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Old 5th October 2009, 11:37 PM   #1791
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Quote:
Originally Posted by noisefree View Post
Hello,

hope there is any interest in this project – seems that I am the only one who tries it :-(

Here are some new details:

Have changed again some resistors with the result that the absolute and differential offset is very stable now:
I came to the decision to put in again the divider across the voltage reference and throw out the frontend loading resistors to ground – have found out that the divider only has the effect of a shifting ground (the supply voltages starts to become unsymmetric) in combination with this output to ground resistors (but I don’t know why this happened).
Also the trimmers have been scaled down: Abs. pot is now 20R and diff. pot 50R – both are 25 turn types.
I have implemented the resistor from FE to OS which I have also seen in the A75 article. (The A75 uses a combined feedback from output and front end.)
In the shown circuit below the feedback is not mixed and only comes from the OS. But mix mode can be realized when changing the 0R resistor to a higher value.
My main goal was to get a really good trimmable offset and this is done now and works very well - both offsets are adjustable to 1-3mV without a problem (but I can’t say if this resistor has a negative effect and how to dimension it!?) and the supply rails stay symmetrical.
The abs. offsets of the FE reaches values in size of +140 and +180mV - think that is acceptable (perhaps it can be reduced with a bit higher resistor value for the upper divider resistor)
Also new are the four resistors in the bias circuit connected to ground – it could be that they are not necessary - perhaps they bring a bit stabilization.
The two resistors which steal the voltage references some current in stand by mode are reduced to 270k which give a stand by output bias of only 26mA (2mA p-fet + 24mA SE-resistor)! That’s a consumption reduction to a tenth. The abs. offset goes down to -120mV and for diff. offset I get about 12mV.
However I need another possibility to throw away some open loop gain which is still to high.
Without the ugs output to gnd loading resistors the open loop gain raises again by 4dB.

Perhaps other people will try it out or have some ideas!???

Regards
Dirk
Hi again, I did not put the 'quote message' in my last note, I would like to know if you have built or if anyone has built the schematic 'ax-sepp.pdf 'and also if PCBs have ever been made from it.

Thank You

scatterbrain001
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Old 6th October 2009, 02:12 AM   #1792
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Quote:
Originally Posted by labjr View Post
I have some un-built boards. PM me if you're interested.
I am interested in buying two the boards you have, are they JFET ready?

Thank You

scatterbrain001
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Old 6th October 2009, 03:30 AM   #1793
labjr is offline labjr  United States
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Quote:
Originally Posted by scatterbrain001 View Post
I am interested in buying two the boards you have, are they JFET ready?

Thank You

scatterbrain001

Sorry, Those were sold a while back.
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Old 26th October 2009, 09:31 PM   #1794
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Welcome to the group You will love it here We all love photos and would love to see your fur crew
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Old 2nd November 2009, 12:32 PM   #1795
jackies is offline jackies  United States
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Is the previous message a spam?
My fur crew??

I'm reading this endless thread, as well as few other Aleph-X threads, and Aleph-X Wiki page is mentioned quite often, but alas, links are dead and I can't find the wiki page no matter how hard I look.. Could you kindly point me to it?
Your help will be greatly appreciated.

Last edited by jackies; 2nd November 2009 at 12:35 PM.
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Old 2nd November 2009, 12:56 PM   #1796
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diyAudio.com Wiki - projects by fanatics, for fanatics
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Old 27th November 2009, 01:44 AM   #1797
jackies is offline jackies  United States
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Thanks for the answer!
I have another question though.. I have 16a rated schottky diodes, will that be enough for one channel of alepx-x with a reasonable amount of capacitance - circa 60-80 mf?
Or they gonna blow?
I'm a little confused after reading this thread - ppl seem to use everything from MUR08 to 35a bridges and I seen recommendations as hearty as 75a and 85a...

Last edited by jackies; 27th November 2009 at 01:55 AM.
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Old 28th November 2009, 06:55 PM   #1798
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I'm pretty sure that 16A Schottkys would be fine.

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Old 30th November 2009, 06:40 AM   #1799
mthoi is offline mthoi  Malaysia
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I am a newbie and would appreciate any assistance in troubleshooting my AX bias-ing problem. The schematics I followed was based on Blitz's AX2 V1.0 (100 watts) design.

After adusting V1 and V3, I have the following voltages across the bias resistors - R5 0.5V; R6 0.62V; R34 0.023V; R41 0.001V. V3 resistance measures around 80KR. Q1 is nice and hot but Q2, Q10, Q11 are stone-cold.

I suspect Q8 (MPSA18) may not be functioning properly since the voltage at collector = 22.98VDC, Vbase = 19.01VDC, Vemitter = 19.02VDC. The power supply is steady at +23.14VDC and -23.15VDC. I have replaced Q8 twice but the problem still remains.

Is there anything that I am overlooking? Any asssitance are appreciated. Reg.
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Old 30th November 2009, 10:56 PM   #1800
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It would be incredibly easier to help if you posted a link to
the schematic. Contrary to popular belief, I cannot recall
everyone else's part numbering schemes.

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