Connecting a mic to a tube guitar amp?

Creating a home studio for recording the classical guitar. Equipment, software and recording techniques. Amplification for live performance.
Ja Sam

Connecting a mic to a tube guitar amp?

Post by Ja Sam » Sun Oct 09, 2016 6:25 pm

Hello to all! :D

I was wondering how is it possible to connect a mic to a guitar tube amp to get that tubey sounding crunch/drive?
So it would be classical guitar - microphone - A/B pedal (A to a PA for classical guitar sound and B to tube guitar amp)...
I dont want to get a fishman, piezzo or anything else that alters guitar in any way...

All suggestions/advice/thoughts/words are welcome and thanks in advance :D

Posts: 578
Joined: Thu Jan 06, 2011 2:15 pm

Re: Connecting a mic to a tube guitar amp?

Post by stevel » Sun Oct 09, 2016 8:33 pm

Simple answer: It is *possible* but I highly doubt the results will be acceptable/practical.

Firstly, guitar amps run at "line level" or "instrument level" (they're actually a bit off standard) and mics run at "mic level".

Mics are generally Low Impedance, Balanced signals, and Tube Amps are High Impedance, Unbalanced signals.

Because of this, some conversion of the signal needs to take place.

Since you're using a PA, that could be the thing that does the conversion.

You run the mic into the PA, and then it goes out as normal to the speakers, then an unbalanced signal (such as from an Aux jack) is taken out to the tube amp. You or someone would have to mute the channel or Aux accordingly.

But this would sound the best (though probably still not be the result you're thinking).

They do make microphones with 1/4" TS connectors (also called Phone or Phono Plugs) that could plug directly into a Tube amp but these are not so common, and generally of low quality (like something that would come with a kid's karaoke toy).

You could use one good mic to send sound to the PA, and then the 1/4" unbalanced mic to send sound to the guitar amp, then on (with another mic!) to the PA.

Really, a guitar with a built in piezo pickup would be the absolute best way to do this if not going the PA route I first described. Even then, a guitar with a pickup may not produce the results you want with an amp.

If you had an Acoustic Amp that accepts a mic signal, and it had an effects loop, you could also place an overdrive pedal in the effects loops. The signal level would be correct, but the type of drive might not be want you want (since PAs and Acoustic Amps are full range, part of the sound of a tube amp is the fact that it's not full range!).

Balanced signals can travel a long distance. Unbalanced gets noisy - picks up interference.

So the idea is to get as "clean" a signal at the source and not convert it to unbalanced until absolutely necessary (usually the cables that go from the power amps to the speaker). When you do that conversion earlier in the chain (the mic cable, or an impedance switcher, or anything of that nature) the more likely you are to get less signal, and more noise.

Ja Sam

Re: Connecting a mic to a tube guitar amp?

Post by Ja Sam » Mon Oct 10, 2016 7:45 am

Thank you stevel for the explanation! :D

So I could use one good mic to go to the mixer that is always on (giving the most natural sound possible).
For overdriven tones i would like to use aux - tuner (that I can also use to mute the signal) - maybe a volume pedal but not likely - amp - amp is miced - mic to the same mixer (different channel :D) - venue PA. So i would use the mixer for fine tuning the volume

In what way do you think it wouldnt be the result Im looking for (its ok if u cant explain it :D )?

This would be much more preferable, but if there is another way of doing this kind of thing without altering the guitar Im very corious to find out! :D
I am open to guitar processors, but i dont think it would be a good investment since I already have a great amp and I only need a overdriven sound (no effects). And btw for electric guitar you cant even compare processor sound to a good tube sound, so I am naturally more inclined to go with an amp...

I was thinking about a piezzo since it does alter the guitar less than fishman (at least I think so?)...
Anyone had experience with piezzos?
Not in the way they sound when amplified (since it wont be a classical guitar sound), but in the way they change the guitar acousticaly?

All comments are welcome! Sorry for my spelling xD

Posts: 578
Joined: Thu Jan 06, 2011 2:15 pm

Re: Connecting a mic to a tube guitar amp?

Post by stevel » Wed Oct 12, 2016 8:44 pm

Most tube amps are designed to work with Electric Guitars and that's kind of the sound we expect from them.

They're also designed to provide input impedance to the pickups themselves. They "load" the pickups - and the amps are not quite "line level" but somewhere in their own special realm.

Since Nylon strings can't be picked up by electromagnetic pickups, essentially any kind of amplification on a nylon string guitar is going to be via direct vibration - either a mic picking up sound waves, or a piezo or transducer picking up physical vibrations from the top.

In both these cases, the signal is mic level typically, and needs to be pre-amplified. Guitar amps don't really pre-amplify in the same way a standalone pre or mic pre in a mixer does. That's not to say they won't work of course, but the biggest difference is going to be signal level getting to the amp.

Furthermore, guitar amps tend to be "filters" in that they handle a narrower frequency range than PA speakers (and "acoustic guitar amps") and with a mic/piezo style pickup, you might be losing more signal than you want - essentially you get "tinny" sound.

Likewise, using guitar effects on a full-range signal are not going to sound the same, and even the tube amp's own overdrive is not going to react the same.

That's not to say it will be "bad", but again, let's just say if you're expecting to plug a classical guitar into a tube amp in some way and have it sound like an electric, or get the same kind of overdrive as the electric, it's probably not going to happen.

There's a reason why vocalists stopped using guitar and bass amps in the 60s and went to PA speakers - tube amps were designed for a different kind of input.

You'll likely get thin, scratchy, maybe "telephone sounding" sound from a mic level signal going into an amp if you overdrive it.

Now clean, the amp could actually sound quite nice (not as nice as a full range acoustic amp though) but since you're talking about overdrive...

Only thing to say is, try it and see what kind of results you get.

There are some soundhole pickups for Nylon string guitars, or some pretty cheap stick-on transducers - those would not alter the guitar in any way.

Barbera makes a saddle transducer - basically replace your saddle with this one - so also reversible - a lot of pros use this, and it may be expensive, but if you're serious about it, this might be the best way to go.

I'd maybe try one of those cheap options first and see what you're going to get.

One of the things with overdrive is it's going to react drastically with input level, so using a mic and then sending that off the aux is likely going to have more variance in level than you'd like - something on the guitar that gives a more consistent signal would always be better (based on what I think better would be!).


Re: Connecting a mic to a tube guitar amp?

Post by 2handband » Fri Nov 25, 2016 2:23 am

As a former pro electric guitar player and current pro sound engineer I have one word of advice: don't.

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