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Old 29th June 2003, 09:07 AM   #1
iceman is offline iceman  Sweden
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Question laptop powersupplies ?

I read this thread
Anyone use Wall warts to run a gainclone
but i dont understand how to connect 2 of these PSU. I've got 2 DELL PSU (20V 4 Amp) and i want to use them as powersupply to my GC. How do i connect them to get
+- 20V ??
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Old 29th June 2003, 06:03 PM   #2
shyfx is offline shyfx  Australia
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I suspect positive from ont to the others negative
where they meet is 0, and either side is positive and negative respective of their originally designated polarity.

By floating ground I think they mean that when they are plugged in as once, they aren't using the same ground for their negative. If this were the case then hooking them up in series like I said wouldn't be good since it would be like a short circuit.
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Old 29th June 2003, 06:08 PM   #3
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These will not sound good at all.
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Old 30th June 2003, 06:49 PM   #4
iceman is offline iceman  Sweden
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I can now answer my own question.
I just build an amp of an old Sanyo LA4282(2x11Watt).
The powersupply i use is one of the laptop-PSU i asked about.
It's an IBM an giv 16V 3.8Amp

How it's sound ??. Well i've heard better, but i build it just as Sanyo's test curcuit. No extra filter for the PSU and it's very little noise from the PSU.
I build it so i could have it at work, so its dosent matter if there is some noise
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Old 30th June 2003, 06:56 PM   #5
iceman is offline iceman  Sweden
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Here is a picture of the amp.
Attached Images
File Type: jpg untitled.jpg (45.9 KB, 224 views)
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Old 30th June 2003, 09:42 PM   #6
jleaman is offline jleaman  Belgium
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id never use any kind of switch mode psu to power a circuit like that. NEVER..
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Old 1st July 2003, 12:58 AM   #7
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Quote:
Originally posted by JasonL
id never use any kind of switch mode psu to power a circuit like that. NEVER..
you can get microvolt level noise if you use the correct switcher chip, but one of these Compaq, IBM, HP supplies is going to disappoint.
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Old 1st July 2003, 07:35 AM   #8
Dirk is offline Dirk  Belgium
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Quote:
id never use any kind of switch mode psu to power a circuit like that. NEVER..
Quote:
These will not sound good at all.
These chips have a PSRR of over 80dB, so why not give it a try?

Only a few months ago, it was common sense to think a chip amp would NEVER sound good, so why not "open yourself up to extreme possibilities" (X-files)?

Dirk
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Old 2nd July 2003, 09:46 AM   #9
gfiandy is offline gfiandy  United Kingdom
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Switching supplies and power amps are a difficult mix. The LM3875 may have a PSRR of >80dB but this is only up to about 1KHz. When you start getting noise in the 100KHz to 1MHz region where switchers put out heaps of it the PSRR is down to 40dB or less.

Fine to run it up on and check it works but if you want it to sound good I would suggest a normal transformer is a much easier approach.

Andy.
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