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#81
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MOSFET output stage
Jorden Verwer wrote: As for your personal attacks towards me, I should mention that I'm under the impression that your experience with electronics outside audio applications is fairly limited, Radar, video, embedded control, computer graphics, DSP. given that you've apparently never heard of the term offset. Offset is IRRELEVANT to output devices you complete MORON ! Do do you know what a 'closed loop' means ? Don, can you smack this guy round the chops for me. He must be a recent product of our educashun system. Graham |
#82
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MOSFET output stage
Don Pearce wrote: Sorry, wrong address http://81.174.169.10/odds/crossover.gif Exactly. You CANNOT get rid of the crossover distortion. Graham |
#83
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MOSFET output stage
Don Pearce wrote: Eeyore wrote: Don Pearce wrote: Eeyore wrote: Don Pearce wrote: You get crossover distortion whatever the topology. The mosfet curves match into each other far far better, plus you're already using more feedback too. That amp I designed, quite seriously had invisible crossover distortion on an AP analyser's output. I'm sure it did, but that is the amp, not the output stage. See my next post. What good is an amp without an output stage ? Or vice-versa. I'm not interested in how many fairies can dance on the head of a pin. I'm intereted in real products you can build reliably in quantity production.. We're talking about the difference between fet and bipolar output stages. It is simple to reduce distortions in amplifiers with either to negligible proportions, which is why, for the purposes of the chat, it is necessary to restrict the chat to output stages per se. I don't recall that being the OP's question. Care to run a sim of the harmonic spectrum of a bipolar output stage vs lateral mosfet ? Graham |
#84
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MOSFET output stage
Trevor Wilson wrote:
"RichD" wrote in message ... Who do MOSFET sound better than bipolar, as an audio amp output driver? **Non-sequitur. If you're saying that MOSFET outputs sound better, they don't. As a device, operating at typical bias currents (say) 10-50mA, MOSFETs exhibit VASTLY more THD than BJTs. Only when bias currents are elevated (around 0.5A - 1A) do MOSFETs exhibit THD characteristics which are almost as good as BJTs. MOSFETs are very tough, have an exceptional ability to deliver high power, high frequency audio (and RF), but distortion is very high. They require lots of Global NFB in order to operate linearly. MOSFETs do not sound better than BJTs. At best, they can sound as good. All things being equal. Ahmm.... welll....here we go... Well, I like mosfet outputs because they are easier to design with, imo. Bipolars, often need an equivelent of 3 stage darlingtons. This makes it a tad harder to stabilse the feedback loop because of each stage pole. Basically, you only need about 6 low current transistors, or so, to achieve silly distortion and bandwidth figures, with mosfets. As far as "sounds better", that's all moot. Any competently designed amp should have thd, imd below audibility. Anyone that claims that a general purpose PA amp, sounds bad or not good, if it has thd and imd 0.005% and slew rates of 100V/us, is pretty much delusional. Roll on the £200 oxygen free mains cable I say.... Kevin Aylward www.anasoft.co.uk SuperSpice |
#85
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MOSFET output stage
Eeyore wrote:
given that you've apparently never heard of the term offset. Offset is IRRELEVANT to output devices you complete MORON ! I know that, and I never claimed otherwise. Offset is a form of noise, in a sense. And like noise, it is caused almost completely by the input transistors. I'm well aware of all that. Do do you know what a 'closed loop' means ? Yes. |
#86
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MOSFET output stage
Kevin Aylward wrote: Trevor Wilson wrote: "RichD" wrote Who do MOSFET sound better than bipolar, as an audio amp output driver? **Non-sequitur. If you're saying that MOSFET outputs sound better, they don't. As a device, operating at typical bias currents (say) 10-50mA, MOSFETs exhibit VASTLY more THD than BJTs. Only when bias currents are elevated (around 0.5A - 1A) do MOSFETs exhibit THD characteristics which are almost as good as BJTs. MOSFETs are very tough, have an exceptional ability to deliver high power, high frequency audio (and RF), but distortion is very high. They require lots of Global NFB in order to operate linearly. MOSFETs do not sound better than BJTs. At best, they can sound as good. All things being equal. Ahmm.... welll....here we go... Well, I like mosfet outputs because they are easier to design with, imo. Bipolars, often need an equivelent of 3 stage darlingtons. This makes it a tad harder to stabilse the feedback loop because of each stage pole. Basically, you only need about 6 low current transistors, or so, to achieve silly distortion and bandwidth figures, with mosfets. As far as "sounds better", that's all moot. Any competently designed amp should have thd, imd below audibility. Seems to be a few that miss that though. Esp those Chinese copies of copies. Anyone that claims that a general purpose PA amp, sounds bad or not good, if it has thd and imd 0.005% and slew rates of 100V/us, is pretty much delusional. Roll on the £200 oxygen free mains cable I say.... Why stop at £200 ? Oh ! http://www.asa.org.uk/asa/adjudicati..._ADJ_44177.htm Kevin, you'd be just the guy to do a harmonic analysis of the distortion spectrum of a properly biased bipolar vs lateral mosfet amp wouldn't you ? Any chance ? Graham |
#87
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MOSFET output stage
Jorden Verwer wrote: Eeyore wrote: given that you've apparently never heard of the term offset. Offset is IRRELEVANT to output devices you complete MORON ! I know that, and I never claimed otherwise. Yes you did. BUGGER OFF YOU IMBECILE. |
#88
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MOSFET output stage
Jorden Verwer wrote: Offset is a form of noise, in a sense. Every one a cracker. Maybe he hasn't heard of DC vs AC analysis ? Graham |
#89
Posted to sci.electronics.design,rec.audio.tech
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MOSFET output stage
Eeyore wrote:
Jorden Verwer wrote: Offset is a form of noise, in a sense. Every one a cracker. Maybe he hasn't heard of DC vs AC analysis ? Let me put it this way... Noise-like phenomena, in increasing order of bandwith: Offset == 1/f noise == white noise |
#90
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MOSFET output stage
On Sep 17, Eeyore wrote:
Who do MOSFET sound better than bipolar, as an audio amp output driver? As a driver ? Now if you said as an output stage it might make sense. There's a difference? -- Rich |
#91
Posted to sci.electronics.design,rec.audio.tech
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MOSFET output stage
Jorden Verwer wrote: Eeyore wrote: Jorden Verwer wrote: Offset is a form of noise, in a sense. Every one a cracker. Maybe he hasn't heard of DC vs AC analysis ? Let me put it this way... Noise-like phenomena, in increasing order of bandwith: Offset == 1/f noise == white noise Noise is AC Offset is DC End of story. |
#92
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MOSFET output stage
RichD wrote: Eeyore wrote: Who do MOSFET sound better than bipolar, as an audio amp output driver? As a driver ? Now if you said as an output stage it might make sense. There's a difference? Damn right there is. Graham |
#93
Posted to sci.electronics.design,rec.audio.tech
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MOSFET output stage
On Sep 18, "Kevin Aylward" wrote:
Who do MOSFET sound better than bipolar, as an audio amp output driver? **Non-sequitur. If you're saying that MOSFET outputs sound better, they don't. As a device, operating at typical bias currents (say) 10-50mA, MOSFETs exhibit VASTLY more THD than BJTs. Only when bias currents are elevated (around 0.5A - 1A) do MOSFETs exhibit THD characteristics which are almost as good as BJTs. MOSFETs are very tough, have an exceptional ability to deliver high power, high frequency audio (and RF), but distortion is very high. They require lots of Global NFB in order to operate linearly. MOSFETs do not sound better than BJTs. At best, they can sound as good. All things being equal. Well, I like mosfet outputs because they are easier to design with, imo. Bipolars, often need an equivelent of 3 stage darlingtons. This makes it a tad harder to stabilse the feedback loop because of each stage pole. Basically, you only need about 6 low current transistors, or so, to achieve silly distortion and bandwidth figures, with mosfets. As far as "sounds better", that's all moot. Any competently designed amp should have thd, imd below audibility. Anyone that claims that a general purpose PA amp, sounds bad or not good, if it has thd and imd 0.005% and slew rates of 100V/us, is pretty much delusional. Do you have any experience designing audio amps? Which did you use? -- Rich |
#94
Posted to sci.electronics.design,rec.audio.tech
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MOSFET output stage
On Thu, 18 Sep 2008 19:55:35 +0100, Eeyore
wrote: Jorden Verwer wrote: Eeyore wrote: Jorden Verwer wrote: Offset is a form of noise, in a sense. Every one a cracker. Maybe he hasn't heard of DC vs AC analysis ? Let me put it this way... Noise-like phenomena, in increasing order of bandwith: Offset == 1/f noise == white noise Noise is AC Offset is DC End of story. Everything is AC when you get right down to it. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com |
#95
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MOSFET output stage
Eeyore wrote:
Noise is AC Offset is DC End of story. Not at all. You're oversimplifying. If offset were truly DC, it wouldn't drift. And it does drift. Likewise, white noise also has an (infinitesimal) component at DC. It isn't all as black and white as you claim it to be. I realize this is a very theoretical approach, but I stand by my claim that offset and noise are conceptually similar. |
#96
Posted to sci.electronics.design,rec.audio.tech
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MOSFET output stage
RichD wrote: "Kevin Aylward" wrote: Who do MOSFET sound better than bipolar, as an audio amp output driver? **Non-sequitur. If you're saying that MOSFET outputs sound better, they don't. As a device, operating at typical bias currents (say) 10-50mA, MOSFETs exhibit VASTLY more THD than BJTs. Only when bias currents are elevated (around 0.5A - 1A) do MOSFETs exhibit THD characteristics which are almost as good as BJTs. MOSFETs are very tough, have an exceptional ability to deliver high power, high frequency audio (and RF), but distortion is very high. They require lots of Global NFB in order to operate linearly. MOSFETs do not sound better than BJTs. At best, they can sound as good. All things being equal. Well, I like mosfet outputs because they are easier to design with, imo. Bipolars, often need an equivelent of 3 stage darlingtons. This makes it a tad harder to stabilse the feedback loop because of each stage pole. Basically, you only need about 6 low current transistors, or so, to achieve silly distortion and bandwidth figures, with mosfets. As far as "sounds better", that's all moot. Any competently designed amp should have thd, imd below audibility. Anyone that claims that a general purpose PA amp, sounds bad or not good, if it has thd and imd 0.005% and slew rates of 100V/us, is pretty much delusional. Do you have any experience designing audio amps? LMAO ! Yes, Kevin had indeed had as have I. Amps that sold commercially into the pro-audio market. I can't even estimate how many tens of thousands in my case. Graham |
#97
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MOSFET output stage
Spehro Pefhany wrote: Eeyore wrote: Jorden Verwer wrote: Eeyore wrote: Jorden Verwer wrote: Offset is a form of noise, in a sense. Every one a cracker. Maybe he hasn't heard of DC vs AC analysis ? Let me put it this way... Noise-like phenomena, in increasing order of bandwith: Offset == 1/f noise == white noise Noise is AC Offset is DC End of story. Everything is AC when you get right down to it. I call it moving DC. It never will stay still. ;~) Graham |
#98
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MOSFET output stage
Jorden Verwer wrote: Eeyore wrote: Noise is AC Offset is DC End of story. Not at all. You're oversimplifying. If offset were truly DC, it wouldn't drift. Drift is a different phenomenon unrelated to noise. Usually thermally caused. Graham |
#99
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MOSFET output stage
Eeyore wrote:
Jorden Verwer wrote: Eeyore wrote: Noise is AC Offset is DC End of story. Not at all. You're oversimplifying. If offset were truly DC, it wouldn't drift. Drift is a different phenomenon unrelated to noise. Usually thermally caused. I meant drift of the offset. Of course drift is different from noise. But offset really does have a lot in common with noise, when you think about it. Also, noise is often thermally caused as well. |
#100
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MOSFET output stage
Jorden Verwer wrote: Eeyore wrote: Jorden Verwer wrote: Eeyore wrote: Noise is AC Offset is DC End of story. Not at all. You're oversimplifying. If offset were truly DC, it wouldn't drift. Drift is a different phenomenon unrelated to noise. Usually thermally caused. I meant drift of the offset. Of course drift is different from noise. But offset really does have a lot in common with noise, when you think about it. Not at all in any remote way shape or form. Also, noise is often thermally caused as well. Do you think you're telling me something I don't already know. I keep Boltzmann's Constant in my head for that pirpose. Graham |
#101
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MOSFET output stage
Exactly. I believe that even the very worst designers were generally able to get a
half-decent result with MOSFETs, whereas bipolars require a little more skill. So it may well be that MOSFETs DO sound better in car audio, consumer-grade home theatre and cheap "pro" sound systems, where the standards of the products and the designers are low. Tony On Wed, 17 Sep 2008 20:52:28 -0500, Damon Hill wrote: RichD wrote in news:b78fc9c2-fe9c-444c-8ac5- : Who do MOSFET sound better than bipolar, as an audio amp output driver? They do? Seems like it's possible to design good amplifiers either way. --Damon |
#102
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MOSFET output stage
Eeyore wrote:
Jorden Verwer wrote: Eeyore wrote: Jorden Verwer wrote: Eeyore wrote: Noise is AC Offset is DC End of story. Not at all. You're oversimplifying. If offset were truly DC, it wouldn't drift. Drift is a different phenomenon unrelated to noise. Usually thermally caused. I meant drift of the offset. Of course drift is different from noise. But offset really does have a lot in common with noise, when you think about it. Not at all in any remote way shape or form. Don't you at least agree there are many similarities between 1/f noise and offset? |
#103
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MOSFET output stage
"Vladimir Vassilevsky" However there are few special cases when a FET output stage has an advantage: 1) With FETs, it is simpler to control bias current, because of the negative dependency from the temperature. ** Completely wrong. The tempco of typical (ie switching) fets is strongly positive - the gate threshold voltage drops by about 6mV per degree C. Bias compensation is non trivial and crucial to get right or thermal runaway is likely. ...... Phil |
#104
Posted to rec.audio.tech
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MOSFET output stage
On Thu, 18 Sep 2008 17:49:59 +0100, Eeyore
wrote: Who do MOSFET sound better than bipolar, as an audio amp output driver? Because you believe they will. Because they CAN. By a country mile. But all people want today is cheap. And if they want esoteric they want the high distortion of tubes instead of ultra-low THD of well-engineered mosfet amps. And just to complicate an already messy thread, vacuum valves can easily have lower intrinsic distortion than any modern device. Lots of other issues, of course, but transfer curves with exponents below 1.05 were delivered before we were born. Before they could even be measured, in fact. But as you say, all people want today is cheap, and there are cheaper ways of delivering a finished product of low distortion than using devices of highest intrinsic linearity. Your attempts to keep the discussion focussed on the small end of signal level are admirable. Too many folks make too many assumptions of monotonicity that aren't (ever!, actually) true. Much thanks, as always, Chris Hornbeck |
#105
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MOSFET output stage
"Arny Krueger" wrote in message ... Good power amps sound the same and they sound like a piece of wire with gain. There are tons of power amps that can't be distinguished from a piece of wire with gain, while driving well-designed speakers. Ah, but since audiophools argue endlessly about cable and wire characteristics, you need to specify exactly what TYPE of wire with gain. :-) :-) MrT. |
#106
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MOSFET output stage
"Fred Bartoli" " " wrote in message ... Please explain how you obtain even distortion products from a symmetrical (suppose paired mosfets) push-pull. Any symmetrical function produces odd (and no even) harmonics. But isn't that part of the problem, producing Mosfets with identically symmetrical characteristics in N-ch and P-ch ? Of course good circuit design can compensate for many such factors, so the final result is what is important, not some evangelical belief, IMO. MrT. |
#107
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MOSFET output stage
In article ,
"Arny Krueger" wrote: "Eeyore" wrote in message Kevin McMurtrie wrote: In article , Damon Hill wrote: RichD wrote in news:b78fc9c2-fe9c-444c-8ac5- : Who do MOSFET sound better than bipolar, as an audio amp output driver? They do? Seems like it's possible to design good amplifiers either way. --Damon Exactly - zero difference in quality capabilities. It's usually a matter of impedance matching. Silicon transistors have a fixed loss around 0.5 volts. MOSFETs have a resistive loss inversely proportional to their voltage rating. That usually makes MOSFETs less expensive for low impedances and transistors less expensive for high impedances. TOTAL AND COMPLETE GARBAGE. Agreed. Actually, what Kevin said is the exact reverse of generally accepted practical knowledge. Bipolar is generally more efficient when the impedances get really low. MOSFETs were trendy for a while, but most new power amp designs seem to have bipolar outputs. Time to check the specs for this decade. Visit IRF. You can get a surface mount MOSFET in package similar to TO-220 that has 0.0008 Ohms on resistance, 300W dissipation, 24V rating, and a 1600A surge rating. Now I remember why I left this newsgroup. -- Google is a pro-spamming service. I will not see your reply if you use Google. |
#108
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MOSFET output stage
"Mr.T" "Fred Bartoli" Eeyore Please explain how you obtain even distortion products from a symmetrical (suppose paired mosfets) push-pull. Any symmetrical function produces odd (and no even) harmonics. But isn't that part of the problem, producing Mosfets with identically symmetrical characteristics in N-ch and P-ch ? ** For switching MOSFETs ( ie Hexfets etc ) there are no true complimentary P and N pairs - not even close. The P ch types all have much higher "on" resistances and lower max drain current ratings compared to their Nch counterparts. OTOH - lateral MOSFETs ( ie 2SK176 and 2SJ56 etc ) are near perfect Nch and Pch compliments - varying slightly in gate capacitance. More symmetrical in an audio output stage than nearly any BJT compliments around. ...... Phil |
#109
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MOSFET output stage
"Kevin McMurtrie" Time to check the specs for this decade. Visit IRF. You can get a surface mount MOSFET in package similar to TO-220 that has 0.0008 Ohms on resistance, 300W dissipation, 24V rating, and a 1600A surge rating. ** So you can use it to replace the engine starter relay in a car. Yawnnnnnnn .... ....... Phil |
#110
Posted to sci.electronics.design,rec.audio.tech
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MOSFET output stage
On Thu, 18 Sep 2008 20:06:43 -0700, Kevin McMurtrie
wrote: In article , "Arny Krueger" wrote: "Eeyore" wrote in message Kevin McMurtrie wrote: In article , Damon Hill wrote: RichD wrote in news:b78fc9c2-fe9c-444c-8ac5- : Who do MOSFET sound better than bipolar, as an audio amp output driver? They do? Seems like it's possible to design good amplifiers either way. --Damon Exactly - zero difference in quality capabilities. It's usually a matter of impedance matching. Silicon transistors have a fixed loss around 0.5 volts. MOSFETs have a resistive loss inversely proportional to their voltage rating. That usually makes MOSFETs less expensive for low impedances and transistors less expensive for high impedances. TOTAL AND COMPLETE GARBAGE. Agreed. Actually, what Kevin said is the exact reverse of generally accepted practical knowledge. Bipolar is generally more efficient when the impedances get really low. MOSFETs were trendy for a while, but most new power amp designs seem to have bipolar outputs. Time to check the specs for this decade. Visit IRF. You can get a surface mount MOSFET in package similar to TO-220 that has 0.0008 Ohms on resistance, 300W dissipation, 24V rating, and a 1600A surge rating. Now I remember why I left this newsgroup. IR is famous for creating incredible specs, with tiny footnotes retracting the wilder numbers. No TO-220 is going to last long at 300 watts; not many milliseconds. John |
#111
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MOSFET output stage
"Eeyore" wrote in message ... Arny Krueger wrote: wrote RichD wrote: Who do MOSFET sound better than bipolar, as an audio amp output driver? MOSFETS HAVE WIDER BANDWIDTH ,less phase shift , lower odd harmonic distortin. on and on. Not in any relevant way for audio power amps. The first two are highly relevevant in ANY circuit using NFB. Basic stability criteria. Only if the bandwidth and the phase margins are small relative to the target audio bandwidth, which is unlikely. |
#112
Posted to rec.audio.tech
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MOSFET output stage
Chris Hornbeck wrote: Eeyore wrote: Who do MOSFET sound better than bipolar, as an audio amp output driver? Because you believe they will. Because they CAN. By a country mile. But all people want today is cheap. And if they want esoteric they want the high distortion of tubes instead of ultra-low THD of well-engineered mosfet amps. And just to complicate an already messy thread, vacuum valves can easily have lower intrinsic distortion than any modern device. Lots of other issues, of course, but transfer curves with exponents below 1.05 were delivered before we were born. Before they could even be measured, in fact. But as you say, all people want today is cheap, and there are cheaper ways of delivering a finished product of low distortion than using devices of highest intrinsic linearity. Your attempts to keep the discussion focussed on the small end of signal level are admirable. Too many folks make too many assumptions of monotonicity that aren't (ever!, actually) true. Thanks for your comments Chris. I consider the small signal area vitally important, since in practive most listening is done there. Another cute little twist is that AIUI (it was reported to me by a Singapore distributor) is that the classic QSC grounded collector circuit has a low level montonicity problem due to the voltage gain of the out darlington output arrangement 'jumping' as the large devices turn on (they're normally off). Graham |
#113
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MOSFET output stage
"Mr.T" wrote: "Fred Bartoli" " " wrote Please explain how you obtain even distortion products from a symmetrical (suppose paired mosfets) push-pull. Any symmetrical function produces odd (and no even) harmonics. But isn't that part of the problem, producing Mosfets with identically symmetrical characteristics in N-ch and P-ch ? Of course good circuit design can compensate for many such factors, so the final result is what is important, not some evangelical belief, IMO. Fred is thinking of push-pull transformer coupled arrangements. He needs to advance about 4-5 decades. That's one reason I never call modern amps push-pull but complementary symmetry instead. Graham |
#114
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MOSFET output stage
Kevin McMurtrie wrote: "Arny Krueger" wrote: "Eeyore" wrote Kevin McMurtrie wrote: Damon Hill wrote: RichD wrote in Who do MOSFET sound better than bipolar, as an audio amp output driver? They do? Seems like it's possible to design good amplifiers either way. Exactly - zero difference in quality capabilities. It's usually a matter of impedance matching. Silicon transistors have a fixed loss around 0.5 volts. MOSFETs have a resistive loss inversely proportional to their voltage rating. That usually makes MOSFETs less expensive for low impedances and transistors less expensive for high impedances. TOTAL AND COMPLETE GARBAGE. Agreed. Actually, what Kevin said is the exact reverse of generally accepted practical knowledge. Bipolar is generally more efficient when the impedances get really low. MOSFETs were trendy for a while, but most new power amp designs seem to have bipolar outputs. Time to check the specs for this decade. Visit IRF. You can get a surface mount MOSFET in package similar to TO-220 that has 0.0008 Ohms on resistance, 300W dissipation, 24V rating, and a 1600A surge rating. These are NOT used in audio amps. Learn something about LATERAL mosfets that were designed for audio. I've already given part number and links to data sheets. Graham |
#115
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MOSFET output stage
John Larkin wrote: IR is famous for creating incredible specs, with tiny footnotes retracting the wilder numbers. No TO-220 is going to last long at 300 watts; not many milliseconds. You simply can't get that many watts through that tiny tab of copper fast enough. I think the highest continuous ratings are in the 50-70W area. Graham |
#116
Posted to sci.electronics.design,rec.audio.tech
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MOSFET output stage
Chronic Philharmonic wrote: "Eeyore" wrote in message Arny Krueger wrote: wrote RichD wrote: Who do MOSFET sound better than bipolar, as an audio amp output driver? MOSFETS HAVE WIDER BANDWIDTH ,less phase shift , lower odd harmonic distortin. on and on. Not in any relevant way for audio power amps. The first two are highly relevevant in ANY circuit using NFB. Basic stability criteria. Only if the bandwidth and the phase margins are small relative to the target audio bandwidth, which is unlikely. Modern audio amplifiers are expected to have a bandwidth far greater than 20kHz. If not, you may experience slew limiting problems and associated THD and IMD IIRC. Yet another one totally out of date with modern practice. Graham |
#117
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MOSFET output stage
On Thu, 18 Sep 2008 20:23:29 -0700, the renowned John Larkin
wrote: On Thu, 18 Sep 2008 20:06:43 -0700, Kevin McMurtrie wrote: In article , "Arny Krueger" wrote: "Eeyore" wrote in message Kevin McMurtrie wrote: In article , Damon Hill wrote: RichD wrote in news:b78fc9c2-fe9c-444c-8ac5- : Who do MOSFET sound better than bipolar, as an audio amp output driver? They do? Seems like it's possible to design good amplifiers either way. --Damon Exactly - zero difference in quality capabilities. It's usually a matter of impedance matching. Silicon transistors have a fixed loss around 0.5 volts. MOSFETs have a resistive loss inversely proportional to their voltage rating. That usually makes MOSFETs less expensive for low impedances and transistors less expensive for high impedances. TOTAL AND COMPLETE GARBAGE. Agreed. Actually, what Kevin said is the exact reverse of generally accepted practical knowledge. Bipolar is generally more efficient when the impedances get really low. MOSFETs were trendy for a while, but most new power amp designs seem to have bipolar outputs. Time to check the specs for this decade. Visit IRF. You can get a surface mount MOSFET in package similar to TO-220 that has 0.0008 Ohms on resistance, 300W dissipation, 24V rating, and a 1600A surge rating. Now I remember why I left this newsgroup. IR is famous for creating incredible specs, with tiny footnotes retracting the wilder numbers. No TO-220 is going to last long at 300 watts; not many milliseconds. John Anything approaching 1600A would blow the leadwires off a TO-220. The fusing current of a long wire of that cross-section area is only in the 30-50A range. 100A-rated wire is around 6mm (1/4") in diameter. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com |
#118
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MOSFET output stage
"Spehro Pefhany" Anything approaching 1600A would blow the leadwires off a TO-220. ** Not if it is only for a few microseconds. That is how the things are usually rated. ...... Phil |
#119
Posted to sci.electronics.design,rec.audio.tech
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MOSFET output stage
"Eeyore" wrote in
message Arny Krueger wrote: This whole "amp sounds better" stuff was fully debunked 30 years ago. Good power amps sound the same and they sound like a piece of wire with gain. There are tons of power amps that can't be distinguished from a piece of wire with gain, while driving well-designed speakers. There are quite a few amps that meet the same criteria while driving even the weirdest speaker load. A really good power amp will destroy a poorly-designed speaker before it starts sounding bad, and really good power amps aren't all that unique. The speaker is a large part of it. Highly reactive ( i.e. lots of inductance or capacitance ) speakers can prematurely trigger device protection. Agreed. Speakers that require heroic amplifiers (heroic amps definitely exist and are easy enough to obtain) are IMO not well designed. We discovered that EV's SX500 was particularly bad in this respect in PA for example. Now that is certainly audible. Agreed. However we have only part of the equation - the name of the speaker. What was the amp? The SX 500i EDS suggests that it might be a handful for weak-kneed amps. Its impedance curve does go down to 4 ohms at several points below 1 KHz. http://www.electrovoice.com/documents/ev/sx500-eds.pdf Using pairs paralleled can be a short road to amp problems. In contrast, the sequel ZX-5 stays above 8 ohms over the same range: http://www.electrovoice.com/document...X560PI_EDS.pdf Needless to say, I have 4 ZX-5s. ;-) |
#120
Posted to sci.electronics.design,rec.audio.tech
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MOSFET output stage
On Sep 18, 5:05*am, "Arny Krueger" wrote:
wrote in message On Sep 17, 6:12 pm, RichD wrote: Who do MOSFET sound better than bipolar, as an audio amp output driver? MOSFETS HAVE WIDER BANDWIDTH ,less phase shift , lower odd harmonic distortin. on and on. Not in any relevant way for audio power amps. This is not true. The phase shift in the output section of a power amplifier is a significant issue. If you want to have much of a gain sacrifice factor in the audio band, the gain cross over point will be well above the audio band. NFB can't make a silk purse out of a sows ear. It can only lower the distortion by about the gain sacrifice factor. This makes if better to start with a low distortion topology. Rumors aside MOSFETs are not really easier to operate in parallel. You still need emitter / source resistors. |
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