The STK465 is a Hybrid IC made by the Sanyo Corporation of Japan. It is a Stereo Amplifier chip in a 16 pin 4016 package. This chip is an IMST Hybrid IC first developed by Sanyo in 1969. The outline package is approximately 78 mm × 66 mm.
This IC contains the circuitry for two channels, and provides a maximum output of 30 watts per channel. It uses a split rail voltage and accepts a maximum voltage of ±41 V. The recommended supply voltage is ±28 V, and the load resistance should be 8 Ω.
Although Sanyo stopped making this, it is still utilised by many hi-fi and electronics enthusiasts for building their first stereo amplifier, because the sound quality is excellent.
This chip is usually in vintage amplifiers, and replacements are always in great demand. There is a moderate market for recycled and new ICs to keep vintage audio amplifiers working.
Understanding the pinout of this IC is vital when repairing stereo amplifiers. I have drawn this diagram showing the power supply and audio output pins. These are the most important pins when diagnosing amplifier faults.
If you had an amplifier that was not working then these are the pins to check. Pin 3 and Pin 12 should both be receiving –Vcc from the power supply. Pin 9 should be receiving +Vcc from the power supply.
Pin 6 and Pin 7 are typically joined as they provide the positive phase and negative phase of the amplified output signal in a push-pull design. These pins should output 0 V DC when there are no input signal. The same applies to the Right channel on Pin 10 and Pin 11.
In a faulty chip the internal transistor pairs -- which are arranged in a Darlington configuration -- become short and one can expect the full rail voltage (+Vcc or –Vcc) at the load output pins. Obviously when this happens, one would want the speaker protection mechanism to prevent the load relay from engaging. If there is no protection circuitry, then obviously the speaker coils will burn out.
Amplifier Circuit Diagram
Here is an application circuit example for 30 watts per channel amplifier. This is the circuit shown in the documentation, which works well.
I have found this circuit to be a very useful reference when repairing vintage amplifiers, especially when I do not have a service manual for it.
Many amplifiers often have additional overload protection circuitry, however ignoring that, I have found many amplifiers that use this chip to follow the same design layout.
|IC||Max Supply Voltage (±V)||Power Output (W)|
These ICs are pin compatible; however, their maximum supply voltage is different. A qualified engineer must observe the voltage range of these packages. Providing the supply voltage is within the maximum range the chip used, then, it can work with minimal modification.
I was looking to buy one of these to repair a vintage amplifier and found that the prices varied quite a lot. This is obviously a discontinued product; however, it appears that small quantities are available from the Far East.
Considering that the amplifier I was repairing was an old one that was not worth much I was willing to go as high as a fiver but not much more.
There are plenty of sellers selling these ICs from China as well. I found a seller on eBay who was providing a one-year guarantee, and accepting returns, and his price was within my budget.
Places such as eBay provide such great buyer protection that it is no problem having a go buying from sellers abroad.
If you are a poor electronics student or hobbyist planning to build an amplifier with this chip, then a Prototype Matrix Board might be an ideal choice. You can get some cheap boards on eBay that would be ideal for this purpose.
Inside STK465 Chip
I was just recently repairing an amplifier that had one of these chips, which needed replacing. I decided to open the faulty chip module to have a look at the IMST Hybrid design and to see if it was possible to repair it. You can see more photographs of the inside in the IMST Hybrid ICs page.
On eBay, there are plenty of sellers with recycled chips. Recycled chips are great as they are very low cost, and sellers in China can sell one for less than five pounds. I have bought twice so far and each time I received a defective chip. However, after contacting the seller, they were happy to send a working chip the second time round.
Recycled chips are good value only if the seller is testing them properly. It is possible to set up an amplifier with a chip socket, to test the chips. Unfortunately, most sellers may not have this type of equipment.
The low cost is tempting, and it is an economical option for an old amplifier that may not be worth much. However, the disadvantages are, having to wait perhaps up to three weeks for delivery, and spending time installing it, only to find out that it is faulty.
De-soldering the previous chip (all 16 pins), cleaning off the heatsink compound, applying fresh compound, soldering the new chip, can take time and a lot of effort can go to waste, if the replacement chip turns out to be faulty. If you have lots of patience and can forgive the seller and wait for a good chip, then it can be advantageous to both sides.
STK465 Amplifier Circuit Diagram
STK465 Transistor Equivalent Circuit Diagram
IMST Hybrid IC Design