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Old 30th July 2007, 02:01 AM   #1
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Default Need some Pearl help - no sound!

Hi all,

I just completed my first NP project unfortunately I need a little help. I measured the voltages as indicated on the board and 2 of 4 are No Good, both channels have the same issue, therefore I am sure I did something wrong!

Q3 - Ok - 27V (a little high)
Q4 - NG - 28V (should be 13.8)
Q5 - NG - 28V (should be 11.7)
R8 - OK - 29V

Any suggestions would be greatly appreciated.

Regards,
Pathmark
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Old 30th July 2007, 07:06 AM   #2
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I doubt I can help, but I can offer some advice anyway: post a couple pictures of your board(s). It will help others to diagnose a problem that you've stared at for too long to see clearly. Good luck!
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Old 30th July 2007, 11:41 PM   #3
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Default Still need help!

Hi all,

I was wondering if anyone has any suggestions. Again, problem appears in both boards therefore I can imagine it is some mis-build but not sure where to look.

Both Q4-Q5 are reading 28V which is not correct according to NP article. Q3 and the regulated voltage of r8 are OK. I have posted a picture of boards.


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Old 31st July 2007, 07:02 AM   #4
cviller is offline cviller  Denmark
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I can't see much on the blur, but you seem to have a problem turning on the ztx devices. Check if they are flipped or burned.

Remember: the better information you give, the more help you'll get.
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Old 1st August 2007, 11:11 PM   #5
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Sorry if the picture is not clear but the boards are identical to the NP boards from the Pearl article. I guess I am looking for more troubleshooting help on possible causes.

Again I have taken more measurements according to the NP article and none of the voltages after the regulation stage are correct.

Per the the schematic, all voltages on 2SK shoud be around 0.04 -0.07v but I am reading 29V.

So I guess I am trying to understand how that voltage can exist througout the board. It seems as though Q4-Q5 are are not doing anything. If orientation is correct is there anything else that can be wrong?

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Old 2nd August 2007, 02:21 PM   #6
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If the source voltages on all your J-FETs are reading 29 volts, then I don't see what it could be than a grounding issue. If you're using those boards from Prometheus, I think there's a ground jumper you gotta install. Have you installed that?

Kinda OT, but both the schematic, article and artwork? are the work of Wayne Colburn. Credit where it's due.
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Old 2nd August 2007, 03:40 PM   #7
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thanks for reply greyhorse, I was aware that this design was by Wayne I should have said Pass Labs not NP.

As for the grounding, I guess I am not sure about ground jumper. I do have the ground indicated in the center of the board tied to a star ground on the chassis.

Is this the jumper to which you refer or is there another?

Pathmark
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Old 2nd August 2007, 04:13 PM   #8
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Take a look at the picture attached to post #10 on the following thread.

http://www.diyaudio.com/forums/showt...97#post1247997

Notice the white line just below C15? That line shows where there should be a jumper that connects the power supply section of the board to the amplifier section. There's even an arrow pointing to it with the caption "Connect Grounds here with a soldered wire". If you haven't installed that jumper, the amplifier section of your board has no potential difference across it. Since you have no current draw, everything is reading 29V with respect to your power supply ground.
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Old 2nd August 2007, 10:51 PM   #9
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greyhorse

yup that is the ground i was talking about also. So I have this connected to star ground, which includes chassis earth from power supply and ground from lp.

I will tak a picture when i return home this weekend thanks for the help so far.

pathmark
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Old 4th August 2007, 05:41 AM   #10
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As long as your PCB -IN connection also goes to your star ground, or if your PCB -IN connection goes to your input connector ground you should be good. All we need is for some ground on the amplifier section of your board to connect to the ground in the power supply section of the board.

If your problem turns out to be the grounding, connecting all those grounds at your star ground will get you going, but there's no guarantee it will be running optimally. A star ground is usually the simplest, most sure fire way of getting acceptable results, but in a lot of cases it's not going to get you the best performance depending on your goals. If you don't install that jumper directly on the PCB, you've already modified the original layout of the PCB, probably for the worse. Because the currents running through a phono preamp are small, your problems should be minimal though.
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