I need help,AC/AC power transformer,please take time and read...

Thread Starter


Joined Jan 2, 2017
I need some help,and i hope you will understand what is bothering me.I apologize up front for my English,and for dumb questions i will probably ask you here.So,i built Objective 2 by NwAvGuy headphone amplifier from scratch(more info here http://nwavguy.blogspot.tw/2011/07/o2-headphone-amp.html this amplifier requires to be powered from AC source,it will not work if power it with DC supply.I can't find where to buy AC/AC wall transformer with EU plug(or it is too expensive).On datasheet for this amplifier it says AC power supply can be used if it is in range 14VAC-20VAC and minimum current should be 200mA(info from website

"The Objective2 accepts the following power adapter characteristics:

Type: AC-to-AC Transformer (AC/AC, not AC/DC!)
Voltage: 14VAC minimum, 20VAC maximum
Current: 200mA minimum, no maximum
Plug Size: 2.1 x 5.5mm (Inner Diameter x Outer Diameter) )

Since i can't find where to buy it I was planing to use things i already have.I have 120VA toroidal transformer,Primary winding requires 230V AC(from wall outlet) and secondary winding outputs 20V AC with maximum current of 6A,(6Ax20V=120VA(W) transformer).

NOW my question is can use this transformer to power up my amplifier.I was thinking to connect power cord to primary winding(and to wall outlet) and to connect secondary winding to AC input on amplifier.I don't want to burn my AMP because i am dumb.

I am electro technician,finished 4 years of school and i still don't know will transformer send 6A to my AMP and smoke it,or will AC devices take only the current it requires.
I believe this will work,but i want someone to confirm it.Common sense tells me if for example i connect light bulb to 200V,and it is 100W bulb it will draw 0.5A of current(W=U*I) because that is preset with bulbs input resistance(lets say 100 Ohm)...so following Ohm's law I=U/R i concluded input voltage and input resistance determine what Amperage will device draw from source.So if i am right input voltage and input resistance of my amplifier will control what current will amp draw in order to operate.

Moderators Note:
The link was corrected.


Joined Jun 4, 2014
Your link doesn't work.
That transformer will produce 20V when you draw 6A from it but its voltage will be higher at lower currents. At 200mA it might be quite a lot higher and above the acceptable voltage.

Your profile doesn't say where you are but I came across the Hornby C912 transformer which I believe is 16VAC at 800mA which should be fine. They are available on ebay UK quite cheaply with UK plug.

Thread Starter


Joined Jan 2, 2017
Sir,you are right.My amplifier can withstand max. 22VAC(due to mfgt. 10% load regulation).Considering my transformers high power it will ouput about 30-32V because of low load.I think i will buy small transformer 15V 10W...and if i am right it should output max. current of 0,67A