LazerBeakShiek
Rad Racing Team
Class A - The signal runs 100% in the tube. Technically no clipping. Both halves of the sine wave are amplified the same. Usually found in single ended amps, but you could create a push-pull Class A. Grid always negative.
Class AB - Signal runs less than 100% but more than 50%. Most of our push-pull amps run here.
Class B - Signal runs 50% in the tube. Only 1/2 of the sine wave is amplified. Most efficient use of power in a push-pull amp, but may not sound the best.
only true class B guitar amp i know is the ADA T100-s
class C is more than 50% grid positive
fuck class D they are retarded
this is really the important one, Class AB, which occupies the space between Class A and Class B.
Virtually all guitar amps with two, four, or six (or really, just pairs) of output tubes have their power amplifier stage
operating somewhere in the Class AB region. And that's the stage you set the bias on. i think VOX AC is still class A pushpull
You don't want to set the bias so low that the amp falls out of Class B and starts playing in the Class C territory,
even a little, because when you do, you get this really ugly sounding type of distortion that is called crossover distortion. So turn up the plate, before biasing or it will fall to C.
If you bias toward Class A, the tubes will run hotter and there is a limit to how close to Class A you can get without damaging
the tubes, which is determined by a number of factors that would be best discussed from a more advanced article than this one.
--
to clarify ,, its not too low that it clips...it is set 'to' low, so it clips...nothing too low about it.
This image shows how a preamp tube in your amp can be biased. The first example in blue would be biased in its central operating point,
a clean stage that doesn't distort. [A typical clean cathode resistor value on a 12AX7/ECC83 preamp tube stage would be 1.5 to 1.8K ohms with a 100K plate resistor. just specs blah blah...[
The second waveform shows overdrive distortion in the form of hi bias, which can be achieved by either increasing the plate resistor value, or decreasing the cathode resistor value. these are/can be on mini rheostats and adjustable
The third waveform is an example of cold clipping. This is achieved by increasing the value of your cathode resistor. [The Marshall cold clipper circuit uses a 10K resistor, while the typical Soldano circuit boosts that resistor value to 39K. again can be done with a rheostat. can verify on DVOM[ just specs ..blah blah
We LIKE the sound of a cold clipper stage. It's very musical. And blending in some overdrive distortion from an adjacent stage can add a lot of character to the sound as well.
Note that the blue first waveform is well within the lines drawn and identified as +Vcc and -Vcc. If we were to increase the gain of the stage being plate voltage in a symmetrical manner, that increases the amplitude (size) of the waveform. If it's taken as high as it can get without crossing those two lines, then that is the maximum clean power available under those conditions. Any increase in drive/bias beyond this point will result in symmetrical distortion, both top and bottom peaks being clipped at the same time.
Now we can adjust that stage for either overdrive or cold clipping by simply adjusting the bias in either direction.
Buddy holly would be class A amplification type sound..vintage
SRV would be cold clip'd AB
hair band squealing would be high biased to clipping.
play around with it..have amp 'on' guitar plugged in. dont zap yourself..use a pencil eraser to turn the ring..this shits tuff. it doesnt break easy.
class A has the best definition/clarity. sine wave.
AB has all the modern growls. set the plate voltage and you pull the bias up or down to clip the highs or lows. to taste.
you cannot do this stuff with a OD pedal in front of the preamp..
Class AB - Signal runs less than 100% but more than 50%. Most of our push-pull amps run here.
Class B - Signal runs 50% in the tube. Only 1/2 of the sine wave is amplified. Most efficient use of power in a push-pull amp, but may not sound the best.
only true class B guitar amp i know is the ADA T100-s
class C is more than 50% grid positive
fuck class D they are retarded
this is really the important one, Class AB, which occupies the space between Class A and Class B.
Virtually all guitar amps with two, four, or six (or really, just pairs) of output tubes have their power amplifier stage
operating somewhere in the Class AB region. And that's the stage you set the bias on. i think VOX AC is still class A pushpull
You don't want to set the bias so low that the amp falls out of Class B and starts playing in the Class C territory,
even a little, because when you do, you get this really ugly sounding type of distortion that is called crossover distortion. So turn up the plate, before biasing or it will fall to C.
If you bias toward Class A, the tubes will run hotter and there is a limit to how close to Class A you can get without damaging
the tubes, which is determined by a number of factors that would be best discussed from a more advanced article than this one.
--
to clarify ,, its not too low that it clips...it is set 'to' low, so it clips...nothing too low about it.
This image shows how a preamp tube in your amp can be biased. The first example in blue would be biased in its central operating point,
a clean stage that doesn't distort. [A typical clean cathode resistor value on a 12AX7/ECC83 preamp tube stage would be 1.5 to 1.8K ohms with a 100K plate resistor. just specs blah blah...[
The second waveform shows overdrive distortion in the form of hi bias, which can be achieved by either increasing the plate resistor value, or decreasing the cathode resistor value. these are/can be on mini rheostats and adjustable
The third waveform is an example of cold clipping. This is achieved by increasing the value of your cathode resistor. [The Marshall cold clipper circuit uses a 10K resistor, while the typical Soldano circuit boosts that resistor value to 39K. again can be done with a rheostat. can verify on DVOM[ just specs ..blah blah
We LIKE the sound of a cold clipper stage. It's very musical. And blending in some overdrive distortion from an adjacent stage can add a lot of character to the sound as well.
Note that the blue first waveform is well within the lines drawn and identified as +Vcc and -Vcc. If we were to increase the gain of the stage being plate voltage in a symmetrical manner, that increases the amplitude (size) of the waveform. If it's taken as high as it can get without crossing those two lines, then that is the maximum clean power available under those conditions. Any increase in drive/bias beyond this point will result in symmetrical distortion, both top and bottom peaks being clipped at the same time.
Now we can adjust that stage for either overdrive or cold clipping by simply adjusting the bias in either direction.
Buddy holly would be class A amplification type sound..vintage
SRV would be cold clip'd AB
hair band squealing would be high biased to clipping.
play around with it..have amp 'on' guitar plugged in. dont zap yourself..use a pencil eraser to turn the ring..this shits tuff. it doesnt break easy.
class A has the best definition/clarity. sine wave.
AB has all the modern growls. set the plate voltage and you pull the bias up or down to clip the highs or lows. to taste.
you cannot do this stuff with a OD pedal in front of the preamp..
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