Hey all,
Just received my sub driver the other day, and got the box etc. all finished. Chucked it in, hooked everything up (Including previously functioning - certainly without a load P68 sub amp) and started running the thing. Produced a nice tone at 20Hz , but upon cranking it up the output stopped. A few seconds later there was a nice "POP" and cap C13 (100uF electro bypass rated 63V from +ve rail to ground) blew.
I've cracked it all open and cleared the smoke etc. and it appears (from LOOKING at the board) that Q6 is also blown - nice charred marks around it etc, and I have a feeling this may have gone before the cap - not that this is just a guess. The +ve rail fuse also blew. Everything else looks fine. I don't have any way of testing transistors etc. in circuit (And don't really know how to do it out of circuit either) but everything looks like it's kosher.
One thing that MAY have caused it is the driver transistors (Supposed to be MJE350's) are marked KSE350. I don't know if these KSE350's are to blame or not - Q6 was one. I've ordered MJE350 replacements.
If anyone has any idea at all as to what may have caused it to blow please let me know! It was running into a 4ohm load at the time of death. (Although at 20Hz the impedance is more like 6ohms)
P68 info/schematic
Photos of my sub amp (Before it blew!!)
Just received my sub driver the other day, and got the box etc. all finished. Chucked it in, hooked everything up (Including previously functioning - certainly without a load P68 sub amp) and started running the thing. Produced a nice tone at 20Hz , but upon cranking it up the output stopped. A few seconds later there was a nice "POP" and cap C13 (100uF electro bypass rated 63V from +ve rail to ground) blew.
I've cracked it all open and cleared the smoke etc. and it appears (from LOOKING at the board) that Q6 is also blown - nice charred marks around it etc, and I have a feeling this may have gone before the cap - not that this is just a guess. The +ve rail fuse also blew. Everything else looks fine. I don't have any way of testing transistors etc. in circuit (And don't really know how to do it out of circuit either) but everything looks like it's kosher.
One thing that MAY have caused it is the driver transistors (Supposed to be MJE350's) are marked KSE350. I don't know if these KSE350's are to blame or not - Q6 was one. I've ordered MJE350 replacements.
If anyone has any idea at all as to what may have caused it to blow please let me know! It was running into a 4ohm load at the time of death. (Although at 20Hz the impedance is more like 6ohms)
P68 info/schematic
Photos of my sub amp (Before it blew!!)
KSE350 are second-sourced MJE350s from Fairchild Semiconductor. While they may not be of as high quality as the OnSemi devices, they're certainly fine, and will have no problems replacing the MJE350 in this application (I use the KSE3x0 devices myself with no problems.)
One thing I can think of is that the load of the DPL12 is highly reactive at ~20hz, as its free-air resonance frequency is between 16 and 18hz (my samples measure 17.5hz average, out of four)
In theory, the amp should handle a reactive load just fine, but know that that particular frequency might stress it more than others.
What were your rail voltages, by the way?
(loaded and unloaded)
One thing I can think of is that the load of the DPL12 is highly reactive at ~20hz, as its free-air resonance frequency is between 16 and 18hz (my samples measure 17.5hz average, out of four)
In theory, the amp should handle a reactive load just fine, but know that that particular frequency might stress it more than others.
What were your rail voltages, by the way?
(loaded and unloaded)
The rails are at +/-58V (40-0-40 transformer rectified and filtered with 6000uF per side) at no load - reduces to +/-54V or so under load. This was measured a while back.
Thanks for the info on the KSE350 - I guess I'd better look a bit more closer. I'm a little perplexed as to why the cap blew in particular. It was rated for 63V so SHOULD have been fine. I've tested the amp (with no load) for several hours etc. before and everything was fine.
I've ordered replacements and will probably receive them within a couple of days. I'll definitely post here when I've replaced them to let ya'll know how it goes.
Thanks for the info on the KSE350 - I guess I'd better look a bit more closer. I'm a little perplexed as to why the cap blew in particular. It was rated for 63V so SHOULD have been fine. I've tested the amp (with no load) for several hours etc. before and everything was fine.
I've ordered replacements and will probably receive them within a couple of days. I'll definitely post here when I've replaced them to let ya'll know how it goes.
That must have been exciting.Jonathan M said:
Odd that a bypass cap blew. I would normally suggest maybe it was in backwards, but you've said you tested the amp so it would have shown up before. And anyways I'm sure you've checked that.
What kind of testing have you done before you tried the subwoofer load? Has it run before at high power, 20 Hz into a dummy (resistive load)?
I think ThingyNess may be right about the reactive load. I wonder if bypass diodes should be added from output to each of the rails, as I've seen in many other amps.
And...have you asked Rod?
Thanks for the replies/suggestions guys!
I don't know if exciting is the word - it made a nice pop and a goodly amount of smoke etc. was produced (From the cap mainly - the transistor burnt up and had a nice plastic smell to it)
I'm 99.9% sure that the output wasn't shorted. It has DC protection on the output and I assume that this kicked in before the thing went bang. I've checked and rechecked the protection circuit and the output from the amp is not being shorted under a fault condition.
As for the cap - that's a bit of a mystery. One would assume that it would take a bit of a large amount of voltage to blow it up - unless it was a negative potential.
I have identified (and fixed) a dodgy signal detection circuit which may have caused mains to be disconnected and then reconnected immediately. This would have occured after the DC protection circuit kicked in. I don't know what could eventuate from power being removed then immediately reapplied - but it COULD have caused the +VE rail fuse to blow.
Once the +ve rail was gone, it does open up a slight possibility for a negative potential across C13 - but this is a HUGE stretch.
Cheers
Jonathan
I don't know if exciting is the word - it made a nice pop and a goodly amount of smoke etc. was produced (From the cap mainly - the transistor burnt up and had a nice plastic smell to it)
I'm 99.9% sure that the output wasn't shorted. It has DC protection on the output and I assume that this kicked in before the thing went bang. I've checked and rechecked the protection circuit and the output from the amp is not being shorted under a fault condition.
As for the cap - that's a bit of a mystery. One would assume that it would take a bit of a large amount of voltage to blow it up - unless it was a negative potential.
I have identified (and fixed) a dodgy signal detection circuit which may have caused mains to be disconnected and then reconnected immediately. This would have occured after the DC protection circuit kicked in. I don't know what could eventuate from power being removed then immediately reapplied - but it COULD have caused the +VE rail fuse to blow.
Once the +ve rail was gone, it does open up a slight possibility for a negative potential across C13 - but this is a HUGE stretch.
Cheers
Jonathan
There are two cases when the cap blows: as is in backwards or the voltage exceedes its voltage is rated for. Becouse you tested your amp before the load was connected to, than the cap wasn't in backward , I think.
Maybe when your protection circuit taken an action, you lost the ground connection and there was rail to rail voltage on the cap.
I would disconnect all protection circuits and than start again.
Regards,
Jarek
"It has DC protection on the output and I assume that this kicked in before the thing went bang."
No, the DC protection circuit is to prevent damage to the speakers _after_ a fault in the amp has occurred.
If you were driving the amp hard into a very rective load, maybe the reactance of the speaker threw back a higher voltage than it was being fed, thus blowing the cap which was already operating near to its rated voltage. Just a guess - is this possible?
Another stab in the dark - 6,000uF reservoir capacitance isn't much for an amp of this size (especially with a 4 ohm load). Maybe the decopling capacitors were exceeding their ripple current rating.
Hope this helps,
Tim.
No, the DC protection circuit is to prevent damage to the speakers _after_ a fault in the amp has occurred.
If you were driving the amp hard into a very rective load, maybe the reactance of the speaker threw back a higher voltage than it was being fed, thus blowing the cap which was already operating near to its rated voltage. Just a guess - is this possible?
Another stab in the dark - 6,000uF reservoir capacitance isn't much for an amp of this size (especially with a 4 ohm load). Maybe the decopling capacitors were exceeding their ripple current rating.
Hope this helps,
Tim.
Hi Jonathan
Just two things:
How does your powersupply look like (i.e. it's schematic) ? Do you use a centere-tapped transformer ?
I ask because there are also possibilities to make a symmetrical PSU with a single output winding only, but this would be inferior to the centere-tap version. I.e. it could lead to situations where the output voltages can get heavily asymmetric and components can be killed of overvoltage.
In Rod Elliotts article the following statement can be found:
The S300 is intended for intermittent duty on 4 Ohm loads, as will normally be found in a subwoofer.
Now I don't know how long your 20 Hz test took ??
Regards
Charles
Just two things:
How does your powersupply look like (i.e. it's schematic) ? Do you use a centere-tapped transformer ?
I ask because there are also possibilities to make a symmetrical PSU with a single output winding only, but this would be inferior to the centere-tap version. I.e. it could lead to situations where the output voltages can get heavily asymmetric and components can be killed of overvoltage.
In Rod Elliotts article the following statement can be found:
The S300 is intended for intermittent duty on 4 Ohm loads, as will normally be found in a subwoofer.
Now I don't know how long your 20 Hz test took ??
Regards
Charles
Hi,
I had exactly the same problem with my amp. It turned out that a cap blew (between rail and GND) because of it's rating (about 2V below input). It took about 10mins of playing to blow up.
On a seperate occasion, two resistors blew up (?!)...I replaced them without changing a thing, and it has been running flawlessly ever since...About a month later, I measured some '1k' resistors only to find that the shop had labelled them wrong...They were 100R! I should have checked them - but I have to agree that 5 band resistors are hard to read!
Anyway - I think that accounts for both blow ups...Not sure if the first one is relevant at all. The caps never blew under test - only in use...Try using well overrated (> 2xrail voltage) if you can get them and run them like that for a while...
Gaz
I had exactly the same problem with my amp. It turned out that a cap blew (between rail and GND) because of it's rating (about 2V below input). It took about 10mins of playing to blow up.
On a seperate occasion, two resistors blew up (?!)...I replaced them without changing a thing, and it has been running flawlessly ever since...About a month later, I measured some '1k' resistors only to find that the shop had labelled them wrong...They were 100R! I should have checked them - but I have to agree that 5 band resistors are hard to read!
Anyway - I think that accounts for both blow ups...Not sure if the first one is relevant at all. The caps never blew under test - only in use...Try using well overrated (> 2xrail voltage) if you can get them and run them like that for a while...
Gaz
Thanks for all the suggestions - some answers to your queries...
Hi all.
First off, the cap was certainly connected around the right way. Secondly, the DC protection is for the speaker only - this is an expensive driver (for me, anyway) so I figured it was worth the $10 or so it took to make sure it was never connected direct to up to 110V DC!!
The power supply is from a centre tapped transformer (40-0-40 secondary) to a bridge rectifier and then to 6000uF/100V per side caps. Rod suggests 4700uF per side in the S300 article.
The 20Hz "test" ran for a Maximum of 30 seconds. I started it at a very low level, then slowly turned it up, watching the woofer pump in and out. After a very short time (4 seconds max) the woofer stopped moving. There was then some relay clicking (Likely due to the faulty signal detect circuit turning the mains on and off - now remedied), and around 5-10 seconds later the cap went pop. I unplugged the power cord as quick as I could at this stage! I should, ofcourse, removed power immediately that the woofer stopped moving. Lesson learned.
I have tested all components - they are all the correct values (within tolerances). The amp also tested fine (correct bias current/little or no DC on the outputs etc.) when I first built it.
The transistor that blew is on the -ve supply rail side. The cap is on the +ve rail. It's the +ve rail fuse that blew. I have thought that perhaps the cap was just running too close to it's max operating voltage (56V versus 63V) but I would think there would be a little bit of head room there. The replacement I've got is another 63V one at present - I may see if I can get hold of some 100V parts locally.
I'll replace everything tonight (Assuming the postie arrives with my replacements) and recheck everything out. I'll probably test without the protection circuit first. The driver is a nice, solid unit, and I'm sure it could withstand plenty of DC for short periods if it has to. (It's rated at 650W)
Hi all.
First off, the cap was certainly connected around the right way. Secondly, the DC protection is for the speaker only - this is an expensive driver (for me, anyway) so I figured it was worth the $10 or so it took to make sure it was never connected direct to up to 110V DC!!
The power supply is from a centre tapped transformer (40-0-40 secondary) to a bridge rectifier and then to 6000uF/100V per side caps. Rod suggests 4700uF per side in the S300 article.
The 20Hz "test" ran for a Maximum of 30 seconds. I started it at a very low level, then slowly turned it up, watching the woofer pump in and out. After a very short time (4 seconds max) the woofer stopped moving. There was then some relay clicking (Likely due to the faulty signal detect circuit turning the mains on and off - now remedied), and around 5-10 seconds later the cap went pop. I unplugged the power cord as quick as I could at this stage! I should, ofcourse, removed power immediately that the woofer stopped moving. Lesson learned.
I have tested all components - they are all the correct values (within tolerances). The amp also tested fine (correct bias current/little or no DC on the outputs etc.) when I first built it.
The transistor that blew is on the -ve supply rail side. The cap is on the +ve rail. It's the +ve rail fuse that blew. I have thought that perhaps the cap was just running too close to it's max operating voltage (56V versus 63V) but I would think there would be a little bit of head room there. The replacement I've got is another 63V one at present - I may see if I can get hold of some 100V parts locally.
I'll replace everything tonight (Assuming the postie arrives with my replacements) and recheck everything out. I'll probably test without the protection circuit first. The driver is a nice, solid unit, and I'm sure it could withstand plenty of DC for short periods if it has to. (It's rated at 650W)
Hi Jonathan,
Are you sure that the contact between transistors and heatsink is good? I had the same problem when I tested one of my amp with a signal. After a some time running transistors got overheat and blew. I find, that these transistors weren' t properly installed on the heatsink.
Maybe it helps.
Regards,
Jarek
Are you sure that the contact between transistors and heatsink is good? I had the same problem when I tested one of my amp with a signal. After a some time running transistors got overheat and blew. I find, that these transistors weren' t properly installed on the heatsink.
Maybe it helps.
Regards,
Jarek
Replaced Q6 and C13 and checked - nice hot resistors
Hi all,
I've replaced Q6 and C13 (The dead components) and repowered with 22ohm safety resistors on the rails. They got hot so there is clearly still a fault. After reading a couple of other threads, I've removed all the output transistors and checked them using an ohm meter between B-E and B-C.
All measured lowish readings in one direction and high readings in the opposite which indicates they are fine - EXCEPT Q7 and Q12.
Q12 was shorted between B-C and Q7 had the same reading in both directions between B-C and B-E. This indicates they are dead. I will check the rest of the transistors later today.
Also, do you guys think there is a way to test the rest of the circuit with power applied with all the output transistors removed from circuit? (Q7 through Q12?) If so, then at least I can verify that section.
Thanks for your help so far - hopefully I can get replacements before Christmas!!
I've attached the schematic...
Cheers
Jonathan
Hi all,
I've replaced Q6 and C13 (The dead components) and repowered with 22ohm safety resistors on the rails. They got hot so there is clearly still a fault. After reading a couple of other threads, I've removed all the output transistors and checked them using an ohm meter between B-E and B-C.
All measured lowish readings in one direction and high readings in the opposite which indicates they are fine - EXCEPT Q7 and Q12.
Q12 was shorted between B-C and Q7 had the same reading in both directions between B-C and B-E. This indicates they are dead. I will check the rest of the transistors later today.
Also, do you guys think there is a way to test the rest of the circuit with power applied with all the output transistors removed from circuit? (Q7 through Q12?) If so, then at least I can verify that section.
Thanks for your help so far - hopefully I can get replacements before Christmas!!
I've attached the schematic...
Cheers
Jonathan
Attachments
Re: Replaced Q6 and C13 and checked - nice hot resistors
Hi,
if C13 goes down, then voltage on C13 was to high, this happen when - pol of C13 is not connected to middle- ground point on power supply and is floating together with + pol of C12, check that all ground point (-C13, +C12) are connected to ground point of power supply, check R23 (for testing could by shortened)
one output section of transistor must be connected for testing,
try bypassing one diode D2 or D3, idle current must be smaller(check voltage on R16,17, or on safety resistors), output voltage must be around 0V
you must check and C-E resistance (both polarisation, high R) when you test BJT
regards
Hi,
if C13 goes down, then voltage on C13 was to high, this happen when - pol of C13 is not connected to middle- ground point on power supply and is floating together with + pol of C12, check that all ground point (-C13, +C12) are connected to ground point of power supply, check R23 (for testing could by shortened)
one output section of transistor must be connected for testing,
try bypassing one diode D2 or D3, idle current must be smaller(check voltage on R16,17, or on safety resistors), output voltage must be around 0V
you must check and C-E resistance (both polarisation, high R) when you test BJT
regards
OK - Got it fixed - bias level needs reducing though
Hi all,
Got my replacement parts, and everything is back running. The amp runs (with no load) with supply rails at +- 53V. Output DC is less than 30mV.
I'm a little worried about the bias current. Supposed to be around 55mA, but is running high at over 85mA. The driver heatsink (on which Q4, Q5, Q6 are mounted, and D2 and D3 are in contact)
gets quite warm - even after a few minutes. Bias current increases as the heatsink gets warmer (Logical) but everything is getting a little warm for my liking.
Moamp - will bypassing one of the diodes D2 or D3 lower the bias or increase it? I might try this if I'm sure it will reduce the bias current.
I'll recheck all the thermal contacts tonight to make sure everything is staying cool, and try and identify which components are warming up the most.
Cheers
Jonathan
Hi all,
Got my replacement parts, and everything is back running. The amp runs (with no load) with supply rails at +- 53V. Output DC is less than 30mV.
I'm a little worried about the bias current. Supposed to be around 55mA, but is running high at over 85mA. The driver heatsink (on which Q4, Q5, Q6 are mounted, and D2 and D3 are in contact)
gets quite warm - even after a few minutes. Bias current increases as the heatsink gets warmer (Logical) but everything is getting a little warm for my liking.
Moamp - will bypassing one of the diodes D2 or D3 lower the bias or increase it? I might try this if I'm sure it will reduce the bias current.
I'll recheck all the thermal contacts tonight to make sure everything is staying cool, and try and identify which components are warming up the most.
Cheers
Jonathan
OK - Amp is now at least powering up, but R14 is getting HOT!!
Hi All,
Well, as I said in my last message, the amp is testing OK as far as the drop to the rail voltage (via safety resistors) and DC output is going. Unfortunately, I'm still having problems.
R14 (220R collector resistor of driver Q6) is getting warm and starting to burn up. Has around 20V or so across it so is dissapating far more than it should be. R13, the resistor from the other rail to the other driver (Q5) has only 0.65V across it, so is all good.
I'm thinking that perhaps Q8 is to blame?? R14 goes between the -ve rail and the collector of Q6, or between the base and emitter of Q8. Should there only be a 0.65V drop across B-E of Q8 if it's working properly??
Any help/guidance would be fantastic.
Cheers,
Jonathan
Hi All,
Well, as I said in my last message, the amp is testing OK as far as the drop to the rail voltage (via safety resistors) and DC output is going. Unfortunately, I'm still having problems.
R14 (220R collector resistor of driver Q6) is getting warm and starting to burn up. Has around 20V or so across it so is dissapating far more than it should be. R13, the resistor from the other rail to the other driver (Q5) has only 0.65V across it, so is all good.
I'm thinking that perhaps Q8 is to blame?? R14 goes between the -ve rail and the collector of Q6, or between the base and emitter of Q8. Should there only be a 0.65V drop across B-E of Q8 if it's working properly??
Any help/guidance would be fantastic.
Cheers,
Jonathan
Hi Jonathan,
I see you have a problem.
I think you can run this amp without Q9, Q11, Q10, and Q12. Also short two diodes D2 and D3. This will minimize bias current.
Before next running I would check Q6 and Q8 (can be blown). The same for positive rail transistors.
Check values R10, R11 and R14. Aren't the diodes D2 and D3 installed in backwards?
Good luck
Jarek
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