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Old 11th February 2019, 12:53 AM   #1
tribute is offline tribute  Australia
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Default Noob question - Sorry

Hi, I have a phono amp I need +28/-28 VDC for.
So I bought this power supply from F/Bay as it said it could deliver up to +/-30DC.
LM317T 337T 317 337 Dual Voltage Regulator Adjust Power Supply Board DIY Kits Y | eBay

Build it and surprisingly it worked, but feeding it with a 30 VDC input I can only get +/- 14 VDC.

How can I achieve the voltage I need.

Cheers

Last edited by tribute; 11th February 2019 at 03:52 AM.
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Old 11th February 2019, 12:57 AM   #2
rayma is offline rayma  United States
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Quote:
Originally Posted by tribute View Post
feeding it with a 30 VDC input I can only get =/- 14 VDC.
The pots should have plenty of range to get the 15V. I think you don't have the right DC inputs. If you only are using one 30VDC input, this cannot work right. You need two 25VDC inputs that are independent, and connect them in series. You probably don't have those.

Instead, use a transformer with two 18VAC secondaries, or else a center tapped 36VAC secondary. This board has the diodes and capacitors to rectify that to 25VDC. Like this: https://i.stack.imgur.com/Z3Nr6.jpg

Last edited by rayma; 11th February 2019 at 01:16 AM.
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Old 11th February 2019, 03:55 AM   #3
tribute is offline tribute  Australia
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Hi rayma, Thanks for the reply. OK 2nd nob question, if I get another 30 VDC SMPS how would I wire the unit up. Cheers
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Old 11th February 2019, 07:40 AM   #4
FauxFrench is offline FauxFrench  France
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Stack the two 30Vdc SMPS.
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Old 11th February 2019, 08:52 AM   #5
jonners is offline jonners  United Kingdom
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Note that the stated dropout is 3-5V. That means that the input DC voltage needs to be between 3V and 5V higher than the output.

Last edited by jonners; 11th February 2019 at 09:04 AM.
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Old 11th February 2019, 06:55 PM   #6
russc is offline russc  England
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Watch your SMPS outputs are not grounded.
Many are.
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Old 11th February 2019, 07:58 PM   #7
gigigirl is online now gigigirl
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HI Guys, Very timely, as I have a similar problem & this blog has answeres most of my questions.

However how do you check that the SMPS outputs are not grounded, I will bhe using 2 of these.
AC Converter 110V 220V DC 36 V MAX 6.5A 180W Regulated Transformer Power Driver 667737756664 | eBay

Cheers
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Old 11th February 2019, 08:13 PM   #8
scottjoplin is offline scottjoplin  Wales
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Old 11th February 2019, 08:14 PM   #9
FauxFrench is offline FauxFrench  France
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You connect the two SMPS to wall outlets but do NOT turn the power on. Then, take your Ohm-meter and measure the resistance between the "-" (GND) outputs of the two SMPS. Below 100KOhm resistance you should not stack them.
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Old 12th February 2019, 02:00 AM   #10
gigigirl is online now gigigirl
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Thanks for that guys. Cheers
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