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Help required on Logitech Z-2300 toroidal transformer

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

  1. mvs sarma

    mvs sarma Well-Known Member

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    i wondered the way you took close shots of many, many things
    and uploaded.
    at times i felt whether you used factory photos, but the mats below indicated that it could be domestic atmosphere.
    All the best for the neat restoration of the z-2300.
     
    Last edited: Jan 5, 2011
  2. RishiGuru

    RishiGuru New Member

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    Yeh, I know now, the safe bet is to keep the volume always within 50%, but when there is a volume knob, you have the right to play at any volume you want.

    It's just the weak technical components that cause the problems in computer speakers so I will be more careful from now on.

    Also, even playing at 90% volume the sound of Z-2300 is so clear, their is not a hint of distortion in the system. How?

    Even if we consider the system has 4 X TDA7296 = 4 X 60 = 240W and the transformer is 150VA = 150/1.27 = 120W so their the amplifier have a headroom of 240 - 120 = 120W.

    So is this 120W absolutely distortion free, i mean system THD < 0.05. Is that the reason why the Z-2300 plays so clearly even at 90% volume?

    Also 2 X TDA7296 for the sub will produce how much power with acceptable distortion? I wonder? Only you guys can help me out.
     
  3. mvs sarma

    mvs sarma Well-Known Member

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    i personally feel that your right would cause damage to the entire system. perhaps you forgot that you should limit the input signal to the system before being able to raise the volume control to full.
    the spec gives a input limit
    so your rights are limited and of course out of ignorance one can kill a working system. but it is not expected of persons like RishiGuru LoL.
     
  4. dave

    Dave New Member

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  5. RishiGuru

    RishiGuru New Member

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    mvs sarma, let be clear your doubts, after the toroid problem I dismantled my Z-2300 subwoofer and took out the bass driver & the amplifier bolted at the back of the subwoofer. I then posted those photos. At the same time I was digging the web & found some photos that are better taken than me. So all the photos are a mixture of mine & found on web but as a whole, all belongs to Z-2300.

    Thanks for all your help.
     
  6. RishiGuru

    RishiGuru New Member

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    The Z-2300 was hooked with my PC & the PC volume was 100%, Z-2300 volume was 90%, bass 100%.

    Well I know since I am an IT engineer I should now at least have some bit of knowledge, but I am a noob in the audio field & also how would I have ever guessed that such an underrated toroid will be used.
     
    Last edited: Jan 5, 2011
  7. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The datasheet for the TDA7296 shows that its output power is only 38W RMS into 8 ohms at low distortion when it has a plus and minus 26VDC supply that you have. The 60W rating is Mickey Mouse Music Power for a duration of only 1 second at high distortion when its power supply voltages are higher which is not real power. Real power is continuous RMS power at low distortion.
    So each satellite speaker would get 38W if the transformer was more powerful.

    The woofer is driven from two bridged ICs for an output of about 120W RMS at low distortion if the transformer was more powerful.
    If the transformer was more powerful then the total power would be 196W plus an additional 196W making heat, but the transformer can supply only about 180VA when overloaded so the total output power of the amplifiers will be about 90W which is 55W for the woofer and 17.5W for each satellite.

    Maybe the system was designed with a 400VA transformer and the spec's were written for it. But then they used a smaller transformer but didn't correct the spec's?
    Then Logitech is a liar and a cheater.
     
    Last edited: Jan 5, 2011
  8. carmusic

    carmusic New Member

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    logitech is cheater and a lot of other companys also (you can list all manufacturer here for the low buget amplifier, receiver) (they have the choice as labelling 120W rms and not selling it or rate it at 200w and get few complaints and sell a lot of them)

    ive just recheck the post and i have a old D-box subwoofer for home theatre (20 years old, i have passe 2 subwoofer in it) that is labeled as 100w rms (10 inch sub) and power consupmtion is over 200W the heatsink is about 3-4 times bigger than the one on logitech!
     
    Last edited: Jan 5, 2011
  9. RishiGuru

    RishiGuru New Member

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    audioguru, I do have a question. I downloaded the TDA7295 (80W) & TDA7296 (60W) spec sheets from the web. Now looking at the output power vs supply voltage graphs I found out that both this power amps at 26VDC (toroid secondary output) produce 38W @ 0.5% THD. Its only when we increase the supply voltage, that TDA7295 is capable of delivering more power.

    But, since we know that Z-2300 toroid can do 26VDC,

    1) Applying 2 X TDA7295 for the sub woofer produces 38 X 2 = 76W @ 0.5% THD @ 26VDC
    2) Applying 2 X TDA7296 will produce the same power which is 38 X 2 = 76W @ 0.5% THD @ 26VDC

    So from a logical point, applying two TDA7295 is a waste of money at 26VDC since both produce same power. Am I right?. Or do TDA7295 have a slight advantage at 26VDC? What do think think about it?
     
    Last edited: Jan 6, 2011
  10. carmusic

    carmusic New Member

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    maybe 7295 is more reliable at high power then the 7296 and Maybe the same pcb is used on several model of logitech with higher power they just change the transformer capacity and voltage.
     
  11. RishiGuru

    RishiGuru New Member

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    Yes, that maybe one of the reasons, but as I see of now there is a high possibility that the second version of Z-2300 used 2 X TDA7296 instead of 2 X TDA7295 of the first version bridged together for the subwoofer. At least performance wise their will be no difference noticeable provided they use the same 26VDC toroid.

    Also I made another discovery, correct me if I am wrong, a Class-AB power amp at a certain voltage, the heat dissipation is not a constant 50%, i.e power dissipation varies with output power.

    Let say at 20W power output, power dissipation maybe 20W i.e. 50%

    Again at 40W power output, power dissipation maybe 10W i.e.25%

    TDA7296 at +/- 24V produces 46W power output at a certain point, when power dissipation is just 9W i.e. only 20%. So, effeciency of TDA7296 at this point is 80%.

    Efficiency is near their of Class-D. Remarkable
     
    Last edited: Jan 6, 2011
  12. mvs sarma

    mvs sarma Well-Known Member

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    if used within the spec, i really feel even the present one serves well for you in a domestic atmosphere, unless you have halls of size of a theatre or mini.
     
  13. RishiGuru

    RishiGuru New Member

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    I understand you do not like sound that is too loud, and I respect that, but I was talking about the difference of performance at a certain input voltage of TDA7295 & TDA296 from a technical aspect.

    Anyway got the toroid back from the shop, and have already bolted the toroid inside the subwoofer. I will now start soldering the secondary wires to the board & the primary to the AC input socket. Wish me luck. Hope nothing else have blown.
     
  14. mvs sarma

    mvs sarma Well-Known Member

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    all the best. RISHI jee
    leave it
    high or low volumes depend on personal habits and also changing age
    when i was at 23 or so i too liked blasting music and especially SoulDrums and Superdrums, Let there be Drums, teen tall etc of SANDY NELSON in 1970s
     
    Last edited: Jan 6, 2011
  15. RishiGuru

    RishiGuru New Member

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    The king is back!!!!!!!!!! I know this is an overstatement, but finally after a lot of what is the VA rating.............., which toroid will be the best........................., found the VA rating............................, puny little toroid..........................., Logitech sucks.................... finally the system is alive again.

    Currently playing a Kenny G "Paradise" track at 25% volume, 50% bass with PC volume set at 50%. Smooth sound with no crackles or distortion. Transformer is slightly hot which is normal, I will observe today & through out next day & update all off you.

    Finally, I want to thank all you TECH GURUS of electro-tech-online who participated in this thread and helped me to find a way to fix this problem, not to mention countless insights to how each equipment of an audio amplifier works. I already feel 10 times smarter.

    I want to continue this thread a little bit more and will appreciate if someone could provide their thought about the bridged TDA7295 or TDA7296 situation, advantages of one over the other at 26 VDC as described in my previous posts.

    Thanking you all, RishiGuru
     
  16. mvs sarma

    mvs sarma Well-Known Member

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    CONGRATS and all the best guru jee
    thanks Audioguru and many other friends and our super moderator, NIGEL.

    for Rishi the new year started well
     
    Last edited: Jan 6, 2011
  17. audioguru

    audioguru Well-Known Member Most Helpful Member

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    No.
    Bridging two amplifiers almost doubles the output voltage swing and almost doubles the current in the speaker. So the output power is (almost 4 times) a little more than 3 times as much as with a single amplifier (120W instead of 38W). Each TDA7296 has an output of 60W RMS which is too high for them. TDA7295 ICs would still be overloaded but would be more reliable. But the puny transformer limits the output power to about 55W/2= 27.5W for each IC in the bridged amplifier which is fine.

    No.
    A single TDA7296 clips when its output is only 38W into 8 ohms with your plus and minus 26V supply (not 46W). Its power dissipation (heating) shows to be 16W so its efficiency is 70% which is pretty good for a class-AB amplifier. The power dissipation increases when the output power is reduced to half.
     
  18. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The percentage of the volume, bass or pc volume controls do not allow you to calculate how much output power. The controls are logarithmic, not linear and the input signal level is not controlled by anything.

    IF the amplifier's gain and input signal level are controlled so that the output has its rated 38W into each satellite speaker when the volume control is turned to max (but of course the gain is much higher) then when the volume control is turned down to 50% the output power is 1/10th at 3.8W not half at 19W.

    Any half-decent modern amplifier has very low distortion when its output is not clipping.
     
  19. RishiGuru

    RishiGuru New Member

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    audioguru, you are a great teacher. I mean, I have posted the same problem in many forums, but no one can describe the solution to a problem in a such lucid language with layman terms that even a noob like me understands just by reading once. Thanks a lot for this help.

    So, let me clarify
    1) Two TDA7296 bridged together will provide a little more than three times the power of a single TDA7296.

    Since TDA7296 produces 38W @ 0.5% THD @ 26 VDC,
    2 X TDA7296 = 38 X 3 = over 114W =~ 120W.

    You said before: "The datasheet for the TDA7295 amplifier IC shows that it begins to clip when the bridged amplifier for the sub-woofer has an output of only 96W into 8 ohms."

    Will the THD of the bridged TDA7296 amplifier be 0.5% at 120W?

    2) Also TDA7296 power dissipation (heating) at 38W @ 0.5% THD @ 26 VDC shows to be 16W so its efficiency is 70% which is pretty good for a class-AB amplifier. The power dissipation increases when the output power is reduced to half.

    Again since the 150.9VA transformer can supply only about 180VA when overloaded so the total output power of the four TDA7296 amplifiers will be 70% of that at max volume which is approx (180/100) * 70 = 126W

    Since Logitech stated 200W --> 120W(Sub) + 80W (Satellites)
    Ratio of power distribution :: 3:2

    So, the sub gets (126/5) * 3 =~ 76W while each satellites get 25W

    Now, 76W to the bridged TDA7296 which is 76/2 = 38W for each of the two amps.
    [Note: Here why don't we do 76/3 = 25W ???]

    3) What is the max output & efficiency of the TDA7295 at the clipping point @ 8 ohms @ 0.5 THD @ 26 VDC? I cannot find it from the graphs of the spec sheet.

    4) Lastly, if I replace all this 60W TDA7296 chips with 100W TDA7294 chips, will it harm the other components of the amplifier? Or rather will the amplifier be more robust ?

    I know I have asked a lot of questions, but at the same time I know you are the one who can help me out? I will love if anybody answers this questions.

    Thanking you, RishiGuru
     
    Last edited: Jan 6, 2011
  20. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The datasheet does not have enough details about bridging so I guessed that the output will be somewhere from 96W at 0.09% distortion to 120W at 0.5% distortion. You can't hear any difference between 96W of music or 120W of music since our hearing's sentitivity to loudness is logarithmic. Ten times the power sounds only twice as loud.

    That is correct now that we looked at the 70% efficiency when the amplifiers are just clipping a little.
    But the momentary power is higher before the filter capacitors discharge too low.

    It is probably 70% like the weaker one.

    I didn't look to see if the more powerful TDA7294 will work in the circuit for the weaker ones. They all might be the same and are tested to see their max voltage, max current and max power. If they are all the same then the TDA7294 ICs will not make any difference because the puny cheap transformer is limiting the continuous output power.
     
  21. RishiGuru

    RishiGuru New Member

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    Also AudioGuru, looking at the fact that the amp has 4 X TDA7296 each capable of handling a max of 5 ampere which brings a total of 20A peak.

    Now the transformer is rated 150.9 --> 20.1V X 2, 3.75A

    Dividing the system current to the four TDA7296 = 3.75/4 = 0.94A for each TDA.

    Also voltage applied to each TDA7296 = +/-20.1 = 40.2V

    Since Watt = Volts X Ampere
    = 40.2 X 0.94A
    = 37.79 = 38W

    This exactly matches with what you said "TDA7296 produces 38W @ 0.5% THD @ 8 ohms @ 26 VDC".

    What is your say on this?
     
    Last edited: Jan 6, 2011

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