john curl said:
There is somebody who has the sig. quote "Condemnation without Examination is Prejudice". If only I could remeber who that is. 😉
Christer,
there is enough good reason for this opinion. Read J.A. Halcro reviews at Stereophile, look at power/impedance curves, read the Halcro manual and put it all together. In case you happened to work with SMPSs, you will know what is it about.
there is enough good reason for this opinion. Read J.A. Halcro reviews at Stereophile, look at power/impedance curves, read the Halcro manual and put it all together. In case you happened to work with SMPSs, you will know what is it about.
PMA and John,
Yes, I am sure you have something more behind it. It was just that John left the goal open by (seemingly) condemning an amp only by suspicion.
It was mostly just a joke with John and his sig. quite, that I couldn't resist. I don't know about english, but in swedish we have the proverb that one shouldn't throw stones if living in a glass house. That is about what John seemed to do here (although he may very well have much more support for his suggestiong than he said).
Yes, I am sure you have something more behind it. It was just that John left the goal open by (seemingly) condemning an amp only by suspicion.
It was mostly just a joke with John and his sig. quite, that I couldn't resist. I don't know about english, but in swedish we have the proverb that one shouldn't throw stones if living in a glass house. That is about what John seemed to do here (although he may very well have much more support for his suggestiong than he said).
john curl said:
I've noticed that it is in fact rare that they test for burst power in the reviews, unfortunately. We're both just speculating at this point anyway. I would REALLY love to get ahold of one of those Halcros and test it.
Bob
What I am trying to do here is to TEACH many of you that there can be limitations with almost any design approach.
Every design approach has limitations, not only in audio and elctronics. Does anybody really have to teach that? Or perhaps I am just being naive to believe that it is not needed.
And John, please note that my previous postings was not really about the Halcro. It was just a joking way to tell you to be a bit careful with what you say if you want to stand by the quote you use. I think you have yourself pointed out when others say similar things. It was all meant in a friendly way, of course, but I know you know that.
And John, please note that my previous postings was not really about the Halcro. It was just a joking way to tell you to be a bit careful with what you say if you want to stand by the quote you use. I think you have yourself pointed out when others say similar things. It was all meant in a friendly way, of course, but I know you know that.
john curl said:
Actually John, this got started by your assertion that VFETs are not up to the task of a high power amplifier. There remains no basis for that assertion.
By all means, I think there are few here that do not realize that there can be limitations with almost any design approach. However, it is also useful to understand where those limitations stem from; in this case, the question is whether the Halcro continuous power limitations into 2 ohms stem from the use of VFETs (or the need to protect them), or from the use of SMPS technology.
Since SMPS technology is being advocated by numerous companies, it is especially relevant to understand if that is a typical source of limited output current, which we all care about. If that were the case, suggesting that the limitation was from the use of VFETs would be a red herring that would NOT serve to educate anyone.
Bob
Christer, I previously read a review in 'Hi Fi News' by Martin Collums on the Halcro power amp. This is in the June, 2004 edition. model DM 38
On p. 62, Bruce Candy says: "...that provididing any higher current than this rating requires is not only unnecessary, but might be dangerous. Accordingly, the Halcro amplifier's peak output current is limited to +/- 15A, Just sufficient for the rated output into 4 ohms, but no more."
Is this evidence enough? Please understand, I seriously believe this is why the Halcro can have Vmos outputs and 200W into 8 ohms.
Bob Cordell has not yet shown how he is going to keep his Vmos working when he heads to 200W or more. He just thinks that I don't know what I am doing.
On p. 62, Bruce Candy says: "...that provididing any higher current than this rating requires is not only unnecessary, but might be dangerous. Accordingly, the Halcro amplifier's peak output current is limited to +/- 15A, Just sufficient for the rated output into 4 ohms, but no more."
Is this evidence enough? Please understand, I seriously believe this is why the Halcro can have Vmos outputs and 200W into 8 ohms.
Bob Cordell has not yet shown how he is going to keep his Vmos working when he heads to 200W or more. He just thinks that I don't know what I am doing.
John, I agree that quote from Candy seem to suggest a limit probably also for bursts. Still, it does not prove anything about where the limitation comes from, as Bob has pointed out. You have different opinioins on the matter, but none of you has provided concrete evidence to support you suspicion. Hence, we really cannot know. We can guess and have opinioins, but not know until further facts are disclosed.
Had I known that piece of information too (and sorry if it was posted before and I missed it) it would have made a difference to that earlier post of yours that I commented on. However, don't take it too seriously. As you may have noticed, I have a tendency to often think and post on a slightly more abstract level than most people here (not in anyway implying this to be better in any way). It is probably my job and training as computer scientist that makes it natural for me to abstract more than people in general and to look more at the arguments and the logic of reasoning in what people post. Hence, it is not seldom that I comment more on the line of reasoning and the arguments in a post than on the factual details of it (which can many times be as important as commenting on the facts). That was the case here. I simply spotted an inconsistency between your way of making an argument in the post (as written there) and the quote, that I presume you like both us and yourself to keep in mind. However, in this case it was mostly because I found that inconsistency somewhat amusing, and perhaps also worth noticing as an example of the difficulty to adhere to ones own preferred standards, that I wrote the comment at all. It is easy to tell others how to behave. It is difficult not to fall into the trap oneself now and then. I guess that was the sensmorale I wanted to point out. It wasn't anything personal either. I would probably have done the same thing if someone else had done something similar. I might even have pointed out in retrospect if I did it myself. 🙂
Had I known that piece of information too (and sorry if it was posted before and I missed it) it would have made a difference to that earlier post of yours that I commented on. However, don't take it too seriously. As you may have noticed, I have a tendency to often think and post on a slightly more abstract level than most people here (not in anyway implying this to be better in any way). It is probably my job and training as computer scientist that makes it natural for me to abstract more than people in general and to look more at the arguments and the logic of reasoning in what people post. Hence, it is not seldom that I comment more on the line of reasoning and the arguments in a post than on the factual details of it (which can many times be as important as commenting on the facts). That was the case here. I simply spotted an inconsistency between your way of making an argument in the post (as written there) and the quote, that I presume you like both us and yourself to keep in mind. However, in this case it was mostly because I found that inconsistency somewhat amusing, and perhaps also worth noticing as an example of the difficulty to adhere to ones own preferred standards, that I wrote the comment at all. It is easy to tell others how to behave. It is difficult not to fall into the trap oneself now and then. I guess that was the sensmorale I wanted to point out. It wasn't anything personal either. I would probably have done the same thing if someone else had done something similar. I might even have pointed out in retrospect if I did it myself. 🙂
It's OK Christer. All that I expect is a little professional courtesy, which is lacking here sometimes. That is why I am giving Bob Cordell such a hard time.
It is my professional opinion that hard current limiting is problematic with many loudspeaker systems, especially the expensive ones. The need for very high peak current for a few milliseconds at least, is well known to many professional designers, and many of us were burned (sonically) in the past with E-I limiting that was so popular in the 1970's.
When I tried to make just a 100W all fet power amp, first using IRF 130's, then 140's in desperation, I contacted Bob Cordell, and he thought that I must have an oscillation. Well maybe, but when I previously made amps with bipolar outputs, and with a 10 ohm resistor in each base (that is important) they could be protected with just a dual circuit breaker in the DC power supply lines. No deal with vertical mosfets at +/-45V for me, at least. Perhaps if I had changed to IRF240 devices, I would have been OK, but probably only because the transconductance was lower in each 240 part than the 140 series. After all, I did not exceed the minimum voltage breakdown of the parts and they 'didn't' have any second breakdown mechanism, did they?
Well, 20 years later, I'm being called on the carpet as being a second rate designer, because I had a problem making my amp work into a short circuit. Maybe, just maybe, I have some experience with this problem.
It is my professional opinion that hard current limiting is problematic with many loudspeaker systems, especially the expensive ones. The need for very high peak current for a few milliseconds at least, is well known to many professional designers, and many of us were burned (sonically) in the past with E-I limiting that was so popular in the 1970's.
When I tried to make just a 100W all fet power amp, first using IRF 130's, then 140's in desperation, I contacted Bob Cordell, and he thought that I must have an oscillation. Well maybe, but when I previously made amps with bipolar outputs, and with a 10 ohm resistor in each base (that is important) they could be protected with just a dual circuit breaker in the DC power supply lines. No deal with vertical mosfets at +/-45V for me, at least. Perhaps if I had changed to IRF240 devices, I would have been OK, but probably only because the transconductance was lower in each 240 part than the 140 series. After all, I did not exceed the minimum voltage breakdown of the parts and they 'didn't' have any second breakdown mechanism, did they?
Well, 20 years later, I'm being called on the carpet as being a second rate designer, because I had a problem making my amp work into a short circuit. Maybe, just maybe, I have some experience with this problem.
john curl said:
Thanks for bringing that quote to our attention, John. If it is true that he is really hard-limiting limiting it to 15A, then that is certainly unfortunate, and I don't agree with his imposing such a limitation. Of course, it is just as likely that he said that as an excuse for the SMPS limiting his ability to deliver current.
It is certainly wrong to say that I don't think you know what you are doing, in spite of the fact that we do not always agree. I really do believe that you are one of the more gifted amplifier designers.
I guess we will have to agree to disagree on your assertion that VMOS is not up to the task of big power amplifiers that can deliver several hundred watts and several tens of amperes of burst current. I know it is not a problem. You think it is not a problem based on your failed experience twenty years ago. Others besides myself have done it.
Cheers,
Bob
john curl said:
John, give me a break, please. Just because I do not agree with everything you say does not mean that I am not showing professional courtesy (unless of course, your version of "professional courtesy" means a free pass on whatever you say not being challenged because you are a professional - not gonna happen here).
Yes, I do remember those numerous times you called me for advice. I was honored to be asked for advice, even well after we had our differences over the Otala thing.
And finally, certainly no-one here is calling you on the carpet for being a second-rate designer. You are only meeting resistance because you made a negative assertion about VMOS that many people do not believe is substantiated. If you cite your own failures to make VMOS work 20 years ago as your evidence, you are the one shooting yourself in the foot. Lighten up a bit. We're all here to learn from each other. Indeed, I learn a heck of a lot from you, either directly or indirectly.
Cheers,
Bob
john curl said:
Haha. This reminds me of the old saying, "If you can't fix it, feature it" 😀.
Absolutely. In addition, there is some info in the Stereophile measurements of the DM88 here. Into 4 Ohms with 1 percent THD, the output power is 525W. This corresponds to a peak current of 16.2A. Into 2 Ohms with 1 percent THD, the output power is 266W. This is a peak current of 16.3A. Sure looks like a hard current limit to me. Different output voltages, same current limit.
But if this technique were really used solely for SOA protection of the output devices, a fixed current limit is a totally incompetent design. Different people may have different views of Candy's design approach, but I suspect there's few that would label him an incompetent. I certainly wouldn't. So this strongly suggests that something else is going on besides just output device SOA protection. I'd have to agree with others that the SMPS is suspect.
Some tests results guys...
Recently I tested 2 amplifiers one with Triple Deep Darlington BJT amp and another one is My version of NVMOS....
The output devices were MJ21196/MJL21195 2Pairs incase of BJT amp and IRFP260N 2 Pairs in case of NVMOS...
Both amps were fed from same power supply +/-95VDC [4KW Toroid + 10 X 10000MFD Caps]idle.....one at a time...
With short brust of 100Hz sinewave with time interval 100mS below are the peak currents obtained from both amps under direct short circuit...no current limiting is involved....The measurement was taken by Current Probe in our friend's test setup....
BJT amp delivered only 78A Peak
NVMOS amp exceeds 126A peak.....
Recently I tested 2 amplifiers one with Triple Deep Darlington BJT amp and another one is My version of NVMOS....
The output devices were MJ21196/MJL21195 2Pairs incase of BJT amp and IRFP260N 2 Pairs in case of NVMOS...
Both amps were fed from same power supply +/-95VDC [4KW Toroid + 10 X 10000MFD Caps]idle.....one at a time...
With short brust of 100Hz sinewave with time interval 100mS below are the peak currents obtained from both amps under direct short circuit...no current limiting is involved....The measurement was taken by Current Probe in our friend's test setup....
BJT amp delivered only 78A Peak
NVMOS amp exceeds 126A peak.....
DM88 distortion
Hello Bob
Interesting that the even the DM88 could not reach the lowest possible THD that the Audio Precision System One can measure on the power sweep test. For the record it can measure down to 0.0005% (-106dB) THD (20-20kHz bandwidth), in practise its lower than this. The power testing was done at 1kHz , where this amp should have the following specs THD: <–140dB (<100ppb) at 1kHz.
Regards
Arthur R
Hello Bob
Interesting that the even the DM88 could not reach the lowest possible THD that the Audio Precision System One can measure on the power sweep test. For the record it can measure down to 0.0005% (-106dB) THD (20-20kHz bandwidth), in practise its lower than this. The power testing was done at 1kHz , where this amp should have the following specs THD: <–140dB (<100ppb) at 1kHz.
Regards
Arthur R
Workhorse:
With short brust of 100Hz sinewave with time interval 100mS below are the peak currents obtained from both amps under direct short circuit...no current limiting is involved....The measurement was taken by Current Probe in our friend's test setup....
BJT amp delivered only 78A Peak
NVMOS amp exceeds 126A peak.....
Workhorse, a thought: this is a maximum possible slew rate of 0.6V/us which gives the NVMOS cct gate zeners plenty of time to react. I would think that a short applied to the output while the amp is operating would be much faster.
Is it possible that the pot down between the Cds and Cgs can produce a high enough gate voltage to blow the device (with a transient fast enough to take the gate zener out of the equation)?
With short brust of 100Hz sinewave with time interval 100mS below are the peak currents obtained from both amps under direct short circuit...no current limiting is involved....The measurement was taken by Current Probe in our friend's test setup....
BJT amp delivered only 78A Peak
NVMOS amp exceeds 126A peak.....
Workhorse, a thought: this is a maximum possible slew rate of 0.6V/us which gives the NVMOS cct gate zeners plenty of time to react. I would think that a short applied to the output while the amp is operating would be much faster.
Is it possible that the pot down between the Cds and Cgs can produce a high enough gate voltage to blow the device (with a transient fast enough to take the gate zener out of the equation)?