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Old 7th February 2012, 11:49 AM   #21
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The oscillations shouldnt be a big problem to stem, I have to wonder if all the potting compound was not the cause of this.

Ill do a simulation of the circuit as it was shown in the other thread, maybe its wortwhile to raise this amp from the dead.
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Old 7th February 2012, 01:17 PM   #22
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A simulation would be good but my guess is that overall loop stability is suspect. The 12 pF or 18 pF depending on schematic around the 'voltage amplifier' (Cdom in Douglass Self's book) is probably too small. If it's increased to lower the gain where the phase shift becomes a problem the slew rate probably suffers. My brief experience is that overall loop stability and local instabilities are difficult to work on.
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Old 8th February 2012, 12:58 PM   #23
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It's interesting that most people have had failures, but maybe that's just what drove everyone to de-pot or wonder what went wrong?

For what it's worth, my SuperMOS1 modules had a VERY hard life - doing many many hours of student parties at full output, as well as being used as my own home-amp day-in day-out for over 15 years. During one party I was driving two speakers in parallel (= ~4R). I noticed after several hours that one speaker wasn't working (the other was), and found that the ~5m 80-strand cable to the second speaker had both ends screwed onto the same binding-post!! I.e. the amp had been driving one loudspeaker (not noticeably quieter than the other channel) plus one shorted length of cable... and still indicating full o/p voltage swing! So these modules weren't exactly weak, and really could deliver a lot of current (one of Les's claims).

My module only failed because one leg of one signal transistor hadn't actually been soldered at all - I guess the potting had held the leg in place for 15 years, but it finally gave up (or perhaps the failure wasn't actually related). I only discovered this after de-potting, of course!
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Old 9th February 2012, 10:30 AM   #24
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Can someone put up the specs claimed for the amp. Ive done a sim so some comparisons can be made. All the parts are no longer available so I used modern replacements although Ill have to tweak some of the model parameters first as some are atrocious. The sim shows that the amp is stable enough although for absolute safety I would increase Cdom to
22p.
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Old 9th February 2012, 01:06 PM   #25
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Default Sage Specifications

Hello I have scanned in the file attached. The Sage Audio Application Notes were stapled to a price list dated May 1987. I think that I had a Superamp not a Supermos.
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File Type: pdf Sage Amplifier Specifications.pdf (92.2 KB, 129 views)
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Old 9th February 2012, 01:29 PM   #26
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I remember the ads, a long time ago.

I thought to myself "b******t", which means "no way", at that time.
Guess he was on to some ideas there.

Now, I haven't spent more than 15 secs looking at the circuits posted.

But, what do people think is that essentially a Hawksford there or an Allison?
Or something else?

I didn't quite see what it was doing with a really fast look because I am dull, slow on the uptake, and lazy too boot!



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Old 9th February 2012, 01:30 PM   #27
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Im afraid the only way those THD figures could possibly be reached is if they were either taken at 1 Watt power or the design is much different than shown. As the LTP currents are unbalanced it makes such numbers impossible.

There are some mistakes on the schematic, like the 33k resistors on driver input.

Pchi is it possible to show all the pages of that document, the text and graph as claimed in the THD figures will be helpfull to make a better comparison.
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Old 9th February 2012, 02:36 PM   #28
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I have scanned all the information that I have. Most of it isn't very useful, no graph unfortunately, I don't think I ever saw one. I was sceptical of the claims at the time and agree that the specifications are optimistic. I laid out the chassis and wiring as in the Recommended Layout Diagram in a home made case.
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Old 9th February 2012, 02:50 PM   #29
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Default Second attempt to attach files

Sorry my first attempt attaching all the information in one file was too large I split the brochure into two files but have only managed to attach one. You aren't missing much useful information.
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File Type: pdf Sage Audio brochure back.pdf (191.3 KB, 99 views)
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Old 9th February 2012, 03:00 PM   #30
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Thanks, it is useful, especially the explanation on the topology. Ill post some figures tommorrow.
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