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** The circuit shown is complete.John Robertson has already taken the cupie doll for spotting that it simply does nothing of any use.
A great many amplifiers have similar LED indicators labelled "Thermal" or "Protedct" but do actually shut the amp down or at least disconnect the speakers.
AFAIK, the P2200 is unique in not doing so.
** No, that's the part number for the tiny front panel LEDs. ** Hmmmm - the man cannot see the wood for the trees ........ Phil
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** ROTFL !!..... Phil
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** Having that -21V a boost rail make the amp work better and matches the benefits of the load side bootstrap on the class A stage.TR107 is a current source so bucks any variation on the plus rail.
My first post said " the amp misbehaves terribly " - not it was merely a bit imperfect.
I have also posted that users could find the amp *unusable* though no faults had developed. Few comparable amps have the same problem.
It is not heat related & the amp does not stop working.
.... Phil
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** Here is a big clue:The "misbehaviour" is an unintended result of the VI limiter.
TR113 & TR114 and their associated parts.
.... Phil
Thanks for the clue but I'm still stumped. Does the C119 thru 122 combo make the amplifier into a gigantic supersonic oscillator with certain speaker loads?
piglet
No, the diodes takes care of that, it only acts on the side with the lower voltage over the transistors (where the current flows). The other side is not supposed to have much current, at least in audio designs.
Motor drivers do, I learned the hard way, they have a four-quadrant load. The SOA computations there are more complex. Same for audio designs with big transformer loads (like for electrostats).
Arie
Is that because of the SOA circuit _foldback_ effect when overload occurs? Any clipping must have sound horrrible (maybe that's why people still like soft clipping tube amps). Even some phase reversal might occur. Hmmm... intriguing, but too busy now to start LTspice.
Arie
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** You real sure about that ?.... Phil
I never add capacitors to my current-limiting transistors; you want it to turn off as fast as it turns on. When the AC level drops you don't want continuing disabling action. And as the polarity rapidly reverses at high frequencies, you want the current-limiting off.
--
Thanks,
- Win
It ought to be fine as long as the amplifier is only connected to dummy load resistors. Reactive loads (speakers?) might cause the current limit to cut in earlier than expected.
Allan
I'll take a swing..
The SOA transistor TR114 has unlimited authority to push current into the drivers TR108 TR109. Current through TR108/109 is limited only by R126 which is 68 Ohms and with >85 Volt supply that is >1 Amp. Probably more than TR108 and TR109 can withstand.
I guess that means with a loud enough audio drive signal and a low Z load that activates SOA protection, TR108 and / or TR109 may fail.
Mark
Sure, but that amp doesn't do it very well.
Do you use a DC coupled signal chain for your music?
In other words, you like this amp design.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
D112/113 increase the current limit of the transistors that are swinging towards the rail, but don't decrease the opposite ones. That would be OK if Iq is set low, but the Vbe multiplier isn't perfect. I think this scheme over-stresses the not-active side on big swings. It will NOT drive reactive loads well.
Speakers are largely ohmic, which makes life a lot simpler for audio amps.
We're designing a class-D amp that will drive a big transformer, then a wide range of loads, including various shunt-to-ground switching regulators. We can tell from the data sheet of the TI class-D chip that they didn't much consider non-speaker loads.
Our latest innovation is to put the heat sink and a fan on the bottom of the board. Got to come up with a nice way to mount the fan to the board. Brackets? Foam tape? Hot melt glue?
I like to do real SOA calculations, namely run a realtime model of junction temperature and use that to limit or shut down. That maximizes use of expensive silicon.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
If you want the fan to stay put, then I recommend securing it with some combination of mounting hardware & brackets.
Hot melt or double sided tape can be problematic when exposed to the real world...
John :-#)#
(Please post followups or tech inquiries to the USENET newsgroup) John's Jukes Ltd. MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3 (604)872-5757 (Pinballs, Jukes, Video Games)
OK, grumble, I guess we don't want the fan falling off into the bottom of the box.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
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** A clearer way to view this is to note that equal amounts of current are available in both polarities at zero output. Available current increases as the output swings towards one or other rail. ** Who's IQ is that then ?** LOL - what a shameless non sequitur.
JL is drowning in his own bullshit here.
** If it's "non-active" how then does it become stressed ? ** Really? Why is that ?JL in on the sniff of a scent here.
** Massive fallacy.** Says an audio hater and ignoramous.
** Nice if you have a known load.
..... Phil
I don't hate audio, I just don't care for music. Well, I do hate
*some* music, as you probably do. But a lot of audio electronics is badly designed, as you have pointed out.No, I use hardware or software to compute mosfet junction temps, using realtime measurement of voltages and currents and heatsink temp, and a thermal model of the chip and heat sink. The computed Tj is realistic, independent of signals and loads. It's a small cost addition that radically improves the use of expensive fets and heat sinks and gets max safe output in all quadrants.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
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** One and the same thing.** Not a lot.
** Not true.
Most professional audio gear is well designed and built for the purpose intended and at very low cost cos the competition is *fierce*.
** Really, so the load's characteristics are irrelevant to your design ?That's cool .....
...... Phil
onsdag den 23. oktober 2019 kl. 16.55.19 UTC+2 skrev snipped-for-privacy@highlandsniptechnology.com:
two holes?
The load should be and is irrevelent to the protection algorithm. I compute a pretty good approximation of actual fet junction temp, and shut down if that gets too high. No simple current limit or foldback does that.
Fets, fans, heat sinks are expensive. May as well use them to their safe limits.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
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