Well I did some tests today.
Without the coupling cap,audio is better for sure.
I think I fixed the treble problem.Don't know what did the trick.
However as I was testing capacitors,I left one channel without a cap and while I was testing the other channel,well it burnt 🙁
Doesn't seem logical why it was burned since there was no signal ,or anything at that channel,just the cap missing.
I'll have to find another one now.The bad thing is that it's impossible to find a genuine one.I'll open it to see if that was original or fake one.
If the one I get is fake and sound awfull ,well there is always this solution
When STK4241V burn...
Without the coupling cap,audio is better for sure.
I think I fixed the treble problem.Don't know what did the trick.
However as I was testing capacitors,I left one channel without a cap and while I was testing the other channel,well it burnt 🙁
Doesn't seem logical why it was burned since there was no signal ,or anything at that channel,just the cap missing.
I'll have to find another one now.The bad thing is that it's impossible to find a genuine one.I'll open it to see if that was original or fake one.
If the one I get is fake and sound awfull ,well there is always this solution
When STK4241V burn...
Without a coupling capacitor it could be your getting high DC on the output and fried the IC and maybe the speaker too ?
Speaker is ok,I have speaker protection with uPC1237.Protection actually engaged and that's how I figured that something was wrong,as I didn't have anything connected to that channel.
The IC got fried,and there is DC output on that channel.
The IC got fried,and there is DC output on that channel.
Once you get new IC I would put coupling cap back and try an RF filter just after coupling cap. Put an R in series then a cap to ground. Use 22K and 100pf to start with.
Yes I will put the coupling cap back.
There is RF filter already as I figured out later.
With testing I solved the noise problems etc.Better routing of the cables,grounding and it did the trick.
I was trying to solve the treble problem,it somehow got fixed,I don't know how and while I was testing for the effect of the coupling cap on the sound quality,the channel got fried.
Too bad ,because I was going to rebuild it tomorrow.
Oh well,I guess I'll buy a couple of things to improve it further.
There is RF filter already as I figured out later.
With testing I solved the noise problems etc.Better routing of the cables,grounding and it did the trick.
I was trying to solve the treble problem,it somehow got fixed,I don't know how and while I was testing for the effect of the coupling cap on the sound quality,the channel got fried.
Too bad ,because I was going to rebuild it tomorrow.
Oh well,I guess I'll buy a couple of things to improve it further.
Have fun removing that blown IC.
I have removed a few TDA IC's and they usually aren't too bad to remove.
I chop off IC leads right up near IC itself to keep them long, then heat up pin then grab it with long nose pliers and pull pin out.
I added a short piece of silicon tube to my solder sucker and that makes a better seal when clearing holes.
I have removed a few TDA IC's and they usually aren't too bad to remove.
I chop off IC leads right up near IC itself to keep them long, then heat up pin then grab it with long nose pliers and pull pin out.
I added a short piece of silicon tube to my solder sucker and that makes a better seal when clearing holes.
Sometimes they blow on no load, and as in your case, infinite gain because there was no capacitor.
I would put a 7293, 7294 or 49xx chip in place of the STK, as it is they were noted for blowing up for no reason.
Take the chips higher up on the heat sink if needed, and the substitutes I suggested are mono, you need pairs for stereo.
I would put a 7293, 7294 or 49xx chip in place of the STK, as it is they were noted for blowing up for no reason.
Take the chips higher up on the heat sink if needed, and the substitutes I suggested are mono, you need pairs for stereo.
Be happy your transformer did not blow.
LM498xx you can choose which variant, and as the supply is +/-50 volts, you can put TDA 7293, the 94 also blows for no reason.
You do get ready PCB and modules, so the conversion is easier.
I had asked you to put a dummy load...I blew a LA4440 because the input cap fell out, bad soldering during manufacture.
Very expensive, chip was INR 28 or about 40 US cents!
Cap was 3 Rupees, 1 hour spent was the main irritant.
Same fault in your case.
In any case the module was old and noisy, so it could have blown within months.
Now plan for the replacement, and a possible general upgrade of the pre-amp section.
If it is within your capacity, do try making the STK substitute if you feel like doing it.
LM498xx you can choose which variant, and as the supply is +/-50 volts, you can put TDA 7293, the 94 also blows for no reason.
You do get ready PCB and modules, so the conversion is easier.
I had asked you to put a dummy load...I blew a LA4440 because the input cap fell out, bad soldering during manufacture.
Very expensive, chip was INR 28 or about 40 US cents!
Cap was 3 Rupees, 1 hour spent was the main irritant.
Same fault in your case.
In any case the module was old and noisy, so it could have blown within months.
Now plan for the replacement, and a possible general upgrade of the pre-amp section.
If it is within your capacity, do try making the STK substitute if you feel like doing it.
I'm back for the update on that project.
I got a new STK,old one was definetely a fake one as I opened it.
I replaced it,also on both boards changed the input capacitors with polypropylene capacitors at 400V and changed the coils at the output as they were made wrong.
I added a bunch of fuses ,a couple after the main capacitors and one on the 12V line just to be sure.
Also wired the cables better,got a better shielded cable for the signal put everything together yesterday.
Sound has vastly improved,no more distortion.Also noise has gone away a lot.It's almost non audible anymore.Quality has gone up too.
The new STK seems to be a better one as sound is coming out warmer than the other one.
Also it has significantly lower DC offset.
15 and 26 mV while the other old STK has 125 and 135mV.
Last things I want to do is add some capacitors parallel to the rectifier bridge to help the diodes when I'm powering up,as there is no room to add a soft start circuit.
Also I will add a thermal shutdown circuit with a couple of thermostats and a relay on the main AC just to be sure.
Thank you for your help guys.I will post a pic too,with the final result.
I got a new STK,old one was definetely a fake one as I opened it.
I replaced it,also on both boards changed the input capacitors with polypropylene capacitors at 400V and changed the coils at the output as they were made wrong.
I added a bunch of fuses ,a couple after the main capacitors and one on the 12V line just to be sure.
Also wired the cables better,got a better shielded cable for the signal put everything together yesterday.
Sound has vastly improved,no more distortion.Also noise has gone away a lot.It's almost non audible anymore.Quality has gone up too.
The new STK seems to be a better one as sound is coming out warmer than the other one.
Also it has significantly lower DC offset.
15 and 26 mV while the other old STK has 125 and 135mV.
Last things I want to do is add some capacitors parallel to the rectifier bridge to help the diodes when I'm powering up,as there is no room to add a soft start circuit.
Also I will add a thermal shutdown circuit with a couple of thermostats and a relay on the main AC just to be sure.
Thank you for your help guys.I will post a pic too,with the final result.
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Overall, a good outcome.
One thing you must note that the replacement is also most likely a clone, as the STK went out of production at Sanyo in about 1990 or so.
The good fakes work but PLEASE don't change the volume suddenly....they blow up. Tip from my relative the components dealer.
And please run less than max volts, set the supply as if you are running 4 ohm loads when running 8 ohms.
Also be careful about heat sinking... that is the cause of most failures.
Also check the input voltage from the pre amps.
One thing you must note that the replacement is also most likely a clone, as the STK went out of production at Sanyo in about 1990 or so.
The good fakes work but PLEASE don't change the volume suddenly....they blow up. Tip from my relative the components dealer.
And please run less than max volts, set the supply as if you are running 4 ohm loads when running 8 ohms.
Also be careful about heat sinking... that is the cause of most failures.
Also check the input voltage from the pre amps.
Thank you for your suggestions.
Yes,it's propably a fake,but a better fake than the old ones I had.
I'll see if I can find genuine ,as a trustworthy store in UK claims it has some from Sanyo.
Voltage is at 48-50V.That's far less than the max voltage and even lower than the suggested which is 53V.So I guess it's ok.
I have attached a big heatsink at each STK with a 80mm fan.I will run them with some load to check temps.Detasheet claims that up to 125 oC is good so what max temp is considered ok for casual use?I'll have to get and the proper thermostat for that temp.
Is 90-100 oC a good max temp at heavy load?
Also what should be the input voltage from the pre amp?
Yes,it's propably a fake,but a better fake than the old ones I had.
I'll see if I can find genuine ,as a trustworthy store in UK claims it has some from Sanyo.
Voltage is at 48-50V.That's far less than the max voltage and even lower than the suggested which is 53V.So I guess it's ok.
I have attached a big heatsink at each STK with a 80mm fan.I will run them with some load to check temps.Detasheet claims that up to 125 oC is good so what max temp is considered ok for casual use?I'll have to get and the proper thermostat for that temp.
Is 90-100 oC a good max temp at heavy load?
Also what should be the input voltage from the pre amp?
Input from pre amp around 250 mV I think.
What are you doing with 2 stereo STK modules?
I would run it about 45 volts to be safe, or use 8 ohm speakers only.
Try to reduce supply volts, and proper heat sink mounting is essential.
If the UK guy is charging more than 10 Euro, possibly genuine.
Here fake ones are 3 or so.
Don't load it beyond 80% of rated load.
That is among the reasons I asked you to go for a 7293 or 498xx chip. they are much more reliable and generate less heat.
What are you doing with 2 stereo STK modules?
I would run it about 45 volts to be safe, or use 8 ohm speakers only.
Try to reduce supply volts, and proper heat sink mounting is essential.
If the UK guy is charging more than 10 Euro, possibly genuine.
Here fake ones are 3 or so.
Don't load it beyond 80% of rated load.
That is among the reasons I asked you to go for a 7293 or 498xx chip. they are much more reliable and generate less heat.
I think 250mV is low.
I had 4 speakers,2x70watts and 2x100 watts and I thought I should make an amp with 4 outputs and someone suggested me the STKs so I made one with these.So that will be the load for the STKs.All of them are 8 ohms so the STKs won't get too stressed.
What do you mean by proper heatsink mounting?They way it will be cooled or the STK needs a special way to be mounted onto the heatsink?
I think I found genuine STKs from a good reseller here too.I'll check them and get a pair if they are.
I had 4 speakers,2x70watts and 2x100 watts and I thought I should make an amp with 4 outputs and someone suggested me the STKs so I made one with these.So that will be the load for the STKs.All of them are 8 ohms so the STKs won't get too stressed.
What do you mean by proper heatsink mounting?They way it will be cooled or the STK needs a special way to be mounted onto the heatsink?
I think I found genuine STKs from a good reseller here too.I'll check them and get a pair if they are.
I can only go on what I have heard and read about STK.
Some people have found them unreliable.
Many years ago I nearly used a STK for a mobile disco but instead chose a discrete class AB amp instead.
Some people have found them unreliable.
Many years ago I nearly used a STK for a mobile disco but instead chose a discrete class AB amp instead.
STK should have an even film of heat sink compound, and proper torque with washers or screws with large heads to mechanically hold it tight to a flat heat sink.
To check, rub it on fine abrasive paper kept upside down on a thick book, the abrasion will show up any uneven surfaces.
STK date back to class A and AB days, there were no class D amps then.
They went out of production because competitors like NEC, Panasonic, ST and NS made better devices, more compact and reliable.
The STK sound is different, but now it is rare to find originals.
It was a bad suggestion to use for a new build, I thought you were repairing an old unit.
That said, STK 4141 based amps with FM module are popular here, about 15 Euros...the STK are Chinese copies, not from Sanyo or ON Semi.
As for output levels, check RIAA, and the old tape deck specifications, that will give you a reasonable figure, phono output is much lower than the output from decks and tuners.
To check, rub it on fine abrasive paper kept upside down on a thick book, the abrasion will show up any uneven surfaces.
STK date back to class A and AB days, there were no class D amps then.
They went out of production because competitors like NEC, Panasonic, ST and NS made better devices, more compact and reliable.
The STK sound is different, but now it is rare to find originals.
It was a bad suggestion to use for a new build, I thought you were repairing an old unit.
That said, STK 4141 based amps with FM module are popular here, about 15 Euros...the STK are Chinese copies, not from Sanyo or ON Semi.
As for output levels, check RIAA, and the old tape deck specifications, that will give you a reasonable figure, phono output is much lower than the output from decks and tuners.
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That's what I have done with the STK cooling.The way you said about the mounting,I thought that it needed a special way.
I gave it a try with a pair of 80 watt speakers and in heavy bass songs temp on the STK was up to 70 oC ,so they are pretty cool and with a 90 oC thermostat I guess it will be ok.
It is an old amplifier I made 10 years ago and I was repairing it now to get a better result.
Of course I would't make from scratch an amp with STKs now.
I gave it a try with a pair of 80 watt speakers and in heavy bass songs temp on the STK was up to 70 oC ,so they are pretty cool and with a 90 oC thermostat I guess it will be ok.
It is an old amplifier I made 10 years ago and I was repairing it now to get a better result.
Of course I would't make from scratch an amp with STKs now.
And here is a couple of pics.The white box to the right a pre amp I made with NE5532.Chinese board but I replaced the NEs with genuine ones.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.