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.
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.
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.
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!
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!
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.
22p.
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.
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.
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!
😀
_-_-bear
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!
😀
_-_-bear
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.
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.
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.
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.
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.
Thanks, it is useful, especially the explanation on the topology. Ill post some figures tommorrow.
Hello bear,
I think that the Sage Supermos is a variation on the standard topology described as the Three Stage Amplifier Architecture by D. Self with the addition of a buffer between the second stage, voltage amplifier and the third stage, output. It also has a resistor between the output and the second stage voltage amplifier to limit the low frequency open loop gain. I believe also called the Lin topology by Bob Cordell amongst others.
I think that the Sage Supermos is a variation on the standard topology described as the Three Stage Amplifier Architecture by D. Self with the addition of a buffer between the second stage, voltage amplifier and the third stage, output. It also has a resistor between the output and the second stage voltage amplifier to limit the low frequency open loop gain. I believe also called the Lin topology by Bob Cordell amongst others.
That would be Great if you could Actually figure out the 100% real circuit etc 🙂
@ PChi
I'm surprised it failed with your testing, as i Know he tested extensively.
Yes i believe it was his first product, which was based around his low distortion & high slew rate etc design. This was incorporated into his Amp modules, but beefed up of course & with other cicuitry. It was called the SA1 which achieved ONLY 1ppm distortion. I know for a fact he sold one to an Amp etc manufacturer.
@ brianmarchant
Good to see you back again 🙂 Amazing to hear how they survived for All those 15 years.
***********
About 18 months ago audiopip who contributed to this thread & the other one asked me to send him scans of a number of Sage Audio brochures etc, which i did. If you PM him he might be kind enough to Attach them in here 🙂 All my stuff is now located quite a distance from where i live.
@ Zero D
Thanks for confirming my memory of the oscillator.
I think that the failure during testing was likely due to the high frequency oscillations. My crude calculations give a unity loop gain at around 2 MHz which is high for a Power Amplifier. I have dabbled in Power Amplifier design and high frequency instability is a real problem not very amenable to design or test. One of the problems is that the transistor parameters vary with current, voltage and temperature which is exactly what is happening in a power amplifier. So extensive testing doesn't guarantee that there will be no problems it just reduces the chances of having instability. I think that the Sage sales information was a little misleading but not too bad compared to some of the utter rubbish quoted by some 'reputable' manufacturers. Some of the specialist HiFi named products were none too clever either.
Thanks for confirming my memory of the oscillator.
I think that the failure during testing was likely due to the high frequency oscillations. My crude calculations give a unity loop gain at around 2 MHz which is high for a Power Amplifier. I have dabbled in Power Amplifier design and high frequency instability is a real problem not very amenable to design or test. One of the problems is that the transistor parameters vary with current, voltage and temperature which is exactly what is happening in a power amplifier. So extensive testing doesn't guarantee that there will be no problems it just reduces the chances of having instability. I think that the Sage sales information was a little misleading but not too bad compared to some of the utter rubbish quoted by some 'reputable' manufacturers. Some of the specialist HiFi named products were none too clever either.
@ PChi
Hi & thanks for the info.
The SuperMos though, used Les's constant Vce/Vbe principles in his Amps which, in his words, elimminated such variations & further helped to reduce distortion.
I expect the high unity loop gain was partly the reason for the high Slew Rate.
Hi & thanks for the info.
.
The SuperMos though, used Les's constant Vce/Vbe principles in his Amps which, in his words, elimminated such variations & further helped to reduce distortion.
I expect the high unity loop gain was partly the reason for the high Slew Rate.
Isnt the schematics given on the other thread more or less correct ?
Sims shows THD at 10W 1khz at 0.0012 and 0.0033 at 20khz. It is what I would expect the circuit to be capable of. Slightly better performance could be had if input pair collector currents were more evenly distributed, this can be done by raising the load resitor from 820 to about 1k2. The resistor from feedback to the vas I however omitted and believe is incorrectly shown, it deteriorates performance by over 50 percent. The driver resistors shown as 33k are also obviously wrong values and I used 33 ohms. What I like about this kind of vas setup is the fact that high frequency distortion does not rise as dramatically with increase in frequency as does say a EF buffered vas.
Interesting results Homemodder,
I can believe that the input pair collector currents need to be better matched.
Looking at the Sage Audio brochure it states 'LOW FEEDBACK ... The superamp and supermos are different in that they use complex multiple local feedback loops....' So it's possible that the feedback resistor to the Voltage Amplifier Stage, R19, may be correct. Though not necessarily a good idea.
It doesn't appear to use 'nested split compensation' also claimed though.
I can't understand the output stage biasing scheme. The brochure states 'DYNAMIC CLASS A' and the driver resistors R24 and R25 (33 k on the schematic) are connected in parallel with the base emitter junctions of Q15 and Q17.
Thanks for the analysis of the vas setup.
I can believe that the input pair collector currents need to be better matched.
Looking at the Sage Audio brochure it states 'LOW FEEDBACK ... The superamp and supermos are different in that they use complex multiple local feedback loops....' So it's possible that the feedback resistor to the Voltage Amplifier Stage, R19, may be correct. Though not necessarily a good idea.
It doesn't appear to use 'nested split compensation' also claimed though.
I can't understand the output stage biasing scheme. The brochure states 'DYNAMIC CLASS A' and the driver resistors R24 and R25 (33 k on the schematic) are connected in parallel with the base emitter junctions of Q15 and Q17.
Thanks for the analysis of the vas setup.
I may possibly have posted this in a ZIP file in the other thread, but for those asking, here's an OCR'd pdf of my Sage Audio brochure and price list, dated 1990. I've got the original scans if anyone wants them. I'd forgotten how expensive these things were; they must have made quite a hole in my student loan at the time ;-)
http://www.fineforcefive.com/RandomPages/SageAudio/SageAudioManual.pdf
http://www.fineforcefive.com/RandomPages/SageAudio/SageAudio1990PriceList.pdf
http://www.fineforcefive.com/RandomPages/SageAudio/SageAudioManual.pdf
http://www.fineforcefive.com/RandomPages/SageAudio/SageAudio1990PriceList.pdf
Thanks for the links to the Sage Audio brochure and price list. I have an earlier version titled 'Application Notes' which is similar. Mine doesn't have a recommended layout for a single case stereo power amplifier or the Power Supply Component Selection page.
My price list is dated May 1987 and the Supermos is listed at £ 59.95. So by July- December 1990 it had risen to £ 70.00.
I only bought the Superamp, bipolar output stage, listed at £ 47.50.
My price list is dated May 1987 and the Supermos is listed at £ 59.95. So by July- December 1990 it had risen to £ 70.00.
I only bought the Superamp, bipolar output stage, listed at £ 47.50.
So no one has a reverse engineering on the SuperMos?
Or is it the same thing but with a Mosfet output variation??
_-_-bear
Or is it the same thing but with a Mosfet output variation??
_-_-bear
Supermos is probably the superamp with mosfet outputs, what we need is a better schematic, I have one but some part values seem wrong or misplaced. Ill upload the schematic I have tommorrow.
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