Transformer Help -What do I need

Discussion in 'The Projects Forum' started by piers, Jul 8, 2012.

  1. piers

    Thread Starter New Member

    May 19, 2009
    I'm trying build the attached circuit, it's a PSU for an audio mixer..

    The 17v is the supply for the mixer itself, the 48v is the Phantom Microphone supply.

    I have NO idea of transformers but the circuit is built and ready..

    I thing trying to get a transformer that will supply both voltages will be tough, so I've settled on the 17v supply and if necessary I'll add a second transformer for the 48v.

    Question is this... Can someone please help the newbie with some advice as to what transformer(s) I'll need please?

    I've scanned farnell and CPC but I don't really have a clue..


  2. paulktreg

    AAC Fanatic!

    Jun 2, 2008
    The transformer is probably custom made for Studiomaster it's the only component that is a "safety critical component".

    It will be difficult to find a transformer that gives 46VAC off load, maybe something with a 40VAC rated output? CPC do this transformer that may do the job. It's 12VA so more than enough and if you put the two 20VAC output windings in series it should provide the required voltage.

    The 20-0-20 transformer is also quoted as no load so something 18-0-18 may be OK. The circuit calls for approximately 1A (fused at 1.6A). The nearest I can find at CPC is this.

    My suggestions may do the job but it may be difficult to get the no load voltage outputs spot-on so just be careful.
  3. crutschow


    Mar 14, 2008
    Based upon the schematic, you need one transformer with 46Vac (48Vac should be ok) output at about 150mA and a second transformer output with a center-tap 20Vac output rated about 1.5A. Both should have an input rated for either 120V 60Hz or 240V 50Hz as needed for your mains supply.
  4. #12


    Nov 30, 2010
    I can see the suck at Farnell. A dual 20V with dual input windings and 6VA: VTX-120-006-520
    I don't even know what CPC is.
    Should make the 48V @ .1A
    (40 x sqrt2) -2.8 - 3 = 50.76 volts available for the 48 you need.
    56.57V x .1a = 5.657VA
    Better use the 12 va transformer with dual 20V windings.

    Problems include:
    Not knowing what country you are in
    Trying to use the specs on the drawing of the transformer instead of calculating the needed part
    Not knowing if you really need dual input voltages
    Farnell UK not listing the power line frequency

    What seems very simple can be a big PIB when it comes time to buy parts!
    And don't worry about the OMG! SAFETY CRITICAL!!
    This schematic has fuses out the ying-yang.
    What more can you do if you're worried about that? Put it all in a metal box or buy a transformer that is fully encased.
  5. Bernard

    AAC Fanatic!

    Aug 7, 2008
    If in desperation:
    "Wall" transformer, 120V 60 HZ, sec 24 V AC, @ 2 A; two in series aiding for 48 V supply, two in series, aiding as center tapped 24-24 V for +- 17 V supplies. US $ 2.40 ea on sale SN: G18960, Electonic Goldmine.
  6. szhighstar


    Jun 26, 2012
    it is lamination transformer, one input winding, and two ouput winding, one is for 48V and other is for 17V, advise to use bobbin with two chambers, input winding is wounded in one chamber, two output windings are wounded in other chamber, add two layer of polyester tape between two winding.
  7. paulktreg

    AAC Fanatic!

    Jun 2, 2008
    CPC are owned by Farnell and based in the UK so the OP is probably UK based?
    #12 likes this.