3 Guitars on 1 pedalboard

[intergalatico]

Hello Guys,

I am planning a setup where I have 3 guitars connect to the same pedalboard. I don't wanna use all the 3 simultaneously (I have only two arms!) but I want to have all the 3 inputs active. So I don't have to sacrifice space in my pedalboard for switches. I was planning to put this box on the back of the board and just roll back the volume pot of the guitar that is not in use.

I did some research and I found that I have to use an active mixer version because all the inputs are simultaneously actives. I found some schematics but I am not sure if is the right input impedance for eletric guitars.

I wanna keep it simple, I don't need volume pots and switches. And would be great if I can power it with 9V from my voodoo lab power supply.

Any help would be great!

Thank you!

[Gus]

I would build 3 buffers and then a mixer stage
I would use 4 opamps (2 duals)
I would set the input resistances at 1meg or less for passive guitars adjust the input cap for the high pass frequency you want
I would add RF rejection at the input
I would send the 3 outputs to a mixer stage
This would work well at 9VDC if you keep the gain at about 1

You could set the gains at the mixer stage a little different if you want

EDIT because you wrote you would turn down the 2 guitars not used we can use an opamp summing amplifier
http://www.electronics-tutorials.ws/opamp/opamp_4.html

here is a screenshot of a idea
1 meg input resistors

[balkanizeyou]

doesn't get any simpler than that. If you're worried that 100k input impendance is too low you can take a quad op-amp and use three of them as input buffers

EDIT Gus beat me to it

[intergalatico]

Wow, Thank you guys! And a Custom Circuit! Thank you Gus!!!!

I Think I gave a Impression that I know things... I don't have any knowledge to change any value to match the impedance of my guitars. I am sorry!

Maybe is better to tell you which guitars I am using:
1. Single coils strat
2. Same guitar but throught Roland Gr55 guitar out (is a output where I can use a hexaphonic pickup to emulate other guitars. Know as COSM technology. I don't know the impedance of this output but is supposed to go direct to a amp. Unfortenelly this output provides a barely acceptable level of hiss when engaged.
3. Acoustic Steel string guitar with a piezo pickup and built in pre amp.

I missed a thing... It WOULD be nice to have the possibility to run the guitar 1 and 2 together. They are the same instrument but with 2 differents outputs. So I could mix a Strat and a "Lp" together, for example. I would have to change something on the circuit?

Another question on the circuit:
1. I have to reproduce this "Input" path for all the 3 inputs, right?
2. Then R3, R4, and R5 will receive signal from the U1 AND from the point "to all input buffer resistors"
3. Which are the pins on the IC's? Can a use TL072?

Thank you so much! You guys are awsome!

[dbp512]

The first guitar you mentioned, single strat coils is a guitar signal, so you don't need to do anything special on the schematics (most schematics on this website are designed for guitar signals). It looks like the GR-55 output is 2k, so I think that should work with a normal channel. For your acoustic guitar, one thing to note is that piezoelectric pickups require extremely high input impedances--around 10M--to avoid it sounding thin and brittle due to a highpass filter removing the low end. Here is a design that others have used with success: http://www.scotthelmke.com/Mint-box-buffer.html.

The circuit as is can mix multiple inputs, so yes you can use both your strat pickups and hexaphics at the same time. If you do, I'd suggest a pot on each input wired as a voltage divider, with the wiper going to the input of the schematic. This will allow you to set the volume of each input so you can balance them better, and will also mute unused channels to prevent hum.

Yes, you will have to reproduce the signal path to R3 3 times, and connect those paths to R4 and R5. U1 would only have signal from one buffer, the invisible U3 and U4 (the replicated U1 for the other channels), would carry the other signals. Only after R3, R4, R5 would the signals get mixed, where they'd go to the last summing amplifier opamp. As for which pins, google search "(opamp) pinout", or check the datasheet, for a nice diagram showing the pins. Typically most opamps are pin for pin comparable, but its always good to double check. Yes a TL072 will work fine (but you'd need a second. if you want a single chip, use its big brother the TL074).

[Gus]

Found this about Gr55 output
http://www.vguitarforums.com/smf/index.php?topic=3196.0
http://www.vguitarforums.com/smf/index.php?PHPSESSID=7858d5e79c0ebbe1132721e99fdceaac&topic=3196.msg111732#msg111732
http://www.vguitarforums.com/smf/index.php?topic=15798.0

If the piezo has a built in amp this will be fine the piezo should be loaded correctly by the built in amp

Yes build 3 buffers C1, R1, R2, R13, C5 and the opamp you like. I would use a jfet input one.
I did not want to show the other two buffers because they are the same

The circuit I posted has no controls
intergalatico posted they would turn down the volume on the unused outputs
Should work with passive guitars at with 9VDC because of the gain of one when only one guitar output is used and the others are turned down
1 meg should work well with passive guitar outputs and low Z outputs
There is a possible issue if both outputs of the GR-55 are used at the same time if one output is inverted compared to the other there will be some cancellation
I have not studied how the GR-55 works
R13 and R2 provide some input protection as well as buffer stability, R12, C5 form a a low pass filter.  You could add a ferrite bead around the wire going to C1 for RF protection.

[intergalatico]

Thank you guys!

I am familiar with the vguitar forum post. Thank you anyway!

If I use a humbucker guitar instead of the single coils, will be some tone lost?

I think I understand! I will order the parts and I will come again if I have more questions. (Sure I will!). The ferrite part I didn't really figured out but I will wait if it will be really needed.

So... now that the this part is clear, I want to ask about the amp loop.

I have two outputs from the pedalboard that I want to send to the return amp loop:

1. The delay and reverbs of my guitar(s) signal
2. The main output from the GR55 (with only the synth sounds and built in effects. No guitar tone)

Can I use the same circuit for this purpose?

I hope I am not bothering you with my newbies questions!

Thanks A LOT! Really!

[intergalatico]

I am ordering the parts. The C2 C3 and C4 are polarized, right?

And what is the position ( + and -) on the circuit?

Thank you!

[balkanizeyou]

C3 and C4 have (-) at the ground, C2 (-) is at the output

[intergalatico]

Thank you ALL for the amazing support here!

I gave a try and design the veroboard layout on DIY Layout Creator. I know that is not the best design but I would be very happy if someone give a look to see if is everything fine:



Here is the DIY Layout Creator file in the case someone wants to change something:
http://www.filedropper.com/mixer3inputs1output_1

Thank you!

[intergalatico]

Hello Guys,

I need your help again! I build the circuit but I am having problems. No sound and I am reading just 1V on the + Pin from C4. Only 1V is coming to the IC so I think that that is the problem but I can't see what I did wrong! Please Somebody help me!

Here is the actual design:



file: http://www.filedropper.com/mixer3inputs1output






Thank you!

[intergalatico]

Damn!!! Nevermind! I messed up the + and - on the IC. Change this on the design and is all good!