Help required on Logitech Z-2300 toroidal transformer

[audioguru]

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 @ 26 VDC".

What is your say on this?

Coincidence.
1) The transformer has its current rated in AC amps but the amplifier operates from DC amps.
2) The rectifiers produce peak voltage that is filtered. The peak voltage is 1.414 times higher than the RMS AC voltage and the power cannot be changed so the DC current rating is 0.707 times the AC current rating.
3) You need to calculate the RMS DC current not guess at the peak DC current.

If the transformer was more powerful then the woofer gets 120W and each satellite gets 38W for a total of 196W. At 70% efficiency the total power required is 280W. Then the RMS current in the 40.2V transformer is 280/40.2= 6.07A.

But nobody plays their sound system at full blast all the time except you at your house party. (smilie)
The sound system in my car has a total continuous output of 288W RMS. I have played it very loud but I have never heard it clipping. It has a real sub-woofer that might be clipping a little but it and the rear seat filter out the distortion harmonics then I don't hear the clipping distortion.
My home stereo has a total continuous output of 140W RMS and I have had it loud enough to clip more than a few times. My dog runs away.
I live in a brick home, not a cloth tent so it doesn't bother the neighbours.

 

[RishiGuru]

Coincidence.
1) The transformer has its current rated in AC amps but the amplifier operates from DC amps.
2) The rectifiers produce peak voltage that is filtered. The peak voltage is 1.414 times higher than the RMS AC voltage and the power cannot be changed so the DC current rating is 0.707 times the AC current rating.
3) You need to calculate the RMS DC current not guess at the peak DC current.

If the transformer was more powerful then the woofer gets 120W and each satellite gets 38W for a total of 196W. At 70% efficiency the total power required is 280W. Then the RMS current in the 40.2V transformer is 280/40.2= 6.07A.

But nobody plays their sound system at full blast all the time except you at your house party. (smilie)
The sound system in my car has a total continuous output of 288W RMS. I have played it very loud but I have never heard it clipping. It has a real sub-woofer that might be clipping a little but it and the rear seat filter out the distortion harmonics then I don't hear the clipping distortion.
My home stereo has a total continuous output of 140W RMS and I have had it loud enough to clip more than a few times. My dog runs away.
I live in a brick home, not a cloth tent so it doesn't bother the neighbours.

Thanks audioguru for the helpful insight.

**broken link removed**

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 (control pod in the picture) 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?

 

[mvs sarma]

Thanks audioguru for the helpful insight. Finally I got hold of how my Z-2300 works.
....My question is why JRC-4565 op-amp is used? Does it have any role in improving the on audio quality. Where do you think the crossovers for the satellites & subwoofer are used?

the op amp is either for deriving lower voltages for preamplifier (again dual power) or as Head phone amplifier
The headphone jack has facility to cut the drive for the main amplifier when headset is plugged.

 

[audioguru]

The Japan Radio Corporation NJM4565 is a pretty good dual audio opamp. Usually three would be used to make an active crossover circuit.
Two to make highpass filters for the satellite amplifiers and one to make a lowpass filter for the woofer amplifier.

 

[mvs sarma]

this item was located on the main psu board where the initial caps are there. This situation made me feel that it might have been used to derive aux power supplies.

 

[RishiGuru]

The Japan Radio Corporation NJM4565 is a pretty good dual audio opamp. Usually three would be used to make an active crossover circuit.
Two to make highpass filters for the satellite amplifiers and one to make a lowpass filter for the woofer amplifier.

Kindly describe what you meant by "dual audio opamp".

Also, I only found one JRC-4565 in the amp. Below is a high resolution picture of the voltage regulators at the top & JRC-4565 in the middle surrounded by six 47uF, 25V capacitors. Are this capacitors used for high pass filters.

I know inductors are used to pass low freq, while caps for high.

**broken link removed**

So how does the Z-2300 manages its crossovers? I have no idea. Also their are four caps below the op-amp:

**broken link removed**

 

[audioguru]

The NJM4565 is a dual opamp which means it has two opamps inside.
Sorry, I was wrong. One opamp can made one highpass or make one lowpass filter.
So the NJM4565 can be the two highpass filters for the satellite amplifiers crossovers and something else can make the lowpass filter for the woofer amplifier.

The 47uf capacitors have a very wide tolerance (maybe from 23.5uF to 94uF) so make horribly inaccurate filters. Usually 5% film capacitors are used in filters.

 

[RishiGuru]

The NJM4565 is a dual opamp which means it has two opamps inside.
Sorry, I was wrong. One opamp can made one highpass or make one lowpass filter.
So the NJM4565 can be the two highpass filters for the satellite amplifiers crossovers and something else can make the lowpass filter for the woofer amplifier.

The 47uf capacitors have a very wide tolerance (maybe from 23.5uF to 94uF) so make horribly inaccurate filters. Usually 5% film capacitors are used in filters.

audioguru, I have got a Z-2300 control pod schematic. I am uploading it so you and others could shed some light on them.

First, some innternal shots of my control pod:

**broken link removed**

**broken link removed**

**broken link removed**


An electric engineer uploaded this schematic in web:

**broken link removed**

As quoted by him:

"Miscellaneous schematic notes:

1)Resistor R108 omitted (serves to buffer supply rail into standby pin; not critical)
2)Potentiometers not measured (10k parts are common and work well in this circuit)
3)Capacitors C100, C101 are optional. Someone with more free time may wish to investigate the frequency response with and without these parts.

The D-15 plug is used to connect the control pod to the sub.

D-15 Connector Pinout:

Pin PCB Name Description
1 SLINE Subwoofer Line Input
2 (unused)
3 SGND Signal/Audio Ground
4 PGND Power Ground
5 STDBY Standby, Active Low
6 RL Right Line Input
7 (unused)
8 (unused)
9 (unused)
10 (unused)
11 RHP Right Headphone Output
12 LL Left Line Input
13 LHP Left Headphone Output
14 (unused)
15 VREG 15V Supply Rail

See images above for connector numbering. Those who wish to quickly test their Z-2300 can ignore most of this. The Z-2300 switches on when Pin 5 is connected to Pin 15. Then, apply audio signals as follows:

Pin 12: Left Input
Pin 6: Right Input
Pin 1: Subwoofer Input
Pin 3: Audio Ground "

I was thinking about the subwoofer low pass filter, where is it? Can you find it. Also do you think the way I described the Z-2300 works is correct or was I missing something?

 

[Domininkas]

Can I make Z-2300 run by 12V? I want to use it in my car without 12V->220V adapter.

 

[audioguru]

Can I make Z-2300 run by 12V? I want to use it in my car without 12V->220V adapter.

The Logitek Z-2300 runs from plus and minus 27.4VDC which is a total of 54.8VDC and will not work from only 12V.

 

[Domininkas]

Is there any cheap way to raise votage from 12VDC to 54VDC?

ps. thanks for respoding so quickly

 

[audioguru]

Cheap means "poor quality".
You can buy a cheap 12VDC to 230V AC pure sine-wave 300W or 500W inverter that is made in China. It uses PWM at a frequency higher than you can hear so it will not produce interference.

 

[Domininkas]

thanx, I think I just buy one of those 12->230 adapters instead of adding some wires with voltage raiser in it