Im wanting to mix the output of two possibly unbuffered electric guitar outputs. The two signals will be coming from 'stomp boxes' where the output may or may not have a buffer so I don't want to drag them down.
I have found references to some simple audio mixers
Practically all guitar boxes have buffered outputs.
No, they are very high impedance inputs, they influence very very little.
This mixer circuit is known as virtual ground mixing. The input to the op-amp is held by feedback very close to ground. The input signals are not influencing each other, because of that. The signal cause some, very small, current through each input resistor, and the op-amp sums the currents.
-- Roger J.
It is indeed advisable to use high impedance buffers for pickups, some expect more than 100k load impedance from a tube amp, and best would be to have these buffers as close to the guitar as possible to avoid the capacitive loading of long cables. Otherwise a treble rolloff will occurr. Most easy would be a dual buffer made with a TL072 opamp as a follower or with low gain, depending on the sensitivity of your pickups. The power will probably come from a 9V battery, so you will need capacitors on input and output and a voltage divider on the +input consisting of two 1Mohm resistors. With the outputs you can directly drive a passive mixer consisting of 10k pots with 10k from the sliders to the summing point which goes to the amp.
-- ciao Ban Bordighera, Italy
The simple answer is yes.
But you can change the input resistors on the mixer circuit we discussed, each channel can have its own special resistor.
If you use a 500k resistor for the guitar it will work. It needs to be high enough, 1M is normal, 500k should be no problem.
The other signals may need to be damped a little to fit together with the un-amplified guitar signal.
If you really need to use the mixer as input stage also it is likely that it will work.
On the other hand.. You can easily build a buffer stage for the guitar, using only one or two fet transistors. Such a buffer can be built to give some tube distorsion, that is it acts as a limiter, compressor.
You can easily find many schematics for such circuits on the web.
There are a lot of guitar circuits at
-- Roger J.
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.