Why do people say that the JCM900 isn't an all tube amp? Doesn't it have tubes in it?

[bonchie]

 

"A distortion pedal is distortion produced by resistors and crap"? LOL No. Try transistors and diodes. Resistors and capacitors only shape the tone by affecting frequency response. And "Its just clipping a signal thats already there"... Clipping is distortion. If you're going to disagree with something, know what you're talking about.

 

 

I meant the diodes are not producing gain the way transistors in a SS pedal do. I corrected myself earlier.

[Bruce Bennett]

after reading agreat deal more of this thread seems to me that that are some very seriously incorrect ideas about how each one of these componants operate..

Bear in mind that this is very simplified. but essentially accurate.

Lets look at the flow of electrons in an given circuit like a small creek of water.. water is always seeking the easiest path downhill.

electrons are always seeking the path with the least amount of resistance and they are always seeking out ground.
(thats only due to the way we designed the circuits, they actually START FROM ground and look for the positive side of the circuit.)

Resistors; are like small damns or gates with varying size holes in them. each different value has a different sized hole in it so to speak and allows varying amounts of electrons to flow through them.

Capacitors; there are two different types and they get used in different ways.
Electrolytics are like high discharge rate batteries, they store energy during times when voltgaes becomes higher than the average, and they release it when voltages become lower than the average.
Coupling or DC blocking caps; these have the unique ability to allow AC signal ( which is what your guitars signal is composed of) to pass through it while stopping any DC voltage this acts as a filter of sorts or a DC blocker.

Potenitometers;
These are nothing more than resistors that are variable on command. they can also be used to "direct traffic" so to speak.

Transformers;
These are used to covert and couple to parts of a circuit together.
they also have the ability to step up or down voltages or impedances. they are used to either step up AC voltages in the power supply or to "mediate" two radically different impedances in the power amp output circuit.
I could write and entier book on transformers and how they do what they do. so I would suggest reading up on them if your interested.
Tubes;
These are the mystery that everyone thinks nees to be solved.. but they are no mystery,
you have a filiment same as in the light bulb over your head.
if you pass a current through it it gets hot and glows. Thomas Edison discovered that when his light bulb was on. Electrons would jump off the filiment and fly around inside the glass bulb.. ( if someone dropped you on the surface of the Sun.. wouldn't you hop around too) Well Ole Thomas never figured out anything to do with this Phenomina. so he label it Edisons effect and went on to build other things..
Several years later another smart guy added a plate inside the light bulb. and discovered that the electrons would go towards it. and that if AC electrcity was used on the filiment. DC would show up at his neew added plate. So the worlds for Diode was discovered... now all a diode is.. is a gate that only opens one way. and won't let anything go back through it.
so now we have the rectifier tube,
now several more years go by and another bright fellow adds a third element to the bulb. and he calls it a grid and he puts in right in between the filiment and the plate, and when he turns on teh current he finds that by chnageing the grids polarity from just a tiny bit positive to a tiny bit negative he can shut on or off the much larger flow of electrons between the filiment and plate.. and thats the basis fo amplifcation.. a small current that can be turned into a larger one.
and by adding all the other componants, you can start to see how and why an amplifier can be built and controlled..

My hands are tired now..

[Wyatt]

I meant the diodes are not producing gain the way transistors in a SS pedal do. I corrected myself earlier.

 

 

Gain is an often misused term. Gain is just amplification...clean pure amplification of a signal. No distortion at all. Think of clean boost pedals, tons of gain, not distortion. Clipping is distortion. Where gain comes in is it creates a signal so large it must clip somewhere. How a tube amplifies is often less characteristic than how a tube clips the previous signal.

[HRM]

'Twould appear this is a touchy subject.

[ashasha]

Quiet, noob. You don't know the first thing about pants.

Busted.

All I want to say is:

If you read the terms of harmony-central user forums you would discover that any tube amp thread has to come to blows at some point. I went to the amp forum one time and barely made it out alive.

[Bruce Bennett]

Gain is an often misused term. Gain is just amplification...clean pure amplification of a signal. No distortion at all. Think of clean boost pedals, tons of gain, not distortion. Clipping is distortion. Where gain comes in is it creates a signal so large it must clip somewhere. How a tube amplifies is often less characteristic than how a tube clips the previous signal.

 

 

your quite right Wyatt. I agree that this term is grossly missused by many players.

 

"gain" is really only a "measurment" of the amount of signal strength a given signal GAINS after it goes through a given amplifier circuit.

 

guitar players often think that ANY amount of "Gain" means distortion..

but not so at all..

 

as with anything, there is threshold at which the amount of available gain excedes the available headroom. and then the signals waveform becomes "Clipped" thats the sound we call distortion.

the wave form up to the clipped point is a nice smooth SINE wave that looks like a series of very smooth, nicely curved topped humps.

they start out as very short humps. but as the gain factor increases. the humps get taller until that hit the Headroom ceiling.

 

then they start to flatten out the tops, if you keep adding more gain, you'll arrive at a point where the humps look like they are perfectly square.

this is a square wave. and we guitar players like it. ( BTW a pair of Diodes have the ability, when used in a "binding circuit" to lower the headroom ceiling so that distortion made at a lower gain factor)

 

the headroom ceiling is really a bit harder to explain.. it sorta the point where the circuit simply can't create more amplication without breaking down the signal.

 

sorta like RPMs on an engine.. you know there is a point where the thing is simply gonna fly apart.. but you still rev it beyond that point whenever you need to...

 

But,

electronic componants are quite hardy and can take a great deal more punishment before they "fly apart" than an engine could.