Aleph J illustrated build guide - Page 6 - diyAudio
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Old 11th September 2013, 07:07 PM   #51
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Quote:
Originally Posted by BobEllis View Post
Soldier style: Standing at attention, with the body vertical. Took this native English
speaker and Navy veteran a second to figure that one out so don't feel bad ticktock.
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Originally Posted by 6L6 View Post
The bigger resistors are mounted soldier-style.

(I thought soldier style was the real term for that... maybe not...)
Thanks, mates. I should have figured it out on my own and at least I'll never forget that.
I even have some resistors that way in my own Ono MC prepre.
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Old 15th September 2013, 01:49 AM   #52
12B4A is offline 12B4A  United States
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Do different bias current points (.85Ax2 vs. 1Ax2) on the output stage affect the overall output power capability or just where the circuit enters push-pull?
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Old 15th September 2013, 02:26 AM   #53
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No push pull here, this is single ended country.

The bias impacts where the amp becomes current limited vs. voltage limited. If you have low impedance speakers, you might see an increase in power output with more bias.

6L6 has done some measurements that show that higher bias decreases distortion. While measurable, you may or may not hear a difference.
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Old 15th September 2013, 02:41 AM   #54
12B4A is offline 12B4A  United States
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So how much different in overall topology is the Aleph J from the Aleph 0?

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While it will not leave Class A on an unclipped positive signal, a single ended Class A design would ordinarily clip at negative currents greater than the bias point, and for this occurrence the Aleph 0 has proprietary pull circuitry in the output stage which allow push-pull operation at negative currents beyond the bias point. This new topology has been designed to source greater negative current than previous amplifiers with single ended bias, in the belief that push-pull Class A operation is preferable to clipping.

So where is the J biased for the 25W@8 ohm rating?
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Old 15th September 2013, 03:25 AM   #55
6L6 is offline 6L6  United States
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The J will make 25W into 8ohm at the .400V bias. I am not sure how the bias actually interacts with total power, but I do know that a 'normal' single ended output stage can not pass more current than the bias, but the Aleph CCS has the ability to change that somewhat... but I honestly don't know exactly what the circuit is doing to make that so.

Maybe somebody more familiar with how this stuff all actually works can help explain?

I do know that I can take some measurements and data points and pass that info onto the thread -- If I get a chance in the next few days I will get some full-power measurements into 8 and 4 ohm at various bias levels.
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Old 15th September 2013, 03:45 AM   #56
12B4A is offline 12B4A  United States
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That's good to know about the recommended bias setting. No matter how many posts I read about the Aleph design I still remain dumb about this AC gain and shifting bias function.
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Old 15th September 2013, 04:26 AM   #57
6L6 is offline 6L6  United States
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Quote:
Originally Posted by 12B4A View Post
No matter how many posts I read about the Aleph design I still remain dumb about this AC gain and shifting bias function.
Have you read Zen Variations 2?


https://www.passdiy.com/project/ampl...n-variations-2
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Old 15th September 2013, 01:16 PM   #58
12B4A is offline 12B4A  United States
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Yep, I think the dumbness sets in when I have to comprehend the interaction with the hybrid SE/PP section of the circuit. I think I just want to understand it as far as being able to bottom-line a total device dissipation-to-output efficiency. It seems like it's 35% in the best case of operation.

Sort of related: I'm getting a value of 21k for R7 in order to achieve the 400mV bias with the BOM parts. At 68k it was 520mV which was a bit too hot for my 4U chassis heat sinks. Even with the lower bias this thing still kicks out some heat. Winter is coming...
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Old 15th September 2013, 01:36 PM   #59
jdg123 is offline jdg123  United States
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Default mica and insulation

I have read the mica and goop thread but I got myself into trouble when I bought micas from Mouser...

TO-220 was said to cover the interface for TO-247 but it is SO close to not covering it! How critical is insulating (electrically) the output transistors and the heavy duty diodes from the casework/heatsinks?

Can anyone point to a source of larger (like 25 x 20mm) micas that don't have to come all the way across the world to the USA? Digikey and Mouser don't seem to have them (which to me means I just can't find them on their sites...)

Cheers!
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Old 15th September 2013, 01:53 PM   #60
jdg123 is offline jdg123  United States
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Never mind, I found them at MCM :-)
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