STK0039 Discrete component replacement?

rudedaddy

Member
2020-01-19 3:33 pm
Hi guys .... I am having a rough time with these STK0039 ICs' . I have ordered a set from China and ebay ( wasting my time and money ) with them failing from the get go.There has to be a schematic with discrete components I can build. I see there is one for the STK0050 but the circuit is a bit different than the STK0039. I love this Pioneer SX 680 AND HATE TO SCRAP IT . Can any one help ?
 

dreamth

Member
2010-11-18 9:12 am
They are simple darlingtons and a superdiode .You can safely replace them with two darlington transistors , 4 1n4148 diodes and a few resistors.Much better compound transistor with discretes as stk chips used to fail because the drivers were sharing the final transistor temperatures.
 

rudedaddy

Member
2020-01-19 3:33 pm
I have an idea in mind .....will this work ?
 

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You can test the circuit without the STK installed,
temporarily solder a couple of 1K resistors from STK pins 0, to 8 and 1 to 3

I agree, but he should close the feedback loop first by connecting two ~500 ohm resistors in series between pins 0 to 8 and 1 to 3, and connect the lower end of the feedback resistor (56k, post # 5) to the midpoint between the two added resistors. And disconnect everything from the amplifier input and output (speakers)!!!
 
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Looks pretty crude to me. Transistor choice aside (oversized and quite slow - what about e.g. BD139/140 + 2SC5200/2SA1943?), just two Si diodes + ~300 mV (~1.7 V max) is likely to be substantially underbiased for 4 B-E drops (~2.2-2.4 V or so). Any chance you could get a traditional Vbe multiplier in, or at least one more diode? Also, R4 is too big (no doubt sized for some cute TO-92L drivers that are happy at little over 2 mA). I'd say ~180R tops even for BD139/140 drivers (120R preferred), and for TIP42s I'd go as low as 75R.
 
You do not have to insist on getting the STK0039, the same can be replaced with STK0049, STK0059 (same housing H6-10, same pinout, quasi-complementary output) or with STK0050, STK0055 (same housing H6-10, same pinout, complementary output) or with STK0060, STK0070, STK0080 (slightly larger enclosure H8-10, same pinout, complementary output) or with ECG1280/ECG1282/NTE1282 (same enclosure H6-10, same pinout, quasi-complementary output) or with ECG1281/NTE1281 (same enclosure H6-10, same pinout, complementary output). Pin #4 is left unconnected on all modules as well as on the schematic of the Pioneer SX-680 receiver. Post a seller link here before buying because 90% of what is on offer is fake, refurbished or busted... and with some luck someone might recognize the real deal for you.
 

rudedaddy

Member
2020-01-19 3:33 pm
I thank you for this info .... I know that these other ICs you mention about are more expensive plus have a higher b+ voltage . This amp has a 35 volt ( +/- ) power supply . I don't know why the original ICs are failing after one or two years ( good heat sink compound used )... right now between 1 and 0 voltage is 1.48 volts ( discrete components )
 
That is correct, you have 1.48V across 2K= 0.74mA
Actuallly the test resistors could be as low as 220 ohm, but this a quick test that the input stage(IPS) and the voltage amp stage (VAS) are working correctly.
The mid point voltage, summing point of the two emitter resistors measured with respect to ground should be close to 0V.
I don't know why the original ICs are failing after one or two years.
I know why, because they are crap, that is why I designed the discrete module version. I put the design out in the public domain for free, you can order your own blank pcb's or you can order the ones on eBay that come with the heatsinks to make mounting easier as the holes match the original STK-00xx.
Good luck
 

dreamth

Member
2010-11-18 9:12 am
Indeed, most of the time i saw the supply rails being higher than the STK specs allowed at maximum rated power.all STK have mentioned 2 max voltages.Probably nobody cares about the second one...
 

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