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Old 18th November 2011, 06:51 PM   #1
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Default Pearl Phono Rev 1 - Help

The top view of stuffed PCB -
Click the image to open in full size.

This is the ground wire that connects the signal ground to the negative lead of C15 - power ground. As recall I read somewhere that it was suggested as one of the grounding options for this board, and that the signal ground and power ground needed to be connect at some point. However, I could find no mention of it in Wayne's paper, but think it maybe was mentioned in a follow up, or letter in aX or something.

Click the image to open in full size.

Anyway, I cut wire when I was having difficulty powering up the board. When I first powered it up I used a 48v regulated supply with short circuit protection. When I powered it up with the wire cut the voltage very gradually increased to 48v.

Click the image to open in full size.

Now, I'm thinking that the wire was not a problem, and that the external power supply was having a difficult time charging up the 30,000uF of capacitance, because of the way the short circuit protection worked. It would allow a certain amount of current and then stop for a couple seconds and turn again allowing some current.

Anyway, I'm not sure, so I'm looking for help. Is the grounding wire okay? I don't see a problem with it except this is a four layer board, and just wasn't sure if I connected something I shouldn't by putting that wire there.

And, another problem - I get 25v at the emitters of Q5 and Q4 which should be 11.7volts and 13.8 volts respectively. Any thoughts/advice?
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Old 18th November 2011, 07:33 PM   #2
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Hello

I've had the same problem in the area of ​​the Q5 and Q3.

I have changed ZTX450 until a voltage of about 13 volts in the area of ​​Q4, but I could not drop below 17 volts in the area of ​​Q5 in both channels.

Still, now I'm using my Pearl with no problem.

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Old 18th November 2011, 09:14 PM   #3
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Thanks Blackdod,

I looked at your thread and someone mentioned something about a possible ground problem. I think that may explain why I'm having the 25v at emitters of Q3 and Q4 since I cut that wire which connected the signal ground to power ground.

I assume you've connected the output signal grounds to power ground at some point? I will try connecting that ground wire again and see if I can get it to power up.

John
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Old 18th November 2011, 09:33 PM   #4
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Okay, just tried connecting the wire and the power supply won't charge the large caps above 11 volts. The goes up to 11, drops down to ten, back to 11, drops to 10 .....

Hmmm ... could still just be the power supply I'm using. With the circuit pulling more current with the ground properly connected, the supply may not be able to charge the large caps, due to it short circuit protection.

But, I don't know.
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Old 18th November 2011, 09:36 PM   #5
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Hello

Nar advised me that the same

I connected the outputs GND to the GND power at the same point by means of a shielded cable as my Pearl is separated from the PSU. Now, I have no noise.

With regard to problems in Q5, Ive checked a several times and can not find where the problem is. I have both channels equally.

Despite this, I'm listening right now my Pearl with no problem.

Have you heard yours?

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Old 18th November 2011, 09:41 PM   #6
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Quote:
Originally Posted by Johnloudb View Post
Okay, just tried connecting the wire and the power supply won't charge the large caps above 11 volts. The goes up to 11, drops down to ten, back to 11, drops to 10 .....
Tomorrow measure the voltage again and I will comment my data.

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Old 19th November 2011, 05:13 PM   #7
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Okay, everything works perfect now. I tried a battery power supply and it works fine.

9.8v at Q5 and 13.7 at Q4. The only reason the voltage at Q5 is 9.8 is because I mistakenly used a 11k ohm resistor R18 - but it should be fine like that. I'll change it to 10k if I'm unhappy with it, but I'll probably be happy.
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Old 19th November 2011, 05:54 PM   #8
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Originally Posted by Johnloudb View Post
Okay, everything works perfect now. I tried a battery power supply and it works fine.

9.8v at Q5 and 13.7 at Q4. The only reason the voltage at Q5 is 9.8 is because I mistakenly used a 11k ohm resistor R18 - but it should be fine like that. I'll change it to 10k if I'm unhappy with it, but I'll probably be happy.
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