 signals. How do I do that here with these two relays, and also have them grounded? Would I need to add 2 more relays?

And also it looks like pins 2 and 4 (the - on the audio signal) on J2/J3/J4 will always be connected. Will that cause any issues?
 
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MakeMineVinyl

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Ok, how does this look now?

View attachment 156596

Edit: Ok, looking at this again, a question: I will need to have both the + and - signal of the L and R channels, per input, be routed to the output. That's 4 signals. How do I do that here with these two relays, and also have them grounded? Would I need to add 2 more relays?

And also it looks like pins 2 and 4 (the - on the audio signal) on J2/J3/J4 will always be connected. Will that cause any issues?
That looks good. The load resistors for the unused pins are really not necessary unless you experience pops when the relays change state. As mentioned above however, the load resistors are to some degree, depending on value, blending the left and right channels together which is not a great thing to do.

Before you pull the trigger on the board, just make sure that the footprints represented by your schematic symbols actually match the pins on the parts which will occupy those places. This is something which is a royal pain we run into sometimes where one engineer's library of footprints might not exactly match another engineer's. The boards get made and the parts don't match the pattern on the PCB.

It looks like you're understanding the importance of your schematic exactly matching every connection you will be making on the board. If a connection isn't on your schematic, its not going to show up on your finished board. The final step in laying out your board should be pouring the ground plane. If its a double sided board, you can pour these on both sides. If there is some area which is land-locked and the pour can't fill in those spaces, place a via there to supply a path which connects the top plane to the bottom. Just make sure that the via is edited to be on the same net as the GND or it won't connect when the pour is made.

For reference, these are images of my active crossover PCB. The top image is the top side of the board with the GND pour. The bottom images is with the GND pour deleted so the traces on both sides of the board can be seen.

Upper Layer With GND Pour.jpg


No Pour.jpg
 
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starfly

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That looks good. The load resistors for the unused pins are really not necessary unless you experience pops when the relays change state. As mentioned above however, the load resistors are to some degree, depending on value, blending the left and right channels together which is not a great thing to do.

Before you pull the trigger on the board, just make sure that the footprints represented by your schematic symbols actually match the pins on the parts which will occupy those places. This is something which is a royal pain we run into sometimes where one engineer's library of footprints might not exactly match another engineer's. The boards get made and the parts don't match the pattern on the PCB.

It looks like you're understanding the importance of your schematic exactly matching every connection you will be making on the board. If a connection isn't on your schematic, its not going to show up on your finished board. The final step in laying out your board should be pouring the ground plane. If its a double sided board, you can pour these on both sides. If there is some area which is land-locked and the pour can't fill in those spaces, place a via there to supply a path which connects the top plane to the bottom. Just make sure that the via is edited to be on the same net as the GND or it won't connect when the pour is made.

For reference, these are images of my active crossover PCB. The top image is the top side of the board with the GND pour. The bottom images is with the GND pour deleted so the traces on both sides of the board can be seen.

View attachment 156603

View attachment 156604

So you're saying, don't change anything in the drawing I posted, and it should work fine? The - (negative) audio signal on the inputs and outputs always being connected will not be an issue, so I don't have to make those switchable with relays?

Not sure I understand yet what you're saying about the pour on the PCB, but I'll get there :) The PCB will be dual layer.

As for the parts, I plan on ordering those soon, once the design is finalized, and will test it all works as intended on a bread board before I finalize the PCB design and send it off to be made. Then I'll also confirm measurements and such to make sure it'll all fit :)
 

MakeMineVinyl

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So you're saying, don't change anything in the drawing I posted, and it should work fine? The - (negative) audio signal on the inputs and outputs always being connected will not be an issue, so I don't have to make those switchable with relays?

Not sure I understand yet what you're saying about the pour on the PCB, but I'll get there :) The PCB will be dual layer.

As for the parts, I plan on ordering those soon, once the design is finalized, and will test it all works as intended on a bread board before I finalize the PCB design and send it off to be made. Then I'll also confirm measurements and such to make sure it'll all fit :)
The ground side of the audio inputs and outputs being connected together all the time shouldn't be an issue unless you want to run those separately through the unused relay contacts, which might be a good idea. Its really up to you how you want to do it - handling grounds can get dicey. Having the grounds for both inputs always connected together can introduce ground loops, so there's that, but pops are possible if you run the ground connections through the relay contacts as you switch inputs.

A 'pour' is the term for pouring a plane, which in your case will be the ground plane. A pour can be anything; I've used it for power planes in addition to ground planes. Look at the examples I posted above with the ground 'pour' and without. Your PCB layout program will give you the option of which net you want to connect the pour to. In your case it will be on the GND net.
 
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starfly

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The ground side of the audio inputs and outputs being connected together all the time shouldn't be an issue unless you want to run those separately through the unused relay contacts, which might be a good idea. Its really up to you how you want to do it - handling grounds can get dicey. Having the grounds for both inputs always connected together can introduce ground loops, so there's that, but pops are possible if you run the ground connections through the relay contacts as you switch inputs.

A 'pour' is the term for pouring a plane, which in your case will be the ground plane. A pour can be anything; I've used it for power planes in addition to ground planes. Look at the examples I posted above with the ground 'pour' and without. Your PCB layout program will give you the option of which net you want to connect the pour to. In your case it will be on the GND net.

I might add a third relay just for audio ground side, so it toggles between both inputs. Here I can just one of these Omron relays, as a minimal chance of crosstalk is not needed for this signal. Don't want the risk of groundloops.
As for pops, my amp has a speaker protection circuit in it (Neurochrome Guardian-86), so that *should* keep the speakers safe.

I'll post the PCB drawing once I have that figured out. Thanks for all the help!!
 
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