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Hafler DH-200/220 Mods
Hafler DH-200/220 Mods
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Old 7th April 2019, 05:27 PM   #1561
Bob Cordell is offline Bob Cordell  United States
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Quote:
Originally Posted by rsavas View Post
Mod away as you desire but if you are messing with the high voltage AC and you create a safety/shock/electrocution hazard, then you become liable, you should correct and take responsibility for your actions. Safety is always first.

to quote Chris

I just worked on a couple of Yamaha P-2200 amplifiers, there is no such device used in this design. There are many designs that do not have a speaker/load disconnect feature. Not like Yamaha stated that if the amp fails/rails it will potentially fry your speakers. Does Yamaha get sued for frying speakers?
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
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Old 8th April 2019, 01:53 AM   #1562
anatech is offline anatech  Canada
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Hafler DH-200/220 Mods
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
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Old 15th April 2019, 10:25 PM   #1563
amp_guy is offline amp_guy  United States
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Do you mean a TRIAC crowbar or a SCR crowbar?
Don't you want it to stay triggered?
I am pretty rusty on thyristor circuits been a long time.
Oh wait I reread your post and think I follow now.

Last edited by amp_guy; 15th April 2019 at 10:30 PM. Reason: re-read previous post
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Old 15th April 2019, 10:50 PM   #1564
scott wurcer is offline scott wurcer  United States
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Quote:
Originally Posted by anatech View Post

You have to have respect for the power available in a fault condition.
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?
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Old 16th April 2019, 02:03 AM   #1565
phase is offline phase  United States
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It can be a big deal if the speakers flame out.
I got my magnepans after the original owner found them in a jacobís ladder state one night. They hadnít 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)?
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Old 16th April 2019, 06:33 AM   #1566
Ozark HiFi Doctor is offline Ozark HiFi Doctor  United States
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Default 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(y) 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.


Quote:
Originally Posted by scott wurcer View Post
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?
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Old 16th April 2019, 04:05 PM   #1567
amp_guy is offline amp_guy  United States
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Quote:
Originally Posted by phase View Post
It can be a big deal if the speakers flame out.
I got my magnepans after the original owner found them in a jacobís ladder state one night. They hadnít 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)?
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.
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Old 16th April 2019, 05:11 PM   #1568
Chamberman is offline Chamberman  United States
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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.
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Old 16th April 2019, 11:01 PM   #1569
rsavas is offline rsavas  Canada
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Quote:
On a different note, will the replacement boards accept a 90v supply(DH500)
Which ones?
I see they use the PC-19c, 100V ecaps, basically the same as DH-220, except 3 pairs of o/p's so I think the DH-220C might be up to it, eek one heck of a supply. need to regulate 90 down to 15 for the servo opamp, higher power R, remote mount? More fun

Last edited by rsavas; 16th April 2019 at 11:14 PM.
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Old 16th April 2019, 11:51 PM   #1570
Ozark HiFi Doctor is offline Ozark HiFi Doctor  United States
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Default Fuse protection in every amp build

Quote:
Originally Posted by Chamberman View Post
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.
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.
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