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:
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
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:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
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
Edwin Dorre said:
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
Edwin Dorre said:
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
Edwin Dorre said:
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
Edwin Dorre said:
Regular Aleph is different than Aleph X in that respect. Get as close as possible with voltage drop on those resistors by matching input mosfet in a circuit. You can adjust the offset by playing with a trimpot in CCS on input differential (which changes the current).
At least it worked for me.
Hi, Edwin,
Very nice amp!!!
The nicest way to reduce offset is what Peter says in post #11.
Second, I used the resistors from common input sources to outputs and I set the value at 4.7k. Bringing it further down to 2.2k increased stability of the offset.
Coupling caps at the input also helps a lot, not only for the zero offset, but also for offset drift.
I never used 100ohm resistors at the output and it works great: 1 to 2mV after 10 to 15 minutes, and very stable.
Look at http://www.diyaudio.com/forums/showthread.php?postid=173696#post173696 and you will see how I mounted the input fets; very handy to change them till they match perfectly.
There's also a post somewhere that says to first adjust V1/V3, then V2. V2 has a great infuence on offset.
These are my findings when building the amp.
What value did you use for R19/29 and for feedback and input R's?
Did you use C2/4?
/Hugo - can't wait to see pics of the finished amps.
Very nice amp!!!
The nicest way to reduce offset is what Peter says in post #11.
Second, I used the resistors from common input sources to outputs and I set the value at 4.7k. Bringing it further down to 2.2k increased stability of the offset.
Coupling caps at the input also helps a lot, not only for the zero offset, but also for offset drift.
I never used 100ohm resistors at the output and it works great: 1 to 2mV after 10 to 15 minutes, and very stable.
Look at http://www.diyaudio.com/forums/showthread.php?postid=173696#post173696 and you will see how I mounted the input fets; very handy to change them till they match perfectly.
There's also a post somewhere that says to first adjust V1/V3, then V2. V2 has a great infuence on offset.
These are my findings when building the amp.
What value did you use for R19/29 and for feedback and input R's?
Did you use C2/4?
/Hugo - can't wait to see pics of the finished amps.
Netlist,
yes, post 11 is all fine and dandy and that is what edwin is doing.
The problem he is having is that he can 0 the dc offset (practically speaking) but that brings produces a somewhat different current flow between the two sides as measured by the voltage drops on the source resistor, that is assuming that all the resistor are exactly equal of course.
yes, post 11 is all fine and dandy and that is what edwin is doing.
The problem he is having is that he can 0 the dc offset (practically speaking) but that brings produces a somewhat different current flow between the two sides as measured by the voltage drops on the source resistor, that is assuming that all the resistor are exactly equal of course.
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