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Old 11th July 2002, 05:59 PM   #11
BDP is offline BDP  United States
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Default dshortt9

Thank you for the reply. After your reply I realized that the feedback capacitor would keep the DC gain to a minimum ( Rfeedback / Xc) thus the output would try to track the input to the differential pair. If the input was 0 volts then the output would try to follow.
Being a true DIY I think I will experiment and omit the feedback capacitor and install a trimmer at R14, probably a 1k resistor paralled with a2K trimmer pot. This will give me three things. One being complete control of the output driver bias and DC offset. The second removing the capacitor from the balanced signal path. Third give me something to adjust!! Has anyone else gone this route with their Aleph's?
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Old 29th January 2013, 04:23 PM   #12
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Quote:
Originally Posted by Nelson Pass View Post
If R19 open does not give enough bias, you can get more
bias by attaching R19 to a voltage divider between the
output and the negative rail and bootstrap the middle
junction to the output through a 220 uF cap. This causes
R19 to draw current out of the junction (Base of NPN
transistor) instead of feeding current in, and so the bias
goes up.
I am sorry to go thread digging but this post from Mr Pass seems very interesting. Has anyone tried it?

Could Mr Pass himself or another kind soul jot down a schematic of this modification?

Thank you
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Old 31st January 2013, 09:52 AM   #13
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no one?

I would really like to try out increasing bias to 4A per rail. Leaving out the 56,2k resistor only gives me 3.10A per rail.

AAAudio
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Old 31st January 2013, 10:46 AM   #14
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decrease source resistors , one notch

then adjust that "56K2" resistor to your liking
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Old 31st January 2013, 11:15 AM   #15
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I removed the resistor completely and would rather not reduce the resistors ( degeneration). The idea of NP seems a good way to increase bias to 4A per channel.
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Old 31st January 2013, 11:18 AM   #16
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well - then just grind your teeth

Pa wrote you everything you need to know
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Old 31st January 2013, 11:21 AM   #17
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Charming as usual....
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Old 31st January 2013, 11:30 AM   #18
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why I have impression of lacking smiley , in your post ........
Attached Images
File Type: jpg Aleph-2-maximized-Iq.jpg (74.1 KB, 63 views)
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Last edited by Zen Mod; 31st January 2013 at 11:34 AM.
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Old 31st January 2013, 11:48 AM   #19
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I hate to ask, but what is max rails for an Aleph 2? Asuumming heatsink to spare, is 70V pushing it?

I have hybrid biamped ESLs (Sanders 10C) and have an itch to build a high voltage A2 amp to try out on the panels.

I have a monster 1.2kv with dual primaries I can series connect to get around 70VDC. I also have a completed A5 and extra output boards, so the some of the work is done...
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Old 31st January 2013, 12:00 PM   #20
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Pa is right Oracle , for that sort of question

even if I could say - go for it , taking care of breaking voltages of small itsies-bitsies
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