Bias adjustment thread

[Jay Mitchell]

Out of curiosity, what class is the Carol Ann OD2? Reason, I ask is because I noticed it is the first amp in the Axe that the bias defaults to something other than .350, in this case, 0.902.

Not the first. The "Class A" defaults to .752. There may be others as well, but I haven't looked at all the defaults.

 

[biggness]

Out of curiosity, what class is the Carol Ann OD2? Reason, I ask is because I noticed it is the first amp in the Axe that the bias defaults to something other than .350, in this case, 0.902.

Not the first. The "Class A" defaults to .752. There may be others as well, but I haven't looked at all the defaults.

Yes, you are right. My mistake.

After looking around the web, I think I have found some information that leads me to believe the OD2 is a class AB amp. http://www.fatsoundguitars.com/store/amps/carol-ann/carol-ann-amps.php I am just wondering why the bias would be set so high for this. :?:

 

[Smilzo]

... I think I have found some information that leads me to believe the OD2 is a class AB amp. http://www.fatsoundguitars.com/store/amps/carol-ann/carol-ann-amps.php I am just wondering why the bias would be set so high for this. :?:

Because Vox is class AB.
They call class A, but it isn't. It's hot biased class AB, hence 0,75 bias.

 

[AdamCook]

... I think I have found some information that leads me to believe the OD2 is a class AB amp. http://www.fatsoundguitars.com/store/amps/carol-ann/carol-ann-amps.php I am just wondering why the bias would be set so high for this. :?:

Because Vox is class AB.
They call class A, but it isn't. It's hot biased class AB, hence 0,75 bias.

That's the case with most "class A" amps. Class A in marketing terms is not the same as technical terms. However, because of convention the marketing definition of "class A" is generally what has become accepted in the community. That's why the Vox and most other amps like it are still called a "class A" amp.

 

[javajunkie]

... I think I have found some information that leads me to believe the OD2 is a class AB amp. http://www.fatsoundguitars.com/store/amps/carol-ann/carol-ann-amps.php I am just wondering why the bias would be set so high for this. :?:

Because Vox is class AB.
They call class A, but it isn't. It's hot biased class AB, hence 0,75 bias.

That's the case with most "class A" amps. Class A in marketing terms is not the same as technical terms. However, because of convention the marketing definition of "class A" is generally what has become accepted in the community. That's why the Vox and most other amps like it are still called a "class A" amp.

Talking about 2 different amps here. OD2 is not a Vox?

 

[AdamCook]

Talking about 2 different amps here. OD2 is not a Vox?

You're right...OD2 is not a Vox. I was just speaking in general terms with regards to how the term Class A is often applied to hot-biased amps as opposed to the true technical definition of Class A.

Here's a cool in depth discussion of the topic: http://www.aikenamps.com/VoxAC30classA_2.html

 

[javajunkie]

Talking about 2 different amps here. OD2 is not a Vox?

You're right...OD2 is not a Vox. I was just speaking in general terms with regards to how the term Class A is often applied to hot-biased amps as opposed to the true technical definition of Class A.

Here's a cool in depth discussion of the topic: http://www.aikenamps.com/VoxAC30classA_2.html

Sorry, that was more directed to the person you were responding to. Just seems like there was some confusion on the amp in question.

 

[GM Arts]

Bias is a negative voltage on the power tubes' grids wrt their cathodes. So more negative grid voltage causes less current to flow from anode to cathode with no signal present. This is referred to as a "colder" bias - the equivalent of reducing the AxeFX setting below 0.35 and moving class AB towards class B.]

Bias is not the control voltage, bias is the current running through the power tubes (more specifically the plate current) when idle.
Bias is controlled/set with the control grid voltage but that voltage itself is not what's generally referred to as the bias (although that mistake is often made).

S.R.

You are correct of course. I was trying to explain here how bias current is set by bias voltage.

 

[fuzznut]

You are correct of course. I was trying to explain here how bias current is set by bias voltage.

Don't know about that. Bias, as a noun, is the voltage applied to achieve a desired operating point. The desired current is a result of applying the correct bias.

 

[wezx]

Everyone is way too biased in this discussion