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What is the main difference between mic input and a guitar input? is it only the source impedance seen in the input of the amplifier? I am designing one pre-amplifier in which i need to input both mic, line and guitar, so for better performance i may have to use an impedance matching section to match the source impedance of all these inputs to input impedance of pre-amplifier IC right? (I am analyzing this from an electronics engineer point of view) correct me if it is not applicable to audio connections.

can someone tell me how these inputs differ in their impedance ?

I am referring THAT Corporations design note DN-140 as my primary reference but it is only dealing with mic and line inputs, can some one tell me how the guitar inputs differ from line inputs ?

does the Guitar input pads are used for this impedance matching ?

if someone can share some guidelines for this, it would be helpful for me..

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migrated from sound.stackexchange.com Aug 18 '16 at 9:03

This question came from our site for sound engineers, producers, editors, and enthusiasts.

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I am designing one pre-amplifier

if you are designing a pre-amp: then there are a couple of things you need to take in consideration

  • Hi-Z vs Lo-Z
  • Balanced vs Unbalanced
  • Line Level vs Mic Level

Usually (but not always)

  • Line Level inputs are Hi-Z (can be both balanced or unbalanced)
  • Mic Level inputs are Lo-Z (and usually balanced)
  • -20dB or -40dB pad's may be used for situations where line level is plugged into a Mic level input
  • Balanced inputs can be XLR or TRS
  • Sometimes someone plugs in an unbalanced Jack into a TRS input (you need to wire correctly for these situations)

(I just find it handy to have some DI boxes ready, knowing your outputs/inputs, and wire accordingly when the situation requires... much easier than catering for every possible combination)

can some one tell me how the guitar inputs differ from line inputs ?

Generally speaking Guitar Outputs are "Line Level" "Unbalanced" "Hi-Z" If the Guitar pickup/electronics are "active" (e.g. there is a battery or so)

If it is a Guitar without active components, then it is likely to be "Mic Level" "Unbalanced" and can be either "Hi-Z" or "Lo-Z" depending on pickup/built-in-mic.

Some "effects" used with guitar may increase even over Line Level, which means you need to attenuate, which can be done either by DI or on the Mixing Desk by "pads" or "attenuators" (terminology differs from brand to brand)

... my 2 cents ...

[EDIT] As this question is migrated from sound.stackexchange.com to electronics.stackexchange.com, this answer is given from a "sound production perspective" without going into further electronics design. While I do have some electronic skills, I would not edit this answer further as I feel I would not be skilled enough to advise on electronic subjects like designing an audio-pre-amp to use with Pro-Audio applications. Please take that into account while you consider voting or commenting on this answer.

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The guitar input is HI-Z , meaning 10KOhm , you should implement a DI functionality for your pre-amp if you want to include guitars and output a line signal.

Passive-DI or Active-DI is another issue you'll have to think about , a passive-DI will be good for active instruments , like a bass with active Pickups.

An active DI will be better for instruments with passive pickups.

This is kind of subjective though as for a lot of people active DI's sound bad , and passive Sound better, but you have to try many of them and find the matching one for your needs.

Also keep in mind that a passive DI is a lot more costly rather than an active DI.

Electro acoustic applications are a very-very hard thing to do , i don't know if you are a novice in all that or whatnot, but you should be able to know what impedance a guitar has, i feel you are asking how to tie your shoelace so you can climb a mountain.This comment though , is made from my perspective of what a pre-amplifier is , and what level of knowledge you must have to make one that's worth looking at but keep in mind that a lot of people are like me when it comes to sound and the competition is insane out there. On the other hand this could only be a school project which cancels the whole comment.

Good luck.

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  • \$\begingroup\$ Welcome to the EE.SE side of things. You may want to update your answer to reflect this question's migration. \$\endgroup\$ – user2943160 Aug 18 '16 at 12:08
  • \$\begingroup\$ You mean the part suggesting the migration ? Or the answer to be more technical? \$\endgroup\$ – frcake Aug 18 '16 at 13:53
  • \$\begingroup\$ Yeah. You can trim the note about migration off your answer if you desire. \$\endgroup\$ – user2943160 Aug 18 '16 at 23:49
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What is the main difference between mic input and a guitar input?

A microphone preamp input is usually designed for a source impedance of roughly 150-300 ohms (for dynamic mics) and a microphone level signal (roughly -60 to -40 dBV nominal). Many modern mic pres have an input impedance of around 1.5-2k ohms and offer around 60dB or so of gain to bring the mic level signal up to line level (professional line level is +4dBu nominal, consumer is -10dBV).

A guitar amplifier is designed for a source impedance of roughly 7-10k ohms (Hi-Z) and an instrument level signal of roughly -15dBV or so (although both guitars and mics vary in terms of output voltage and source impedance). Most guitar amps have an input impedance somewhere around 1M ohm.

can someone tell me how these inputs differ in their impedance ?

Instruments and microphones can have wide ranges of impedances as I mentioned, but line level sources usually have low enough output impedance to ignore loading effects in many cases. Your main concern here is stepping down the voltage and impedance of your guitar or other instrument.

i may have to use an impedance matching section to match the source impedance of all these inputs to input impedance of pre-amplifier IC right?

You could just design a mic pre with as much gain as you need, add a switchable pad at the input if you're feeding it line level signal (-20 or -40dB should be okay), and then keep a 12:1 audio transformer (basically a DI like @frcake mentioned) connected to the guitar input jack so the instrument level signal will be appropriately stepped down to microphone level (both in terms of signal strength and impedance).

Hope this helps.

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