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Old 7th May 2005, 08:59 PM   #281
mikeks is offline mikeks  United Kingdom
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Quote:
Originally posted by Lars Clausen
But on the other hand you don't seem too open towards other people's suggestions......

On the contrary, i LOVE 'other people's suggestions'....provided these 'suggestions' are not merely articles of faith....

Faith and engineering are mutually incompatible....alias:an oxymoron...
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Old 7th May 2005, 09:00 PM   #282
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Mikeks: OK it's simple math. I will demonstrate it tomorrow, if you give us the story on that girl !!!
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Old 7th May 2005, 09:02 PM   #283
mikeks is offline mikeks  United Kingdom
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Old 7th May 2005, 09:05 PM   #284
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Old 8th May 2005, 03:00 AM   #285
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"MJ15XXX something, or the good old BCV64/65 or TIP35/36 and push them to the limit, your slope circuit would be a must. Those devices have no power dissipation tolerance at just slightly over 30V .. "

The MJ15015/16 have 180W SOA at 60V

The MJ15022/23 have 160W SOA at 80V

The MJ21195/96 have 240W SOA at 80V

The only MJ series I am aware of that has a SOA curve that bends at 30V are the old MJ802/4502
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Old 8th May 2005, 06:19 AM   #286
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Quote:
Originally posted by Lars Clausen
Mikeks: IŽd say lets take your amp and my amp, crank them up to full power and short the outputs. Then let's see which one last longer

I gather you have given a lot of thought to this issue, but as i see it there is one particular reason that close SOA monitoring on the reactive load side is simply unnecessary, and a waste of time. But on the other hand you don't seem too open towards other people's suggestions, so i'll just let you work this one out yourself ....

At least i can say that any circuit that limits the current in the output stage - like the one that limits the current in the output stages, according to the SOA slopes - will always influence the sound quality. Enough for me to not even consider it.

It limits the current, but you don't accept that people call it a current limiter ???

Have a nice weekend

We will feel glad, if you also compare the short circuit with our mosfet amp also, which upon short circuit will go into latch mode for indefinate period, till the user resets it.
Regarding the influence of protection circuit on sound quality, i dont agree with you , since we have set the current limit of our to be 3 times the RMS current at max voltage and thats the worth of simply using mosfets. Bipolars wont stand in such conditions.

meanwhile your Zeta will do the right work for you..........
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Old 8th May 2005, 01:27 PM   #287
anatech is offline anatech  Canada
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Hi Workhorse,

I don't see the usefullness of comparing an amp that will shut down on a short in this test. Whether you use mosfets or bipolar transistors in this situation is immaterial since the amp has shut down. No SOA issues since you are now talking about short protection. As you have over built your amp, the same could be done with bipolars. Big deal.

Your point about SOA issues with mosfets was made a while ago. Now back to other useful input from others.

-Chris
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Old 8th May 2005, 05:14 PM   #288
sam9 is offline sam9  United States
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I sense a certain amount of semantic confusion. VI-limiting and short circuit protection are not synonomous. They may, however, intersect to a greater or lesser degree.

I expect most VI-limiters deal with a short at least briefly. Hopefully, long enough to deal with someone who forgets to turn off the amp while connecting the speakers. While persistent shorts may result in thermal damage after a while, I think that circumstance is relatively rare at least for home the user.

A pure short circuit protection scheme (I saw a schematic recently of one) may do a hard shut down when the load drops below say1 ohm but leave you unprotected from speakers with dips just short of 1 ohm. This might be all that's needed if use many, many parallel output devices beyond what usual for the supply rails. Brute force solutions have the merit of simplicity.
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Old 8th May 2005, 05:26 PM   #289
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Sam, indeed. If you take enough output devices, you may not need SOA modelling, because of the massive overkill to ANY possible complex load situation. Nelson Pass' designs come to mind. In such a case, a simple short protection may be all that is needed. But it has a price, of course.

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Old 8th May 2005, 07:19 PM   #290
mikeks is offline mikeks  United Kingdom
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Quote:
Originally posted by sam9
VI-limiting and short circuit protection are not synonomous.
True!

VI protection limits current as a function of device voltage..(as Jan pointed out somewhere)....

...while crude short circuit protection provides a constant current limit regardless of device voltage......


...in other words, the short-circuit locus is merely a flat horizontal line across the SOA plot (linear-linear scales assumed)....

...this makes for grossly inefficient use of available SOA, as the flat short-circuit locus HAS to reside below the max. voltage, power dissipation parabola (MOSFETs), or the secondary breakdown parabola (BJTs), leaving more than 90% of available SOA unused.....

Therefore, it should be apparent that simple short-circuit protection is exceedingly crude...and inefficient...and reeks of lack of commitment...laziness.....ineptitude.....cluelessn ess....rank amateurishness.....(have i missed any choice adjectives here.... Let me know... )
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