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Old 12th January 2011, 01:45 PM   #901
anilva is offline anilva  India
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Default Successful Aleph J build

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Originally Posted by anilva View Post
I bought new 1uF input capacitor, unmounted the PCB from the heatsinks, replaced the old 1uF with the new one. Resoldered the removed Q3 previously and reseated the JFETs, which had gone through some bit of manhandling earlier. Checked for shorts, cleaned up and mounted back on the heatsinks.

Connected this amp board to preamp and speaker. Started playing music for the first time from this board. No problem. Gain was there, frequency response was there. Extremely delighted. Quickly changed the old test speaker to my regular Fostex fullrange, eager to hear the music.

Turned on, nothing happens. Noticed one of the wires of the primary of the transformer has come loose from the connector. Reconnected and switched on. Nothing. Checked fuse. Blown. Replaced fuse. Blown again.

Disconnected my speaker. Connected the light bulb back in series with the power and checked after replacing the fuse. Bulb glows full bright indicating short. Disconnected the amp from the power supply. Bulb comes up and turns off, indicating the problem is with the amp board.

With the amp connected back, the bulb continues to glow. Amp output measures around 220mv. Checked heatsinks for any short with the MOSFETs. No problem.

Need advice, as to how to debug the faulty board. Are the outputs blown? or is the other transistors? I am completely disappointed. I am not back to square one, but back to -10.

TIA.
My apologies to everyone first. I don't know what I was smoking last night. The fuse did blow two times. Could be because the transformer wire came out and touched something or just the power line voltage had a surge.

After I replaced the fuses and disconnected the amp and just checked the power supply, fuse did not blow. Led me to believe that there was something wrong with the amp. My first mistake.

Once I connected the bulb in series and when the light bulb started glowing bright enough, I made the second mistake - that the light should not glow at all (from my F5 testing hangover and due to whatever I was smoking).

With disappointment of having incorrectly assumed that the amp board has gone bust...I went about assembling another board. Tested the board with the bulb and had the same behavior as the supposedly "bad board". That's when the light bulb in my head truly came on. That the series bulb is not going to go off but will remain lighted (unlike a F5) when testing a Aleph J.

Then went about disconnecting the light bulb, adjusted the offset, connected the preamp input and speaker. Played music. Absolutely wonderful sound. Full impact of Mr. Pass's brilliant design. Played for sometime to let the electronics settle, readjusted the offset and now I am all set with two fully working boards.

Now the story of the discarded board - Nothing wrong with it. Works perfectly, after having replaced C1.

To sum up the experience, there were only two major problems in my Aleph J build. Both are related to faulty components. First one is using fake FETs and the second one being a faulty decoupling capacitor C1. Just that. Everything else I did was a load of BS.

Thanks for all the help and advice. This forum is super. I will come back after I have my pot, with more questions

Cheers.
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Old 12th January 2011, 01:51 PM   #902
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Glad you now have three working amps. Frustrating, but you learned a lot. Getting ready for a surround system?

Slow blow fuses...
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Old 12th January 2011, 02:47 PM   #903
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Glad you now have three working amps. Frustrating, but you learned a lot. Getting ready for a surround system?

Slow blow fuses...
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Old 12th January 2011, 05:26 PM   #904
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Old 13th January 2011, 06:14 AM   #905
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Congrats Anil. When do I listen to your AlephJ amps?
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Old 13th January 2011, 01:28 PM   #906
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Originally Posted by Samuel Jayaraj View Post
Congrats Anil. When do I listen to your AlephJ amps?
Thanks Sam. At the moment you can listen to my F5 amp. You can listen to AlephJ once I mount the boards into it's enclosure.

I am planning to use two channels of F5 and two channels of AlephJ in a biamped configuration with my Altec Onkens. Wish I could build a B5....that will be the perfect setup.

Cheers.
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Old 24th January 2011, 06:49 PM   #907
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Hello,
I need help with Aleph J...
What is the reason of changing voltage in output?
When I use input "+IN", the output shows about 300 mV and it's going down fast to about 100mV.
I set 10mV with potentiometer, but it changing again +/- 20mW
When i use input "-IN", everything is alright.
Could it be that my JFets are not matched very well, or maybe the 2sj109 is bad?

Thank you.
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Old 24th January 2011, 07:32 PM   #908
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while setting offset - you need to ground both inputs

both settings - biasschmias & output offset must be made in state of temp equilibrium of entire amp
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Old 25th January 2011, 12:33 PM   #909
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Quote:
Originally Posted by Zen Mod View Post
while setting offset - you need to ground both inputs

both settings - biasschmias & output offset must be made in state of temp equilibrium of entire amp
Hello again,
I tried to make it like you said - same problem, the output voltage is changing anyway. I do not use balanced inputs, I use RCA.
As I mentioned the problem is when I use input "+IN". The voltage is changing like this:
I turn on the amp, the output voltage – about 330mV and going down, waiting about an hour, when amp. reaches 50-60C temp, then with potentiometer I set 20…30mV in output. After 15 min. it change to –(minus)40..55mV, next 20 min. it changes to positive potential about +15mV, and so on and on (the numbers are given always changing, it just an example).
One more thing, for example I set output voltage to aprox. 0 and turned off the amp. When I turn it on output voltage is 330mV again. It just fails to set.
With the input “-IN” there are no such problems. I noticed when I just turn Amp, output voltage is showing aprox. 35mV and for an hour voltage stops to 10…8 mV and don’t go any further up or down , like it should be.
Thanks
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Old 25th January 2011, 01:06 PM   #910
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which input you'll use - that's your choice , but be sure that unused one is grounded .

what you wrote is normal behavior of all Aleph amps - nothing to worry about
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