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Audio Through Relays

nintendoeats

Oct 18, 2013
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There's something I've wanted for a while, and I thought I might try to make one for my Dad as a christmas present. I want to make a device which allows you to plug in 3 or 4 guitar pedals and then switch the order around without unplugging them. The only way that I am aware of to do this would be to use an Arduino controlling many MANY relays. I'm certainly open to other suggestions, but assuming I go ahead with that plan I haven't been able to decide on what kind of relays I need. I believe the correct thing to use is TRIAC opto-isolators since I will be dealing with AC and would prefer small non-magnetic devices (don't want to introduce noise into the signal), but I'm not entirely confident in that decision.

Thanks!
Adrian
 

AnalogKid

Jun 10, 2015
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If you have multiple sources and multiple destinations, what you are describing is a routing switcher.

Are all audio signals at guitar pickup voltage levels?
How many audio signals are there?
Are any stereo, or all mono?
Balanced or unbalanced?
What do you mean by "switch the order around"?
Can you draw a sketch or schematic of what you want to achieve?

So much for design data, now about those triacs - no. A triac is a device designed specifically to switch AC power into a load like a light bulb, motor, etc. For several reasons it would introduce tremendous distortion if it conducted at all. Since a triac is diode-based, there is a minimum signal level needed before anything flows through it.

A better alternative is a photomos or some other kind of photo-MOSFET based SSR (solid state relay). These are common in telephone switching systems. For the best signal quality you might be headed for audio-optimized analog switches.

ak
 

BobK

Jan 5, 2010
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What you need is analog switches. Google it.

Bob
 

Martaine2005

May 12, 2015
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Hello,
Why do you want to switch the order?
The whole point of multiple pedals is to place them in an order that suits the individual guitarist.
It really is a personal touch!.
I bet your Dad has some pedals he uses less than the others.
A DIY pedalboard would be a nice christmas present. I made a two tier pedalboard for my son. The pedals that were not used all the time went on the top tier.
The fuzz, wha, phase etc he uses regularly, went on the bottom. But he was quite adamant that the fuzz was first on the left.
They are all patched together so only needs two cables. One guitar IN and one AMP out.
Some professional guitarists insist on a specific order because some pedals affect the next in line, and they like that particular sound.
You can also put a power supply on-board to power all the pedals too. No batteries. My sons were all 9v so it was easier.
The best part is, unplug the guitar and amp and put the lid on!
All the last settings are saved! And set up time is just as quick as plugging in one pedal.
Finally, it's only limited by your imagination!

Martin
 

nintendoeats

Oct 18, 2013
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Thanks guys, I have to work through a bunch of info posted here so bear with me. To answer the question on everybodies lips, the point is that being able to reorder thepedal chain quickly allows for ease of experimentation. If you are deciding which pedal to put first (say tremolo, EQ and delay, a favourite of mine) It would be nice to be able to try all of the available combinations without having to rewire everything while holding a guitar.
 

AnalogKid

Jun 10, 2015
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For a fully reconfigurable system with three pedals you'll need 15 relays or analog switches, 16 if you want a full bypass mode.

ak
 

nintendoeats

Oct 18, 2013
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1.Are all audio signals at guitar pickup voltage levels?
2.How many audio signals are there?
3.Are any stereo, or all mono?
4.Balanced or unbalanced?
5.What do you mean by "switch the order around"?
6.Can you draw a sketch or schematic of what you want to achieve?
Routing switcher sounds exactly right.

1.Generally yes, but some pedals do amplify signals so there needs to be a good amount of overhead.
2.In the case of 3 pedals you would have the guitar input, the output to amplifier, and then 3 ins and out (one for each pedal). Of course, each input and output consists of two wires that much be switched.
3.All mono
4.Unbalanced
5.If I have my delay outputting to my tremolo, I may want to hear what is sounds like going the other way. Normally you have to unplug everything and rewire it. I want to be able to control the order of pedal connection with a microcontroller.
6. Here is a quick sketch. The pushbuttons are the aspect of interest as I'm sure you can see.

Pedal_Switcher.jpg
 

AnalogKid

Jun 10, 2015
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Since the entire rig is mono and unbalanced, everywhere you show two switches there actually is only one. You do not want to switch the grounds if you can avoid it. If you have relays or solid state switches, they must be powered and controlled. For all analog switches, how were you going to control them, with some kind of visual indication of what the configuration is? For every electronic switch there is a control signal, which means there has to be a switch (mechanical/electrical/computer) controlling the switch.

OR - why not just use switches? For your diagram it would take six SPST toggle switches. No power system to power the control electronics, no control electronics, and the switches themselves are the indicator of the current configuration. K.I.S.S.

ak
 

nintendoeats

Oct 18, 2013
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Since the entire rig is mono and unbalanced, everywhere you show two switches there actually is only one. You do not want to switch the grounds if you can avoid it. If you have relays or solid state switches, they must be powered and controlled. For all analog switches, how were you going to control them, with some kind of visual indication of what the configuration is? For every electronic switch there is a control signal, which means there has to be a switch (mechanical/electrical/computer) controlling the switch.

OR - why not just use switches? For your diagram it would take six SPST toggle switches. No power system to power the control electronics, no control electronics, and the switches themselves are the indicator of the current configuration. K.I.S.S.

ak
My understanding was that a guitar (or indeed any audio) signal is AC, hence I was intending to switch both wires for each connection. If that isn't the case then it does make things much simpler. As for the automation, I am planning to use an Arduino (I have an interface in mind but the details of that aren't important). That diagram only has 2 pedals, ultimately I want to have at least 3 and possibly 4 so manually switching would be impractical and defeat the purpose of the whole project which is to make it super convenient.

I've ordered some analog switches intended for telecoms and other applications of that sort. Not much I can do until they arrive I'm afraid. Luckily NOT coming from China.
 

CDRIVE

Hauling 10' pipe on a Trek Shift3
May 8, 2012
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My understanding was that a guitar (or indeed any audio) signal is AC, hence I was intending to switch both wires for each connection.
Well that's two misconceptions that need to be dismissed. The first one,... that all audio signals are AC is untrue and the second, that both conductors need to be switched is also untrue.

Regarding the first misconception; yes it is true but only the signal that is driving the speakers. The circuitry inside an amplifier is amplifying a modulated DC representation of the signal. When it outputs from the amplifier it will be converted to true AC to drive the speakers.

Chris
 

AnalogKid

Jun 10, 2015
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My understanding was that a guitar (or indeed any audio) signal is AC, hence I was intending to switch both wires for each connection.

What comes out of a guitar pickup is about as AC as AC can get. And if it is kept as a balanced signal, then you do indeed have to switch both lines. But if you ground one end (as many amps do), then it is one unbalanced signal line and a ground. Straight out of the guitar, the voltage alternates above and below ground, something the downstream circuits have to be able to handle.

ak
 

GPG

Sep 18, 2015
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I've ordered some analog switches intended for telecoms and other applications of that sort.
What part?
I have done research and this is the best I can find.
http://www.analog.com/en/products/s...hes-multiplexers/adg442.html#product-overview
They are individually addressable, very low on R
Draw a 4x4 matrix. (4 inputs, 4 outputs) place a switch at each crossing Not all of the switches need be used. eg input to output of the same pedal. Will require 3 switch chips. You will need to be able to address each sw individually so you need a 12 bit bus. or.4x3 latch.. Using a +- supply means no biasing.
Oh and its available in DIP for breadboarding
Expand as necessary
 
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nintendoeats

Oct 18, 2013
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What comes out of a guitar pickup is about as AC as AC can get. And if it is kept as a balanced signal, then you do indeed have to switch both lines. But if you ground one end (as many amps do), then it is one unbalanced signal line and a ground. Straight out of the guitar, the voltage alternates above and below ground, something the downstream circuits have to be able to handle.
That is more consistent with my understanding. I am going to have to do some reading and fiddling To work out exactly how the switching should work

What part?

These: http://www.vishay.com/docs/70037/dg201b.pdf

They appear pretty similar to my eyes, and I could get these ones cheaply from North America.
 

GPG

Sep 18, 2015
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AnalogKid

Jun 10, 2015
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The MAX4359 is a fully integrated 4x4 routing switcher, but it is designed for video and might not have the noise/distortion performance you need. Still, I'd look into it because it might save a ton of work.

ak
 
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