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Help required on Logitech Z-2300 toroidal transformer

Discussion in 'General Electronics Chat' started by RishiGuru, Dec 23, 2010.

  1. RishiGuru

    RishiGuru New Member

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    Hi, i am a newbie in this forum, and require help on my Logitech Z-2300 2.1 multimedia speaker system. My Z-2300 toroidal transformer have died and i need a replacement. But i do not know the VA rating of this transformer.

    I was also able to gather the following information from the net:

    Transformer Details
    Manufacturer: Ten Pao International Ltd.
    Model No: TOG433028F0
    Input: AC 230V/50Hz
    Output: AC 20.1V x 2
    Diameter: 95 mm;
    Height: 45 mm.
    Amperage: Unknown
    VA: Unknown

    I opened my Z-2300 subwoofer and clicked some pictures, which i am posting below:

    [​IMG]

    [​IMG]

    Based on the size - I would guess that this one is about 120VA.

    But I don't know since Z-2300 is capable to deliver 200W RMS & 400W RMS peak power.

    Z-2300 Specifications
    Total Continuous Power(RMS): 200W
    Total Peak Power(RMS): 400W

    Also Z-2300 amplifier uses

    i) Two STMicroelectronics Class-AB, 80W, TDA7295 amplifiers bridged together to provide a total of 2 X 80=160W for the subwoofer.[Assumed]

    ii) Two STMicroelectronics Class-AB, 60W, TDA7296 amplifiers powering each of the satellites.

    So, do you think since it powers 4 TDA chips, it is 300VA rather than 120VA considering its size?
     
  2. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hello,


    The woofer does 120watts and satellites 80 watts so that's a total of 200 watts so the power transformer would have to be able to deliver at least that much times 1.27 as a min, or 255 watts approximately.. 300va would be better than 260va if you got a replacement.
     
    Last edited: Dec 23, 2010
  3. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    The power rating will be highly imaginary - with the transformer unable to supply enough power - which is probably why it's failed.

    Replacing with a correct size (larger) transformer is probably a good idea - however, it's quite likely that the rest of the design (particularly the heatsinking) isn't big enough either.
     
  4. dave

    Dave New Member

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  5. crutschow

    crutschow Well-Known Member Most Helpful Member

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    If you pick a transformer with the required voltages but a larger physical size, then it should have adequate capacity and less likely to fail again.
     
  6. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hello again,


    I updated my previous post as the power demand from the dc side will be 1.27 times the ac side which is the ratio of the integral of sin(wt) over the integral of sin^2(wt). That means the transformer has to have a true rating of 255 watts to power a 200 watt output amplifier if in fact it really does so.
    I've seen too many bogus ratings too to believe any ratings on audio amps anymore anyway, and if the transformer is under rated the rest of the circuit probably is too.

    So the bottom line is buy at least a 260va (prefer 300va) transformer but never turn the volume up all the way :)

    Alternately, contact Logitech and see if you can purchase a 10 pack of these transformers for future required replacements :)
     
    Last edited: Dec 23, 2010
  7. carmusic

    carmusic New Member

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    but i doubt the subwoofer really get 120W rms, could you tell us what the consuption rating on the name plate of the system. a system can have specs of 200w but will never deliver it.
    i have a mini-hifi system which claims it has 300w rms output, but on the name plate consumption is 155W!
     
    Last edited: Dec 23, 2010
  8. RishiGuru

    RishiGuru New Member

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    Which one to choose?

    MrAl, thanks for your great insight. It really helped me out to come to a conclusion. The only thing that I currently know about my Z-2300 toroid is 2 X 20.1 V.

    From a local transformer manufacturer, I got the following choices of toroids to fit in my Z-2300 :

    1) 120 VA --> 2 x 20 V, 3.00A
    2) 120 VA --> 2 x 22 V, 2.72A

    3) 160 VA --> 2 x 18 V, 4.44A
    4) 160 VA --> 2 x 22 V, 3.63A

    5) 225 VA --> 2 x 18 V, 6.25A
    6) 225 VA --> 2 x 22 V, 5.11A

    7) 300 VA --> 2 x 18 V, 8.33A
    8) 300 VA --> 2 x 22 V, 6.82A

    Now, I want to know which one according to you will be the best replacement? Which one to choose? I am a novice in this field, and though I am an engineer(IT), I have no prior knowledge in audio field.

    Just think this Z-2300 is yours, and what toroid you have chosen to fit inside it. I am impatiently waiting for your reply.
     
  9. RishiGuru

    RishiGuru New Member

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    Am I right?

    State whether I am right or wrong

    Z-2300 toroid stated secondary = 20.1V (AC)

    TDA7296 max capacity = 35V (DC)

    Power capacitor rating = 35V (DC), 10000uF

    Transformer primary: 250V (AC)

    Transformer actual secondary:
    20.1V + 10% (mains tolerance) + perhaps 4% (transformer regulation) = 20.1 + 2.1 + 0.9 = 23V (AC)

    Passing through rectifier : Output voltage = (23V (AC) X 1.414) – 2 = 32.5 – 2 = 30.5V (DC)

    Voltage gap between TDA7296 max capacity & toroid = 35 V (DC) – 30.5 V (DC) = 4.5 V (DC)

    Voltage gap in AC = {4.5 V (DC)} / 1.414 = 3.2 V (AC)

    Max. Voltage of the toroid that can be used: 20.1V (AC) + 3.2 V (AC) = 23.4 V (AC)

    -----------------------------------------------------------------------------

    Also, in order to produce Z-2300 clamied 200W RMS one needs a transformer that is capable of to deliver a minimum of 1.27 times the claimed watt. Since Watt = Volts X Ampere = VA

    200W requires = 200 X 1.27 = 254 watt or 254VA = ~ 255VA transformer as a minimum requirement.

    Also considering Z-2300 have four TDA7296 capable of 60 X 4 = 240W

    240W requires = 240 X 1.27 = 305VA = ~ 300VA as a minimum requirement.

    My Choice : 300 VA --> 2 x 22 V, 6.82A.
     
    Last edited: Dec 25, 2010
  10. Diver300

    Diver300 Well-Known Member

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    Your calculations are right but I think that you are running too close to the 35 V limit with a 22 V transformer. I suggest buying an 18 V transformer and getting one that has a hole through the middle. You can then add a few turns to increase the voltage if needed. You will get about 0.5 V per turn on a transformer that size. You can use any sort of wire that will take the current. Transformers are made with enamelled wire so that the windings are as compact as possible, but for just a few turns it doesn't matter if you use wire that is larger diameter.
     
  11. RishiGuru

    RishiGuru New Member

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    So, you think it will be best to use a 300VA toroid with secondary output voltage of 20V ?

    I know this is a noob's question, but we always talk about output voltages but the not the ampere rating?

    After all the difference between a 120VA & 300VA transformer with same output voltages is their ampere rating. Now, suppose my system used a 120VA transformer & i replace it with a 300VA of same output voltage.

    Will the increase of ampere rating be destructive for my amplifier?
     
    Last edited: Dec 26, 2010
  12. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Only if you try and run the amplifier louder.

    With too small a transformer the transformer will overheat and fail if you run it too high, if the transformer is large enough the amplifiers will tend to run too hot (depending if they are correctly heatsinked or not).

    With a cheap make like Logitech I would imagine the heatsinks are too small as well as the transformer.

    I had a big row with Sony a number of years ago about a really nice amplifier, rated at 120W RMS per channel. One particular customer suffered multiple mains transformer failures, but the transformer was far too small - there was room for a larger transformer, and presumably it had been designed for such, but a much too small transformer had been used in production (presumably to save money).

    Sony's ultimate reply, after many months, was that they had not had many failures of the transformer - they always refused to tell me what rating the transformer was, and wouldn't admit it was too small (but it was blindingly obvious).
     
  13. RishiGuru

    RishiGuru New Member

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    Here are some pictures of the heatsink. The heatsink is 9 inch in height, 4 inches wide and 1.5 inch deep containing 9 fins. It is use to support 4 TDA7296 CLASS-AB chips.

    [​IMG]

    I am also providing some pictures of the amplifier below:

    Amplifier
    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    Torroidal tranformer
    [​IMG]

    Do you think a 300 VA --> 2 x 20 V, 7.50A will be a better option than a 300 VA --> 2 x 22 V, 6.82A. for my Z-2300 as Diver300 said?

    Kindly help me out.
     
  14. RishiGuru

    RishiGuru New Member

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    Kindly reply, I will buy the toroid that you tech gurus will recommend.
     
    Last edited: Dec 26, 2010
  15. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    The 2x20 sounds a better bet, you don't want to push it too high.

    BTW, that's not a very great heatsink for the supposed power output of the amp.
     
  16. RishiGuru

    RishiGuru New Member

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    I downloaded the TDA7296 datasheet from STMicro website. As we know TDA7296 is capable of producing 60W of power. Since TDA7296 uses 4 of them we get 4 X 60 = 240W.

    The picture of the data sheet is provided below:

    [​IMG]

    As, you said I found out it can handle a maximum input voltage of 35V, but in the power output section the chart is divided into two parts :

    1) RMS Continuous Output Power --> 30W

    2) Music Power (RMS) Δt = 1s (*) --> 60W

    What are the differences between these two types of power and why one is half of the other? And also since RMS Continuous Output Power is regarded my many as real power does that mean this chips are only capable to deliver 30W of real power?

    All, my speakers are rated at 8 ohms rather than 4 ohms which is the general norm. But TDA7296 are perfectly capable to handle 4 ohm loads.

    So, is it because the power supply [transformer + capacitors] are incapable to supply the amount of watts required at 4 ohms that the impedance of the system is increased to 8 ohms so that power supply is relieved a bit.

    But those 10,000uF, 35V capacitors in the power supply seems really monstrous and can handle a lot of load.

    [​IMG]
     
  17. mvs sarma

    mvs sarma Well-Known Member

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    If you are located in India, the same can be got rewound with reasonable efficiency. Perhaps such service is available from many countries.
    The weird thingie (lol) is a bridge rectifier. The transformer could be OK and rectifier faulty . then it shows up transformer heating up.
     
    Last edited: Dec 26, 2010
  18. #12

    #12 New Member

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    Thanks for the pictures. The way glue is used on this amplifier is very educational (to me). I'm so old that I use brackets and bolts, even if I have to make the brackets.
     
  19. mvs sarma

    mvs sarma Well-Known Member

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    In all probability, I suspect a break in primary winding. if the break is on the outer layer, Please check for any possible integrated (thermal )fuse.
    Check the voltages , if you have some means, with bridge diodes disconnected from the secondary winding. you would get 20V AC approx.
     
    Last edited: Apr 6, 2015
  20. Diver300

    Diver300 Well-Known Member

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    If you can buy a 2 x 20 V, 7.5 A transformer, that would be fine. I thought that you could only buy 18 V or 22 V at 300 VA.
     
  21. RishiGuru

    RishiGuru New Member

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    I live in Kolkata, India. mvs sarma, can you provide some names of toroidal transformer manufactures so that I can buy the toroid of Z-2300 in Kolkata.

    Transformer Details of Z-2300
    Manufacturer: Ten Pao International Ltd.
    Model No: TOG433028F0
    Input: AC 230V/50Hz
    Output: AC 20.1V x 2
    Diameter: 95 mm;
    Height: 45 mm.
    Amperage: Unknown

    Do you think it is a 120VA judging by its size?

    I have come with the name "Miracle Transformers" but their website quotes no delars in Kolkata.

    I want a 300VA , with 2 X 20V.
     
    Last edited: Dec 26, 2010

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