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Author Topic: Is there a simple channel switching scheme?  (Read 7283 times)

Ripthorn

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Is there a simple channel switching scheme?
« on: February 21, 2009, 09:27:20 PM »
Hi guys, this is my first post, though I have looked around for a while.  I am in the process of building my own amp using discrete components and have a design that I like.  I have breadboarded it and all.  The thing that is troubling me is that I want to have "channel" switching.  Really what I want is to be able to send the signal either to the power amp for cleaner tones or through an extra gain section to give me a high gain tone.  I would really like to do this with a footswitch, but if the footswitch is unplugged, it just gives me clean.  I was thinking I could do it with a switched jack and a dpdt stomp switch, but I also want another button in the same footswitch to activate a single onboard effect.  The effect will also have a toggle on the front panel, so I figure I can just use a relay for that.  The problem is that I want to use a single TRS cable to flip the relay for the effect and also to route the signal from the clean stage but I don't know how I would do the routing of the clean signal with (basically) a TS connection (since the ring would be used for the relay).  I am hoping that you guys can help me out here.  Would I need to use relays for both?

J M Fahey

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Re: Is there a simple channel switching scheme?
« Reply #1 on: February 22, 2009, 06:03:00 AM »
Basically yes.
You will use 2 relays in the head to do whatever you like .
To switch them you´ll use sleeve as common ground, and tip and ring will activate each its own relay coil.
Since you don´r run audio along this cable, it doesn´t need to be shielded and can be any reasonable length.
J M Fahey

Ripthorn

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Re: Is there a simple channel switching scheme?
« Reply #2 on: February 22, 2009, 07:47:59 PM »
So let me see if I am getting this right, I will have a trs jack with sleeve being ground.  Channel switching will be on tip and effect on ring.  I will have a relay for channel switching where NC is just the clean channel and then activated is high gain.  For effect, NC will be no effect and activated for effect, right?  I guess my question is now what if I want panel switches for both? 

I found this article (http://www.geofex.com/Article_Folders/pffootsw.pdf) by RG and was wondering if this would be implementable with TRS or if I would need the same power supply in the head and in the switch (i.e. would i need four contacts as opposed to 3 to pull this off) in order for the relays to work properly.  If I can use separate power (e.g. a battery in the footswitch for 6V relays instead of 12V) then I know I can use a trs for just two channels of that method and I would be perfectly okay with that.

J M Fahey

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Re: Is there a simple channel switching scheme?
« Reply #3 on: February 22, 2009, 09:11:49 PM »
Hi Ripthorn.
For God´s sake, no!! The article is interesting and technically correct but not very practical, specially considering the need for independent power at the footswitch´s end and even more the beginner-unfriendly design (except maybe the first example).
When you get that complex, they usually use 5 pin DIN connectors, using 2 or 3 for ground and DC power, and the remaining ones to send some kind of coded data, which is then decoded at the amp´s end.
In that case they go for Cmos Logic ICs or dedicated chips (very unlucky when they become obsolete/extingished) or even Pics
I´ll draw a *very* simple example and post it here.
By the way, what supply voltage do you have available in your project?
Bye.
J M

Ripthorn

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Re: Is there a simple channel switching scheme?
« Reply #4 on: February 22, 2009, 10:12:29 PM »
I will have 12 and 6Vdc available in my project.  I really appreciate all your help.  I have been thinking and dreaming switching schemes for the last several days and haven't been able to figure out how I could get panel switches and footswitches to play together (and hopefully LED's as indicators).

syndromet

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Re: Is there a simple channel switching scheme?
« Reply #5 on: February 23, 2009, 05:33:01 AM »
relay switching is definitivly the way to go. You should also have a preamp on the clean side of the switch, so that you hit the preamp with the gain it prefers. It should also allow some toneshaping to make the amp more versetile. Something like an inverted lm072 with a tonestack or something.

Ripthorn

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Re: Is there a simple channel switching scheme?
« Reply #6 on: February 23, 2009, 09:41:49 AM »
Thanks for the response syndromet.  The structure of the amp will look like the input, clean preamp section, switch to either send that through a tonestack to the power amp or bypass tonestack into additional gain stages which then go through a tone stack to the power amp.  The effect will stand between whatever gets sent from the preamp to the power amp (kind of like an internal effects loop).  I am glad that relays seem to be the solution, now I am just really curious as to how to switch two different things on a TRS cable.  I am pretty certain that I will just need to use spdt relays (signal in on the pole and then the two throws determine whether the signal goes through the clean tonestack or through the high gain portion), but I would also like panel switches if at all possible.  That just seems to complicate things, though, so that is where my own abilities meet their match.

syndromet

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Re: Is there a simple channel switching scheme?
« Reply #7 on: February 24, 2009, 07:36:44 AM »
Hi.

Drew this up for you, but I'm not really sure you are gonna understand it.


I think you should use DPDT relays, So that you can have true bypass on all the effects. Let me know if you need some explaining. ;)

J M Fahey

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Re: Is there a simple channel switching scheme?
« Reply #8 on: February 24, 2009, 09:13:43 AM »
Hi RipThorn, here it is.
You can use spdt relays as shown to switch between the outputs of preamps or whatever, or dpdt relays to fully switch entire blocks of your circuit.
It´s all passive, you can easily build it on perfboard if needed.
Switching any Relay "on" will also light its associated Led (your choice of color).
The panel switches also work; only you should remember that, being in parallel with the footswitches, if you panel-switch something "On", you won´t be able to switch it "Off" from the FSW:
Short rule: use the panel switches OR turn them off and use the Footswitch.
To minimize clicks send the panel and jack grounds straight to the power supply ground with an independent wire.
Bye.

Ripthorn

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Re: Is there a simple channel switching scheme?
« Reply #9 on: February 24, 2009, 09:37:06 AM »
Thanks to both of you so much for this! I think I will probably go with spdt relays since I don't anticipate ever needing to bypass something completely, I just need to route where the signal goes (e.g. whether it goes out from the clean pre to the dirty pre or to the power amp).  This looks perfect.  I knew there had to be a simpler way, and panel switch in parallel with the footswitch is no problem, I just wanted to be able to switch channels, etc. if the footswitch is not plugged in.

Syndromet, that is a cool scheme and I may well use it in a future project where I think I am going to build several things in one box and true bypass would be nice.

I can't say thanks enough, guys.

syndromet

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Re: Is there a simple channel switching scheme?
« Reply #10 on: February 24, 2009, 01:29:21 PM »
You're welcome. And you should deffinitivly listen to J M Fahey. That schem looked great and easy enough to build.

 

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