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Old 5th February 2013, 08:13 PM   #31
AAAudio is offline AAAudio  United States
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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

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Old 5th February 2013, 08:38 PM   #32
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Out of curiosity, are you measuring amp draw with a current meter on the AC line? If you are, it should come out to 2.5A as stated in the service manual.
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Old 5th February 2013, 08:52 PM   #33
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Quote:
Originally Posted by MEGA-amp View Post
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?
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Old 5th February 2013, 09:01 PM   #34
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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:
DC offset / Bias setting for Aleph 2
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Old 5th February 2013, 09:08 PM   #35
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Quote:
Originally Posted by MEGA-amp View Post
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:
DC offset / Bias setting for Aleph 2
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 ..."!
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Old 5th February 2013, 09:11 PM   #36
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bias schmias

(ref Aleph 2 schm , as Mega-amp said)
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Old 6th February 2013, 08:15 PM   #37
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I measured 1.2v drop across 1ohm resistor. My transformer is boosted to 250v primary. I am using 300w of power. Strange for an aleph 2 with no 56.2k resistor!

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Old 6th February 2013, 08:22 PM   #38
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Quote:
Originally Posted by AAAudio View Post
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.

Quote:
Originally Posted by AAAudio View Post
My transformer is boosted to 250v primary.
This one needs clarifcation.
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Old 6th February 2013, 08:26 PM   #39
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I usually measure bias using the 1ohm 1% resistors in the rc network. 3.5A on the positive rail and 3.2 on the negative rail.

My transfor is deisgned for 230v but i increased mains to 250 via a step up transformer to increase voltage output. Simple.
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Old 6th February 2013, 11:25 PM   #40
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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

Last edited by MEGA_amp; 6th February 2013 at 11:41 PM.
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