Acoustic Guitar - Signal Mix

[wcampagner]

Hello,
I've got a Crafter acoustic guitar that came with a traditional onboard piezo system.
Now i've bought an active Lr Baggs M1 soundhole pickup.

I've played with both systems, and i've found the best sound when both are working together.
I just need to adjust the volume and tone individually and them they are ready.

What i want to do is a schematic that mix both signals together and send them to the output guitar jack.
I'm thinking of building buffer for this.

The schematic is below, and i'd like to ask if this schematic is allright to mix both signals.
I don't need individual volume control or tone in this schematic, because i already have these controls in each system.



I'm planning to put this circuit inside the guitar.
And it'll use a 9V battery, so i also want to ask if i can use the 9V battery of the piezo system to power the buffers too.

Thanks in advance.
Wagner

[alanlan]

You'd be better off with a pan pot so you can blend between the two pickups to dial in the best mix.  This could be buffered if required.  You could wire it between the outputs of IC1A and IC2A.  In any case you could do with resistors on the outputs of IC1A and IC2A for them to combine properly.

[wcampagner]

Hello Alanlan,
Thanks for the answer.
I've already have volume control on the pickup and on the piezo system.
So i don't need any pan control.

What i want is just put the two signals together.
I made the buffers because i think this way there will be no impedance problem.
But i don't know if this is the right way to do.
That's why i'm asking.

Thanks again.

[andymac1962]

why not just use a simple resistor mixer. 10k from the output of each preamp, to the hot side of the guitar outlet jack.....

[Ben N]

Assuming you are feeding buffered and/or preamped signals to this thing, buffers should not be necessary, per Andrew's suggestion. If you were sending it raw piezo and magnetic outputs, then an FET-input opamp, like a TL-0x2, would be needed for the buffers, not a 5532, which has an unacceptably low input impedance for this application and is also a current hog, and also a higher value for R2 to show a high enough input-Z to the piezo. From what I've been told, you should probably change the mixer stage to an inverting "virtual earth" configuration, but someone else around here can probably give you better advice on this. You can use a 5532 (or its single opamp equivalent, 5534) for the mixer, but for an onboard application you should probably find a less thirsty alternative.

[wcampagner]

Hello,
Thanks for all the answers.
Ben, the output of both the soundhole pickup and the piezo system are already preamplified / buffered i think.
The soundhole pickup is a LR Baggs M1 Active, it uses a 3v baterry inside.
And the piezo system is the system that already came with the guitar, it uses a 9V baterry and have all the controls on the guitar (volume, bass, middle, treble and presence).
So, with that information can i assume both systems are already preamplified / buffered?
If they are, i don't need buffers then?
To put together both signals i only need to put the two output wires together and send to the hot site of the guitar jack?

Thanks again,
Wagner.

[Ben N]

Use a pair of resistors in series with the signals, joined at the mixer input. I'm not sure about values. Fender amps used 220k in some amps, but I don't know if that would apply here at all.

[wcampagner]

ok Ben,
Thanks for the answers.
I'll try it and report the results here.
Kind regards.

[Ben N]

Just to be clear, it probably is a good idea to include an active mixer ahead of the jack, but that should be an inverting opamp stage. Do a search for basic mixers and you will find something.

[wcampagner]

hello Ben,
Thanks for the answers.
So i think i need one of these:

http://www.muzique.com/schem/mixer.gif - AMZ Simple Mixer
http://www.generalguitargadgets.com/diagrams/mixer_sc.gif - RG Simple Mixer
http://sound.westhost.com/project94a.htm - Universal Mixer
http://www.all-electric.com/schematic/simp_mix.gif - Basic Mixer

The last link shows 4 kind of mixers.
The first (passive mixer) was the suggestion that i tried, but i think an active mixer provide better sound.
But i didn

[wcampagner]

hello Ben,
Thanks for the answers.
So i think i need one of these:

http://www.muzique.com/schem/mixer.gif - AMZ Simple Mixer
http://www.generalguitargadgets.com/diagrams/mixer_sc.gif - RG Simple Mixer
http://sound.westhost.com/project94a.htm - Universal Mixer
http://www.all-electric.com/schematic/simp_mix.gif - Basic Mixer

The last link shows 4 kind of mixers.
The first (passive mixer) was the suggestion that i tried, but i think an active mixer provide better sound.
But i didn't try yet.

So if i go to the active mixer, is it possible to use the 9V battery from the piezo system to power the mixer aswell?

Thanks again.

[Ben N]

I don't know if you can use the same battery--depends on the current draw of the all the parts. (BTW, doesn't the magnetic system also have a battery?) It'll most likely work, but you will have to change the battery a little more often.

Try to find a low current IC for the mixer, preferably one with a JFET input. A TL061 should do, but there are ones with better performance and lower current consumption. Someone else may be able to help with that.

You only need one opamp stage, as per the AMZ Mixer--the second stage in the other designs is just to to invert the output so that it is back in phase with the input, and this should make no difference to you. If you do use a dual opamp, like a TL062, you may want to use the second opamp as a simple non-inverting voltage follower (no extra parts required--well, maybe one resistor) to buffer your output and drive a long cable.

For simplicity, I will refer to the AMZ schematic. Since you are using a battery, I think you can leave out the extra 100 ohm resistor and 47uf electrolytic, since they are there as power supply filtering. In fact, if your piezo system already has a similar voltage divider (very likely), you can probably tap Vr (4.5v) as well from there and skip the whole power supply, which makes your little mixer a lot smaller. You won't need any volume control after the mixer so you can go straight from the DC blocking cap to the jack. I would experiment with the value of R2 (noting that Jack has 150k, but most of the others have 100k) to get the gain down to where you aren't adding any extra distortion, since a unipolar 9v supply doesn't give you much headroom. Gain on a non-inverting opamp is R2/R1, so an R2 of 100k would produce unity gain. Your two inputs also probably wont need those 1uf caps (C1), since the sources themselves probably have DC blocking caps on their outputs. You can tweak the input resistors (R1) to match up the overall levels of your two sources. Read Jack's explanation of how to do this here.