Help required on Logitech Z-2300 toroidal transformer

[audioguru]

The power output of the amplifier is rated at 120W RMS for the subwoofer and 40W RMS each for the two satellites but at a horrible-sounding 10% distortion. Nobody listens to music when the amplifier is clipping like mad and producing horrible 10% distortion. It begins to clip at a total of only about 160W. Don't forget that in addition to the 160W of output there is an additional amount of maybe 160W of heat. Then the transformer must be able to supply 320VA if the amplifier plays at full blast all the time.

 

[mvs sarma]

obviously no one uses a system at its peak volume and try to enjoy the quality (distortion). the spec appears to indicate distion at max wattage. suppose one uses at 60% of capacity it would be much less. Distortion can not be zero , nor even .05% as specified by the manufacturer. May be at test lab they may be able to prove, with sophisticated enecho chambers etc..As such the power mains comprise of leaked noises from choppers like fan regulatos etc in domestic front. thus even the psu section, becomes a medium for Noise sources.

in this post, the main intention is to restore the amplifier from the suspected transformer failure( if really failed).

 

[RishiGuru]

mvs sarma & MrAl, it was very nice to know that you all tech gurus really care about a noob like me. Right now I am out stationed due to official reasons, but will be back this week. I have already given the toroid to the local shop, and when i get back I will see it they could get it right, and if not, buy a brand new. And I will update you all of the proceedings.

Cheers, RishiGuru

 

[audioguru]

obviously no one uses a system at its peak volume and try to enjoy the quality (distortion).

Some Western people listen to "acid rock" at max volume. It is already severely distorted with electric guitar fuzz.

The spec appears to indicate distortion at max wattage.

The power output of most inexpensive amplifiers is rated with the volume control turned up too high so that the amplifier is badly clipping which produces a higher power number and 10% distortion. If the volume control is turned up higher so that the output is square-waves then the distortion is 50% and the power output is doubled because the additional power produces all the harmonics.

Distortion can not be zero, nor even .05% as specified by the manufacturer.

Modern amplifiers have very low distortion when the output is not clipping. The TDA7296 amplifier IC's datasheet shows that its typical distortion plus noise when its supply is plus and minus 24V and its load is 8 ohms is only 0.004% at an output power of 25W or less.
Most people with normal hearing can hear distortion at 0.1%, and some people can hear less.

 

[mvs sarma]

thanks AudioGURU !!

 

[RishiGuru]

Found the VA rating of the transformer

Great news.

While still out stationed, I received a mail from the toroid manufacturer Ten Pao. 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: (E-Mail Removed)
MSN: (E-Mail Removed)
website: Ten Pao International Ltd

From: RishiGuru
Sent: Sunday, December 12, 2010 9:39 PM
To: (E-Mail Removed)
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 you TechGurus, 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.

Am I right or wrong. Kindly help

 

[MrAl]

Hi again,


Wow 150.9VA, they really know how to very accurately rate their transformers huh with four digit accuracy? <chuckle chuckle>
Now a normal company would have either said 150VA or 151VA

If that figure is correct (which i have a few doubts about because of the extreme stated accuracy) then yes, the max output would be about 119 watts. We might actually say less than that because of the inefficiencies of the input rectifiers too.

 

[RishiGuru]

Hi again,


Wow 150.9VA, they really know how to very accurately rate their transformers huh with four digit accuracy? <chuckle chuckle>
Now a normal company would have either said 150VA or 151VA

If that figure is correct (which i have a few doubts about because of the extreme stated accuracy) then yes, the max output would be about 119 watts. We might actually say less than that because of the inefficiencies of the input rectifiers too.

Also MrAl, 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.

 

[mvs sarma]

leave all those calculations
but what your repairer said?
he need not open it
he can test and say proimary break
primary short something?
he need not takes weeks for that
as you had a dmm you could also check
just saying that my transformer broke with no further details makes us wander around possibilities of failure.
i suppose, all ready told that , even if the diode bridge is partly (say one diode) short, it would show up as transformer getting HOT. etc
please speak of what you tested .

 

[audioguru]

The 20.1V windings of the transformer produce a supply of plus and minus 26VDC.
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.
The datasheet for the TDA7296 amplifier IC shows that it begins to clip when each satellite amplifier has an output of only 32W.
So the total output power is 160W and the heating is also 160W for a total of 320W.
The puny little 151VA transformer is severely overloaded when the music is played at full blast all the time.

I think the puny transformer limits the total output to maybe 80W of output power plus 80W of heating. Then it is still pretty badly overloaded. No wonder it failed.

 

[mvs sarma]

yes, AG,
at the best it can give 50 watts

 

[RishiGuru]

leave all those calculations
but what your repairer said?
he need not open it
he can test and say proimary break
primary short something?
he need not takes weeks for that
as you had a dmm you could also check
just saying that my transformer broke with no further details makes us wander around possibilities of failure.
i suppose, all ready told that , even if the diode bridge is partly (say one diode) short, it would show up as transformer getting HOT. etc
please speak of what you tested .

After reading your post, I gave a call to the repair shop, they told me that the internal fuse was blown. I never new their is a fuse plug in there. They also told me that the primary & secondary winding are perfectly OK. I have told them to repair that and make it ready by Thursday. I will be home by Thursday and try to fit in my Z-2300. You guys be with me. I still need all your help.

But, I am so happy that I do not need to buy a new one. Thank you all.

 

[audioguru]

The internal fuse in the transformer will blow again if you play music at full blast all the time, again.
What kind of music? Acid rock?

 

[RishiGuru]

The internal fuse in the transformer will blow again if you play music at full blast all the time, again.
What kind of music? Acid rock?

I love a lot of bass heavy songs. And I know this bass requires a lot of power from the transformer in order to push the 8 inch subwoofer. So, I think from now on I should never go beyond 50% volume. Am I right?

 

[mvs sarma]

Congrats to you and to your repairer

 

[blueroomelectronics]

Computer speakers are no substitute for a home auto system. That Z-2300 is a very good 2.1 computer speaker setup, but cranking the bass up to max will either blow the fuse or can damage the speaker.

 

[audioguru]

A little 8" speaker is an ordinary woofer, not a sub-woofer. That is why you turn up its volume control too high.
If it is half-decent or better then it will have a flat response down to about 60Hz.
A half-decent or better sub-woofer has a flat response down to 20Hz or lower so you can feel the vibrations.

A volume control is never made to provide full power when it is turned to max. It allows you to turn up the volume much higher for sounds that are played softly. If the volume control is turned up to max rotation then with normal music the amplifier will be clipping like mad.

A volume control is not linear, it is logarithmic. So when it is turned down to half-rotation then the power is 1/10th as much as when it is turned to max. 1/10th the power sounds half as loud. 10 times the power sounds twice as loud. That is why volume controls are logarithmic.

 

[mvs sarma]

yes Bill
those were the days where we used to home brew Philips Stereo amplifier designs with complete graphic equalizer etc
we used to get the boxes for the high wattage speakers with dividing network etc for tweeters, lot of anti echo filling with felt inside the boxes, and finally derive satisfaction .

 

[RishiGuru]

The 20.1V windings of the transformer produce a supply of plus and minus 26VDC.

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 the rectifier :

Output voltage = (23V (AC) X 1.414) – 2
= 32.5 – 2 = 30.5V (DC)

Am I right. Or is it 26V (DC). Please rectify me if I am wrong. Also I am to very disappointed to find that the Z-2300 have only 80W of real power. Then how on earth can they state 200W & 400W peak power. Can you show some light here?

How can these manufactures blatantly lies about power outputs & nobody notices this?

With Regards, RishiGuru

 

[mvs sarma]

how about power variation between 180 to 260?
what you calculated is open voltage with no load.once loaded the voltage comes down
@ AudioGURU,
we used to have two standards of Log potentiometers
log and anti-log?
one goes step at beginning and tapers off after 30% rotation
\ second starts flat till almost 60% and then steep raise