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Old 3rd July 2007, 09:37 AM   #1
Peppe is offline Peppe  Italy
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Default Zen-like headphone amp trouble

Hallo,

I am working on my second DIY-project and exactly on 'tortello' (Marcello) project:

http://www.diyaudio.com/forums/showt...p?postid=19396

http://www.headwize.com/projects/sho...lerano_prj.htm

I used the second version of 'digi01' (Zang) boards:

New MINI ZEN Headphone Amp PCB group order...

The first time the amp worked perfect; bias set at 175 mA. After a couple of hours the bias of one channel dropped to 30 mA. The second day I monitored both channels and the bias of the broken channel started perfectly and slowly dropped to the minimum.

I checked the transistor and both the mosfets and they seem to work, also the trimmer that set the bias works ok.

In the weekend I hope to have time to fix the problem, can somebody have idea on what I have to looking for?

Thanks in advance for the answers and thanks to Marcello and Mr. Nelson to give me the possibility to have a fun with this project.

Ciao
Peppe
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Old 3rd July 2007, 09:47 AM   #2
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Q3 sholdn`t be near Q1 heatsink!
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Old 3rd July 2007, 10:03 AM   #3
Peppe is offline Peppe  Italy
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Quote:
Originally posted by bogdan_borko
Q3 sholdn`t be near Q1 heatsink!
Yes Bogdan, Q3 is far from the heatsink.

Q1 and Q2, instead, are thermally coupled and electrically isolated.
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Old 9th July 2007, 12:29 PM   #4
Peppe is offline Peppe  Italy
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Update:

I sostituited both Q3: no changing!

I inverted Q1 and Q2 from one to the other channel and now both channels have the same problem: when the temp rise the bias current goes down!

Never saw the temp raise more than 40 C.

What's strange is I made two amps: the first one works incredible well! The only difference is the imput caps, on the second one are electrolit instead non polar MKT.

Nobady have an idea to help a newebe?
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Old 9th July 2007, 02:30 PM   #5
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Hi Peppe,
check the DC voltage values as pubblished in the Headwize page: you should find similar values.
As soon as the amp goes warm and bad, re-check them all and probably you will find the problem.
Even a passive component (R2 for example...) can drift from the nominal value, and so to change the bias point of the circuit.
These problems are quite easy to discover.
Feel free to contact me, the email address is in the HW page.
Good luck!


Marcello
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Old 9th July 2007, 02:48 PM   #6
Peppe is offline Peppe  Italy
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Hi Marcello,

understud! I have time only in the week-end and hope to find the problem.

In a way to have trouble is not too bad ... probably a good way to learn more.

Thank you very much, Marcello.

Regards
Peppe
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Old 9th July 2007, 03:24 PM   #7
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Peppe:

Looks nice! What parts did you decide to use? Are those red capacitors Black Gates?!
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Old 9th July 2007, 03:35 PM   #8
Peppe is offline Peppe  Italy
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Quote:
Originally posted by luvdunhill

Looks nice! What parts did you decide to use? Are those red capacitors Black Gates?!
Thanks

No, they are Elna Cerafine for audio like the smaller ones.

The psu caps are panasonic.

Ciao
Peppe
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Old 9th July 2007, 05:08 PM   #9
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Quote:
In a way to have trouble is not too bad ... probably a good way to learn more.
Wise words!
This is the diyAudio spirit!

No jokes, if you are in trouble, please send me an email...
All the best from Chiavari

Marcello
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Old 10th July 2007, 08:31 AM   #10
Peppe is offline Peppe  Italy
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I will Marcello, I will...
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