Logitech Z-2300 Chip Amps

[RishiGuru]

I found on net that Z-2300 uses Class-AB power amplifiers from STMicroelectronics. But i am not sure what type of chip it uses. Can anybody help me out? Thanks in advance.

Some websites are saying it uses 2 X TDA7295 chips bridged together for the subwoofer & two TDA7296 for the two satellites.

Now, this quite justifiable considering two TDA7295 bridged together will pump out 80 X 2 = 160W. Subwoofer is rated at 120W by Logitech, so the amplifier have enough headroom to produce distortion free bass even a full volume.

While for satellites it uses TDA7296 each capable to deliver 60W. Satellites are rated 40W by Logitech, so their is enough headroom.

Currently some websites are calming Z-2300 has four TDA7296. So the subwoofer have 2 X 60 = 120W with no headroom with still matches the Logitech's claimed sub output.

From the Logitech website I found out that Z-2300 have two model generations
1) M/N: S-0118A
2) M/N: S-0118B
This numbers are printed at the back of the subwoofer.

Is the second model a low grade model than the previous one?

 

[RishiGuru]

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

http://www.freeimagehosting.net/uploads/11e8e9a168

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 TDA7295 ?

 

[RishiGuru]

Here is the picture of the voltage regulator :

An externally hosted image should be here but it was not working when we last tested it.

 

[Minion]

Why don"t you look at the chips and find out what they are ?? It seems that you allready have the amp opened ......

Those Voltage regualtors (7818/7918) do exactly what the name suggests , they regulate Voltage , in this case +/-18v ......

The Power amp chips run at a higher Voltage and the Opamps at a lower Voltage so they use the Voltage regulators to Drop the Voltage going to the power amp chips to a Level that is acceptable for the opamps , in this case +/-18VDC , they also help keep the Voltage stable so it doesn"t drop under a Load .......

I had an older Logitec 5.1 system that used 5 TDA7293 chips for the Satalites and 2 Bridged TDA7293 for the Sub ...... I ended up useing it for parts .....

Cheers

 

[RishiGuru]

Why don"t you look at the chips and find out what they are ?? It seems that you allready have the amp opened ......

Those Voltage regualtors (7818/7918) do exactly what the name suggests , they regulate Voltage , in this case +/-18v ......

The Power amp chips run at a higher Voltage and the Opamps at a lower Voltage so they use the Voltage regulators to Drop the Voltage going to the power amp chips to a Level that is acceptable for the opamps , in this case +/-18VDC , they also help keep the Voltage stable so it doesn"t drop under a Load .......

I had an older Logitec 5.1 system that used 5 TDA7293 chips for the Satalites and 2 Bridged TDA7293 for the Sub ...... I ended up useing it for parts .....

Cheers

Thanks Minion, for explaining to me about the use of the voltage regulators in my Z-2300. Though I am an engineer(IT), I am quite a novice in the audio field, so I require a lot of help from you guys.

My Z-2300 is under warranty, so i am afraid that removing the aluminium bar pressing the power amp chips against the heat sink will void it. Also the screws holding the bar is colored in red so that, if i remove it, the colors will go out and my warranty will be void.

Now here is another question. I found there is a JRC-4565 op-amp in by Z-2300 as shown below:

An externally hosted image should be here but it was not working when we last tested it.

What are the difference between power amp chips like TDA7295 & 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?

 

[jackand08]

The main amplifiers are capable of putting out much higher currents and voltages than the smaller op-amps. That is the main difference, but both can still be used as audio amplifiers, just the power output for the 4565 will be much much less.

Another difference between the two types of op-amps is that the 4565 can be operated at unity gain and still be stable (basically, it can be operated as a buffer which does no amplification). The more powerful op-amps are not stable at unity gain and will oscillate and cause all sorts of problems.

Your assumption is correct: the op-amps are used to power things that do not need to be loud (headphones) when compared to the speaker outputs (which are driven using the class AB power op-amps).

 

[RishiGuru]

The main amplifiers are capable of putting out much higher currents and voltages than the smaller op-amps. .........

............to the speaker outputs (which are driven using the class AB power op-amps).

Thanks jackand08, for showing me the light. Now i do know what that 4565 does.

I made a list of my finding inside the Z-2300 as below:
The amplifier uses:
i) Two STMicroelectronics Class-AB, 80W, TDA7295 amplifiers bridged together to provide a total of 2 X 80=160W for the subwoofer.[Assumed]

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

iii) A Japan Radio Corporation’s JRC-4565 operational amplifier required for the headphones in the control pod.

iv) Filtering of the audio signal is done by two beefy SamXon/ CapXon 10,000 uF, 35V capacitors.

v) The amplifier board have two voltage regulators/ stabilizers a 78M18 and a 79M18, making positive and negative 18 volts respectively.

Total amplifier power of Z-2300 = 2 X 80 + 2 X 60 = 160 + 120 = 280W

Why does Logitech quotes Z-2300 have 200W when the total power reserve is 280W?

Also the toroidal transformer details are as below:

Manufacturer: Ten Pao International Ltd.
Model No: TOG433028F0
Input: AC 230V/50Hz
Output: AC 20.1V x 2
Diameter: 9.5 cm;
Height: 4.5 cm.
Amperage: Unknown
VA Rating: Unknown

Judging by the size of the toroid some are telling it is 120VA. My question is can a 120VA toroid provide 200W power Logitech claims for Z-2300?

Specifications of Z-2300 are provided below:

Audio Quality Certification: THX certified
Total Continuous Power(RMS): 200W
System THD: Better than 0.05% before clipping
Total Peak Power(RMS): 400W
Power distribution: 120 W (Subwoofer) + 2 X 40 W (Satellites)
Subwoofer: 120 W @ 8 ohms
Subwoofer Size (inch): 8
Satellites: 80 W (2 X 40 W) @ 8 ohms
Satellite Size (inch): 2.5
Frequency response: 35 Hz - 20 kHz
Signal to noise ratio(SNR): @ 1kHz > 100dB
Sound Pressure Level (SPL): 117db
Subwoofer dimensions(HWD): 11" X 11" X 15"
Satellite dimensions(HWD): 6.75" X 3.5" X 6"
Total weight : 15 Kg

 

[RishiGuru]

Picture of my toroidal transformer

An externally hosted image should be here but it was not working when we last tested it.

 

[cent88]

Are you modifying your z2300?

 

[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?

 

[Minion]

There are many reasons why a regular opamp might be used in the amp .....

1) Could be used as a Buffer as to make sure the amp chips get fed a constant low impedance signal .....

2) Could be used for creating a ballanced line driver to bridge the 2 Subwoofer Amp chips .....

3) Could be used for summing the Left and Right channels for the subwoofer .....

4) could be used as to create a Low pass filter for the subwoofer .....

Without seeing a schematic I couldn"t tell you but these are probably the most common uses for an Opamp in front of the amp chips ....

 

[boonAxe]

4) could be used as to create a Low pass filter for the subwoofer .....

Minion,

Looking at (4). Given one dual opamp (which most likely is used for stereo), are you also thinking that the Z2300 could possibly give full frequency range to the satellites and use the opamp as a low pass filter for the sub - tuned somewhere the lower limits of the 2.5" drivers?