Help required on Logitech Z-2300 toroidal transformer

[Resqueline]

Yes, you could put it that way, & there's 40.2V (AC) between yellow & orange. Yellow & orange each alternates between being + & - since a transformer deals with AC.

I did show you a rough calculation of it, but to be sure about the maximum allowable voltage level please get the transformer's regulation spec's from the supplier.

A higher VA transformer means better regulation, and less sag when "cranking it up".
A higher voltage will mean better "punch". Of course it also places a little higher demands on the cooling. I was not able to see from the pic's if that might be marginal.

Clearly the original transformer was the weakest link, failing before the amps & the drivers. It's hard to guess what's "next in line" but I'd guess the drivers are.

Since the manuf. claims it's a 200W system I'd expect it to have a 250VA transformer, but you have shown the drivers to amount to only 94W so 120VA "should suffice".

On the other hand there's a "rule" stating that an amplifier really should be able to handle so-&-so much more than the speakers, to be able to deliver unclipped music.
Clipping amp's produces higher frequency harmonics which are more detrimental to speakers than if they had been supplied with the unclipped higher-power burst instead.

This is where the "as-high-as-possible" power supply voltage comes in handy. 25V is cutting it close but I don't think 22V is; unless the regulation is worse than expected.
Toroids have better regulation than ordinary square transformers do btw.

Whether the solid foundation of a possibly excessive powered transformer is a waste of money will depend on your feelings, situation, & nationality, but I won't get into that.
You'll have to decide whether this is a repair or an upgrade or whatever. I wouldn't hesitate to use a 22V 250VA transformer, costing perhaps just a little more than a 200VA.

Do you have a multimeter btw.? Would you also be able to get real numbers of the mains voltage variations in your area throughout the year from your mains supplier?

 

[RishiGuru]

Yes, you could put it that way, & there's 40.2V (AC) between yellow & orange. ....................................... Would you also be able to get real numbers of the mains voltage variations in your area throughout the year from your mains supplier?

My computer & its accessories (Z-2300 included) runs through an UPS with built in Auto Voltage Regulation(AVR). So I do not have to fear about voltage fluctuations.

And I have decided, that I want a good upgrade and hence gunning for 22V 250VA transformer, instead of the 20V one.

Z-2300 Toroidal Transformer close up:


Resqueline I wonder, if there is a 40.2V (AC) between yellow & orange of this toroid, then how does the TDA7296 with a maximum of 35V (DC) handling capability can deal with 40.2V (AC)? Or am I getting it wrong somewhere?

I post below the picture of Z-2300's 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 TDA chips.



Since I live in a tropical country where summers are 35-45 degree Celsius, I wonder this heatsink is enough to handle 4 chips. Also you said increasing the voltage of the toroid will produce more heat in the amps.

 

[Resqueline]

Ok, is it a so-called Online or a Line-Interactive UPS? If it's a Line-Interactive i wonder how fast it adjusts, and how fast & far your mains might fluctuate.

The 35V figure is a +/- value, totalling 70V end-to-end.
When you get the new toroid you should measure to make double sure there's no more than 51V AC end-to-end before connecting the secondary to the amp.
The 44V transformer rating should give you a safety margin of 15.7% where 10% would have been alotted for mains fluctuation and 5.7% for transformer regulation.

That heatsink is quite big. It has an area of 279 sq. in. or 1800 sq. cm. which according to an online calculator translates to a thermal resistance of 1.2 deg. C / W.
So, in theory, with the amp going full blast with that transformer, melting your drivers, it'll dissipate 250W*0.27 = 67.5W and thus get 81 degrees C warmer than room temp.
With the old transformer it could only get 39 degrees warmer than room temp., before melting the transformer. I don't know if these figures are the real-world ones though.

Notice this isn't "twice" as hot. The IC's can stand 150 deg. C internally, thus leaving only 24 deg. margin in the "new" version, where the "old" had 66 degrees of headroom.

You'll just have to test how hot it can get. If it get's hotter than a 2 second touch allows I'd consider setting up a computer fan to blow up on the heatsink on demand.
It doesn't take much of a draft to double the heatsink efficiency, and it's possible to get it up to four times the "passive" value. But don't worry about this at the time being.

The above worst-case figures can only be reached with continuous pink noise at full blast. It's the music you play (and how you play it) that determines the real world figures.

 

[RishiGuru]

Ok, is it a so-called Online or a Line-Interactive UPS? If it's a Line-Interactive i wonder how fast it adjusts, and how fast & far your mains might fluctuate................................ that determines the real world figures.

Resqueline, it is a Line-Interactive UPS. Not an Online one.

Also while interacting with you, I found I have much to learn for sure. Though I am an engineer in IT, I want to learn more about how audio amplifiers work and what is the role of the individual components of an audio amplifier.

For example, looking at the picture below I still do not no know what "close up cap" portion of the amplifier with many 25V small capacitors doing in there. Six small caps are surrounding the JRC4565 and another four in square formation below them.


And also adding a voltage regulator would have been even better, isn't it.

Power Supply --> Transformer + Rectifier + Smoothing(Capacitors) + Regulator

Though we found this two chips a 78M18 and a 79M18. In web they are calling it +/-18V voltage regulators but they are for JRC4565 used for headphones and not for the TDA power amps


Can you specify some websites where I can learn about them & how they work? I will be glad if anybody can help me out.

Thanking you, RishiGuru

 

[RishiGuru]

Found the VA rating of the transformer

Resqueline, I am sorry to reply so late, but right now I am out stationed due to official work and thus cannot post, but hope to be back in home this week.

I have deferred buying the new toroid since I will be out stationed, and have given the Z-2300 toroid to the local winding shop. When I get back I will see it they could get it right, and if not, buy a brand new as per your recommendation.

Today I got this GREAT NEWS. I repeatedly made a dozen requests to know the VA rating of this toroid in their "Online Inquiry" & "Contact" section of their website.

My request to Ten Pao -->

Kindly inform me about be the VA rating of this toroidal transformer

Model No: TOG433028F0
Input: AC 230V/50Hz
Output: AC 20.1V x 2

This transformer is used by my Logitech Z-2300 and had gone dead. Since my Z-2300 is outside warranty & thus no support from Logitech, I need to buy one from the market. So, I need the VA rating of this toroidal transformer. I have repeatedly asked for help in the "Online Inquiry" section of you website with no reply.

Kindly please help me.

Thanking You,

RishiGuru
Country : India

Their answer after a dozen request :

Dear RishiGuru,

After confirming with our engineer, the VA rating for this model is 150.9, and our company didn't set any retail place in India, so please contact with your Logitech Z-2300 supplier.

Best Regards
Sam Su
Marketing Department
TEN PAO INTERNATIONAL LTD.
Tel: 86-752-2312309
Fax: 86-752-2312813
Skype: sam_su85
Email: [email protected]
MSN: [email protected]
website: Ten Pao International Ltd

From: RishiGuru
Sent: Sunday, December 12, 2010 9:39 PM
To: [email protected]
Subject: 線上查詢

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

The toroid is 150.9VA
So, it seems 150.9 VA --> 2 x 20.1 V, 3.75A

It seems that 200W claimed output is to much for the 150.9 VA transformer after all.

Also what I learned from TechGurus like you, 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.

Since here we have 150.9VA.
Maximum output of the system = 150.9/ 1.27 = 119W =~ 120W.

Also since Z-2300 uses Class-AB amplifiers generally having an efficiency of at around 50%, that real power that is sent to the speakers is = 120/2 = 60W only.

Man I cannot believe what I am writing. Am I right or wrong. Kindly help me.

 

[RishiGuru]

Need my Resqueline

Resqueline where are you?

 

[Resqueline]

Oh, I'm here, but my time & energy is sometimes somewhat limited. Sorry to keep you waiting but I'll get back to you in not too long. I'm amazed at your achievements btw..

 

[RishiGuru]

Oh, I'm here, but my time & energy is sometimes somewhat limited. Sorry to keep you waiting but I'll get back to you in not too long. I'm amazed at your achievements btw..

Ok, I am waiting, but be back soon? Remember that this stupid student of yours is waiting with a bucket full of questions.

 

[(*steve*)]

Ok, I am waiting, but be back soon? Remember that this stupid student of yours is waiting with a bucket full of questions.

It might be wise to make it obvious you meant:

Ok, I am waiting, but be back soon? Remember that this stupid student of yours is waiting with a bucket full of questions.

I'm sure you meant the latter, and Resqueline is probably too polite to call you on it, but what you wrote can read as demanding. I'm sure you didn't mean it to.

I've seen flame-wars erupt over trivia like this, and although that won't happen here, it's still worth bearing in mind.

I'll have a quick read and see if I can help you...

 

[RishiGuru]

It might be wise to make it obvious you meant:



I'm sure you meant the latter, and Resqueline is probably too polite to call you on it, but what you wrote can read as demanding. I'm sure you didn't mean it to.

I've seen flame-wars erupt over trivia like this, and although that won't happen here, it's still worth bearing in mind.

I'll have a quick read and see if I can help you...

*steve*, you got me completely wrong. What I wanted to say is that Resqueline have been the best teacher I had in any technical forum until now who tirelessly helped me in answering every question I asked.

He was in no compulsion in do so, but he still answered all my questions. Sometimes my questions have been very basic & maybe stupid, but he understood that I am a noob (which is quite so) and answered my questions in a very lucid language so that I can understand.

Recently, I got a very important info regarding the thread topic and so I requested him to help me out when he is free. Though I am young, I have a very simple mind & don't like to hurt anybody's personal feeling in any way. Thats all.

It will be very kind of you, if you can provide any help

 

[(*steve*)]

Yes, it s true that if an amplifier is rated as 200WRMS, then to provide that continuously you need a power source capable significantly more peak power.

However, most amplifiers do not have power supplies capable of driving their rated power continuously. This is because music is not like a continuous sine wave. It has peaks of intensity, then relatively quiet periods. The (often large) power supply filter capacitors provide the extra power for a short time during these peaks. The filter capacitors can charge back up during the relatively quiet periods.

If music has a 20dB dynamic range then if the peaks are 200W, the average power is probably around 5W. Turn up the volume more than that and you'll get clipping and distortion of those peaks.

So a 150VA transformer for a 200WRMS amplifier is not that awful (It's not that flash either).

 

[RishiGuru]

Yes, it s true that if an amplifier is rated as 200WRMS, then to provide that continuously you need a power source capable significantly more peak power.

However, most amplifiers do not have power supplies capable of driving their rated power continuously. This is because music is not like a continuous sine wave. It has peaks of intensity, then relatively quiet periods. The (often large) power supply filter capacitors provide the extra power for a short time during these peaks. The filter capacitors can charge back up during the relatively quiet periods.

If music has a 20dB dynamic range then if the peaks are 200W, the average power is probably around 5W. Turn up the volume more than that and you'll get clipping and distortion of those peaks.

So a 150VA transformer for a 200WRMS amplifier is not that awful (It's not that flash either).

So, according to you 150VA transformer for a 200W system is just ok & will somehow do the job. I got this part.

From my recent discovery I found out Z-2300 uses

Z-2300 uses Class-AB amplifiers from STMicrolectronics.

The amplifier uses:
i) Two STMicroelectronics Class-AB, 60W, TDA7296 amplifiers bridged together for the subwoofer.
ii) Two STMicroelectronics Class-AB, 60W, TDA7296 amplifiers powering each of the satellites.
iii) Two ripple filters SamXon/ CapXon 10,000 uF, 35V capacitors for smoothing the DC output.
iv) A Japan Radio Corporation’s JRC-4565 operational amplifier required for the headphone socket in the control pod.
v) Two voltage regulators a 78M18 and a 79M18, making positive and negative 18 volts respectively to feed the JRC4565 op amp.

I also learnt from other forums that bridging two amplifiers almost doubles the output voltage swing and almost doubles the current in the speaker.

Now, from the graphs of TDA7296 data sheet I have found that TDA7296 produces 38W @ 0.5% THD @ 26 VDC. [Helped by a AudioGuru]

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).

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.

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) 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 the graph said "TDA7296 produces 38W @ 0.5% THD @ 8 ohms @ 26 VDC".

What is your say on this? Did Logitech calibrated the transformer to reach this goal of 38W?

5) 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 & Resqueline are the ones who can help me out? I will love if anybody answers this questions.

Thanking you, RishiGuru

 

[(*steve*)]

If you can, connect a meter in a supply rail and measure the average current being drawn.

You may be quite surprised at how low it is at differing volume levels.

Quick answers

1) Theoretically you will get 4x the power from a bridged amplifier compared to a single amplifier. (Power is proportional to the voltage swing squared and this will double the voltage swing)

2) Is this a question?

3) I'd need the specs. But in a bridged configuration for a sine wave, the max voltage swing would be 26/sqrt(2) VRMS = 18VRMS, and therefore the power would be just over 42 WRMS

4) if those 4 amplifiers are in pairs (in bridge config) then the max current is 10A, not 20, since the same current flows through 2 of them. And even if they're not, the 4 of them in a non-bridged config will be drawing either 5A from either one supply rail or the other, with a duty cycle of 50%.

5) Replacing a 60W module with a 600W module would make the amplifier sound significantly louder. You may not even notice 60W to 100W. You may notice clipping more though.

 

[RishiGuru]

If you can, connect a meter in a supply rail and measure the average current being drawn.

You may be quite surprised at how low it is at differing volume levels.

Quick answers

1) Theoretically you will get 4x the power from a bridged amplifier compared to a single amplifier. (Power is proportional to the voltage swing squared and this will double the voltage swing)

2) Is this a question?

3) I'd need the specs. But in a bridged configuration for a sine wave, the max voltage swing would be 26/sqrt(2) VRMS = 18VRMS, and therefore the power would be just over 42 WRMS

4) if those 4 amplifiers are in pairs (in bridge config) then the max current is 10A, not 20, since the same current flows through 2 of them. And even if they're not, the 4 of them in a non-bridged config will be drawing either 5A from either one supply rail or the other, with a duty cycle of 50%.

5) Replacing a 60W module with a 600W module would make the amplifier sound significantly louder. You may not even notice 60W to 100W. You may notice clipping more though.

Thanks for clearing some of my doubts.

Now, since my Z-2300 is a 2.1 speaker system I know their is a crossover which is separating the audio frequency spectrum and directs portions of that spectrum to the satellites & the subwoofer.

I also came to know that inductors pass low frequencies and capacitors block low frequencies. Capacitors pass high frequencies and block low frequencies. But I cannot locate the crossover in the Z-2300 amplifier as shown below.










The Z-2300 amplifiers are bolted to the big heat sink in the back.

 

[RishiGuru]

Principles of Z-2300 Operation

Finally I got hold of how my Z-2300 works.

Principles of Z-2300 Operation:

1. A stereo audio signal comes in through the green 3.5mm connector.

2. Signal passes through the remote’s main volume potentiometer for attenuation.

3. Signal is then fed down to the subwoofer enclosure for pre-amplification. A JRC-4565 operational amplifier is used. Two voltage regulators a 78M18 and a 79M18, making positive and negative 18 volts respectively is used to feed the JRC-4565 op amp.

4. The pre-amplifier distribute the audio into two places:
a) To the left and right satellite power amplifiers each using a TDA7296 (and subsequently to the 2 satellite speakers)
b) Back up to the remote.

5. Inside the remote, the signal is split again:
a) To the headphone jack
b) To the subwoofer bass volume potentiometer (where it is combined to mono at this point)

6. Output from the subwoofer potentiometer finally gets fed back into the sub enclosure and last, into the bridged TDA7296 subwoofer power amplifiers.

The power train consists of a 150.9 VA TenPao center tapped toroidal transformer as below:
150.9VA --> 20.1V X 2, 3.75A

Two CapXon 10,000 uF, 35V capacitors for smoothing the DC output are used.

My question is why JRC-4565 op-amp is used? Does it have any role in improveing the on audio quality. Where do you think the crossovers for the satellites & subwoofer are used?

 

[morphemes]

My question is why JRC-4565 op-amp is used? Does it have any role in improveing the on audio quality. Where do you think the crossovers for the satellites & subwoofer are used?

For the sake of leaving no stone unturned...

The op-amps are just digital potentiometers. They allow the remote to control the amplifier gain.

Can't 'improve' audio quality from source, the best you can do is preserve it. The op amps improve the quality of your experience by enabling variable gain controls via the remote control. That's about it.

The crossovers for the satellites don't exist, the TDA mosfets connected to the satellites deliver a full range signal. The sub-woofer amps employ lower capacitance in the gains feedback loop (likely 1uf instead of 22uf). I can clearly see them in the photographs. They're the tall skinny green caps.

The TDA mosfet amps are quite simple. The reference circuit consists of only a handful of caps & resistors. Assuming you already have power delivery covered, you could build a working 100 watt TDA stereo amplifier for well under ten dollars. Everything else on the logitech board is fluff.