The Aleph-X - Page 54

yldouright · 8th September 2002, 07:55 PM

The Saint

It depends on how you build it out. A 128W rms 8 ohm version will use 25.6V rails and have a total of 16A of bias current. If you look earlier into this thread GRollins explains how to build it out to your required size.

Nelson Pass

I have just two questions about source resistors in the Aleph-X. GRollins advised us to use 0.5V/current load on each mosfet to calculate the source resistor.

Why does he use this 0.5V value to make the calcuation when the rails are 12V? Is it because the maximum input signal is only this value?

How does GRollins calculate the source resistor power rating? It would appear that the source resistor would need to be the same as the power dissipated by each mosfet but according to the circuit this doesn't seem to be the case.

skaara · 8th September 2002, 08:08 PM

Wont you fry the o/p fets with that high rail voltage?

yldouright · 8th September 2002, 08:14 PM

skaara

Well, it depends on how many mosfets you use and how closely you match them.

skaara · 8th September 2002, 08:20 PM

Can you use/paralell more than one for each side in alephx?

yldouright · 8th September 2002, 08:27 PM

skaara

Exactly! Just like in the XA-200 or any other of the larger amps. Nelson parallels mosfets to keep the power dissipation per device to a reasonable amount so they don't fry up. The problem you run into with paralleling mosfets in the increasing capacitance. That's why you should choose your mosfets carefully. The reason you match closely is so each parallel device is carrying its fair share of the power burden.

skaara · 8th September 2002, 10:50 PM

I know about capacitance, and matching, but I read somewhere that there is a problem with parlelling mosfets in aleph x, but I guess it wasnt true.

AudioFreak · 8th September 2002, 11:28 PM

Paralleling multiple output devices is one thing that we have yet to completely iron all the bugs out of in this design, it's mostly a matter of increasing the drive current and decreasing the front end impedance but this amp also seems to show stability issues under some situations so we have approached it on a case by case basis thus far.

The Saint · 8th September 2002, 11:38 PM

Has anyone thought of putting a zobel network across the two O/Ps of the Aleph X. to help with stability problems..

Values of a 10 Ohm 5 watt and 100nf ~250 AC rated Cap works well for me.
In my 1kw design it was very important that this was in place.

Regards

Anthony Holton
Aussieamplifiers

The Saint · 8th September 2002, 11:41 PM

Even from each O/P to ground would be of use as well.

Regards

Anthony

yldouright · 9th September 2002, 02:39 PM

The Saint

The issues of stability were addressed earlier in this thread. GRollins stated the circuit was rock solid and HarryHaller provided a solution to address unruly oscillations.

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8th September 2002, 07:55 PM	#531
yldouright diyAudio Member Join Date: Aug 2002 Location: New York, NY	The Saint It depends on how you build it out. A 128W rms 8 ohm version will use 25.6V rails and have a total of 16A of bias current. If you look earlier into this thread GRollins explains how to build it out to your required size. Nelson Pass I have just two questions about source resistors in the Aleph-X. GRollins advised us to use 0.5V/current load on each mosfet to calculate the source resistor. Why does he use this 0.5V value to make the calcuation when the rails are 12V? Is it because the maximum input signal is only this value? How does GRollins calculate the source resistor power rating? It would appear that the source resistor would need to be the same as the power dissipated by each mosfet but according to the circuit this doesn't seem to be the case.

8th September 2002, 08:08 PM	#532
skaara diyAudio Member Join Date: Jun 2002 Location: Europe, Slovenia	Wont you fry the o/p fets with that high rail voltage?

8th September 2002, 08:14 PM	#533
yldouright diyAudio Member Join Date: Aug 2002 Location: New York, NY	skaara Well, it depends on how many mosfets you use and how closely you match them.

8th September 2002, 08:20 PM	#534
skaara diyAudio Member Join Date: Jun 2002 Location: Europe, Slovenia	Can you use/paralell more than one for each side in alephx?

8th September 2002, 08:27 PM	#535
yldouright diyAudio Member Join Date: Aug 2002 Location: New York, NY	skaara Exactly! Just like in the XA-200 or any other of the larger amps. Nelson parallels mosfets to keep the power dissipation per device to a reasonable amount so they don't fry up. The problem you run into with paralleling mosfets in the increasing capacitance. That's why you should choose your mosfets carefully. The reason you match closely is so each parallel device is carrying its fair share of the power burden.

8th September 2002, 10:50 PM	#536
skaara diyAudio Member Join Date: Jun 2002 Location: Europe, Slovenia	I know about capacitance, and matching, but I read somewhere that there is a problem with parlelling mosfets in aleph x, but I guess it wasnt true.

8th September 2002, 11:28 PM	#537
AudioFreak Warp Engineer On Holiday Join Date: Oct 2001 Location: Queensland, Australia	Paralleling multiple output devices is one thing that we have yet to completely iron all the bugs out of in this design, it's mostly a matter of increasing the drive current and decreasing the front end impedance but this amp also seems to show stability issues under some situations so we have approached it on a case by case basis thus far.

8th September 2002, 11:38 PM	#538
The Saint diyAudio Member Join Date: Jul 2002 Location: Launceston, TAS, Australia	Has anyone thought of putting a zobel network across the two O/Ps of the Aleph X. to help with stability problems.. Values of a 10 Ohm 5 watt and 100nf ~250 AC rated Cap works well for me. In my 1kw design it was very important that this was in place. Regards Anthony Holton Aussieamplifiers

8th September 2002, 11:41 PM	#539
The Saint diyAudio Member Join Date: Jul 2002 Location: Launceston, TAS, Australia	Even from each O/P to ground would be of use as well. Regards Anthony

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9th September 2002, 02:39 PM	#540
yldouright diyAudio Member Join Date: Aug 2002 Location: New York, NY	The Saint The issues of stability were addressed earlier in this thread. GRollins stated the circuit was rock solid and HarryHaller provided a solution to address unruly oscillations.