Help required on Logitech Z-2300 toroidal transformer

[RishiGuru]

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:





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.

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

Total RMS Power = 80(TDA7295) + 80(TDA7295) + 60(TDA7296) + 60(TDA7296) = 280 W

I think any amplifier will produce a lot of distortion & noise at the peak. So, in order to produce distortion free sound at peak volume the amplifiers generally need to reduce its output peak power by 25% or more & also to comply with THX certification.

Reduced Total RMS Power = 60(TDA7295) + 60(TDA7295) + 40(TDA7296) + 40(TDA7296) = 200W

I think to comply with THX, Logitech have limited the power output. But i can be wrong.

So, do you think since it powers 4 TDA chips, it is 260VA rather than 120VA considering its size?

Since my Z-2300 toroid is bust, I got the following choices of toroids to fit in my Z-2300 from a local transformer manufacturer :

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 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. I am impatiently waiting for your reply.

 

[Resqueline]

I'm no autority on amplifiers or THX but here are my basic considerations:

The TDA7295 tolerates a supply voltage of up to +/- 40V while the TDA7296 only tolerates a supply voltage of up to +/- 35V. They have no dissipation limiting issues.

I'd choose the maximum size transformer I could fit in the amp. It has the advantage of having improved regulation, enabling one to choose as high a voltage as possible.

Regulation is expressed in % and is how much higher the output voltage is at no load compared to full load. Bigger tranformers have a lower (& better) % regulation number.

Secondary voltage selection: you need to allow for the highest possible mains voltage in your place and add the transformer regulation while keeping within +/-35V DC.

As it is (was) you have (had) 20.1V + 10% (mains tolerance) + perhaps 4% (transformer regulation) giving a maximum of 23V AC on the secondary side.
The resulting DC Voltage is 23VDC * 1.414 - 2VDC = +/- 30.5VDC

So it seems you can select a transformer with up to 4.5VDC / 1.414 = 3.2VAC higher secondary voltage, provided it has the same (or better) regulation. I'd go for #8 (22V).

It should give you better undistorted peak power values while still keeping the amplifiers safe. You may need to upgrade the amp mains fuses however.
Also check the secondary rectifiers and any fuses there. An upgrade there might allow you to take even better advantage of the higher transformer power capacity.

 

[RishiGuru]

I'm no autority on amplifiers or THX but here are my basic considerations:

The TDA7295 tolerates a supply voltage of up to +/- 40V while the TDA7296 only tolerates a supply voltage of up to +/- 35V. ................ Also check the secondary rectifiers and any fuses there. An upgrade there might allow you to take even better advantage of the higher transformer power capacity.

Thanks, for the reply & the explanation. It was very informative. Now i have a clear idea as of which toroid to buy & fit:
300 VA --> 2 x 22 V, 6.82A

I also have another two options which the vendor mentioned today:
1) 300 VA --> 2 x 25 V, 6.00A
2) 500 VA --> 2 x 25 V, 10.00A

But I think 25V will to much for the amp. Or will go for the number 500VA one as in #2.

Upon the topic of beefing up my secondary rectifier's (and i don't know how they look like), I am posting below the pictures below of Z-2300 amplifier board & the weird thingie which I think is the rectifier of the toroid.

Amplifier Board


Weird thingie


Now how to upgrade this rectifier for the new toroid? I have no idea?

And is it because that the TDA7296 are capable to handle +/- 35V only, that the two beefy 10,000uF power capacitors are also rated at 35V?

 

[Resqueline]

Yep, that weird thingie is a rectifier, and those metal cased ones don't come in less than 10A ratings so you don't need to do anything about that. It's good to go.
Its number (printed on one of its four sides) will reveal its rating if you want to know exactly how much it can handle.
500VA may be overkill but it won't hurt anything but your wallet. Bigger toroids can have larger turn-on (inrush) currents though which may need addressing if taken too far.
Yes, 25V is too close for comfort. There won't be enough headroom to allow for high mains voltages. Both the cap's & the TDA7296's sets the (same) limit here.

 

[RishiGuru]

Yep, that weird thingie is a rectifier, and those metal cased ones don't come in less than 10A ratings so you don't need to do anything about that. It's good to go....................Both the cap's & the TDA7296's sets the (same) limit here.

Thanks again Resqueline, I will buy the 300 VA --> 2 x 22 V, 6.82A.

Since I got you here as an expert, I have a few more questions to ask you.

First, I found this two chips a 78M18 and a 79M18. In web they are calling it +/-18V voltage regulators/ stabilizers as below:



What do they actually do? I am a novice, so kindly help me out. Do they stabilize the power coming out from the transformer and feed them to the speakers? Or do they stabilize the power and provide them to the chip amps like TDA7296?

Secondly, I found there is a JRC-4565 op-amp in by Z-2300 as shown below:



What are the difference between power amp chips like TDA7296 & operational amplifiers like JRC-4565. Both are amplifiers after all. Also in a blog i found out that this op-amp is used for the headphone socket in control pod and have no operation is powering the drivers. Z-2300 have only one op-amp.

So, is it that the Class-AB power chips are used to power the drivers where as the op-amp is used for the headphone speakers?

 

[Resqueline]

The 7xM18A's will take anything between 19V to 40V in and put out 18V. The M version can handle max 0.5A - but there's also a power loss limit.
I'd guess they're used for supplying the op-amp/pre-amp with a hum-free voltage here. +/- 18V is the maximum the 4565 can take btw.

Quoting from the datasheet: "The NJM4565 is a high-gain, wide-bandwidth, dual low noise operational amplifier capable of driving 20V peak-to-peak into 400Ω loads."
Looking at the graphs it seems it can actually drive this voltage into half of that resistance, making it capable of up to 50mA peak output current.
35mA rms only makes 40mW in 32 ohm headsets but that's usually enough for normal listening.

Actually there seems to be no functional difference at all between these TDA's and op-amp's. Only the output stage capability and the supply voltage range sets them apart.
However, in many audio power chips there are internal feedbacks that sets their gain, while op-amps always require this being set with external components.

I can't say if the JRC is used for sub filtering the signal before feeding it to the TDA7295's, or if it's used as a headphone amp. It could be either.

 

[RishiGuru]

Output power question

The 7xM18A's will take anything between 19V to 40V in and put out 18V. ..............................It could be either.

Thanks man, you solved me out. I will buy the toroid and fit it in my Z-2300. I had just one last wish which i could not fulfill, I was not able to know the actual VA rating of the toroid that came with Z-2300. It seems that Logitech deliberately do not want anyone to know the VA rating.

If Z-2300 comes with a 120VA toroid, at by the size it seems so, I do not know how Logitech can tout 200W RMS with the Z-2300.

Any light you can show upon this?

 

[Resqueline]

Hehe, audio manufacturer power ratings have never been easy to understand, suffice to say it may not be surprising that the transformer (internal thermal fuse) blew..
Size and weight are the determining factors for transformers of the same type & frequency and VA/weight(or size) can be directly compared between brands.
Transformers can however survive heavy overloading for a minute or so from a cold state, maybe that's all it takes for a manufacturer to justify making his claim.

 

[davenn]

Hehe, audio manufacturer power ratings have never been easy to understand, suffice to say it may not be surprising that the transformer (internal thermal fuse) blew..
Size and weight are the determining factors for transformers of the same type & frequency and VA/weight(or size) can be directly compared between brands.
Transformers can however survive heavy overloading for a minute or so from a cold state, maybe that's all it takes for a manufacturer to justify making his claim.

Not to mention that many domestic audio amplifier manufacturers GREATLY over-exaggerate the power output capabilities of their amplifiers. In most cases you are lucky if you get half of the power level of what they state.

Dave

 

[RishiGuru]

Abysmal power quoted my manufactures

Hehe, audio manufacturer power ratings have never been easy to understand, suffice to say it may not be surprising that the transformer (internal thermal fuse) blew..
Size and weight are the determining factors for transformers of the same type & frequency and VA/weight(or size) can be directly compared between brands.
Transformers can however survive heavy overloading for a minute or so from a cold state, maybe that's all it takes for a manufacturer to justify making his claim.

You & davenn are absolutely right. While my toroid will take three days to come, I spend some time on the web, and found some proof of the highly overrated power ratings of the current multimedia speaker systems.

Here below in the Logitech Z-Cinema quoted to have 180W RMS.



Subwoofer gets 110W where as the two satellites 70W.

Subwoofer internals



Clearly the switching power supply & the amplifier board can be seen.

Considering the case of Logitech Z-Cinema claimed 180W, I found out

1) One Philips TDA8920 100 watts Class D amplifier for the subwoofer.

2) One Philips TDA8922 50 watts Class D amplifier supplying 25W to each of the midrange speakers of the two satellites.

3) One STMicroelectronics TDA7269 20 watts Class AB amplifier supplying 10W to each of the tweeters of the two satellites.

Total maximum amplifier chip power of Z-Cinema is 100 + 50 + 20 = 170W

Now taking a closer look at the Z-Cinema's switching power supply powering the amplifier as below:



Take at even closer look at the main component of the Z-Cinema's switching power supply :



It is clearly stated, MAX TOTAL OUTPUT POWER 83.3W

The simple rule is, you are always going to get less power (Watts) from the amplifier to what you are able to deliver to the amplifier. Now if you consider that the Z-cinema amplifier is receiving 83.3 W from the switching power supply, I don't know how Logitech claims that Z-Cinema have 180W .

Anybody to help me out?

 

[Resqueline]

Hehe, yep, it's pathetic, but that's the way it's always been, even from reputable manufacturers.. Switching PSU's can't be overloaded the same way as transformers btw..
Since music has a complex and non-definable power spectrum it's pretty much up to the industry how to add up numbers.
I'll grant them that defining/measuring power is not as easy as just adding numbers, since curve peaks may come at different times and frequencies may be separated.
Look here for some info, and use Google and Wikipedia for further reading. It makes my head hurt so I won't try to research it to try to find any bottom line..
It's not all all about power anyway. One can make great/loud sound/music with only 10W, and 100W would only sound twice as loud.

 

[RishiGuru]

Hehe, yep, it's pathetic, but that's the way it's always been, even from reputable manufacturers.. Switching PSU's can't be overloaded the same way as transformers btw..It's not all all about power anyway. One can make great/loud sound/music with only 10W, and 100W would only sound twice as loud.

Resqueline, I did a math. Correct me if i am wrong.

Z-2300 uses drivers from TangBand. From their website I got the following figures:

Bass Driver --> 8 inch long throw 70W, 8 ohms Tang Band (W8-670Q)

Satellites --> 2.5 inch 12W, 8 ohms Tang Band (W3-594SB)

Total capacity of these drivers = 70 + 12 + 12 = 94W

I posted the same toroid problem in another forum, and though they were no where near you in providing a valid solution that seems at least justifiable, one of them said "one needs a transformer that is capable of to deliver a minimum of 1.27 times the claimed watt"

Example : A 200W sound system requires = 200 X 1.27 = 254VA = ~ 255VA transformer as a minimum requirement.

Now, if I consider that Z-2300 toroidal transformer is 120VA considering its size,

Amplifier is capable to deliver = 120 / 1.27 = 94W

Amazingly, the total power the drivers can handle & the amplifier output are both equal, considering it uses 120VA toroid.

 

[Resqueline]

I've seen trusty old brand speakers where the sum of the driver wattage was nowhere near the total rating on the label on the back of the speaker case.
I'd guess it has something to do with music not being anywhere near white (or pink) noise. It becomes almost like the difference between W & VA ratings.
White (or pink) noise would strain the transformer to the full sum of the individual wattages, while music only loads some frequency bands simultaneously.

The 1.27 number may be true for class AB amp's while it could go below 1.1 for class D amp's. It is simply the inverse of their different efficiency numbers at full power.

So, amazingly there seems to have been a reason behind their component selection after all... Good detective work there!

So next time you may have to buy new drivers instead of the transformer..

 

[RishiGuru]

I've seen trusty old brand speakers where the sum of the driver wattage was nowhere near the total rating on the label on the back of the speaker case. ... Good detective work there!

Resqueline, 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:



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.

 

[Resqueline]

Apart from the obvious differences; 10% vs. 0.5% distortion and the different supply voltages, notice the asterisk there:
"Note (*):
MUSIC POWER is the maximal power which the amplifier is capable of producing across the rated load resistance (regardless of non linearity)
1 sec after the application of a sinusoidal input signal of frequency 1KHz."

Music power is the short burst capability of a complete amplifier. It is dependent on the transformer & capacitor sizes, and is not very applicable to a chip only (of this type).

Look at the curves "Output Power vs. Supply Voltage." at page 6 for the "full" story.
Notice you can get 4W more in 8 ohms compared to 4 ohms. That is pretty much due to the peak current limit of 5A in that chip, giving a max of 50W rms in 4 ohms.
The 54W in 8 ohm (= 29.4V peak) "limit" is obviously due to the supply voltage of +/- 30V. With a +/- 35V supply it would be able to drive 74W rms sine in 8 ohms.

The "ideal" load impedance for this chip appears to be 6.88 ohms (34.4V / 5A) in which it would be able to drive a maximum of 86W rms sine.

Amp chips may have a dissipation limit &/or a temperature derating factor in addition to voltage & current limits.

Bridging amp's with low impedance speakers may put the current limit in action thereby limiting the useful power available.

For the same power 4 ohm speakers requre 1.414 times the current of 8 ohm speakers, and 8 ohm speakers require 1.414 times the voltage compared to 4 ohm speakers.

Transformer voltages sag under load - limiting the peak power (but big capacitors help), and their temperature increases - limiting the long term power that can be drawn.

Those capacitors are used to store energy between the 100Hz pulses that are supplied by the rectifier. Without them the music would be modulated by hum.
10000uF is usually good for 5-10A rms. The more current being drawn the higher is the risk of clipping being hum-modulated.

 

[RishiGuru]

Apart from the obvious differences; 10% vs. 0.5% distortion and the different supply voltages, notice the asterisk there:
"Note (*):....................more current being drawn the higher is the risk of clipping being hum-modulated.

Very informative & a thousand thanks to you. I have no words other than to say thanks to you for helping out a noob like me.

You said : "...........That is pretty much due to the peak current limit of 5A in that chip, giving a max of 50W rms in 4 ohms........"

Does this mean, considering I am using 300 VA --> 2 x 22 V, 6.82A toroid, this 6.82 A is useless, since 5.00A is the maximum TDA7296 can handle.

So, better to use 220VA --> 2 X 22V, 5.00A toroid

 

[Resqueline]

Remember there's two 7296's à 5A and two 7295's à 6A totalling 22A peak, so I don't consider 300VA being overkill though 220VA will surely cut it and be a nice upgrade.

 

[RishiGuru]

Remember there's two 7296's à 5A and two 7295's à 6A totalling 22A peak, so I don't consider 300VA being overkill though 220VA will surely cut it and be a nice upgrade.

I have gone for the 220VA --> 2 X 22V, 5.00A. Delivery will be on this Friday. Any way Resqueline, I found no matter what the make or model of any amplifier in these computer audio systems, there are always two capacitors to help the transformers out instead of one.

I mean my Z-2300 uses two 10,000uF, 35V capacitors. Why not one big 20,000uF, 35V? I mean it will save cost for sure.

Among the cheap chinese speaker systems there is a norm of using STMicro TDA2030A power amps in multiples. And always there are two capacitors in the power supply part using 4700uF, 25V capacitors, irrespective of make or model.

Is the number of caps is in any way related to the number of power amps in use? Would it have been even better to use 10,000uf caps for each of the four power chips used in Z-2300?

Why two caps? why not one?

 

[Resqueline]

In "the old days" one usually used only one capacitor, a so-called single-ended power supply.
In order to be able to make a signal swing an ordinary amp has to have a neutral position of its output of half the supply voltage.
The drawback with this is that you then need capacitors in series with the amp output in order to remove the DC present there, making a total of three big cap's, for stereo.
There was also the issue that hum on the power supply would go straight to the speakers, only halved in amplitude, and always being present.
These days one has gotten wiser. The power supply is split in two, with a neutral tap in center (hence the +/- term). This does away with one capacitor (+ the hum issue).
So a +/- 30V supply has a total of 60V present between its ends. A single-ended amp can then give 30V peak out, but a bridged amp can give 60V peak to the speakers.
A bridge amp does not need a split psu, it can make do with a single-ended one w/o any fundamental drawbacks (except it would not have a real "ground" for the signal).
So the number of cap's is not related to the number of amp's, but here the bridged sub-amp could in theory have used a single 5000uF 70V capacitor.

 

[RishiGuru]

In "the old days" one usually used only one capacitor, a so-called single-ended power supply.
In order to be able to make a signal swing an ordinary amp has to have a neutral position of its output of half the supply voltage...........have used a single 5000uF 70V capacitor.

Resqueline, you are a great teacher. I mean, I have posted the same problem in may 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.

I can find three wires on my Z-2300 toroid --> YELLOW-BLACK-ORANGE.
Manufacturer: Ten Pao International Ltd.
Model No: TOG433028F0
Input: AC 230V/50Hz
Output: AC 20.1V x 2
Diameter: 95 mm
Height: 45 mm

Do you mean that:
YELLOW --> -20.1V
BLACK --> 0V
ORANGE --> +20.1V

Am I right?

Also, Resqueline other members are telling me 22V will be to close, better to stay with 20V and play safe.

They also state 300VA toroid will be waste of money for Z-2300 costing $110. Better stick with 200VA. There are still time. So will I ask them to deliver me a 200VA toroid?

200VA --> 2 X 20V, 5A

What is your opinion?