What BIAS current is suitable for me? - Page 2 - diyAudio
 What BIAS current is suitable for me?
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 31st January 2006, 07:48 AM #11 lscangus   diyAudio Member   Join Date: Oct 2005 " To the left of the peak you are current limited - to raise power increase the bias. to the right of the peak you are voltage limited, increase rail voltage to increase power. " sorry my english isn't very good . can you explain this? i think the BIAS current is what i can set on the board using a variable resistor, as well as the rail voltage. any one have any suggestion of what rail voltage and BIAS current i go for? Angus
Dr.Gone
diyAudio Member

Join Date: Feb 2005
Location: G... (Think cheese)
Quote:
 Originally posted by lscangus " To the left of the peak you are current limited - to raise power increase the bias. to the right of the peak you are voltage limited, increase rail voltage to increase power. " sorry my english isn't very good . can you explain this? i think the BIAS current is what i can set on the board using a variable resistor, as well as the rail voltage. any one have any suggestion of what rail voltage and BIAS current i go for? Angus
Did you take a look at the AXE-1.2 spreadsheet? There is a graph displaying the maximum power output for different impedances. There is a peak in the graph where the amplifier has its maximum power. At a lower impedance the amplifier is limited by the amount of current it can supply and with a higher impedance the amplifier is limited by the voltage at the fets.

I'm not sure if this post helps you but what i would do is this:
Take a look at the spreadsheet and fiddle with the numbers of
BIAS and 'voltage at fets'. Raising the 'voltage at fets' will move the peak output towards a higher impedance and raising the bias will move the peak towards a lower impedance (both resulting in more heat to be dissipated).

You can go as crazy as you like on the specs (although there is an upper and lower limmit), but remember you've got to get rid of the heat! And using 2 x 500 Watt class A amplifiers in your listening room will heat up the room considerably.

Regards,
Jacco

lscangus
diyAudio Member

Join Date: Oct 2005
Quote:
 Originally posted by Dr.Gone Did you take a look at the AXE-1.2 spreadsheet? There is a graph displaying the maximum power output for different impedances. There is a peak in the graph where the amplifier has its maximum power. At a lower impedance the amplifier is limited by the amount of current it can supply and with a higher impedance the amplifier is limited by the voltage at the fets. I'm not sure if this post helps you but what i would do is this: Take a look at the spreadsheet and fiddle with the numbers of BIAS and 'voltage at fets'. Raising the 'voltage at fets' will move the peak output towards a higher impedance and raising the bias will move the peak towards a lower impedance (both resulting in more heat to be dissipated). You can go as crazy as you like on the specs (although there is an upper and lower limmit), but remember you've got to get rid of the heat! And using 2 x 500 Watt class A amplifiers in your listening room will heat up the room considerably. Regards, Jacco

I have looked at the spreadsheet, the problem i am having is where is the peak is the best? 8 ohm? 6 ohm? 12 ohm?

 31st January 2006, 10:07 AM #14 wuffwaff   diyAudio Member     Join Date: Aug 2001 Location: Ingolstadt Germany 5 ohm __________________ een ooievaar is geen konijn want zijn oren zijn te klein!
 31st January 2006, 12:16 PM #15 lscangus   diyAudio Member   Join Date: Oct 2005 thank you very much. why is it 5 ohm? is it the nature of Aleph or becasue of my speaker? what is the default BIAS current of a Aleph 2?
 31st January 2006, 03:55 PM #16 wuffwaff   diyAudio Member     Join Date: Aug 2001 Location: Ingolstadt Germany Hi, the impedance of your speaker has a minimum of 5 Ohms so no need to have more power at lower impedances. An Aleph2 is not an Aleph X and has a bias setting of around 3.3A There is no default bias setting AND the voltage at the fets can only be changed by changing trafos!!!!! Not by changing resistors or fiddling with a pot!!! William __________________ een ooievaar is geen konijn want zijn oren zijn te klein!
 31st January 2006, 07:56 PM #17 Nelson Pass   The one and only     Join Date: Mar 2001 If quality of sound is the criterion, then the highest bias possible is what you want. Often this is not practical....
lscangus
diyAudio Member

Join Date: Oct 2005
Quote:
 Originally posted by Nelson Pass If quality of sound is the criterion, then the highest bias possible is what you want. Often this is not practical....

Wow, thank you Mr. Pass. So do you think about 50-60W output enough for me? People said the output from Aleph amplifier are very powerful Watts.

 31st January 2006, 08:19 PM #19 Nelson Pass   The one and only     Join Date: Mar 2001 Yeah, that's the ticket.... 50 watts with 100 amp bias!
lscangus
diyAudio Member

Join Date: Oct 2005
Quote:
 Originally posted by Nelson Pass Yeah, that's the ticket.... 50 watts with 100 amp bias!

i have now decided to use a 17V rail and 10Amp bias. will it be fine?

Angus

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