Ideas for my switching system.

[wcampagner]

Hello,

I'm planning to implement a switching system for me like the picture below:



My setup is:

- 4 electric guitars
- 2 acoustic guitars
- 1 amp
- 1 tunner

My amp has one electric input and one acoustic input. So what i'd like to do is to make a stompbox to switch between the 4 guitar and the 2 acoustic guitars... and also i'm using a tunner so when i want to tune some instrument, the amp input is muted.

I think the picture is self explanatory... the stompbox will have 3 buttons... 1 for electric switching, 1 for acoustic switching and 1 for selecting the tuner. The S3, S4 and S5 switches work together to mute the amp input that is used by the tunner.

I have already a good knowledge about electronic switching so i'm planing to do all this switching with digital electronics (D type Flip-flop's) and JFET's for the switching interface or maybe the 4066 IC (i need to make more tests with this IC, but i'm already having good results with the FET's (silent switching!!!)).

I'd like to know is if there is any problem with this setup and some advices and ideas to guide me in this task. Maybe i may have hum problems and need to put some transformers for grounding isolation... i don't know... any advice is welcome.

Thanks in advance,
Wagner.

[Pushtone]

Looks like a very ambitious switching project.
Electronic switching is something I'm working up too just because it can do such a complex switch job like this.
It's fun to dream them up. Yours looks very practical for the number of instruments.

But are you sure your not going to add another amp at some time? Devils Advocate here.


You might want to consider doing more with the tuner output to prevent it from injecting noise and loading down the signal.

Most cheap, and some expensive tuners can inject noise into your signal.
Whistles, hash, pops, ticking, all sorts of junk. You might consider making the tuner out a buffered output, to block noise traveling back on the signal wires.
A buffered tuner output could also be used as an auxiliary output, like to a direct box or recorder.

Or you could make the tuner out a "tuner Mute". This would only allow silent tuning.
The input to the tuner would be earthed during playing and only pass signal to the tuner when the TUNER footswitch is pressed.
This could also feed another amp in an A-B setup (no Y).

As it looks now I think you will find that kicking in the tuner while playing will cause the level of the amp to drop.
Looks like I would stomp the TUNER switch once to tune the electrics and again to tune the acoustics.
A third stomp would turn the tuner off and out of the signal path. That cool, but the level might drop a bit.




Question for ya: What kind of electronic switching can be made to do what S1 and S3 are doing. I' under the impression that electronic switch means you can have as many SPDT switches as you need. But how do ya emulate a rotary switch electronically?

I hope you share some of your switching schematics for this project. When your done testing.

[Dave_B]

Question for ya: What kind of electronic switching can be made to do what S1 and S3 are doing. I' under the impression that electronic switch means you can have as many SPDT switches as you need. But how do ya emulate a rotary switch electronically?

PT, check out the CD4051 cmos chip.  It can be set up as an "8-position rotary."   The CD4052 is a 2P4T. 

From what I remember reading (I've got some but never used them) they spec out the same as the 4066 switch, so they should be good for low-level audio if you bias them right.

[toneman]

Hi Wagner,
Since U have no preamp included,
Might I suggest a completely non-powered switcher?
That is--no CMOS switches that require power, and must be biased correctly for pop-less-ness.
All the switches, except for S1 seem to be DT  (DoubleThrow)
S1 could be made up from 2 DT''s.
Also,  If U *must* use DC, how about small relays??  TriplePole (3P) are available with 5V coils.
Very easy to interface, and no regulators needed.
Maybe U need to do a little more doodling like Pushtone suggested(?)
Nice drawing!!....helps very much to understand what U want to do!!!
afn
T

[wcampagner]

Thanks for the answers PureTube and Dave_B and Toneman,

Well, answering your questions... i think i won't need another amp for a long time... this switching system is for my setup right now... and if i change something i need to do another... it is already over-designed... because at the moment i have only one guitar and one acoustic guitar... i'm planning in having a 12 string acoustic guitar and a 2 neck slide guitar... so i'm already starting to plan how to switch all this stuff...

About the tunner injecting noise in the signal path... i think i can avoid using buffers as you said... all the input and output of the switching system will be buffered... i think it is needed by the electronic switching... at least for what i've done until now... and if you take a look at the picture, when the tunner is used, the amp input (electric or acoustic) is muted by putting the input to ground. (when the tuner is on the electric path, the electric amp input is grounded and the acoustic input is on (i can still play the acoustic while tunning the electric)... the same happens in the acoustic path... and then on the 3rd stomp, the tunner is grounded and both paths (electric and acoustic) are on the amp).

About the sugestion of Toneman, i think i'll be going in the electronic switching... i have made 1000 or more tests with all kind of DPDT and 3PDT and all of them i can hear a loud POP when switching... i've already tried all kind of things to avoid it like (1M resistors in the input and output) but nothing solves this noise... i've already have good results with electronic switching so i think i'll go this way... i have a fender Acoustasonic SFX amp... and i think this amp is very "sensitive" about POPs... i got good results only when using electronic-switching...

For the digital / analog interface there is a lot of options... like Dave_B suggested, there are some analog MUX/DEMUX... there are the analog switches 4066 and there are singles JFET's... that's what i'm using in all my stompbox with good results... i think i'll go in this way... but it will take 13 JFET's for this switching!!! I think i'll get mad in this project... but if it works it will be very nice...

Pushtone, about the electronic switching... i think you mean not the interface digital / analog, but the control signals that will control this interface... am i right?

Well, there is a lot of way to do this... the way i'm doing is called "State Machine"... you can search any electronic site and read more about it... you deal with states... in this example is something like this: 1st state (guitar 1 is selected in S1) -> condition to change (stomp on the electric button) -> 2nd state (guitar 2 is selected in S1)... and so on... with this on your mind you can do whatever you dream of... that's another reason to do electronic switching... i think at least in theory... i'll check if it works on practise now...

This picture shows the digital part... i didn't test it yet... but i think it is quite accurate... sorry for the picture... i think it is a little messy:



Thanks a lot again,
Wagner.

[Branimir]

I have used 4066 for some switching duties, actually, it was two sansamp gt 2's in a rack footswitchable, you could choose first gt or second via footswitch that operated a true bypass wired 4066 chip matrix.

I had problems with intereference! for instance, I used one 4066 to turn on the input and the output of the first gt2, and to turn on the led indicator of the chanell... and the second 4066 for the second one, the same manner, and it was okay, but...

I tried to operate input on output on for the first gt2 and the input off and output off for the second gt2 in a same 4066, I got mixed signals!! While playing through one gt you could hear barely the second one too (even though the 4066 had it "bypassed"), That occured with higain setups, I noticed this when the first gt2 was clean and ON, and the second one was higain and off, I could clearly hear it!

But then I seperated the signals and used two 4066 and had no probs...

Just my two cents!

[d95err]

I would also recommend a completely passive system with regular stompswitches. You don't really need 3 buttons. The easy solution would be to use one switch to select Electric/Accoustic and the other to switch the Tuner on/off (and Mute).

Use a 3PDT swich for Electric/Accoustic. Use one pole to select output, one to ground the unused output and one for the indicator LED(s).

For the tuner, use two poles to disconnect both ground and signal to the tuner when not in used. Also, make sure the main signal path is grounded when the tuner is active.

If you want a buffer, you could simply add one in front of the chain.

This would make the whole project extremely simple and reliable. Although, the CMOS and FET version would perhaps be more fun to build...