Thank you. Now a mosfet is cold!
I am thinking the batch was flawed. I ordered 1% 5w 1ohm resistors for the mosfet source. I hope this improves the matching!
The funny thing is that bias drops with time. it is supposed to be 3A and that value is reached only in the beginning when the amp is cold. then it drops to 2.56A. could it be a "cold" mosfet is causing this?
I am thinking the batch was flawed. I ordered 1% 5w 1ohm resistors for the mosfet source. I hope this improves the matching!
The funny thing is that bias drops with time. it is supposed to be 3A and that value is reached only in the beginning when the amp is cold. then it drops to 2.56A. could it be a "cold" mosfet is causing this?
no pictures , no measurements in important points , and you are expecting even additional confirmation of everything we replied to you ?
I understand lack of experience , but you really need to read what people are replying
temperature equilibrium is just that - equilibrium - it doesn't matter is it on 35 or 50C
crank up that bias and enjoy
I understand lack of experience , but you really need to read what people are replying
temperature equilibrium is just that - equilibrium - it doesn't matter is it on 35 or 50C
crank up that bias and enjoy
I haven't measured with new configuration of rc. The amp is completely silent with my ear placed directly on high efficiency speakers. The caps are 50v 69,000uf
The amp is quite manageable. It will be encased in black plexy once finished
Inviato dal mio GT-I9001 con Tapatalk 2
The amp is quite manageable. It will be encased in black plexy once finished
Inviato dal mio GT-I9001 con Tapatalk 2
Remove R19 (ref Aleph2 schem) and leave open. Sweet amps!!
Why remove R19? What is the value and where is it in the circuit? What does it do?
R19 trims DC bias, it's found in the upper portion of the output stage current source. 56.2K is the value for Aleph2.
More discussion:
http://www.diyaudio.com/forums/pass-labs/5007-dc-offset-bias-setting-aleph-2-a.html
More discussion:
http://www.diyaudio.com/forums/pass-labs/5007-dc-offset-bias-setting-aleph-2-a.html
R19 trims DC bias, it's found in the upper portion of the output stage current source. 56.2K is the value for Aleph2.
More discussion:
http://www.diyaudio.com/forums/pass-labs/5007-dc-offset-bias-setting-aleph-2-a.html
Thanks.
A friend of mine built me a pair of Aleph 2's about 6 years ago using KK boards. I had planned to have a look at their internals anyway and see what could be upgraded. This goes into the box of "must check ..."!
I measured 1.2v drop across 1ohm resistor.
The 1 ohm you have in the PS? That's not how you measure the amplifier bias.
My transformer is boosted to 250v primary.
This one needs clarifcation.
Ok, got it on the transformer front.
Bias for Aleph 2:
Looking at the lower portion of the output stage (the 6 drive outputs):
(voltage across Source resistor / Source resistor value = current in that device)
0.5V/1R=0.5A or 500mA multiply that by 6, which is 3A.(0.5*6)
I'm not quite sure what the voltage across the lower source resistors will be when R19 is removed, but it will no doubt be higher, my guess is prob 10mV or slightly higher. For ex. when I removed R19 in my Aleph5, it jumped from the standard 0.5V to around .64-.66
You don't measure amplifer bias by voltage across a PS resistor. And the positive half of a Class A amp bipolar power supply will generally have a slightly higher draw than the negative half.
Looks to me like you're right on target. Hope that helps! To the experts, correct me if I'm wrong. I just read stuff and regurgitate it.
-John
Bias for Aleph 2:
Looking at the lower portion of the output stage (the 6 drive outputs):
(voltage across Source resistor / Source resistor value = current in that device)
0.5V/1R=0.5A or 500mA multiply that by 6, which is 3A.(0.5*6)
I'm not quite sure what the voltage across the lower source resistors will be when R19 is removed, but it will no doubt be higher, my guess is prob 10mV or slightly higher. For ex. when I removed R19 in my Aleph5, it jumped from the standard 0.5V to around .64-.66
You don't measure amplifer bias by voltage across a PS resistor. And the positive half of a Class A amp bipolar power supply will generally have a slightly higher draw than the negative half.
Looks to me like you're right on target. Hope that helps! To the experts, correct me if I'm wrong. I just read stuff and regurgitate it.
-John
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