PART-I
INTRODUCTION
Logitech Z-2300
When Logitech introduced the Z-2300 way back in 2004, it was a THX certified premium quality top of the range product. The Logitech engineers in the lab where given a clear goal i.e. to create the best 2.1 multimedia speaker system for the computers. They were not concerned about the price, they were more concerned about the performance & quality which lead in using premium quality components, be it electronic components, speakers used, wooden casings of the subwoofers, plastic casings of the satellites and even the wires used to connect the components. Price was never an issue, performance was. This single mindedness of the engineers produced a unique product, and Z-2300 was born.
If you consider that way back in the year 2000 when Logitech was known as a cheap speaker manufacturer and could not even meet the standards of Altec Lancing let alone Klipsch computer audio products, they made a huge effort back then in order to make a big step forward and used better quality components for their THX certified audio system lineup than they have ever done before thus increasing cost. My "Price was never an issue, performance was" statement is in context of my above view. Today when we compare the Z-2300 from an el chepo manufacturer Logitech with the HiFi maker company like Klipsch producing Promedia 2.1 as a computer multimedia speaker system, you find both of them being in the same segment going head to head in terms of audio performance and in many occasions Z-2300 coming out as a clear winner. Atleast we have to give credit to Logitech that that could produce a multimedia speaker system that can meet the standards of a Klipsch product. I give full marks to Logitech only for this effort.
Logitech Z-623
Logitech introduced Z-623 in 2010 six years after Z-2300 reign. Actually I cannot recall of a 2.1 PC speaker that remained at the top of the performance charts for straight six years. They had to make the successor not because Z-2300 was getting old and becoming incompetent, believe me it is still is the king, but because the rival manufactures like Altec Lansing, Edifier, Creative, Sony etc are producing cheaper sets of same wattage and same configuration and labeling them as their premium product. Also 2.1 speakers sets are no more the cash cows of audio manufactures, rather these companies makes a lot of profit from selling the 5.1 & 7.1 speakers sets.
Z-2300 Specifications
Audio Quality Certification: THX certified
Total RMS Power: 200W [FTC Rated Power]
System THD: Better than 0.05% before clipping
Total Peak Power(RMS): 400W < 10% THD
Power distribution: 120 W (Subwoofer) + 2 X 40 W (Satellites)
Subwoofer: 120 W @ 8 ohms @ 10% THD @ 100Hz
Subwoofer Size (inch): 8
Subwoofer Type: Long throw
Satellites: 80 W (2 X 40 W) @ 8 ohms @ 10% THD @ 1kHz
Satellite Size (inch): 2.5
Satellite Type: Polished aluminum phase plug driver
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
UNPACKING
The satellites & Control Pod neatly packaged in the box
SUBWOOFER
The subwoofer is huge, in every sense of the word. The behemoth measures 11†(H) X 11†(W) X 15†(D), and its output could rattle the paint off your walls.
To give a comparison of how big the subwoofer is, look at the picture below where the Z-2300 sub is kept aside Altec Lansing VS2421.
Subwoofer made of thick MDF
The wall of the sub is made of 16 mm thick medium density fiberboard (MDF) which is quite impressive. It has been further strengthened with internal clamps in the joints. This adds tremendous strength to the box in order to withstand the slamming, heavy duty sound waves produced by the bass driver. The subwoofer weighs 12 kilograms and is a back breaker for sure.
Actually, this subwoofer was designed for Z-560 way back in the year 2000. Z-560 was the first THX certified multimedia speaker system from Logitech and was a big gamble at that time. Nobody was quite sure how the market will react in accepting a high end computer speaker from this unknown brand. But it seems that the gamble finally paid off and ever since this Holy Grail subwoofer have been used in their THX certified speaker systems line up for the past decade as below:
Z-560 [first THX certified 4.1 system, launched in the year 2000]
Z-680 [first THX certified 5.1 system, launched in the year 2002]
Z-2200 [first THX certified 2.1 system, launched in the year 2003]
Z-2300 [second THX certified 2.1 system, with minor updations on Z-2200 launched in the year 2004]
Z-2300 Bass Driver
Z-2300 subwoofer has a front facing massive 8 inch long throw bass driver. It has a Rated Power Input of 80W and maximum power input capability of 160W.
This history of 8 inch bass drivers began when Logitech choose Tang Band as the OEM manufacturer for their first THX certified multimedia speaker system Z-560 way back in the year 2000. It used direct off the shelf 8 inch Tang Band W8-670C with rated power input of 80W, maximum power input capability of 150W having a max excursion capability of 7mm. I guess at the time of release, Logitech was entering a new domain in computer audio, changing their image from relatively ordinary PC speaker manufacturer to a high end computer speaker manufacturer, and was themselves not quite sure about how many units of Z-560’s they will be able to sell.
There is a department in Logitech that exclusively deals with audio products and are better known as Logitech Sound Central. The link to the website is provided here: Logitech Sound Central
They state: “We don’t simply buy parts off the shelf. We laser tune different types of drivers. We modify the shapes, experiment with materials, and use digital components to improve sound quality. Our goal is to deliver fidelity as close to the original sound as possible.â€
Logitech Sound Central testing the bass driver of Z-5500
When Z-560 successor, Z-680 was launched in the year 2002, they shifted to an unknown speaker manufacturer which builds speakers in accordance to Logitech specifications.
I personally own a Z-560 & Z-2300. After minutely inspecting both the drivers of Z-560 & Z-2300, I found out
1) Both have same magnet size & weight thus having identical rated power handling capabilities.
2) Z-2300 bass driver have more excursion capability that that Z-560 ones, maybe 10mm [estimated] where Z-560 ones have only 7mm. This is evident since Z-2300 ones have slightly longer & elongated stamped steel basket section between the spider & the magnet compared to Z-560 ones, providing the space for more excursions capability.
3) The cooling efficiency of the Z-2300 bass driver with its bigger vented pole piece is significantly higher than Z-560 ones.
The bass driver of Z-2300 with even higher excursion capability than Z-560 ones will definitely offer better sensitivity & accuracy not to mention the ability to handle more power over its rated input power with better cooling efficiency.Later I found out that Z-2300, Z-2200 & Z-680 all used this new driver.
Look below at the increase of the hole diameter of the vented pole piece:
Tang Band Z-560 subwoofer with smaller vented pole piece
Z-680 aka Z-2200 aka Z-2300 subwoofer with bigger vented pole piece
Z-2300 Bass Driver
Comparing Z-2300's aka Z-680 monstrous 8 inch bass driver on the left with the Onkyo's 8 inch bass driver on the right.
Note: Normally people confuse this bass driver as used in Z-680, Z-2200 & Z-2300 with the Tang Band W8-670Q model. Though both units look near identical, Z-2300’s bass driver is different from the W8-670Q in the rear section. It became absolutely certain when my friend’s Z-2300 bass driver went dead and I have to personally contact TangBand via email to ask the model of the driver used in Z-2300 & its price. I also send them the above pictures of the driver to help them identify. To my surprise, they replied after inspecting the pictures sent to them, that this bass driver do not belong to them or in any way represent one of their models. But they did agree that they supplied W8-670C drivers for Z-560. So, you see Z-680, Z-2200 & Z-2300 are not TangBands. Prior, I was also the victim of this case.
The subwoofer enclosure also houses a patented “U†shaped exponentially increasing bass reflex port to produce distortion free deep and rich bass experience. The enclosure is very deep, which is obviously good from an acoustical standpoint.
Z-2300 Satellites
Z-2300 uses 2.5 inch polished aluminum phase plug drivers in their satellites and are beautifully crafted to look like a piece of art. The 12W satellite drivers that Z-2300 uses are again from an unknown speaker company and does not in any way relate to 3 inch Tang Band (W3-594SB) units. I estimate a rated power of 10W & a max of 20W. But since these drivers get audio frequencies ranging from 150Hz to 20kHz, the power handling capability increases by at least two times. So these speakers can handle anything between 20W to 40W.
Satellite Drivers
With the polished aluminum phase plug drivers helping to reduce the path length differences about the cone surface, you get a smoothing and reinforcing the frequency response, particularly in terms of the highest frequencies the driver is capable of. There is some thermal dissipation one gives up by doing this, but the phase plug itself can serve as a heat sink for the voice coil and magnet pole.
CONTROL POD
The control pod of the Z-2300 is quite simple and minimalistic, which I prefer. No fancy lights just a big volume knob, a bass control, a 3.5 mm headphone jack, power LED and a power button. You can keep the control pod on your desk where ever you like and the controls are very convenient.
Here are some pictures of Z-2300 control pod innards
AMPLIFIER DETAILS
Audio design has always been a subject that stirs the passions of most electronics engineers and a subject where the pursuit of perfection has many times comes before considerations of cost. That aside sometimes the simplest circuits can offer the best solutions in terms of cost and performance. Z-2300 houses the amplifier in their subwoofer assembly.
Power Supply
The power supply of an audio amplifier is of vital importance, since it provides all the juice required by power amplifiers to drive the big speakers. An underperforming power supply will seriously limit the performance of an amplifier.
The power supply consist of:
i) A center tapped toroidal transformer manufactured by Ten Pao International. This transformer is rated at 150.9VA with +/- 20.1VAC secondary, 3.75A.
ii) A metal cased bridged rectifier to provide full-wave rectification from +/- 20.1 VAC to DC.
iii) A pair of CapXon 10,000 uF, 35V capacitors one for + 20.1 VDC and the another for – 20.1 VDC acting as ripple filters in order to smooth the DC output.
Toroidal Transformer Details
Manufacturer: Ten Pao International Ltd.
Part No: Z-2200 EU
Model No: TOG433028F0
VA Rating: 150.9 VA [Confirmed by Ten Pao]
Primary Input: AC 230V/50Hz
Secondary Output Voltage: AC 20.1V x 2
Secondary Output Current: 3.75 A
Diameter: 95 mm
Height: 45 mm
A toroidal transformer uses a doughnut shaped core & is much slimmer than a conventional (EI) transformer. It has numerous advantages over EI type such as low weight, low hum, low noise and also being smaller in size than an equivalent EI type. On the downside they are much more expensive than a conventional EI transformer. But it is worth the pay since you get better performance. A toroidal transformer has so many other performance advantages over EI type that it is hard to describe here other than to provide the performance ratio. Toroidal : Conventional(EI) :: 158 : 5 . It you want to know more in details go to the link below:
Bryston Transformers
The Bridge Rectifier
The Ripple Filter Capacitors
The transformer used here is rated to have an output of two times 20.1VAC when it has its rated load. So its resistance has already dropped the open circuit voltage and its peak will be 1.414 times higher which happens to be 28.4VAC. A single rectifier here drops it by 1VDC to 27.4VDC and smoothing the ripple by the power capacitors drops it by another 1.4VDC to 26VDC.
So, DC voltage supplied by the power supply is +/- 26 VDC, the current being 3.75 A.
Amplifier Chips
Z-2300 uses four Class-AB power amplifiers from STMicrolectronics. STMicrolectronic is a very renowned name in audio amplifier market.
The amplifiers used are:
i) A Japan Radio Corporation’s JRC-4565 operational amplifier. JRC-4565 is a dual op-amp which means it has two op-amps inside it to handle stereo channels.
ii) Two voltage regulators a 78M18 and a 79M18 supplying +/- 18 VDC respectively to feed JRC-4565 op-amp from the +/- 26.4 VDC power rail.
iii) One STMicroelectronics, Class-AB, 60W, TDA7296 power amplifier for each of the two satellites while the other two STMicroelectronics, Class-AB, 80W, TDA7295 are bridged together powering the subwoofer.
JRC-4565 operational amplifier
78M18 and 79M18 voltage regulators
Logitech Z-2300 Amplifier Innards
Reasons for using Class-AB Power Amplifiers
A quick look at many new low power speaker amplifiers on the market highlights the move to Class-D audio performance, but when it comes to low distortion and low noise and best sound quality, Class-AB still has the edge.
Class-AB architecture offers a signal to noise plus distortion ratio of up to 10 times better than its equivalent Class-D neighbour as well as providing a much simpler architecture which can be tweaked as required, without the need for reactive filter components on the output and the electromagnetic radiation resulting from an output stage switching at a few hundred kHz. Class-D amplification has inherent distortion in it and therefore is predominantly used in lower bandwidth amplification like in subwoofers. In other words it is quite impossible for a Class-D to achieve the level of linearity in frequency response produced by a Class-AB amplifier.
Ultimately it comes down to what you want, for efficiency and cost effectiveness Class-D are best, but if you are ready to sacrifice some efficiency & increase cost for the sake of sound quality then Class-AB are the best. In other words Class-A amps sound the best, cost the most, and are the least practical. They waste power and return very clean signals. Class-AB amps dominate the market and rival the best Class-A amps in sound quality. They use less power than Class-A, and can be cheaper, smaller, cooler, and lighter. Class-D amps are even smaller than Class-AB amps and more efficient, because they use high-speed switching rather than linear control.
The most important reason behind which multimedia speaker manufactures are switching from Class-AB to Class-D is to increase profit margin. Class-D is very cheap to produce and does not need require a big extruded aluminum heat sink or expensive toroidal transformers. They are basically switching power supplies but utilize pulse width modulation so as to be able to reproduce and amplify an alternating current. There are ok for subwoofers, but I honestly think that it is ridiculous to use a Class-D amplifier in a high end studio monitor.
In short, Class-D amps are more efficient but are only good for low frequencies applications like subwoofer amplification. Class-AB amps can be used full range amplification i.e from 20Hz – 20kHz. Class-D amps cannot be used on highs frequency response because they only produce square waves because of the technology involved, so they will make your highs sound lifeless and tinny. Class-AB amplifiers produce full variable signals and can capture subtle nuances better, sound warmer and generally have more depth in their sound.
Principles of Amplifier Operation in Z-2300:
1) A stereo audio signal comes in through the green 3.5mm audio connector with the control pod.
2) In the control pod, the signal passes through the main volume logarithmic potentiometer for attenuation.
3) This attenuated audio signal is then send down from the control pod to the subwoofer enclosure through a D-Sub connecter where the amplifier module exists. A JRC-4565 operational amplifier first receives this audio signal. The JRC-4565 having stereo handling capability distributes the audio signal into two places:
a) To the left and right satellite TDA7296 power amplifiers and then subsequently to the 2 satellite speakers.
b) Back up to the remote through the D-Sub connector.
4) Inside the remote, the stereo audio 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)
5) Audio signal output from the subwoofer bass potentiometer finally gets fed back into the subwoofer enclosure through the D-Sub connector to the bridged TDA7295 subwoofer power amplifiers and then to the bass driver.
The four power amplifier chips operate at 8 ohms load in Z-2300 amplifier module.
Technical analysis of Class-AB, STMicroelectronics of TDA7295 & TDA7296 DMOS Audio Amplifiers
The TDA7295 & TDA7296 are both monolithic integrated circuit in Multiwatt15 package, intended for use as audio class AB amplifier in Hi-Fi field applications (Home Stereo, self powered loudspeakers, Topclass TV). Thanks to the wide voltage range and to the high out current capability it is able to supply the highest power into both 4 & 8 ohm loads even in presence of poor supply regulation, with high Supply Voltage Rejection. The built in muting function with turn on delay simplifies the remote operation avoiding switching on off noises. TDA7295 have a maximum output capacity of 80W while TDA7296 has 60W.
Remembering that the power supply of Z-2300 is +/- 26 VDC, the current being 3.75 A.
TDA7296
Output Power vs. Supply Voltage @ 8 ohms
Looking at the Output Power vs. Supply Voltage graph of TDA7296 above, we see it can produce 38W of power at 26 VDC at a respectable 0.5% THD.
So, at +/- 26 VDC --> 38W @ 0.5% THD @ 8 ohms
Distortion vs. Output Power @ 8 ohms
Distortion vs. Output Power graph of TDA7296 shows that at 38W @ 0.5% THD @ 8 ohms @ 26 VDC it starts to clip & distort. So in order to produce distortion free sounds this id the effective maximum of the chip.
Effective maximum of TDA7296: 38W @ 0.5% THD @ 8 ohms @ 26 VDC
Power Dissipation vs. Output Power @ 8 ohms
The Power Dissipation vs. Output Power graph of TDA7296 shows it as a very efficient Class-AB amplifier. At 38W @ 0.5% THD @ 8 ohms @ 26 VDC, the power dissipation is just 12W. This means if 50W is fed by the power supply to this TDA7296, it will deliver an output of 38W to the speaker whereas only 12W will be lost as heat.
So, this TDA7296 have an efficiency of 76% when it is producing 38W @ 0.5% THD @ 8 ohms @ 26 VDC. The power dissipation increases when the output power is reduced to half.
TDA7295
Two TDA7295 are bridged together into an 8 ohm load to power the subwoofer. Each of these TDA7295 sees effectively a 4 ohm load when bridged into an 8 ohm load. If you bridge an amplifier, the available power is the power of a single channel into half the load impedance multiplied by two.
Output Power vs. Supply Voltage of a single TDA7295@ 4 ohms
Looking at the Output Power vs. Supply Voltage graph of a single TDA7295 above, we see it can produce 65W of power at 26 VDC at a respectable 0.5% THD.
So, at +/- 26 VDC --> 65W @ 0.5% THD @ 4 ohms
Now if we bridge a pair of TDA7295, the available power is the power of a single channel into half the load impedance multiplied by two. Since TDA7295 produces 65W into 4 ohms, bridged it will produce 65 X 2 = 130W into 8 ohms.
So, at +/- 26 VDC a pair of bridged TDA7295 will produce --> 130W @ 8 ohms
Distortion vs. Output Power of a pair of bridged TDA7295@ 8 ohms
Distortion vs. Output Power graph of TDA7295 shows a pair of bridged TDA7295 after 100W starts to clip & distort. So in order to produce distortion free sounds this 100W is the effective maximum of the bridged TDA7295.
Power Dissipation vs. Output Power of a single TDA7295@ 4 ohms
The Power Dissipation vs. Output Power graph of TDA7295 shows it as an efficient Class-AB amplifier. At 65W @ 4 ohms @ 26 VDC, the power dissipation is 30W. This means if 95W is fed by the power supply to this TDA7295, it will deliver an output of 65W @ 4 ohms to the speaker whereas 30W will be lost as heat. In a bridged format it will deliver an output of 130W @ 8 ohms to the speaker whereas 60W will be lost as heat.
So, a pair of bridged TDA7295 have an efficiency of 68% when it is producing 130W @ 8 ohms @ 26 VDC. The power dissipation increases when the output power is reduced to half.
Looking at the above figures its seems that Logitech’s claim of 200W is true, since each satellites will have 38W while the subwoofer will get 130W which sums up to: 38 + 38 + 130 = 206 W @ 8 ohms @ 26 VDC
But, unfortunately that is not the case.
Z-2300 amplifier’s continuous power output capability
In order to produce 200W of continuous power, an amplifier will need a transformer that is capable of to deliver a minimum of 1.27 times the claimed wattage. Since Watt is volts multiplied by ampere, 200W of output requires 254 watts or 254VA transformer as a minimum requirement.
So, Z-2300’s supplied 150.9VA will produce a maximum of: 150.9/1.27 = 119W =~ 120W of continuous power @ 8 ohms @ 26 VDC
Since the ratio of power distribution between the subwoofer and the satellites are in the order of 1.71:1, the subwoofer will get 76W of continuous power while each satellite gets 22W of continuous power.
This becomes even more evident from the fact that the bass driver has a rated input power 80W, while the satellite speakers can handle anything between 20 to 40 watts.
The Total RMS Continuous Output Power of the four amplifier chips = 50(TDA7295) + 50(TDA7295) + 30(TDA7296) + 30(TDA7296) = 160W whereas the Total RMS Continuous Output Power of these four amplifier chips is 120W for Z-2300 since the the power supply limits the maximum power output.
Also these amplifiers will produce a lot of distortion & noise at the peak 160W power output. So, in order to produce distortion free, linear sound the amplifiers generally needs to reduce its output peak power by 25% or more. Using an amplifier with some extra “headroom†will help assure that only clean, undistorted power gets to your speakers. Reducing the maximum power from 160W to 120W Z-2300 creates a 25% headroom and justifies the stated system THD of better than 0.05% before clipping & signal to noise ratio of > 100dB.
INTRODUCTION
Logitech Z-2300
When Logitech introduced the Z-2300 way back in 2004, it was a THX certified premium quality top of the range product. The Logitech engineers in the lab where given a clear goal i.e. to create the best 2.1 multimedia speaker system for the computers. They were not concerned about the price, they were more concerned about the performance & quality which lead in using premium quality components, be it electronic components, speakers used, wooden casings of the subwoofers, plastic casings of the satellites and even the wires used to connect the components. Price was never an issue, performance was. This single mindedness of the engineers produced a unique product, and Z-2300 was born.
If you consider that way back in the year 2000 when Logitech was known as a cheap speaker manufacturer and could not even meet the standards of Altec Lancing let alone Klipsch computer audio products, they made a huge effort back then in order to make a big step forward and used better quality components for their THX certified audio system lineup than they have ever done before thus increasing cost. My "Price was never an issue, performance was" statement is in context of my above view. Today when we compare the Z-2300 from an el chepo manufacturer Logitech with the HiFi maker company like Klipsch producing Promedia 2.1 as a computer multimedia speaker system, you find both of them being in the same segment going head to head in terms of audio performance and in many occasions Z-2300 coming out as a clear winner. Atleast we have to give credit to Logitech that that could produce a multimedia speaker system that can meet the standards of a Klipsch product. I give full marks to Logitech only for this effort.
Logitech Z-623
Logitech introduced Z-623 in 2010 six years after Z-2300 reign. Actually I cannot recall of a 2.1 PC speaker that remained at the top of the performance charts for straight six years. They had to make the successor not because Z-2300 was getting old and becoming incompetent, believe me it is still is the king, but because the rival manufactures like Altec Lansing, Edifier, Creative, Sony etc are producing cheaper sets of same wattage and same configuration and labeling them as their premium product. Also 2.1 speakers sets are no more the cash cows of audio manufactures, rather these companies makes a lot of profit from selling the 5.1 & 7.1 speakers sets.
Z-2300 Specifications
Audio Quality Certification: THX certified
Total RMS Power: 200W [FTC Rated Power]
System THD: Better than 0.05% before clipping
Total Peak Power(RMS): 400W < 10% THD
Power distribution: 120 W (Subwoofer) + 2 X 40 W (Satellites)
Subwoofer: 120 W @ 8 ohms @ 10% THD @ 100Hz
Subwoofer Size (inch): 8
Subwoofer Type: Long throw
Satellites: 80 W (2 X 40 W) @ 8 ohms @ 10% THD @ 1kHz
Satellite Size (inch): 2.5
Satellite Type: Polished aluminum phase plug driver
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
UNPACKING
The satellites & Control Pod neatly packaged in the box
SUBWOOFER
The subwoofer is huge, in every sense of the word. The behemoth measures 11†(H) X 11†(W) X 15†(D), and its output could rattle the paint off your walls.
To give a comparison of how big the subwoofer is, look at the picture below where the Z-2300 sub is kept aside Altec Lansing VS2421.
Subwoofer made of thick MDF
The wall of the sub is made of 16 mm thick medium density fiberboard (MDF) which is quite impressive. It has been further strengthened with internal clamps in the joints. This adds tremendous strength to the box in order to withstand the slamming, heavy duty sound waves produced by the bass driver. The subwoofer weighs 12 kilograms and is a back breaker for sure.
Actually, this subwoofer was designed for Z-560 way back in the year 2000. Z-560 was the first THX certified multimedia speaker system from Logitech and was a big gamble at that time. Nobody was quite sure how the market will react in accepting a high end computer speaker from this unknown brand. But it seems that the gamble finally paid off and ever since this Holy Grail subwoofer have been used in their THX certified speaker systems line up for the past decade as below:
Z-560 [first THX certified 4.1 system, launched in the year 2000]
Z-680 [first THX certified 5.1 system, launched in the year 2002]
Z-2200 [first THX certified 2.1 system, launched in the year 2003]
Z-2300 [second THX certified 2.1 system, with minor updations on Z-2200 launched in the year 2004]
Z-2300 Bass Driver
Z-2300 subwoofer has a front facing massive 8 inch long throw bass driver. It has a Rated Power Input of 80W and maximum power input capability of 160W.
This history of 8 inch bass drivers began when Logitech choose Tang Band as the OEM manufacturer for their first THX certified multimedia speaker system Z-560 way back in the year 2000. It used direct off the shelf 8 inch Tang Band W8-670C with rated power input of 80W, maximum power input capability of 150W having a max excursion capability of 7mm. I guess at the time of release, Logitech was entering a new domain in computer audio, changing their image from relatively ordinary PC speaker manufacturer to a high end computer speaker manufacturer, and was themselves not quite sure about how many units of Z-560’s they will be able to sell.
There is a department in Logitech that exclusively deals with audio products and are better known as Logitech Sound Central. The link to the website is provided here: Logitech Sound Central
They state: “We don’t simply buy parts off the shelf. We laser tune different types of drivers. We modify the shapes, experiment with materials, and use digital components to improve sound quality. Our goal is to deliver fidelity as close to the original sound as possible.â€
Logitech Sound Central testing the bass driver of Z-5500
When Z-560 successor, Z-680 was launched in the year 2002, they shifted to an unknown speaker manufacturer which builds speakers in accordance to Logitech specifications.
I personally own a Z-560 & Z-2300. After minutely inspecting both the drivers of Z-560 & Z-2300, I found out
1) Both have same magnet size & weight thus having identical rated power handling capabilities.
2) Z-2300 bass driver have more excursion capability that that Z-560 ones, maybe 10mm [estimated] where Z-560 ones have only 7mm. This is evident since Z-2300 ones have slightly longer & elongated stamped steel basket section between the spider & the magnet compared to Z-560 ones, providing the space for more excursions capability.
3) The cooling efficiency of the Z-2300 bass driver with its bigger vented pole piece is significantly higher than Z-560 ones.
The bass driver of Z-2300 with even higher excursion capability than Z-560 ones will definitely offer better sensitivity & accuracy not to mention the ability to handle more power over its rated input power with better cooling efficiency.Later I found out that Z-2300, Z-2200 & Z-680 all used this new driver.
Look below at the increase of the hole diameter of the vented pole piece:
Tang Band Z-560 subwoofer with smaller vented pole piece
Z-680 aka Z-2200 aka Z-2300 subwoofer with bigger vented pole piece
Z-2300 Bass Driver
Comparing Z-2300's aka Z-680 monstrous 8 inch bass driver on the left with the Onkyo's 8 inch bass driver on the right.
Note: Normally people confuse this bass driver as used in Z-680, Z-2200 & Z-2300 with the Tang Band W8-670Q model. Though both units look near identical, Z-2300’s bass driver is different from the W8-670Q in the rear section. It became absolutely certain when my friend’s Z-2300 bass driver went dead and I have to personally contact TangBand via email to ask the model of the driver used in Z-2300 & its price. I also send them the above pictures of the driver to help them identify. To my surprise, they replied after inspecting the pictures sent to them, that this bass driver do not belong to them or in any way represent one of their models. But they did agree that they supplied W8-670C drivers for Z-560. So, you see Z-680, Z-2200 & Z-2300 are not TangBands. Prior, I was also the victim of this case.
The subwoofer enclosure also houses a patented “U†shaped exponentially increasing bass reflex port to produce distortion free deep and rich bass experience. The enclosure is very deep, which is obviously good from an acoustical standpoint.
Z-2300 Satellites
Z-2300 uses 2.5 inch polished aluminum phase plug drivers in their satellites and are beautifully crafted to look like a piece of art. The 12W satellite drivers that Z-2300 uses are again from an unknown speaker company and does not in any way relate to 3 inch Tang Band (W3-594SB) units. I estimate a rated power of 10W & a max of 20W. But since these drivers get audio frequencies ranging from 150Hz to 20kHz, the power handling capability increases by at least two times. So these speakers can handle anything between 20W to 40W.
Satellite Drivers
With the polished aluminum phase plug drivers helping to reduce the path length differences about the cone surface, you get a smoothing and reinforcing the frequency response, particularly in terms of the highest frequencies the driver is capable of. There is some thermal dissipation one gives up by doing this, but the phase plug itself can serve as a heat sink for the voice coil and magnet pole.
CONTROL POD
The control pod of the Z-2300 is quite simple and minimalistic, which I prefer. No fancy lights just a big volume knob, a bass control, a 3.5 mm headphone jack, power LED and a power button. You can keep the control pod on your desk where ever you like and the controls are very convenient.
Here are some pictures of Z-2300 control pod innards
AMPLIFIER DETAILS
Audio design has always been a subject that stirs the passions of most electronics engineers and a subject where the pursuit of perfection has many times comes before considerations of cost. That aside sometimes the simplest circuits can offer the best solutions in terms of cost and performance. Z-2300 houses the amplifier in their subwoofer assembly.
Power Supply
The power supply of an audio amplifier is of vital importance, since it provides all the juice required by power amplifiers to drive the big speakers. An underperforming power supply will seriously limit the performance of an amplifier.
The power supply consist of:
i) A center tapped toroidal transformer manufactured by Ten Pao International. This transformer is rated at 150.9VA with +/- 20.1VAC secondary, 3.75A.
ii) A metal cased bridged rectifier to provide full-wave rectification from +/- 20.1 VAC to DC.
iii) A pair of CapXon 10,000 uF, 35V capacitors one for + 20.1 VDC and the another for – 20.1 VDC acting as ripple filters in order to smooth the DC output.
Toroidal Transformer Details
Manufacturer: Ten Pao International Ltd.
Part No: Z-2200 EU
Model No: TOG433028F0
VA Rating: 150.9 VA [Confirmed by Ten Pao]
Primary Input: AC 230V/50Hz
Secondary Output Voltage: AC 20.1V x 2
Secondary Output Current: 3.75 A
Diameter: 95 mm
Height: 45 mm
A toroidal transformer uses a doughnut shaped core & is much slimmer than a conventional (EI) transformer. It has numerous advantages over EI type such as low weight, low hum, low noise and also being smaller in size than an equivalent EI type. On the downside they are much more expensive than a conventional EI transformer. But it is worth the pay since you get better performance. A toroidal transformer has so many other performance advantages over EI type that it is hard to describe here other than to provide the performance ratio. Toroidal : Conventional(EI) :: 158 : 5 . It you want to know more in details go to the link below:
Bryston Transformers
The Bridge Rectifier
The Ripple Filter Capacitors
The transformer used here is rated to have an output of two times 20.1VAC when it has its rated load. So its resistance has already dropped the open circuit voltage and its peak will be 1.414 times higher which happens to be 28.4VAC. A single rectifier here drops it by 1VDC to 27.4VDC and smoothing the ripple by the power capacitors drops it by another 1.4VDC to 26VDC.
So, DC voltage supplied by the power supply is +/- 26 VDC, the current being 3.75 A.
Amplifier Chips
Z-2300 uses four Class-AB power amplifiers from STMicrolectronics. STMicrolectronic is a very renowned name in audio amplifier market.
The amplifiers used are:
i) A Japan Radio Corporation’s JRC-4565 operational amplifier. JRC-4565 is a dual op-amp which means it has two op-amps inside it to handle stereo channels.
ii) Two voltage regulators a 78M18 and a 79M18 supplying +/- 18 VDC respectively to feed JRC-4565 op-amp from the +/- 26.4 VDC power rail.
iii) One STMicroelectronics, Class-AB, 60W, TDA7296 power amplifier for each of the two satellites while the other two STMicroelectronics, Class-AB, 80W, TDA7295 are bridged together powering the subwoofer.
JRC-4565 operational amplifier
78M18 and 79M18 voltage regulators
Logitech Z-2300 Amplifier Innards
Reasons for using Class-AB Power Amplifiers
A quick look at many new low power speaker amplifiers on the market highlights the move to Class-D audio performance, but when it comes to low distortion and low noise and best sound quality, Class-AB still has the edge.
Class-AB architecture offers a signal to noise plus distortion ratio of up to 10 times better than its equivalent Class-D neighbour as well as providing a much simpler architecture which can be tweaked as required, without the need for reactive filter components on the output and the electromagnetic radiation resulting from an output stage switching at a few hundred kHz. Class-D amplification has inherent distortion in it and therefore is predominantly used in lower bandwidth amplification like in subwoofers. In other words it is quite impossible for a Class-D to achieve the level of linearity in frequency response produced by a Class-AB amplifier.
Ultimately it comes down to what you want, for efficiency and cost effectiveness Class-D are best, but if you are ready to sacrifice some efficiency & increase cost for the sake of sound quality then Class-AB are the best. In other words Class-A amps sound the best, cost the most, and are the least practical. They waste power and return very clean signals. Class-AB amps dominate the market and rival the best Class-A amps in sound quality. They use less power than Class-A, and can be cheaper, smaller, cooler, and lighter. Class-D amps are even smaller than Class-AB amps and more efficient, because they use high-speed switching rather than linear control.
The most important reason behind which multimedia speaker manufactures are switching from Class-AB to Class-D is to increase profit margin. Class-D is very cheap to produce and does not need require a big extruded aluminum heat sink or expensive toroidal transformers. They are basically switching power supplies but utilize pulse width modulation so as to be able to reproduce and amplify an alternating current. There are ok for subwoofers, but I honestly think that it is ridiculous to use a Class-D amplifier in a high end studio monitor.
In short, Class-D amps are more efficient but are only good for low frequencies applications like subwoofer amplification. Class-AB amps can be used full range amplification i.e from 20Hz – 20kHz. Class-D amps cannot be used on highs frequency response because they only produce square waves because of the technology involved, so they will make your highs sound lifeless and tinny. Class-AB amplifiers produce full variable signals and can capture subtle nuances better, sound warmer and generally have more depth in their sound.
Principles of Amplifier Operation in Z-2300:
1) A stereo audio signal comes in through the green 3.5mm audio connector with the control pod.
2) In the control pod, the signal passes through the main volume logarithmic potentiometer for attenuation.
3) This attenuated audio signal is then send down from the control pod to the subwoofer enclosure through a D-Sub connecter where the amplifier module exists. A JRC-4565 operational amplifier first receives this audio signal. The JRC-4565 having stereo handling capability distributes the audio signal into two places:
a) To the left and right satellite TDA7296 power amplifiers and then subsequently to the 2 satellite speakers.
b) Back up to the remote through the D-Sub connector.
4) Inside the remote, the stereo audio 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)
5) Audio signal output from the subwoofer bass potentiometer finally gets fed back into the subwoofer enclosure through the D-Sub connector to the bridged TDA7295 subwoofer power amplifiers and then to the bass driver.
The four power amplifier chips operate at 8 ohms load in Z-2300 amplifier module.
Technical analysis of Class-AB, STMicroelectronics of TDA7295 & TDA7296 DMOS Audio Amplifiers
The TDA7295 & TDA7296 are both monolithic integrated circuit in Multiwatt15 package, intended for use as audio class AB amplifier in Hi-Fi field applications (Home Stereo, self powered loudspeakers, Topclass TV). Thanks to the wide voltage range and to the high out current capability it is able to supply the highest power into both 4 & 8 ohm loads even in presence of poor supply regulation, with high Supply Voltage Rejection. The built in muting function with turn on delay simplifies the remote operation avoiding switching on off noises. TDA7295 have a maximum output capacity of 80W while TDA7296 has 60W.
Remembering that the power supply of Z-2300 is +/- 26 VDC, the current being 3.75 A.
TDA7296
Output Power vs. Supply Voltage @ 8 ohms
Looking at the Output Power vs. Supply Voltage graph of TDA7296 above, we see it can produce 38W of power at 26 VDC at a respectable 0.5% THD.
So, at +/- 26 VDC --> 38W @ 0.5% THD @ 8 ohms
Distortion vs. Output Power @ 8 ohms
Distortion vs. Output Power graph of TDA7296 shows that at 38W @ 0.5% THD @ 8 ohms @ 26 VDC it starts to clip & distort. So in order to produce distortion free sounds this id the effective maximum of the chip.
Effective maximum of TDA7296: 38W @ 0.5% THD @ 8 ohms @ 26 VDC
Power Dissipation vs. Output Power @ 8 ohms
The Power Dissipation vs. Output Power graph of TDA7296 shows it as a very efficient Class-AB amplifier. At 38W @ 0.5% THD @ 8 ohms @ 26 VDC, the power dissipation is just 12W. This means if 50W is fed by the power supply to this TDA7296, it will deliver an output of 38W to the speaker whereas only 12W will be lost as heat.
So, this TDA7296 have an efficiency of 76% when it is producing 38W @ 0.5% THD @ 8 ohms @ 26 VDC. The power dissipation increases when the output power is reduced to half.
TDA7295
Two TDA7295 are bridged together into an 8 ohm load to power the subwoofer. Each of these TDA7295 sees effectively a 4 ohm load when bridged into an 8 ohm load. If you bridge an amplifier, the available power is the power of a single channel into half the load impedance multiplied by two.
Output Power vs. Supply Voltage of a single TDA7295@ 4 ohms
Looking at the Output Power vs. Supply Voltage graph of a single TDA7295 above, we see it can produce 65W of power at 26 VDC at a respectable 0.5% THD.
So, at +/- 26 VDC --> 65W @ 0.5% THD @ 4 ohms
Now if we bridge a pair of TDA7295, the available power is the power of a single channel into half the load impedance multiplied by two. Since TDA7295 produces 65W into 4 ohms, bridged it will produce 65 X 2 = 130W into 8 ohms.
So, at +/- 26 VDC a pair of bridged TDA7295 will produce --> 130W @ 8 ohms
Distortion vs. Output Power of a pair of bridged TDA7295@ 8 ohms
Distortion vs. Output Power graph of TDA7295 shows a pair of bridged TDA7295 after 100W starts to clip & distort. So in order to produce distortion free sounds this 100W is the effective maximum of the bridged TDA7295.
Power Dissipation vs. Output Power of a single TDA7295@ 4 ohms
The Power Dissipation vs. Output Power graph of TDA7295 shows it as an efficient Class-AB amplifier. At 65W @ 4 ohms @ 26 VDC, the power dissipation is 30W. This means if 95W is fed by the power supply to this TDA7295, it will deliver an output of 65W @ 4 ohms to the speaker whereas 30W will be lost as heat. In a bridged format it will deliver an output of 130W @ 8 ohms to the speaker whereas 60W will be lost as heat.
So, a pair of bridged TDA7295 have an efficiency of 68% when it is producing 130W @ 8 ohms @ 26 VDC. The power dissipation increases when the output power is reduced to half.
Looking at the above figures its seems that Logitech’s claim of 200W is true, since each satellites will have 38W while the subwoofer will get 130W which sums up to: 38 + 38 + 130 = 206 W @ 8 ohms @ 26 VDC
But, unfortunately that is not the case.
Z-2300 amplifier’s continuous power output capability
In order to produce 200W of continuous power, an amplifier will need a transformer that is capable of to deliver a minimum of 1.27 times the claimed wattage. Since Watt is volts multiplied by ampere, 200W of output requires 254 watts or 254VA transformer as a minimum requirement.
So, Z-2300’s supplied 150.9VA will produce a maximum of: 150.9/1.27 = 119W =~ 120W of continuous power @ 8 ohms @ 26 VDC
Since the ratio of power distribution between the subwoofer and the satellites are in the order of 1.71:1, the subwoofer will get 76W of continuous power while each satellite gets 22W of continuous power.
This becomes even more evident from the fact that the bass driver has a rated input power 80W, while the satellite speakers can handle anything between 20 to 40 watts.
The Total RMS Continuous Output Power of the four amplifier chips = 50(TDA7295) + 50(TDA7295) + 30(TDA7296) + 30(TDA7296) = 160W whereas the Total RMS Continuous Output Power of these four amplifier chips is 120W for Z-2300 since the the power supply limits the maximum power output.
Also these amplifiers will produce a lot of distortion & noise at the peak 160W power output. So, in order to produce distortion free, linear sound the amplifiers generally needs to reduce its output peak power by 25% or more. Using an amplifier with some extra “headroom†will help assure that only clean, undistorted power gets to your speakers. Reducing the maximum power from 160W to 120W Z-2300 creates a 25% headroom and justifies the stated system THD of better than 0.05% before clipping & signal to noise ratio of > 100dB.
hyeah:
