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Hi-z to low-z


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(Sorry, the title isn't quite right. It's not actually hi to low z.)

 

I would like to use a mini-mixer in order to hook up three guitars to one amp. Only one guitar will ever be used at one time. The little mixer I was looking at had an Input Impedance of 10K ohms. My guitar pickups are anywhere from 7- 15k ohms. Would this unit be suitable for my purposes? It is an active unit so I am worried about gain staging. Would I be better off with a passive mixer? Any help greatly appreciated.

 

Thanks,

Anonpostguy

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I'm not quite sure where you got the values for your pickups... are they passive or active? Did you by chance try to measure the DC resistance of the pickup by looking into the output jack of the guitar? (Won't give anywhere near accurate value)

 

I agree that a switcher is probably the best solution. Or, just switch the cable and mute the line while switching over the guitar. Some cables have a shorting plug that will mute as you unplug. Don't use that cable for a speaker cable though.

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I think my understanding of Hi Z to Lo Z is weak so forgive me if I go off on a tangent a little bit.

 

Here's what I don't really understand:

 

My guitar outputs a Hi Z signal and my amp accepts a Hi Z signal. However, what happens when I put a Boss TU-2 tuner pedal between my guitar and amp? The TU-2 input impedance is 1 M ohms. The output impedance is 2 k ohms. Further, I generally run the TU-2 into a Boss GT-8, which has an input impedance of 1 M ohms and an output impedance of 2 k ohms. I then go into the amp which has a 1 M ohms input impedance. So my signal is going from Hi Z output to Hi Z input then out a Lo Z output and back into a Hi Z input then out a Lo Z output and back into a Hi Z input. What kind of effect does this have on my signal? My head is spinning just trying to keep track of my signal. Any help shedding some light on this would be greatly appreciated.

 

Thanks,

Anonpostguy

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As a general rule: output impedances should be smaller or equal then input impedance. Smaller (as a in a lot smaller) is preferred but not always practical.

 

Output impedances are:

Passive guitar, bass or piezo pickups: High (hundreds of kOhm to several MOhm)

Line outputs: Low (tens or hundreds of Ohms)

Dynamic Mics: Low (hundreds of Ohms)

 

Input impedances are:

Guitar amp, tuner, stomp box, etc.: High

Line inputs: Medium (tens of kOhm)

Mic input: Low

 

It's not as complicated as it looks, you are usually okay if:

a) Make sure that passive guitars get a high Z input

b) Plug a dynamic microphone into a mic input

 

Even an impedance mismatch is not the end of the world. Plugging a passive guitar into a regular line in might result in some high end loss and mteh tone control response will be slighty off, but it's still usable.

 

Your signal chain is fine, since the output impedances are always smaller or equal to the input impedances.

 

Hope that helps

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Here's a rule of thumb. The input impedance should be many times higher than the output impedance which is driving it (I wouldn't call 2k output impedance particularly lo incidently). The idea is that the less current you draw from the driving device (source), the less likely you are to load down that source output stage and degrade the signal.

 

There are drawbacks to taking this to an extreme (there are others here on this site who are much more qualified to accuratly describe these to you than me).

 

Here's another rule of thumb. When dealing with a totaly passive device (I.E. Guitar coil pickups or Piezzo pickups), the higher the imput impedance the better 2 meg ohm or more is a place to start (this doesn't apply to dynamic mics because most already have an impedance matching transformer inside (allowing the signal to be shipped a long distance more easily)).

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As a general rule: output impedances should be smaller or equal then input impedance. Smaller (as a in a lot smaller) is preferred but not always practical.


Output impedances are:

Passive guitar, bass or piezo pickups: High (hundreds of kOhm to several MOhm)

Line outputs: Low (tens or hundreds of Ohms)

Dynamic Mics: Low (hundreds of Ohms)


Input impedances are:

Guitar amp, tuner, stomp box, etc.: High

Line inputs: Medium (tens of kOhm)

Mic input: Low


It's not as complicated as it looks, you are usually okay if:

a) Make sure that passive guitars get a high Z input

b) Plug a dynamic microphone into a mic input


Even an impedance mismatch is not the end of the world. Plugging a passive guitar into a regular line in might result in some high end loss and mteh tone control response will be slighty off, but it's still usable.


Your signal chain is fine, since the output impedances are always smaller or equal to the input impedances.


Hope that helps

 

 

I think we're saying the same thing. Looking at it from opposite ends LOL.

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