Hi, yes i managed to verify all the traces on the pcb. It works now 100% ok, no matter how i turn it on or off. That realy beggins to pis* me off. 
what fears me totaly is the vcc rails at ±92v.
I will do some other test, and measure dv/dt at the mosfets. I already changed the gate resistor from 5 ohm to 10 ohm, and replaced the cap on the op amp that limit the free running freq.
It now osc. at 90khz.
what fears me totaly is the vcc rails at ±92v.
I will do some other test, and measure dv/dt at the mosfets. I already changed the gate resistor from 5 ohm to 10 ohm, and replaced the cap on the op amp that limit the free running freq.
It now osc. at 90khz.
believe me. i dont trust it either.
And, believe me or not...it works right now since 1 hour at medium volume.
I havent changed any major components. Once i figured that it worked, i did get 10 ohm gate to the drivers, and changed the osc cap. Thats it.
Mine also gives moderate hum, music or not. I believe it is due to the total absence of proper regulation to the op amps.
It is originaly filtered by only few 100nf caps. I added 2x 10uf and it is already far more silent.
Here is a picture...you can see on the top my IR based module, and the weird board on its left...i let you find...
And, believe me or not...it works right now since 1 hour at medium volume.
I havent changed any major components. Once i figured that it worked, i did get 10 ohm gate to the drivers, and changed the osc cap. Thats it.
Mine also gives moderate hum, music or not. I believe it is due to the total absence of proper regulation to the op amps.
It is originaly filtered by only few 100nf caps. I added 2x 10uf and it is already far more silent.
Here is a picture...you can see on the top my IR based module, and the weird board on its left...i let you find...
Attachments
Hi Pat,
Slowing turn on with the 10 ohms might not be a bad idea at all, 10 is still very reasonable, and they're bypassed for turn off as well. Do the mosfets run much warmer for it?
Perhaps you have some sort of an intermittent problem. I know you made a decent heatsink for it, not all parts would be getting cooled by it though, and it was enclosed. Maybe while you've got it out and apart, keep it playing and take a heat gun to it, see what happens. Just don't melt anything.
Regards,
Chris
Slowing turn on with the 10 ohms might not be a bad idea at all, 10 is still very reasonable, and they're bypassed for turn off as well. Do the mosfets run much warmer for it?
Perhaps you have some sort of an intermittent problem. I know you made a decent heatsink for it, not all parts would be getting cooled by it though, and it was enclosed. Maybe while you've got it out and apart, keep it playing and take a heat gun to it, see what happens. Just don't melt anything.
Regards,
Chris
Hi, sorry to bother this board again...
New issue. Wow. It played at least 2 hours while i listened to a movie, very medium volume. All on a sudden, sssstac !! then hummmmmm. I said, oh my, you lasted 2 hours this time, good boy. But, the loud tac it made prompted me to open it again.
One of the main new cap have its hat off !!! man oh man.
I have no clues to that now. I made several test to see if the amp was pumping up the vcc, it was not , at full power on a resistive load, and within the full bandwitdh wich is 25hz to 150hz. I did try after with a sub and it was not pumping either, anyway, when it blew, it was at very low volume.
So, what could have caused that? a bad new cap? certainly not hein? the whole unit was hot, but not that much imho. I realy dont know what to do now. The caps were nichicon 100v with unknown surge voltage, 85deg max. I may have ordered 105deg instead, but i dont think that could help here. I still have the other ones wich are 100v 2200uf with 125 surge, +105deg.
I think something went wrong with the oscillation and then it pumped hard the vcc, but i barely heard a thing when it poped.
How about some big martha tvs on the vcc rails?? i got some 1000amp of those with 100v clamp voltage
No, seriously, i would like to get an advice as to what can cause that.
Thanks group.
New issue. Wow. It played at least 2 hours while i listened to a movie, very medium volume. All on a sudden, sssstac !! then hummmmmm. I said, oh my, you lasted 2 hours this time, good boy. But, the loud tac it made prompted me to open it again.
One of the main new cap have its hat off !!! man oh man.
I have no clues to that now. I made several test to see if the amp was pumping up the vcc, it was not , at full power on a resistive load, and within the full bandwitdh wich is 25hz to 150hz. I did try after with a sub and it was not pumping either, anyway, when it blew, it was at very low volume.
So, what could have caused that? a bad new cap? certainly not hein? the whole unit was hot, but not that much imho. I realy dont know what to do now. The caps were nichicon 100v with unknown surge voltage, 85deg max. I may have ordered 105deg instead, but i dont think that could help here. I still have the other ones wich are 100v 2200uf with 125 surge, +105deg.
I think something went wrong with the oscillation and then it pumped hard the vcc, but i barely heard a thing when it poped.
How about some big martha tvs on the vcc rails?? i got some 1000amp of those with 100v clamp voltage
No, seriously, i would like to get an advice as to what can cause that.
Thanks group.
Hi,
Quoting from IRF regarding pumping:
"-Significant at low frequency output
-Significant at low load impedance
-Significant at small bus capacitors
-Largest at duty = 25%, and 75%"
Explains why it went at lower power.
The big martha might be a good idea, since it is a half bridge sub, but I'm sure you'd rather get to the root of the problem too.
What's DC offset like? I'd say go with bigger caps, and/or with more of a margin on them, you do not want to rely on surge capability at all because that's about good for a one time short duration pulse and anything more than that will make them "take their hat off" eventually.
Shoot for a minimum margin of say 20%, 120V caps would be nice, this way they can pump a little more safely, and the more uF the less affect the pumping will have, basically, squeeze in the biggest suckers you can, maybe even forget about bad it looks at this point.
Regards,
Chris
Quoting from IRF regarding pumping:
"-Significant at low frequency output
-Significant at low load impedance
-Significant at small bus capacitors
-Largest at duty = 25%, and 75%"
Explains why it went at lower power.
The big martha might be a good idea, since it is a half bridge sub, but I'm sure you'd rather get to the root of the problem too.
What's DC offset like? I'd say go with bigger caps, and/or with more of a margin on them, you do not want to rely on surge capability at all because that's about good for a one time short duration pulse and anything more than that will make them "take their hat off" eventually.
Shoot for a minimum margin of say 20%, 120V caps would be nice, this way they can pump a little more safely, and the more uF the less affect the pumping will have, basically, squeeze in the biggest suckers you can, maybe even forget about bad it looks at this point.
Regards,
Chris
Hi. I did work on it this morning.
Well, first to say, when it blew it was BARELY playing. I was also hearing some random pop, sound or not.
So, i put it on my power supply, powered it up with 35v rails, and it fired up ok, so nothing is realy fry in it.
I have disconnected the preamp section so anything that can go wrong will be into the module itslef. Here is the fun part: while i was probing here and there (carefully) i heard the inductance ticling and then a LOUD paouf !!, It was into my power supply: the -vcc cap did it too !!!, jeeeeeezzzz. It is a 50volts cap, and the vcc to it was 35...that means a minimum of 70% more voltage pumped to it because of the amp...and it blew like if there was 1kv to it. It looks very ugly. There was no signal at all applied to the amp. Could it be the inductance that is shot? since i am looking at it closely, it dont look good, i mean it looks like it have overheated a bit.
The ofset is below .5v.
the random pop i was hearing tell me that something i not stable into this amp, and the problem is indepedant of the audio signal. Thats it for today i think.Thanks.
Well, first to say, when it blew it was BARELY playing. I was also hearing some random pop, sound or not.
So, i put it on my power supply, powered it up with 35v rails, and it fired up ok, so nothing is realy fry in it.
I have disconnected the preamp section so anything that can go wrong will be into the module itslef. Here is the fun part: while i was probing here and there (carefully) i heard the inductance ticling and then a LOUD paouf !!, It was into my power supply: the -vcc cap did it too !!!, jeeeeeezzzz. It is a 50volts cap, and the vcc to it was 35...that means a minimum of 70% more voltage pumped to it because of the amp...and it blew like if there was 1kv to it. It looks very ugly. There was no signal at all applied to the amp. Could it be the inductance that is shot? since i am looking at it closely, it dont look good, i mean it looks like it have overheated a bit.
The ofset is below .5v.
the random pop i was hearing tell me that something i not stable into this amp, and the problem is indepedant of the audio signal. Thats it for today i think.Thanks.
Pat,
Have you checked your choke L1 yet? That can be a source of popping and thumping if it's bad.
On a separate note, regarding my "light hum" on my sub, it is definentally from the audio input since as soon as I shut off the home stereo, the hum goes away.
I gave my sub the harsh burn in test yesterday. 8 hours straight of extremely heavy bass and hard music, and at significantly elevated volume levels! She worked like a charm, never once letting me down!
Daddy like!
Jer
Have you checked your choke L1 yet? That can be a source of popping and thumping if it's bad.
On a separate note, regarding my "light hum" on my sub, it is definentally from the audio input since as soon as I shut off the home stereo, the hum goes away.
I gave my sub the harsh burn in test yesterday. 8 hours straight of extremely heavy bass and hard music, and at significantly elevated volume levels! She worked like a charm, never once letting me down!
Daddy like!
Jer
Pat,
Depending on what size reservoir caps you have, 0.5V offset is more then enough to cause serious PSU pumping - especially with smaller value caps - say less then 10000uF.
With all the talk of half bridges, I recently experimented with a half bridge design with 3300uF caps on symmetrical rails operating from a bench PSU - even 50mV of offset started PSU pumping - I run away from half bridges designs after this – well after I blow the first set of FETS.
Most PSU can only source - and not sink...
I really strongly disagree with designers who think its ok to use a half bridge design in a sub amp - forget it no way!
Good luck - I would not spend so much time on such a flawed concept.
If you insist on resurrecting what should be long dead (ignoring the fact you have learnt so much about Class D during you valiant attempt), Jan-peters posted a simple Over-voltage circuit on one of the UCD threads – about as simple it gets. So unless you’re doing something really stupid – like caps the wrong way around – the OV circuit will solve the problem.
John
Depending on what size reservoir caps you have, 0.5V offset is more then enough to cause serious PSU pumping - especially with smaller value caps - say less then 10000uF.
With all the talk of half bridges, I recently experimented with a half bridge design with 3300uF caps on symmetrical rails operating from a bench PSU - even 50mV of offset started PSU pumping - I run away from half bridges designs after this – well after I blow the first set of FETS.
Most PSU can only source - and not sink...
I really strongly disagree with designers who think its ok to use a half bridge design in a sub amp - forget it no way!
Good luck - I would not spend so much time on such a flawed concept.
If you insist on resurrecting what should be long dead (ignoring the fact you have learnt so much about Class D during you valiant attempt), Jan-peters posted a simple Over-voltage circuit on one of the UCD threads – about as simple it gets. So unless you’re doing something really stupid – like caps the wrong way around – the OV circuit will solve the problem.
John
No , i just think it cant look more bad. It looks like thunder fallen on itTekko said:Pat, one kilovolt?
Is this really true ?
I will change the inductor, i have few somewhere...
How can it pump the rails that much if there is no signal applied to it, even if there is a small offset?
Thats what happened the second time on my psu, no signal at all, then pow !!
Hi,
Pat like JohnW was sayin, a little DC offset is a really bad thing, and .5V seems like alot.
Probably even more so with no signal, then nothing is ever going to tell it to "modulate the rail the other way now" and it will just keep pumping up the same cap. 50mV max is the industry accepted standard for DC offset (perhaps that's the only accepted standard in audio even, who knows), but as JohnW was saying that could be too much as well, especially with small caps.
Perhaps the changing values of the cap on that op amp would have affected your DC offset? You should try to minimize it somehow.
Best Regards,
Chris
Pat like JohnW was sayin, a little DC offset is a really bad thing, and .5V seems like alot.
Probably even more so with no signal, then nothing is ever going to tell it to "modulate the rail the other way now" and it will just keep pumping up the same cap. 50mV max is the industry accepted standard for DC offset (perhaps that's the only accepted standard in audio even, who knows), but as JohnW was saying that could be too much as well, especially with small caps.
Perhaps the changing values of the cap on that op amp would have affected your DC offset? You should try to minimize it somehow.
Best Regards,
Chris
Sorry, i meant 5mv for the dc ofset, not .5v.
here is some note that i found funny into the service manual...
1: Mild Audible Hum under all circumstances when power cord is plugged in outlet.
This may be a mechanical hum caused by the power transformer. Note that a slight hum, within design limits,
may be noticeable in a very quiet room, when you are close to the unit. This is acceptable within the PB10/12’s
product and price category to most customers, but not to others. If the mechanical hum is unacceptable to the
customer, then replace Power Transformer. PB10: JBL part# 80135. PB12: JBL part# 80116
Price category?? cheap, thats it.
2: Loud Hum, under all circumstances. It may be louder when LED’s are Green vs. Red ; it may be affected by the
position of the Level control. The subwoofer may “thump” or “pop” approximately every 10 seconds.
Reset the digital subwoofer amplifier by unplugging the AC power cord. Wait 30 seconds, then plug the cord back in. Repeat 2-3 times if necessary
I wonder what it does if i repeat this procedure...
3: In the event you receive a PB12 subwoofer with the complaint: “The subwoofer “thumps” or “pops”
every few seconds of play”, follow the procedure below:
Probable Cause:
Inductor L1 (220uH) may be damaged.
Yeah, mine looks like it have overheated. I will change it.
I think i can afford to spend few buck on it, and some time too, just for the fun of the thing, i HAVE to find whats going on in it.
here is some note that i found funny into the service manual...
1: Mild Audible Hum under all circumstances when power cord is plugged in outlet.
This may be a mechanical hum caused by the power transformer. Note that a slight hum, within design limits,
may be noticeable in a very quiet room, when you are close to the unit. This is acceptable within the PB10/12’s
product and price category to most customers, but not to others. If the mechanical hum is unacceptable to the
customer, then replace Power Transformer. PB10: JBL part# 80135. PB12: JBL part# 80116
Price category?? cheap, thats it.
2: Loud Hum, under all circumstances. It may be louder when LED’s are Green vs. Red ; it may be affected by the
position of the Level control. The subwoofer may “thump” or “pop” approximately every 10 seconds.
Reset the digital subwoofer amplifier by unplugging the AC power cord. Wait 30 seconds, then plug the cord back in. Repeat 2-3 times if necessary
I wonder what it does if i repeat this procedure...
3: In the event you receive a PB12 subwoofer with the complaint: “The subwoofer “thumps” or “pops”
every few seconds of play”, follow the procedure below:
Probable Cause:
Inductor L1 (220uH) may be damaged.
Yeah, mine looks like it have overheated. I will change it.
I think i can afford to spend few buck on it, and some time too, just for the fun of the thing, i HAVE to find whats going on in it.
Hi,
5mV is reasonable I think, especially for a half bridge, I wouldn't expect it could be any better.
One has to admire your persistance, a true DIY'r! I see at this point it's personal in nature
Probably explode, but that would cure the pop n hum. I think you've possibly cured the cause of that issue already though.
I don't think the price they sold this thing for was any kind of reflection as to its cheapness.
You already added up the the more expensive parts in the modulator, if you really want to be shocked, do it again with mass production in mind. Each component = a few pennies each.
Anyway, forget the quality of the amp, how about that service manual ??
Keep us posted.
Chris
5mV is reasonable I think, especially for a half bridge, I wouldn't expect it could be any better.
One has to admire your persistance, a true DIY'r! I see at this point it's personal in nature
Probably explode, but that would cure the pop n hum. I think you've possibly cured the cause of that issue already though.
I don't think the price they sold this thing for was any kind of reflection as to its cheapness.
You already added up the the more expensive parts in the modulator, if you really want to be shocked, do it again with mass production in mind. Each component = a few pennies each.
Anyway, forget the quality of the amp, how about that service manual ??
Keep us posted.
Chris
MORE EXPERIANCE TO COME!!!
Well, I just didn't have enough "FUN" with the first sub, so I went ahead and bought 2 more "dead" JBL PB12's. They should be arriving next week. One is said to not power on at all (same problem as the first one) and the other sounds like Pat's P.O.S. (popping noises).... should be fun!
Jer
Well, I just didn't have enough "FUN" with the first sub, so I went ahead and bought 2 more "dead" JBL PB12's. They should be arriving next week. One is said to not power on at all (same problem as the first one) and the other sounds like Pat's P.O.S. (popping noises).... should be fun!
Jer
Hi, im back...
Id like to adress few questions about the output filter. It is done with a 220uh inductance and a plain 4.7uf cap. The inductance looks like it have overheated a bit.
I am searching in my school books the formulae of l-c filters...
Is there any improvements could be done here ?
thanks.
Id like to adress few questions about the output filter. It is done with a 220uh inductance and a plain 4.7uf cap. The inductance looks like it have overheated a bit.
I am searching in my school books the formulae of l-c filters...
Is there any improvements could be done here ?
thanks.
3 JBL PB12's and GOING!
Ok, I think I may have gone overboard on the subwoofers.... Tuesday I got my second sub... all that needed was 2 capacitors (the 2200uF main caps) and that was up and running! That one was the PCB ver 7.2.
Then on Wednesday, I got my 3rd one. Blown fuse. Looking at the caps, it had a blown one (top was split and full of the lovely black ooze). So, I put 2 new caps in that one too, and low and behold? IT WORKS TOO! That one is also PCB ver 7.2.
So, I left the amp modules intact, since, if it ain't broke, don't fix it! Also, all the mods to the previous versions are already done to the PCB ver 7.2. Just thought I would let all of you out there know that little factoid.
Total cost invested in the 3 subs? Less than 140 USD including shipping and parts! Worth every penny!
Time to put all of em to the big test............
Good luck BOOMIN! (I know I am)
Jer
Ok, I think I may have gone overboard on the subwoofers.... Tuesday I got my second sub... all that needed was 2 capacitors (the 2200uF main caps) and that was up and running! That one was the PCB ver 7.2.
Then on Wednesday, I got my 3rd one. Blown fuse. Looking at the caps, it had a blown one (top was split and full of the lovely black ooze). So, I put 2 new caps in that one too, and low and behold? IT WORKS TOO! That one is also PCB ver 7.2.
So, I left the amp modules intact, since, if it ain't broke, don't fix it! Also, all the mods to the previous versions are already done to the PCB ver 7.2. Just thought I would let all of you out there know that little factoid.
Total cost invested in the 3 subs? Less than 140 USD including shipping and parts! Worth every penny!
Time to put all of em to the big test............
Good luck BOOMIN! (I know I am)
Jer