Does this circuit have any kind of speaker protection. And if so could you explain it.
While testing a new speaker the speaker shorted and after that one chanell is dead. (Back to square one for me). It was a 250 watt speaker. But locally made.
If this thing has no speaker protection I think its time to bin this amp and just build something with Mosfets / transistors that way the parts are easy to get and replace.
Im on a low budget and plan to continue running crappy locally made speakers. That is not going to change.
The Left channel has stopped working. Again lol.
While testing a new speaker the speaker shorted and after that one chanell is dead. (Back to square one for me). It was a 250 watt speaker. But locally made.
If this thing has no speaker protection I think its time to bin this amp and just build something with Mosfets / transistors that way the parts are easy to get and replace.
Im on a low budget and plan to continue running crappy locally made speakers. That is not going to change.
The Left channel has stopped working. Again lol.
The circuit around TR2 ... TR5 and RL1 seems to be a DC protection for the loudspeakers.
When there is a big positive DC voltage at one of the outputs, the voltage across C35 increases until TR2 turns on. With a big negative DC voltage, the voltage across C35 goes negative and TR3 turns on.
TR2 or TR3 then pulls down the base of TR4. TR4 then cuts off the base current to TR5, turning off the relay RL1 and protecting the loudspeakers, assuming the relay can handle the voltage and current.
TR1 also turns off the relay when there is something wrong, but I don't know what kind of fault it is supposed to protect against. The STK2250SL datasheet may explain that.
When there is a big positive DC voltage at one of the outputs, the voltage across C35 increases until TR2 turns on. With a big negative DC voltage, the voltage across C35 goes negative and TR3 turns on.
TR2 or TR3 then pulls down the base of TR4. TR4 then cuts off the base current to TR5, turning off the relay RL1 and protecting the loudspeakers, assuming the relay can handle the voltage and current.
TR1 also turns off the relay when there is something wrong, but I don't know what kind of fault it is supposed to protect against. The STK2250SL datasheet may explain that.
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Maybe the overcurrent protect signal is coming from pins 3, 5, 12, 14 of the STK2250, then turning on Q1 or Q4?
But there are very few protection schemes that can guarantee an amp channel will survive a speaker short!
If STK2250's are expensive or hard to get in your part of the world, maybe a discrete design would be more practical. But it may challenge your troubleshooting skills if/when it does fail. 😉 And it's likely the protection circuit won't be a whole lot more more reliable.
Cheers
But there are very few protection schemes that can guarantee an amp channel will survive a speaker short!
If STK2250's are expensive or hard to get in your part of the world, maybe a discrete design would be more practical. But it may challenge your troubleshooting skills if/when it does fail. 😉 And it's likely the protection circuit won't be a whole lot more more reliable.
Cheers
What do you think off the speaker protection boards being sold on amazon.in
Just enter Speaker Protection and they show up.
Then this is also this dedicated IC.
https://diyaudiocart.com/image/data/downloads/C1237HA/C1237HA.pdf
Im wondering what kind of impact they have on sound quality.
They are cheap as chips so I plan to buy one and test it on the scope. May make a video of it.
The basic design seems to be same on all of them with only the relay ratings changing.
I was kinda hoping that one of the FR would offer some kind of protection.
There are some options on amazon that also sell STk Boards i.e. the complete board built externally. So if one part fails you can just replace that.
I dont think its possible to find NOS of these chips pretty much everything in the market is a china clone.
I really like the audio off these STKs though they sound so much better than the new class D amps.
I have some audiophile friends who wont let me play music unless its off a class A amp or a class a/b lol.
Thanks for your replies and inputs.
The discreet route. Seems to be a good option. Maybe with something like this.
https://www.amazon.in/B-Tech-Audio-...=stk&qid=1653038530&sprefix=st,aps,416&sr=8-8
Just enter Speaker Protection and they show up.
Then this is also this dedicated IC.
https://diyaudiocart.com/image/data/downloads/C1237HA/C1237HA.pdf
Im wondering what kind of impact they have on sound quality.
They are cheap as chips so I plan to buy one and test it on the scope. May make a video of it.
The basic design seems to be same on all of them with only the relay ratings changing.
I was kinda hoping that one of the FR would offer some kind of protection.
There are some options on amazon that also sell STk Boards i.e. the complete board built externally. So if one part fails you can just replace that.
I dont think its possible to find NOS of these chips pretty much everything in the market is a china clone.
I really like the audio off these STKs though they sound so much better than the new class D amps.
I have some audiophile friends who wont let me play music unless its off a class A amp or a class a/b lol.
Thanks for your replies and inputs.
The discreet route. Seems to be a good option. Maybe with something like this.
https://www.amazon.in/B-Tech-Audio-...=stk&qid=1653038530&sprefix=st,aps,416&sr=8-8
I checked the schematic and must say:
This amp AKAI AM-U310 has a fully developed protection circuit for
The Basis pin of TR4 is the trigger to pull for any turn-off condition. It goes from +14.3V in normal on-condition to near 0V when pulled. Consequentially TR5 releases speaker protection relay RL1.
The typical aging problem with protection circuits is the DC filter capacitor C35 (220µF 6.3V). Electrolytics with this low voltage rating I will always replace immediately without wasting time measuring. Use min 25V types instead.
With amps of this age I replace all protection electrolytics.
- Johannes
This amp AKAI AM-U310 has a fully developed protection circuit for
- over-current (TR1 and TR? below)
- DC offset positive (TR2) or negative (TR3)
- loss of power to drop relay contact immediately (D3, D6, D7)
The Basis pin of TR4 is the trigger to pull for any turn-off condition. It goes from +14.3V in normal on-condition to near 0V when pulled. Consequentially TR5 releases speaker protection relay RL1.
The typical aging problem with protection circuits is the DC filter capacitor C35 (220µF 6.3V). Electrolytics with this low voltage rating I will always replace immediately without wasting time measuring. Use min 25V types instead.
With amps of this age I replace all protection electrolytics.
- Johannes
+1 on replacing those caps. The circuits are designed to behave properly when the caps are NEW, but go to hell in a hand basket if the caps get the slightest bit leaky or develop high internal resistance. Small electros with low (or no) DC bias are the WORST offenders. And higher rated voltage caps will often fare better. When I design one of these circuits, I use ceramic caps if at all possible. Increasing the resistances and decreasing the caps in the circuit to maintain the right time constants. If you can get an X5R cap that will FIT by all means use it. Doesn’t matter if the dielectric is nonlinear or if the voltage coefficient is high - it will do better than any electrolytic in 10 years. The caps might cost two or three dollars each but you never have to eff with it again.
Actually they do - and WHEN they do the contacts need cleaning. Oxides are partially rectifying and produce distortion. Sometimes GROSS distortion at low levels.
When I have one that does this, my usual way of “clearing” it is to crank the music way up. It will basically fry the “diode” and turn it back into a resistor. If that doesn’t work Emory paper will. If you worry about the last .0001% of distortion this may not be good enough - the solution in that case is a better quality relay. They do vary, depending on what they are made for. Contact materials matter.
In the Real World I find it hard to:
On the other side,the OP is worried about an amp which burned shorted and fried a speaker but maybe those are minor matters.
when talking about a commercial 1982 amplifier which brags about:
and which already has a Relay there (ugh! metallic contacts!!! 😱 ) since Day 1 , but hey, this is DIY Audio and we MUST worry about things!!!!!
On the other side,the OP is worried about an amp which burned shorted and fried a speaker but maybe those are minor matters.
If the relay failed to open when output transistors shorted, but wasn’t welded shut - maybe the caps should have been replaced a long time ago. They are not completely fail safe - just a whole lot better than nothing.
Because the speaker protection circuit did not work as designed. It took out the speaker and the amp.
I was mistaken the speaker protection circuits being sold as modules only protect your speakers if the amp acts up. It does not protect your amp if the speaker shorts at least in this case. The best idea I could come up with for amp protection is a fuse on the speaker line.
Im not sure what took out what. But I now have one shorted speaker and one dead channel on the amp.
Kinda done with these fake STK Ics. Will now go with something better. Hope to retain most of the amp and just replace the blown STKs with a 7293 or a 5200/1943 transistor setup.
I replaced every single cap and transistor on this board as part of the fix. Including both the STKs. I wanted zero compromise thats just my way of working. To be specific all electrolytic caps were replaced. Non electrolytic were pulled tested and put back. If found ok.
Its nice to be able to talk to other Audio DIY guys. I could always just buy a new amp. But this is a kinda therapy for me. And I have some memories from the 70s and 80s of my dads music system which I am trying to re-create. I got his Hitachi HT-350 up and running. It too just needed a few caps to be changed and some VRs to be set to get the speed right. And a new Audio Technica cartridge. Sounds amazing.
That's very unfortunate. I didn't even know loudspeakers can fail shorted, the (few) broken loudspeakers I've seen all failed open or had some mechanical defect. In fact that's one of the reasons why I didn't understand the opening post.
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Do not ever overlook testing resistors if you do this. They can look just fine but be way off value or open if they have been overloaded in just the right (wrong?) way. Very high short duration pulse currents can do this - and many oxide types are fusible and intended to do this (rather than start a fire).
Yes sir every single resistor checked. Every single Transistor also also replaced. TR1B was dead. TR8 and TR9 where ok so those were the only 2 that did not get replace.
Right now I am stuck deciding between replacing both STKs with a TA7293 or a LM3886 voltage rail is 38-0-38 or 42-0-42.
3886’s are much harder to get these days - I would design around the ST parts because of availability. Pretty much a chip amp is a chip amp these days.
Some around here have resorted to making their own STK replacements, with varying levels of success.
Some around here have resorted to making their own STK replacements, with varying levels of success.
Well lucky for me both can be sourced quite easily here.
The 3886 just costs more than the 7294. About 2$ more. Per board.
But my selection is being swayed by the fact that the supply rails are 38-0-38 and I have been told that the 7294 is able to handle the higher voltage better.
Though if you go as per the data sheet the 3886 is supposed to handle upto 92 volts.
I guess worst case is I get both and see which sounds better. They are all sub 10$ boards.
I have read and read hundreds of posts but no definitive answer as to which is better.
Expect for the fact that one of them does not have the problem of making a sound when powered on. Not sure which one. lol.
You know how it is when your reading hundreds of posts. lol
I have ordered the STKs this time they swear its the real deal but it will take a few months to get here. As it has to jump a few countries. And is being carried in by friends. I think the term for what Im doing is called a gainclone.
I would make my own STK as the gerber and bom is available over on audio karma but that replaces only one of my STKs. I need two. I was told the DIY STK could be used to replace my STK2250 I would still need a STK3240. Or some kind of pre-amp. Plus I am not sure if the DIY STKs can take a differential input.
The 3886 just costs more than the 7294. About 2$ more. Per board.
But my selection is being swayed by the fact that the supply rails are 38-0-38 and I have been told that the 7294 is able to handle the higher voltage better.
Though if you go as per the data sheet the 3886 is supposed to handle upto 92 volts.
I guess worst case is I get both and see which sounds better. They are all sub 10$ boards.
I have read and read hundreds of posts but no definitive answer as to which is better.
Expect for the fact that one of them does not have the problem of making a sound when powered on. Not sure which one. lol.
You know how it is when your reading hundreds of posts. lol
I have ordered the STKs this time they swear its the real deal but it will take a few months to get here. As it has to jump a few countries. And is being carried in by friends. I think the term for what Im doing is called a gainclone.
I would make my own STK as the gerber and bom is available over on audio karma but that replaces only one of my STKs. I need two. I was told the DIY STK could be used to replace my STK2250 I would still need a STK3240. Or some kind of pre-amp. Plus I am not sure if the DIY STKs can take a differential input.