[Asterix]

What is the difference between a guitar amp and a hi-fi amp? What does 'overdrive' mean? Why do most guitar players prefer tubes? Thanks.

 

[kramer5150]

Heres the basics to it Others Im sure can fill in more details (and please correct me when I am wrong) guitar amps are typically designed to be pushed into overdrive... loud enough so that the tubes reach their output limit and begin to distort notes and tones, as you gradually turn up the volume.

When a tube begins to distort its output the sine wave becomes less smooth, and the wave peaks begin to slowly alter their shape as the volume is cranked. With solid state circuits when they reach their amplitude limits they clip the signal, rather than re-shape. If volume is turned up high enough the sine wave begins to acquire a more square wave shape, for severely distorted sounds.

Overdrive is the term used to over-drive the tube circuits and force them into distortion... IE altering that smooth sine-wave, into more of a square-wave.

Some examples...

Clean tones that are not overdriven = George Benson, Joe Pass.

Mildly Overdriven tones = SRV and Eric Johnson, power tube circuits pushed just into overdrive.

Severely overdriven , pushed into distortion (near square wave) = Metallica, AC/DC.

Thats the basics....
Garrett

 

[rickcr42]

Input impedance needs to be much higher,a guitar pickup is not a low z device,gain needs to be higher to amplify the pickup to a usable level,Bandwith requirements are are more relaxed-you do not need (and in fact do not want) 20hz-20khz response.
Plus a guitar is a Mono source so unusable with a stereo amp unless at the minimum it has a mono/stereo switch or you have a "Y" connector.

totally different animals at the front end,can be identical at the power delivery end (instrument preamp to power amp stage)

 

[Mikey01]

There is no "Twang" in an Audio Amp.

 

[allenf]

Note that a wave overdriven into a square wave contains the fundamental frequency plus a large number of harmonics - which gives the notes that thick tone.
Also note that at this level of distortion the dynamics are very compressed, and aided by high SPLs give the notes that creamy sustain...yum!

Generalisation follows:
Historically, electric guitarists have tended to favour valve (tube) amps because they tend to produce more even-order harmonics, whereas transistors pushed into distortion produce more odd-order harmonics. Even-order harmonics are more pleasing to the ear.
Good modern solid-state guitar amps can be very close to the tube-sound (if required) and tend to weigh less - better for humping the gear in and out of vans, up & down stairs etc.

Of course the goal of a Hi-Fi amp is to produce a sound with the least distortion possible.

 

[rickcr42]

I should add that not all guitar styles use distortion as part of the sound and there the preamp stages resemble the hi-fi stage more and you see a predominance of the SS over the triode stage.

Overdriven is not simple a state of overdriving the output which would be called clipping and would mean you must have a high volume at all times (otherwise no clipping !) but a means if controlling input gain to drive the first stage with either a clean signal or enough gain to overdrive that stage while also providing an overall volume control for absolute levels.

Breaking down the guitar amp it is better considered as a highly specialised preamp stage or front end mated to a straight power amp stage with overall volume control.This last closer to a hi-fi amp than the first and in fact you can mate a guitar preamp front end to just about any power output amp,including a headphone amp.

 

[dwc]

Quote:

Originally Posted by rickcr42 Breaking down the guitar amp it is better considered as a highly specialised preamp stage or front end mated to a straight power amp stage with overall volume control.This last closer to a hi-fi amp than the first and in fact you can mate a guitar preamp front end to just about any power output amp,including a headphone amp.

(btw I'm going to generalize heavily so pick apart at will.)

To follow on to Rick's notes, the point about the two halves of the guitar amp is significant. To go along with the two gain sections are two types of distortion. Older amps have only have one volume control, the master volume. Newer amps often have two sets of volume controls, one set for each gain stage. That gives tha player independent control over the amount of distortion and the overall volume of their sound. In the "old days" if you played quiet you had clean tone and if you played loud you had a distorted tone. Today you can have distorted tone at "bedroom" volume levels through the use of distorted preamp stages.

Overdriving the preamp stage gives a certain type of distortion tone. Overdriving the input stage is often done with a signal boost pedal of one type or another. For me a good example of this preamp distortion would be Joe Satriani's sound. Very smooth and liquid sounding fuzz. He can acheive distorted tones at low volumes, because the distortion is happening in the preamp section.

Overdriving the output tubes gives a different set of sound characteristics. For a prime example of this check out vintage ac/dc. ("let there be rock", for example) You will notice that when Angus plays quiet passages, his guitar tone cleans up. When he plays louder (strums harder) the sound distorts. In order to get this tone you have to turn up the master volume the point where the output tubes generate the distortion. You can then buy a "power brake" to absorb the volume before it hits your speaker, or put your speaker in a sealed box, or cover it with blakets, etc, etc.

anyway that's probably enough info to get me in trouble.
Dan

 

[SnoopyRocks]

More concisely, a guitar amplifier is designed to color the sound whereas a hifi amp strives (ostensibly) to faithfully reproduce it. In this respect a guitar amp is as much a part of the instrument as the (electric) guitar itself.

 

[D-EJ915]

Well, basically the actual amplification sections are the same. The difference is that guitar amps (heads) have built-in pre-amplifiers with gain stages for distortion (except for some which are just volume + eq).

 

[dominator]

Quote:

Originally Posted by dwc (btw I'm going to generalize heavily so pick apart at will.) To follow on to Rick's notes, the point about the two halves of the guitar amp is significant. To go along with the two gain sections are two types of distortion. Older amps have only have one volume control, the master volume. Newer amps often have two sets of volume controls, one set for each gain stage. That gives tha player independent control over the amount of distortion and the overall volume of their sound. In the "old days" if you played quiet you had clean tone and if you played loud you had a distorted tone. Today you can have distorted tone at "bedroom" volume levels through the use of distorted preamp stages. Overdriving the preamp stage gives a certain type of distortion tone. Overdriving the input stage is often done with a signal boost pedal of one type or another. For me a good example of this preamp distortion would be Joe Satriani's sound. Very smooth and liquid sounding fuzz. He can acheive distorted tones at low volumes, because the distortion is happening in the preamp section. Overdriving the output tubes gives a different set of sound characteristics. For a prime example of this check out vintage ac/dc. ("let there be rock", for example) You will notice that when Angus plays quiet passages, his guitar tone cleans up. When he plays louder (strums harder) the sound distorts. In order to get this tone you have to turn up the master volume the point where the output tubes generate the distortion. You can then buy a "power brake" to absorb the volume before it hits your speaker, or put your speaker in a sealed box, or cover it with blakets, etc, etc. anyway that's probably enough info to get me in trouble. Dan

Yeah, that's pretty much correct.

I have a guitar tube amp at home, and even though I don't turn it up loud enough for power amp distortion, I still find that it sounds better then pretty much any solid state I've heard. The tubes just give it a warmer sound in general, and even my wimpy "bedroom volume" preamp distortion sounds good (if I blasted it loud enough for power amp distortion in my room, I'd probably be literally breaking windows). That's why pretty much all big name guitarists use tube amps instead of solid state, even if they don't utilise the power amp distortion they are capable of. The only famous guitarist I can think of that used solid states is Dimebag Darrell from Pantera, and I think his tone sounds quite harsh compared to a lot of guitarists.

 

[rickcr42]

Quote:

I have a guitar tube amp at home, and even though I don't turn it up loud enough for power amp distortion, I still find that it sounds better then pretty much any solid state I've heard.

that is due to the harmonics of a tube amp when pushed to clipping fall on the side of litenable while SS when pushed into clipping produces a sound that will chase most humans from the room so rather than traditional clipping as in a tube amp where the front end is overdriven to produce harmonics the SS version foregoes this entirely and uses a diode to produce a similiar harmonic envelope.

The statement about tube guitar amps meant to distort is also not strictly true.Many styles of music call for a very clean sound,more akin to home hi fi sound and that is the target audience where the solid state guitar amp is sold.Having no need for distrotion the goal is for an utterly clean sound like one would get by plugging a guitar directly into the recording console instead of by using a direct box.