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Old 1st June 2003, 12:02 PM   #1
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Default Another Aleph-X coming up!

Hello,

one channel of my Aleph-X running on 25V-0-25V and 6.7A of bias is up and running. I have some problems with my DC offset (0.221V) but I have probably not matched my 9610's correctly. Strangely I did the same procedure for my 'old' Aleph 4 and there it worked out ok (0.03V).

Changes to Grey's circuit (hifizen PCB):

22-0-22 1000VA transformer (gives 25-0-25 DC)
BIAS resistors = 0.56 ohm
R17 = 6k8 (6mA running through zener diode).
R14, R31 = 1k5
R15, R32 = 1k5
R34, R12 = 1K potmeter which I adjusted by hand (ACS gain)

I have adjusted the ACS by running 9V RMS of 1K sine through the amp. I will replace the potmeter with a resistor when all is stable.

I am running without the 'ground' resistors for the absolute DC but I have to let the amp run for more than an hour, but I do not trust him at this stage to run for an hour. It looks to drift and kind of stabilize after 10 minutes (does not drift to fast any more).

I am using 2 times 10W 0.22 (=0.11) ohm for the CRCRC filter.

Here come the first pictures:

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.


It will deliver:

Watts Ohm
124.47 8.50
132.25 8.00
141.07 7.50
151.14 7.00
145.89 6.50
134.67 6.00
123.45 5.50
112.23 5.00
101.00 4.50
89.78 4.00
78.56 3.50
67.34 3.00
56.11 2.50
44.89 2.00


More info to come,

Edwin
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Old 1st June 2003, 12:12 PM   #2
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O yes,

one question, do you match the IRF9610 on 10mA or on 20mA ??? Because they are running 10mA each, but Mark Finnis his 'old' document mentioned matching on 20mA ?

Edwin
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Old 1st June 2003, 12:23 PM   #3
nar is offline nar
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That's right, we want them matched to 10mA each !!!

Impressive . I have trouble with an Aleph2 . Please read the thread I started on Passlabs forum too.

Hope you can help...

Regards
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Old 1st June 2003, 04:02 PM   #4
grataku is offline grataku  United States
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Quote:
Originally posted by Edwin Dorre
O yes,

one question, do you match the IRF9610 on 10mA or on 20mA ??? Because they are running 10mA each, but Mark Finnis his 'old' document mentioned matching on 20mA ?

Edwin

OH YEAH BABY!!! VERY NICE INDEED. Finally someone put the boards to good use.
Never mind the 10ma or 20 ma, you got to measure the voltage on the 390 ohms resistors and make sure it's the same.
Also, the value of the source resistors is really important, did you match those?? They can vary by quite a bit. especially since all bunched up like that they are getting infernally hot and their thermal caracteristics are going to be all over the place
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Old 1st June 2003, 05:10 PM   #5
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Quote:
Originally posted by grataku



OH YEAH BABY!!! VERY NICE INDEED. Finally someone put the boards to good use.
Never mind the 10ma or 20 ma, you got to measure the voltage on the 390 ohms resistors and make sure it's the same.
Also, the value of the source resistors is really important, did you match those?? They can vary by quite a bit. especially since all bunched up like that they are getting infernally hot and their thermal caracteristics are going to be all over the place

All 0.5W resistors are 0.1% so the 220 ohm's. All .56 ohm are 2% and not matched... On which resistors are you targetting? The output resistors (stay cold) the 0.56 bias (stay cold) or others?

Hmmm... I will look further!

Thanks alot for the compliment!

Edwin
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Old 1st June 2003, 05:18 PM   #6
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Quote:
Originally posted by grataku


Never mind the 10ma or 20 ma, you got to measure the voltage on the 390 ohms resistors and make sure it's the same.

One is 4.63V and one is 4.58V ... not a big difference...

My old 'test' 25W Aleph-X had 4.77V and 4.85V and only 0.048V of offset...

Edwin
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Old 1st June 2003, 05:38 PM   #7
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Default Wonderful feat, Edwin!

I hope your amp brings you many hours of joyful listening.

John
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Old 1st June 2003, 05:58 PM   #8
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Default Re: Wonderful feat, Edwin!

Quote:
Originally posted by carpenter
I hope your amp brings you many hours of joyful listening.

John

Thanks,

I forgot to thank everybody who worked on this project; ofcourse Nelson Pass, Grey Rollins, Hifizen, Carpenter and many many others who contributed to the original Aleph-X thread, Aleph-X Highpower thread and the Aleph-X PCB thread !!!

Edwin
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Old 1st June 2003, 06:38 PM   #9
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Quote:
Originally posted by Edwin Dorre



One is 4.63V and one is 4.58V ... not a big difference...

My old 'test' 25W Aleph-X had 4.77V and 4.85V and only 0.048V of offset...

Edwin

I have changed the pair but it did not help really. It fell back to 0.101V, but the values of the 390ohm resistors are now about .1V apart instead of the old .05V

I only get the DC offset away by turning up the left side bias to about .520V each resistor and turning down the bias to the right to about .435V each... Only then is the DC offset about 34mV !

Why o why?

Edwin
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Old 1st June 2003, 06:44 PM   #10
grataku is offline grataku  United States
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Quote:
Originally posted by Edwin Dorre



One is 4.63V and one is 4.58V ... not a big difference...

My old 'test' 25W Aleph-X had 4.77V and 4.85V and only 0.048V of offset...

Edwin

The difference is 50mV could certainly be better.
As far as the resistor go I was talking about the voltage drop on the .56 resistors? Are they all the same? Any difference there will probably cause the DC offset you are seeing.
Have you tried putting a couple of 100 ohms to gnd on the output to see if it helps? I have many other things you can check for.

PS A little shameless self promotion: I am the "pr" stamped on your board
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