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Old 7th November 2008, 03:39 AM   #1
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Default zen v1 build problems????

ok so i just finished my first zen amp. i biased it at 3 amps using the .22ohm resistor for r1 i also used a 30v secondary power supply with the goal of using a choke and cap. i was lead to believe after reading online that the choke would add resistance to the voltage and would reduce the input voltage back down to 34v but for some reason when i powered this puppy up i was getting 42-43v @1.4 times the rated ac secondary voltage. was there something i am missing here? so of course i assumed everything was good to go originally so i expected all to work when powered up but nothing happened. nothing got warm. nothing popped or smoked. i found power after r1 to be equal to the input power where mr. pass says i should see .66 volts. i have zero volts at the drains of the mosfets. i am so lost right now. any help would be greatly appreciated as i am tired of reading how awsome this amp will sound and want so bad to here mr. pass's creation.

note the picture is before i added the main power feed, i used a 6 amp fuse which does not blow obviously because there is no draw........?


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Old 7th November 2008, 03:51 AM   #2
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Zero volts on the source resistors means no current is flowing. Zero volts on the drain means there's no power on the board.

Make sure you have all components wired correctly.

Go around with a voltmeter and make sure power is getting to the board. Do you have volts on both sides of the filter chokes?

This has got to be a very simple mistake. Just take some time and go through with a clear head - you will find your mistake.

The reason you power supply is so high is that there is no load so the caps are charging up to the peak voltage (=1.414 X rms (rated) voltage) when you start drawing your 2x3A the rail will drop.

Good luck!
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Old 7th November 2008, 12:10 PM   #3
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Your voltage is higher than the schematic asks for, but it is not bound to be a problem.

I have played a bit around with pushing things a lot harder than the 3A 30V, and have actually found big benefits of doing so.

What I would do for a start, would be to lower the bias to 2A, to not push the envelope to hard, till you know everything is working properly. Simply replace the 0R22 with 0R33.

Once you got it running, doing as Iain says, you can see if you got enough heatsinking to push it harder. I have had a similar circuit running at above 45V at 3A bias, but the heatsinking capabilities of your chassis is crucial to success.


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Old 7th November 2008, 10:06 PM   #4
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after checking i have found that i do have power to the board. i checked power between r1 and negative at the rectifier and it shows 42-43v.
both channels are acting exactly the same way.
i also have power at the outs of the chokes.
the mosfets are wired correctly per manufacturer's diagram which is why i had to remotely wire them to correct the piouts.
thanks guys for the help! please if you have any other ideas let me know.
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Old 7th November 2008, 10:06 PM   #5
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ok i screwed up here. i do have power at the drains. the power is the same as the input power bu the amp isnt drawing any current. any new ideas?
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Old 7th November 2008, 10:27 PM   #6
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It is apparent that this is being conducted via email to me as well, so I
officially move the discussion here.

Clearly with 40+ volts on the Drains Q1 is not conducting any current. What
is the Gate to ground DC voltage on Q1?

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Old 7th November 2008, 10:34 PM   #7
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can you post your schematic?
is it this one?
http://www.passdiy.com/pdf/zenamp.pdf

So the full 43V supply is appearing across the drain-source of the FET?

How many volts on the gate of the top FET Q2?

edit: you're in good hands now!
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Old 7th November 2008, 11:07 PM   #8
Magura is offline Magura  Denmark
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Just a thought, I have seen people turn the board upside down, and hence getting the mosfets mounted mirrored.

Make sure it's the source pin of the 9240 that is connected to the power resistor, and that the drain pins of the 9240 and 240 are connected.


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Old 8th November 2008, 12:14 AM   #9
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ok the gate at Q1 on both channels shows zero volts when the negative probe is on the negative out of the choke and /or the negative out of the bridge rectifier. there are 0 ohms between ground and the gates of Q1 on both channels. if i put the negative probe on the gate/s and positive probe to positive out of the choke i read @43v--- rated power in
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Old 8th November 2008, 12:14 AM   #10
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Q2 gate has 43v when probe is on posiive input
yes Q2 shows 43v across drain-source
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