12 VAC power supply for audio amp - diyAudio
Go Back   Home > Forums > Amplifiers > Power Supplies
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 10th January 2017, 07:36 AM   #1
DIM44 is offline DIM44  South Africa
diyAudio Member
 
Join Date: Nov 2016
Location: urban
Default 12 VAC power supply for audio amp

My question may sound dumb but I really have been looking and cannot find much on AC power supplies, either kits to build or ready built items for my audio amp that requires 12 Volts 2 amp AC current. There are plenty of materials for DC output units and some adapters for AC output but these are invariably in the 500MA output range and insufficient for my application.
Can some kind soul please point a newbie in the right direction? I will build one if I can finds some schematics or even buy a ready made to get my amp going.
Our mains current is 230VAC 60 cycles.
Thanks
Nico
  Reply With Quote
Old 10th January 2017, 07:52 AM   #2
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
It would help to know a bit more about the amp you want to power because ultimately all amps will require the supply to be DC.

If you really do need just 12 volts AC at 2 amp capability then you are looking at a single transformer of appropriate rating.

I somehow don't think that is what you mean though
__________________
-------------------------------------------------------
Installing and using LTspice IV. From beginner to advanced.
  Reply With Quote
Old 10th January 2017, 09:31 AM   #3
DIM44 is offline DIM44  South Africa
diyAudio Member
 
Join Date: Nov 2016
Location: urban
Thanks.
Follow the link below to the item I have in mind.
Hope the information is sufficient.
Nico

NE5532 OP-AMP HIFI Amplifier Preamplifier Volume Tone Control Board Sale - Banggood.com
  Reply With Quote
Old 10th January 2017, 10:13 AM   #4
LLPe is offline LLPe  Denmark
diyAudio Member
 
Join Date: Apr 2009
Hi

With 2 NE5532 the current consumption would be max 30mA DC, and from the photos on the page you referred to, the power input states "AC-GND-AC", so what you are looking for is a transformer with the rating 12-0-12VAC, app 100mA or minimum 2VA (not A) should do the trick. The 2A you referred to is the VA (Volt Ampere) wich translates to 2VA/(12VAC+12VAC) = 83mA. Usually this means a small PCB mounted transformer.

On the face of it, 12VAC is a bit on low side (12V * 1,41 = 17V, a bit low for the LM7815 and LM7915), but these tiny transformers have a much higher output voltage when not loaded, around 15-16 V would be my guess. In this case the current consumption is quite low (20-30mA) so there should be no problem.

Lars
  Reply With Quote
Old 10th January 2017, 11:03 AM   #5
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
You need a mains transformer.
12Vac is a bit low, but should work. I'd prefer to use a 15Vac transformer to feed 15V regulators.

Now the details.
you need either a centre tapped transformer 230:12-0-12vac of about 5VA or higher.
Or you can use a dual secondary 230:0-12, 0-12Vac again >=5VA - And convert this to centre tapped.

A 5VA transformer has a maximum continous output current of 5/(12+12) = 208mAac
When fed into a capacitor input filter you must de-rate that to ~ half ending up with ~ 110mAdc This will make the transformer run hot.
To operate cooler I suggest your maximum continuous DC current be limited to ~ 50% of that maximum, i.e. 55mAdc and that is plenty to operate that tone control circuit.
A typical quiescent current for the 5532 is 8mA total for both channels, but the maximum is specified as 16mA. Each regulator could take another 5mA back to the centre tap.
Two 5532 could theoretically draw 32mA (+5mA for reg.) of quiescent current continuously. In addition any output current has to be added to that, but this addition is not continuous. So the 55mA from the 5VA is sufficient.

BTW,
a 15-0-15Vac 5VA has a maximum continuosu AC current of 166mAac and I recommend a maximum continuous DC current after the capacitor input filter of 42mAdc. Note this still exceeds the absolute max of 37mA quiescent for the two 5532+regs.

DO NOT use a 2VA transformer !!!!!!!!
__________________
regards Andrew T.
Sent from my desktop computer using a keyboard

Last edited by AndrewT; 10th January 2017 at 11:10 AM.
  Reply With Quote
Old 10th January 2017, 12:13 PM   #6
DIM44 is offline DIM44  South Africa
diyAudio Member
 
Join Date: Nov 2016
Location: urban
Thanks for the inputs.

I have a number of small PCB transformers scavenged from old crt monitors, pc main boards etc and will look at what I have there first but perhaps purchasing a new one with the correct pecs might be more prudent.
Since I am a little confused, not having any electronic experience or knowledge perhaps someone could write me the specs I should search for in sourcing attempts. We have a local RS Components where I usually get what I need - if I know what to specify.

Thanks again.

Nico
  Reply With Quote
Old 10th January 2017, 12:36 PM   #7
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally Posted by DIM44 View Post
............... We have a local RS Components where I usually get what I need - if I know what to specify..........
Quote:
centre tapped transformer 230:12-0-12vac of about 5VA
dual secondary 230:0-12, 0-12Vac again >=5VA
__________________
regards Andrew T.
Sent from my desktop computer using a keyboard
  Reply With Quote
Old 10th January 2017, 12:45 PM   #8
DIM44 is offline DIM44  South Africa
diyAudio Member
 
Join Date: Nov 2016
Location: urban
Thanks Andrew!
  Reply With Quote
Old 10th January 2017, 01:19 PM   #9
DIM44 is offline DIM44  South Africa
diyAudio Member
 
Join Date: Nov 2016
Location: urban
Here are the ones I have found. The prices are similar with the toiroidal slightly more expensive but quite affordable. I tend to lean towards the toiroidal 15VAC but advice will be welcome if these are indeed the right ones...

Toiroidal transformers
12VAC

Primary Voltage Rating
115V ac, 230V ac

Secondary Voltage Rating
2 x 12V ac

Power Rating
5VA

Number of Outputs
2

Secondary Current
208mA

Weight
144g

Dimensions
49.7 x 49.7 x 19.5mm

Minimum Operating Frequency
50Hz

Maximum Operating Frequency
60Hz

Mounting Type
PCB

Termination Type
Pin

Fixing Hole Diameter
M4

Maximum Temperature
+60C

15VAC
Primary Voltage Rating
115V ac, 230V ac

Secondary Voltage Rating
2 x 15V ac

Power Rating
5VA

Number of Outputs
2

Secondary Current
167mA

Weight
144g

Dimensions
49.7 x 49.7 x 19.5mm

Minimum Operating Frequency
50Hz

Maximum Operating Frequency
60Hz

Mounting Type
PCB

Termination Type
Pin

Fixing Hole Diameter
M4

Maximum Temperature
+60C

Mains transformers
15VAC

Secondary Voltage Rating
15V ac

Power Rating
5VA

Primary Voltage Rating
230V ac

Number of Outputs
2

Length
44mm

Width
33mm

Depth
37mm

Dimensions
44 x 33 x 37mm

Weight
190g

Mounting Type
Through Hole

Maximum Temperature
+50C

12VAC

Secondary Voltage Rating
12V ac

Power Rating
5VA

Primary Voltage Rating
230V ac

Number of Outputs
2

Length
44.25mm

Depth
32.25mm

Dimensions
44.25 x 37 x 32.25mm

Weight
200g

Mounting Type
Through Hole

Maximum Temperature
+50C

Minimum Operating Frequency
50Hz

Maximum Operating Frequency
60Hz

Nico
  Reply With Quote
Old 10th January 2017, 02:28 PM   #10
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
build a Mains Bulb Tester.
use it to power on any new project or any modified project.
__________________
regards Andrew T.
Sent from my desktop computer using a keyboard
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
300V & 12.6V regulated power supply. totaltech Power Supplies 1 24th November 2016 07:33 PM
Great Class D power supply 12 VDC - 17 AMP!!! tabarddn Class D 7 20th June 2016 09:33 PM
12 Volt 30 Amp Power Supply andreyambalov Power Supplies 22 17th November 2014 07:25 PM
Trouble Designing -/+12 & 24V power supply ZLyzen Power Supplies 43 23rd December 2011 12:00 AM
Convert 230 VAC amp to 120 VAC?? chuck55 Solid State 8 7th February 2006 02:22 PM


New To Site? Need Help?

All times are GMT. The time now is 07:46 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2
Wiki