Bangkok motor show 2008 Thailand

Hi just to share with you some photoes from Bangkok International Motor Show 2008 Thailand, so I'm not prefer to write so much here now just have a look to the showed car and pretty women..

Lexus IS-F

New Honda Jazz 2008

Subaru

Hankook

Honda Motocycle

Will be continue...

DIY Power Amplifier

Introduction to DIY Power Amplifier project.
As my requirement for a small power amplifier by do it by yourself or let say DIY power amplifier with reasonable construction cost, it intended to be a 2 channels power amplifier for my home theater drives for a rear speaker pair, so at this moment my next DIY power amplifier design target/objective and specifications are following:

1. Quite simple circuit.
2. 40-50 Wrms/channel.
3. Compact body dimension.
4. High grade devices to the points which provide stand out sound quality.
5. Fully complementary circuitry by solid state devices.
6. Stand alone operation without pre amplifier.
7. 220 VAC electrical power input.
8. Nice and simplicity.

Design and construction :
This is a second power amplifier design and construction by myself, a previous one 100 Wrms/channel one has been in 1997 since I was a student, its name is TH200 and then upgraded in 1998 and rename to TH-200SE for better sound quality.
TH-60 is the name of a new one as above target I wrote, so I start the exterior works with below is the empty universal case which easy to purchase.

Empty chassis.

Transformer and I/O devices are installed inside.

Hi current power supply circuit
This is the simple power supply circuit, normally is a double voltage rectifier I deliberately use several smaller filter capacitors connect parallel, rather than few of bigger one such 10,000 or 15,000 uF, thus 6 of 4,700 uF are here, the output voltage is +- 32 VDC

The rectifier schematic.

The advantage of this technique is the sound for power amplifier is provides more fitting, expeditiously at especially bass timing.

Rectifier on PCB.

Regulated power supply of voltage amplifier stage.
A pair of +-38 VDC output from Regulated power supply of voltage amplifier circuit is only uses for the differential input stage and voltage amplifier stage, due to those stages are sensitivity impact the sound quality with the ripple voltage or unstable voltage level generated from the higher current load such output stage and normally from ordinary rectifier circuit, so this is the reason why separate power supplies for each voltage amplifier and current amplifier are necessary.

Voltage regulator schematic

The advantages according to the sound quality of this technique are such lower noise, high dynamic headroom and more…

Voltage regulator on PCB.

How it works, this regulated power supply is use high power opamp working as voltage multiplier from the referenced voltage and the the error voltage is feedback for correction.

As to now all kinds of power supply are installed into the power amplifier chassis.

Main power amplifier circuit, the TH-60 power amplifier is transistor-based, I try to design it simply. The difference input stage, voltage amplifier stage, current drive and output stage and fully complimentary. The bias current or idle current level are be class A biasing, current mirror is improve overall slew rate.

Each side of power amplifier schematic.

Input coupling capacitors are high grade made in Italy, but I forget their brand.

Match pair output power transistor.

2SC3263 and 2SA1294 is a match pair power transistor from Sanken, like most hi-end power amplifier TH-60 is used hi-end power transistors as well, they FT parameter is so high 60 MHZ and 130 W power dissipation . Output idle current is set to 100 mA.

Remove Re at emitter of power transistor.

Reduce output impedance by remove some small resistance resistors Re at Emitter, I’m confidence that the temperature bias controller circuit can copes with increasing of heat sink temperature at high driving level.
One out of the advantages of low output impedance in power amplifier impact to the output sound listens from loudspeakers is amplifier can better adroitly stop and control the loud speaker’s voice coils, so the sound is well-fitting.

TH-60 DIY power amplifier on PCB .

Finish work for 1st my DIY power amplifier.

Finally it has been finished.

Let go the first listening first sound from TH-60 my DIY power amplifier, so my first test system comprised of VCD/DVD/CD player (the cheap one made in China) with unbalance connection to amplifier directly without preamplifier.
Unbelievable!, My first feeling while listening “ it provides so much distortion sound via speaker”.

On test TH-60 my DIY power amplfier.

2nd time test, I just change the previous one the CD Player, so then “ it was very nice sounding amplifier, extremely difference sound quality compare with the first test.

Let listen sound from DIY TH-60 Power amplifier without pre amplifier or goto youtube video.

Output power signal delivered to load.

My next post is to be the output power measurement, see you.