An alternative to a series disconnect device for the loudspeakers is a TRIAC crowbar. In simplified terms, DC on the output of a certain amount for a certain amount of time causes the TRIAC to be fired and short the output. This assumes that the control circuitry can still function properly under the fault condition. This also should only be used when the amplifier itself can survive a short at the output - in other words, short circuit protection of some kind that does not rely on an output relay.
One also needs to recognize that if the output stage was fried and was the cause of the output DC, shorting the output of the amplifier to save the speakers is still the right choice, since the output stage is already damaged. In any case, if the short circuit protection can't limit current to a safe continuous value, then something like rail fuses may be used. If rail fuses are used, reverse rail diode clamps from the rails to ground should be included to prevent potentially damaging rail voltage reversal if only one rail fuse blows.
If the cause of large DC on the output is not due to a fried output stage, but rather a fault in the IPS or VAS, another protection approach is to use a relay or some other device to short both ends of the bias spreader to the output rail, depriving the output stage of drive; then only the VAS current will flow into the speakers and will probably not be enough to damage them. If the VAS current under these conditions is considered too high (for example, if a VAS transistor is shorted), then a crowbar can be activated with less likelihood of damaging the output stage.
Cheers,
Bob
I can attest to the fact that a triac crowbar can be very effective. However, it may trip due to dv/dt limitations. So with a higher powered amplifier, you will probably use a lower value of G-MT1 resistor, and probably a capacitor as well. With the really big amplifiers, a crowbar or electronic shutdown (Carver) is going to be more trustworthy for cutting off the power to the load. Even the big relays can melt and burn as they open and short. Magnets beside the contacts can help blow some of the arc out. When a triac shorts across the speaker terminals, it fails in a safe condition (for the speakers). I have seen traces to such a triac burn away, and they were about 3/8" wide. With that one, traces to various transistor terminals also burned away.
You have to have respect for the power available in a fault condition. Even mid-power Marantz receivers can weld contacts 10A contacts together. That's pretty awesome to see actually.
-Chris
You have to have respect for the power available in a fault condition. Even mid-power Marantz receivers can weld contacts 10A contacts together. That's pretty awesome to see actually.
-Chris
Is it really that big of a deal, the first thing I did with my Hafler mods was to solder wires across all the fuses? Maybe because I never play music loud I don't have problems?
It can be a big deal if the speakers flame out.
I got my magnepans after the original owner found them in a jacob’s ladder state one night. They hadn’t ignited anything in his 100 year old house at that point, so he just placed the entire setup outside and said to come and get it.
I also got a free Phase Linear amp with those too, no plans for repairing that one however.
On a different note, will the replacement boards accept a 90v supply(DH500)?
I got my magnepans after the original owner found them in a jacob’s ladder state one night. They hadn’t ignited anything in his 100 year old house at that point, so he just placed the entire setup outside and said to come and get it.
I also got a free Phase Linear amp with those too, no plans for repairing that one however.
On a different note, will the replacement boards accept a 90v supply(DH500)?
In 40 years of use...
I have never popped (speaker protection or in line DC) fuses .at any point., in home use... by comparison, in store demo of stock Hafler amps [in the 80's] was a different experience for me. *My main speakers, Maggies are fused... I have no concerns. none.
I am with you Scott, from 'my first mods' ...the speaker protection fuses were removed... as with every Musical Concepts build which I have done. The difference in a resolving system is readily apparent. The 'compromises' in competently built amps, nearly non-existent.
For that matter, worthy of the mention; I have never overheated an
amp, in home use, regardless of speakers used, I never have triggered the Hafler in line AC protection. In contrast, I have "overheated" my listening room spaces, with OTL tube amps and even a pair of hot running Mark Levinson ML-2's running Quad ESL-57s... but never with the hot rodded Haflers sitting next to them... always holding their own.
** I have always regarded any 'in the music path', music robbing relays and 'saftey' circuitry as serving more to honor the manufacturers warranty, covering their own behinds, averting potential liabilities... as a component crosses over to instability or from overt abuse (more common?) **
It stands beyond any reasonable argument, 'sensibly built' Hafler amps, stock or heavily modded and optimized, like mine ~ are fundamentally very stable ~ the load they are connected to... the unmentioned variable... though not remotely a factor, in my case.
I have never popped (speaker protection or in line DC) fuses .at any point., in home use... by comparison, in store demo of stock Hafler amps [in the 80's] was a different experience for me. *My main speakers, Maggies are fused... I have no concerns. none.
I am with you Scott, from 'my first mods' ...the speaker protection fuses were removed... as with every Musical Concepts build which I have done. The difference in a resolving system is readily apparent. The 'compromises' in competently built amps, nearly non-existent.
For that matter, worthy of the mention; I have never overheated an
amp, in home use, regardless of speakers used, I never have triggered the Hafler in line AC protection. In contrast, I have "overheated" my listening room spaces, with OTL tube amps and even a pair of hot running Mark Levinson ML-2's running Quad ESL-57s... but never with the hot rodded Haflers sitting next to them... always holding their own.** I have always regarded any 'in the music path', music robbing relays and 'saftey' circuitry as serving more to honor the manufacturers warranty, covering their own behinds, averting potential liabilities... as a component crosses over to instability or from overt abuse (more common?) **
It stands beyond any reasonable argument, 'sensibly built' Hafler amps, stock or heavily modded and optimized, like mine ~ are fundamentally very stable ~ the load they are connected to... the unmentioned variable... though not remotely a factor, in my case.
And that is a great example of why protection is crucial in power amps. The good news in the case of magnepans is that they are totally repairable. That is not always the case with many sometimes $$$$$$$ speakers. I have lost some nice tweeters over the years from amps oscillating at R.F. frequencies.
Not repairing the Phase (flame) Linear is probably a good plan. I repaired a Klipsch La Scalla once that was set on fire by a Flame Linear 700B when a rock drummer using it as a stage monitor decided it would be fun to drum on an overhead microphone.
I will typically short out the speaker protect fuses but only if there's DC rail fuses upstream of them.
You guys aren't proposing to folks that its safe to eliminate that protection as well are you? If so this seems foolhardy to me....
OzarkHifiDoc,
I've never needed the airbags in any of my automobiles either but I'll be damned if I'd bypass their operation in any way or imply to others its okay to do so.
You guys aren't proposing to folks that its safe to eliminate that protection as well are you? If so this seems foolhardy to me....
OzarkHifiDoc,
I've never needed the airbags in any of my automobiles either but I'll be damned if I'd bypass their operation in any way or imply to others its okay to do so.
Fuse protection in every amp build
No where have I ever suggest that which you mention...
~ SPELLING IT OUT ~ If that helps better
understanding my views [in this thread]
I .always do. have incoming AC / transformer primary protection fuses.
I .always do. have fuses supplying DC to the boards... always have,
.always will. have fuses, should be no confusion
about this sound practice.
I'll REPEAT [for added clarity] my fuses ..never blow..
These amps are bullet proof... an important distinction is that
I never use old stock amps / parts, with aged leaky caps,
'that which 'others' should be more concerned about'. Those
are criticalities that secondary (fuse) protection is key.
Not remotely a factor in my builds.
No where have I ever suggest that which you mention...
~ SPELLING IT OUT ~ If that helps better
understanding my views [in this thread]
I .always do. have incoming AC / transformer primary protection fuses.
I .always do. have fuses supplying DC to the boards... always have,
.always will. have fuses, should be no confusion
about this sound practice.
I'll REPEAT [for added clarity] my fuses ..never blow..
These amps are bullet proof... an important distinction is that
I never use old stock amps / parts, with aged leaky caps,
'that which 'others' should be more concerned about'. Those
are criticalities that secondary (fuse) protection is key.
Not remotely a factor in my builds.
Glad to hear that you do believe in fuses.
FWIW I've never blown a fuse in normal operation on any of my amps dating back to the late 80's. I've popped a few in 4 ohm load testing, but that's to be expected. Usually older rail fuses that needed to be replaced anyway.
However the fuses aren't there just to cover for engineering or parts deficiencies. It doesn't matter how perfect the design is it can still fail due to things which have nothing to do with the design or parts quality. The fuses are as much for real world environmental problems that you cannot design around as they are for actual design failures.
As an example,
The time someones wife vacuums too close to the speaker wires getting one of them tangled in the rollers and pulling one of them loose causing it to sit perfectly across the speaker terminals just waiting for the clueless husband to come and turn on the amp later that evening.
Or when someone's nephew Timmy comes over and thinks its funny to shoot his water gun at his cousins which happen to be standing right in front of the powered up electronics rack.
Or when a cover screw from a component two shelves up works its way loose and bounces off the cables landing perfectly onto one of the vent holes in the top cover of the amplifier which just happens to be right over the live rail voltages.
There are more failure scenarios than there are Hafler amps out there in the field and there is no way to design around them all. Those are the things that manufacturers have to worry about.
I had hopes that your BC boards that are in progress would function in my 1981 DH500.
The servo power supply would need to be tamed down a bit from 90V, am assuming you have a 2w r to bring it down from the DH220 rails.
Lets hope they will work one day Getting closer
Will ask Bob about using them with a 90V supply.
I see that they are using a 27k, 1/2W(R101) in the DH-500 for the Lm339 supply. Using two 10V zeners in parallel, D101,108.
DH-220C has a 2W footprint for those R's.
I have one soldered up, just waiting for the jfets.
Getting closerWill ask Bob about using them with a 90V supply.
I see that they are using a 27k, 1/2W(R101) in the DH-500 for the Lm339 supply. Using two 10V zeners in parallel, D101,108.
DH-220C has a 2W footprint for those R's.
I have one soldered up, just waiting for the jfets.
Rick,
In checking Bob’s design for use on the DH 500 it would seem the dissipation for the dropping resistors for the servo power supply and the VAS devices (almost a watt each) are the main areas of concern. If there is room for a decent TO 220 heatsinks the VAS devices should be OK. Otherwise everything else looks to be well under maximum dissipation. Of course if Bob has other concerns I look forward to his comments.
I note the local compensation caps on the output stage that Hafler used aren’t shown in the schematic,
i suspect they are removed (or just not shown)?
In checking Bob’s design for use on the DH 500 it would seem the dissipation for the dropping resistors for the servo power supply and the VAS devices (almost a watt each) are the main areas of concern. If there is room for a decent TO 220 heatsinks the VAS devices should be OK. Otherwise everything else looks to be well under maximum dissipation. Of course if Bob has other concerns I look forward to his comments.
I note the local compensation caps on the output stage that Hafler used aren’t shown in the schematic,
i suspect they are removed (or just not shown)?
Hi,
Good to have you looking over the design, power and required cooling. There is area reserved for a al plate or local HS's, for the drivers. The way it is now, rev A0, the VAS will need to use local coolers.
I have already started an new rev, incorporate a dual footprint, sot-23-6 jfets on the backside, since they are in a lower cost package. Will see what else is needed, once Bob goes over it and is powered up.
I have the design in ltspice simulation, so need to go over the design with the higher rails and let it calculate static Pd of all the devices.
Happy Easter
Good to have you looking over the design, power and required cooling. There is area reserved for a al plate or local HS's, for the drivers. The way it is now, rev A0, the VAS will need to use local coolers.
I have already started an new rev, incorporate a dual footprint, sot-23-6 jfets on the backside, since they are in a lower cost package. Will see what else is needed, once Bob goes over it and is powered up.
I have the design in ltspice simulation, so need to go over the design with the higher rails and let it calculate static Pd of all the devices.
Happy Easter
Hi Rick,
Whenever you are ready, I’d appreciate if you could sell me six DH-220C boards. I’d prefer them with the SOT 23-6 JFETs installed, if that’s still an option.
Thanks and regards,
Rob
I prefer the TO 71 option, also its easier to change if you ever have to. Saving $1 or 2 using harder to install surface mount isn’t worth it to me. Just my vote, and there’s a box of Krispy Kreme in it for you.and if the DH 500 looks workable increase the boards I want to 16 . Thanks
I’m thinking to try and use it on the Perreaux 3150b I’m rebuilding. Same Hitachi lateral output stage as the Hafler DH 500, convection cooled with big heatsinks and +/- 97 volt supplies. it uses a copy of the original Hitachi suggested lateral fet driver circuit, it works and measured reasonably well, updated with better caps and resistors its better sounding, but it isn’t as low distortion, low noise, or as linear as Bob’s design.
If I got a pair of boards soon, I’d try to have it ready for Junes’s DIY BBQ, if i bias it hot enough i won’t need the grill.
I’m thinking to try and use it on the Perreaux 3150b I’m rebuilding. Same Hitachi lateral output stage as the Hafler DH 500, convection cooled with big heatsinks and +/- 97 volt supplies. it uses a copy of the original Hitachi suggested lateral fet driver circuit, it works and measured reasonably well, updated with better caps and resistors its better sounding, but it isn’t as low distortion, low noise, or as linear as Bob’s design.
If I got a pair of boards soon, I’d try to have it ready for Junes’s DIY BBQ, if i bias it hot enough i won’t need the grill.
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No need for Krispy Kreme. The jfets will be a dual footprint using TO-71-6(socketed) and sot-23-6 on the back, in the 2nd rev, the first rev was only the TO-71, agree, there is not much $ to be saved with the sot-23, thus the choice.
+/-97V, man that is pushing it, using 100V spec'd cap parts, yes it is BBQ season for sure.
maybe time order up your jfets, I am still waiting for mine. I asked trendsetter if they could snail mail them to me, they obliged, since they wanted 2x more money to ship than what they were worth. They only had one lsj689 in stock, but I see that they have re-stocked. I have the contact info if you need it.
+/-97V, man that is pushing it, using 100V spec'd cap parts, yes it is BBQ season for sure.
maybe time order up your jfets, I am still waiting for mine. I asked trendsetter if they could snail mail them to me, they obliged, since they wanted 2x more money to ship than what they were worth. They only had one lsj689 in stock, but I see that they have re-stocked. I have the contact info if you need it.