CD-PRO2 Power Supply (Alessandro Galavotti design) problems - diyAudio
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Old 23rd November 2003, 04:34 PM   #1
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Question CD-PRO2 Power Supply (Alessandro Galavotti design) problems

Hello all,

I have followed the plans Alessandro made for his power supply unit but I am having problems with the negative section and I was wondering if you could help...

I have followed the power supply test of Nico (http://www.daisy-laser.nl/homeoptics/page22.html) and in Step 2, I am reading a voltage of -13.7 V instead of the -22V that should come. This is with the potentiometer at maximum, I get far smaller values with the potentiometer down. Is this the normal value for your circuit, or have I done something wrong?

I have followed the plan exactly, the only difference is that the fourth transformer (the 28V one) I had to replace with a 36V one (they couldn't get one at my store). Could this be the reason?

Also, when I try to read the voltage on the zener diode, I read 16V. I think I should be reading 22 Volts, no? (Could it be that the Zener Diode is broken?)

I realise that your time is precious, but I have been spending the last 5 weeks trying to work out what was wrong, and I write to you out of despair!

Kind regards from Germany,
Andrew
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Old 30th November 2003, 05:58 PM   #2
wazzup is offline wazzup  Netherlands
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Hi,

I had some difficulties understanding the scematic at first, I`m also building the cdpro2 using his schematics.

Ok, It is quite simple -errr- the way he gets his negative volts, is by switching polarity. -Connect the - where normaly the + would be, and the other way around.-

By using a bigger transformer u are getting a less negative voltage. So I think u need to put an other transformer in there, like the one he uses, or use a regulator.
The fourth transformer must be 8, the fifth 28.

Are u sure you`re getting a POSITIVE 13.... volt? U might be measuring wrong. - -

I`m no expert, but maybe this helps, btw Nico might also be able to anwser your question ; he`s a really nice guy.

Plz keep us updated!

Good luck.
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Old 2nd December 2003, 06:18 PM   #3
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I got the answer from Alessandro direct:

Hi Andrew,
the problem you're reporting probably lies in the 4.7K resistor before the
zener. Try lover its value: 2,2K should work fine provided you have a 1W
zener. chek the voltage and if necessary lowera bit more ( i.e. 1K ).

The display should work fine with 15-20 volts anyway: I'm using my with 11
Volts. Keeping brigtness at a low value increase the life of the display.
Hope this helps & Keep me informed.

Bye
alessandro

Hi andrew,
I forgot another tip: first of all disconnect the 10K fixed resistor in
parallel with the brigtness pots.
Bye
Alessandro

I disconnected the 10k resistor, and hey presto!

Wish I had more knowledge, but it's working - now to order the thing!!!!

Andrew
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Old 2nd December 2003, 08:19 PM   #4
wazzup is offline wazzup  Netherlands
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Thats great news! I`m looking forward to see your cd pro2 on this site.
My power supply has yet to be completed, so I have no idea what it will sound like.

Btw, what caps do u use in the ps?

Rikkert
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