double the BIAS in an Aleph 30

audionut · 1st April 2006, 02:51 PM

I've got the power supply capacity, and the heatsinking...can I safely double the bias in an Aleph 30.

I figure .75 amps are going through each Mosfet now...so I guess with a doubling of BIAS there would be 1.5 amps going through each mosfet...

Would I double the BIAS by halfing the resistance of each source resistor? (total of twelve)

Thanx in advance

jleaman · 1st April 2006, 03:23 PM

Quote:

Originally posted by audionut
I've got the power supply capacity, and the heatsinking...can I safely double the bias in an Aleph 30.

I figure .75 amps are going through each Mosfet now...so I guess with a doubling of BIAS there would be 1.5 amps going through each mosfet...

Would I double the BIAS by halfing the resistance of each source resistor? (total of twelve)

Thanx in advance

Why do you want to do this ?

audionut · 1st April 2006, 04:27 PM

Why do I want to double the BIAS??

I noticed when driving low impedences of 1 ohm or so, the amp can only swing about 10 volts before clipping, (if memory serves)...At 8 Ohms, the amp can swing 20 volts or so....

If I double the BIAS...the amp will be able to swing more volts before clipping....

In my DIY readings...I am under the impression that the more BIAS the sweeter the amp...

I also notice that if I parrallel the channels, the amp will swing more volts into low impedences.

wuffwaff · 1st April 2006, 05:10 PM

Hi,

yes halving the source resistors would aprox. double the bias.

1.5A times 25V = 37,5 watt per fet wich is quite high but still ok if your heatsinks are big enough.
Be shure that the mica / kapton isolators are good enough and measure the fet temperature at the case (below 80°C would be nice).

10V at 1 ohm is quite high, probably more like 5V or lower. Even with 4,5A bias and 50% ac-current-gain peak current is "only" 9A
and peak voltage only 9V into one ohm

I´m shure the amp will sound better this way if the rest is up to it.

William

mpmarino · 1st April 2006, 05:20 PM

Quote:

I´m shure the amp will sound better this way if the rest is up to it.

Although I have never 'doubled' the bias, experience leads me to agree that this will almost certainly be true

wufffaff, wouldn't the halving of source resistors require halving of the speaker resistors to keep ac gain the same?

audionut · 1st April 2006, 06:49 PM

thanx guys...we'll see what happens.

wuffwaff · 2nd April 2006, 06:41 AM

mpmarino,

yes ac-current-gain must be reset but this could also be done with R19 (wich connects the current source to the output).

William

mpmarino · 2nd April 2006, 12:35 PM

Quote:

Originally posted by wuffwaff
mpmarino,

yes ac-current-gain must be reset but this could also be done with R19 (wich connects the current source to the output).

William

Yes..yes.. You must be tired of saying that

Blues · 2nd April 2006, 12:47 PM

audionut,

I started a thread about more current/ voltage on an Aleph 3 which I called HotRod Aleph in SuperCharge or Turbo modes...do a search and send me an e-mail if you have any questions. These cool names are just killing me...

audionut · 2nd April 2006, 03:26 PM

thanks blues...I'm sure I'll have questions...

1st April 2006, 02:51 PM	#1
audionut diyAudio Member Join Date: Jan 2002 Location: Cleveland ohio	double the BIAS in an Aleph 30 I've got the power supply capacity, and the heatsinking...can I safely double the bias in an Aleph 30. I figure .75 amps are going through each Mosfet now...so I guess with a doubling of BIAS there would be 1.5 amps going through each mosfet... Would I double the BIAS by halfing the resistance of each source resistor? (total of twelve) Thanx in advance

1st April 2006, 05:10 PM	#4
wuffwaff diyAudio Member Join Date: Aug 2001 Location: Ingolstadt Germany	Hi, yes halving the source resistors would aprox. double the bias. 1.5A times 25V = 37,5 watt per fet wich is quite high but still ok if your heatsinks are big enough. Be shure that the mica / kapton isolators are good enough and measure the fet temperature at the case (below 80°C would be nice). 10V at 1 ohm is quite high, probably more like 5V or lower. Even with 4,5A bias and 50% ac-current-gain peak current is "only" 9A and peak voltage only 9V into one ohm I´m shure the amp will sound better this way if the rest is up to it. William __________________ een ooievaar is geen konijn want zijn oren zijn te klein!

2nd April 2006, 06:41 AM	#7
wuffwaff diyAudio Member Join Date: Aug 2001 Location: Ingolstadt Germany	mpmarino, yes ac-current-gain must be reset but this could also be done with R19 (wich connects the current source to the output). William __________________ een ooievaar is geen konijn want zijn oren zijn te klein!

2nd April 2006, 12:47 PM	#9
Blues Lightning In A Bottle diyAudio Member Join Date: Sep 2003 Location: Bremerton, WA	audionut, I started a thread about more current/ voltage on an Aleph 3 which I called HotRod Aleph in SuperCharge or Turbo modes...do a search and send me an e-mail if you have any questions. These cool names are just killing me... __________________ Quad Matched Toshiba 2SK1530/2SJ201 MOSFETs http://www.diyaudio.com/forums/swap-...ml#post2086375

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1st April 2006, 04:27 PM	#3
audionut diyAudio Member Join Date: Jan 2002 Location: Cleveland ohio	Why do I want to double the BIAS?? I noticed when driving low impedences of 1 ohm or so, the amp can only swing about 10 volts before clipping, (if memory serves)...At 8 Ohms, the amp can swing 20 volts or so.... If I double the BIAS...the amp will be able to swing more volts before clipping.... In my DIY readings...I am under the impression that the more BIAS the sweeter the amp... I also notice that if I parrallel the channels, the amp will swing more volts into low impedences.

1st April 2006, 06:49 PM	#6
audionut diyAudio Member Join Date: Jan 2002 Location: Cleveland ohio	thanx guys...we'll see what happens.

2nd April 2006, 03:26 PM	#10
audionut diyAudio Member Join Date: Jan 2002 Location: Cleveland ohio	thanks blues...I'm sure I'll have questions...

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