Aleph 2 ac current setting ?

ndhennin · 9th May 2007, 03:06 PM

Well, after 2 years of service I have decided to adjust R19 and R21 to be sure to have the best of my babies (especially now that I have 2 brand new DIY speakers that really deserve it (JP3 ribbon tweeter with audiotechnology 18H52 and audiotechnology 10C102 : a sarastro like speaker ! ))

What I found is that I had only 2.3 as bias value. And this is a maximum value I think as the heatsinks temperature is about 60°C (despite the fact that my heatsinks are huge, but...).
The DC after the filter is 44.7V.
My speaker are 4 ohms. And I think they are something like 89db.
What current gain should I choose then ? I know nelson recommand 50%, but then with my low bias and according to the well known excel file for calculating power, the power at 8 ohms is 84.6 W and at 4 ohms it is only 42.3 W !
At 70% I would have 105,1 W at 8 ohms and 117,6 W at 4 ohms
At 60%, 105 W 8 R; 66 W 4 R

I don't know what to choose on the paper, as a starting point. Do you have any idea on the side effects of setting the AC current gain as high as 70% ??

Manu · 9th May 2007, 04:39 PM

http://www.diyaudio.com/forums/showt...053#post107053

Cordialement
Manuel

wuffwaff · 9th May 2007, 07:01 PM

Hi,

I wouldn´t go higher than 60-65%. Just try as it´s an easy adjustment.
I´ve put some sockets in the resistor holes so I can swap ac-current-gain resistors very fast. This way you can listen for what you like best.
It really depends on the load what sounds best.

The other (more expensive) option would be to lower the supply voltage as it is a bit too high for the bias your running. 35V would be more than enough in your case.

William

GRollins · 9th May 2007, 07:22 PM

If I'm understanding the question correctly, I think the better solution would be to increase the overall bias rather than monkey with the ratio of the current source.

Grey

ndhennin · 9th May 2007, 07:28 PM

But to increase the bias, I would need to increase the heatsinks....This is complex as the one I am using are allready big (not big enough though...)

GRollins · 9th May 2007, 08:48 PM

There's no such thing as a free lunch.
If you want a class A amp, you're going to bump into the heat problem sooner or later.
Try fans.
I went water cooled. Cheap. Effective. Quiet.

Grey

ndhennin · 9th May 2007, 09:35 PM

I was also thinking about water cooling.
What solution did you use ? do you have any website where I could see what it looks like and the way you implement it ?

ndhennin · 9th May 2007, 09:43 PM

I will make a search tomorrow : from what I have seen you have built your own system with an old pump you had. I will have to study this...

9th May 2007, 03:06 PM	#1
ndhennin diyAudio Member Join Date: Apr 2002 Location: Lille (France)	Aleph 2 ac current setting ? Well, after 2 years of service I have decided to adjust R19 and R21 to be sure to have the best of my babies (especially now that I have 2 brand new DIY speakers that really deserve it (JP3 ribbon tweeter with audiotechnology 18H52 and audiotechnology 10C102 : a sarastro like speaker ! )) What I found is that I had only 2.3 as bias value. And this is a maximum value I think as the heatsinks temperature is about 60°C (despite the fact that my heatsinks are huge, but...). The DC after the filter is 44.7V. My speaker are 4 ohms. And I think they are something like 89db. What current gain should I choose then ? I know nelson recommand 50%, but then with my low bias and according to the well known excel file for calculating power, the power at 8 ohms is 84.6 W and at 4 ohms it is only 42.3 W ! At 70% I would have 105,1 W at 8 ohms and 117,6 W at 4 ohms At 60%, 105 W 8 R; 66 W 4 R I don't know what to choose on the paper, as a starting point. Do you have any idea on the side effects of setting the AC current gain as high as 70% ??

9th May 2007, 07:01 PM	#3
wuffwaff diyAudio Member Join Date: Aug 2001 Location: Ingolstadt Germany	Hi, I wouldn´t go higher than 60-65%. Just try as it´s an easy adjustment. I´ve put some sockets in the resistor holes so I can swap ac-current-gain resistors very fast. This way you can listen for what you like best. It really depends on the load what sounds best. The other (more expensive) option would be to lower the supply voltage as it is a bit too high for the bias your running. 35V would be more than enough in your case. William __________________ een ooievaar is geen konijn want zijn oren zijn te klein!

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9th May 2007, 04:39 PM	#2
Manu diyAudio Member Join Date: Nov 2002 Location: Vienna, Ostrich	http://www.diyaudio.com/forums/showt...053#post107053 Cordialement Manuel

9th May 2007, 07:22 PM	#4
GRollins diyAudio Member Join Date: Feb 2001 Location: Columbia, SC	If I'm understanding the question correctly, I think the better solution would be to increase the overall bias rather than monkey with the ratio of the current source. Grey

9th May 2007, 07:28 PM	#5
ndhennin diyAudio Member Join Date: Apr 2002 Location: Lille (France)	But to increase the bias, I would need to increase the heatsinks....This is complex as the one I am using are allready big (not big enough though...)

9th May 2007, 08:48 PM	#6
GRollins diyAudio Member Join Date: Feb 2001 Location: Columbia, SC	There's no such thing as a free lunch. If you want a class A amp, you're going to bump into the heat problem sooner or later. Try fans. I went water cooled. Cheap. Effective. Quiet. Grey

9th May 2007, 09:35 PM	#7
ndhennin diyAudio Member Join Date: Apr 2002 Location: Lille (France)	I was also thinking about water cooling. What solution did you use ? do you have any website where I could see what it looks like and the way you implement it ?

9th May 2007, 09:43 PM	#8
ndhennin diyAudio Member Join Date: Apr 2002 Location: Lille (France)	I will make a search tomorrow : from what I have seen you have built your own system with an old pump you had. I will have to study this...

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