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preamp design
I hope this is an appropriate news group to post this (I apologize if not)
Well first of all I'll say a bit about myself... I'm an electrical engineering student with an interest in audio electronics. In the third year of my program we covered basic amplifier design, which I loved, and I've been considering a career in this field since. At the moment I'm particularly interested in microphone preamplifiers since I'm a poor student who has his own project studio, but doesn't own (and can't afford) a nice preamp like the Great River. I'm having a good bit of trouble finding any info on design strategies that are specific to microphone preamps. I've found some schematics on the net but there's rarely any very detailed explanation given about why they were designed the way they were, and what considerations were made. I understand all the basic principles like CMRR, slew rate, etc... but there seems to be some sort of understanding gap, and I'd like to bridge that gap. I realize it's probably something I'm not going to be able to grasp over night, I'm just looking for some kind of direction. If anyone knows of any resources that would help me, I'd appreciate it. Thanks, Dave |
#2
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preamp design
At the risk of blowing my own horn, I've written several articles on preamp
designs, both solid-state and vacuum tube based, in what is now audioXpress magazine (the solid-state series was published in 1996, when the magazine was called Audio Amateur). In the articles, I talked about some basic principles of design which apply to microphone preamps in general, not only to these designs. Peace, Paul Stamler |
#3
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preamp design
David Grant wrote:
I hope this is an appropriate news group to post this (I apologize if not) Well first of all I'll say a bit about myself... I'm an electrical engineering student with an interest in audio electronics. In the third year of my program we covered basic amplifier design, which I loved, and I've been considering a career in this field since. At the moment I'm particularly interested in microphone preamplifiers since I'm a poor student who has his own project studio, but doesn't own (and can't afford) a nice preamp like the Great River. I'm having a good bit of trouble finding any info on design strategies that are specific to microphone preamps. I've found some schematics on the net but there's rarely any very detailed explanation given about why they were designed the way they were, and what considerations were made. I understand all the basic principles like CMRR, slew rate, etc... but there seems to be some sort of understanding gap, and I'd like to bridge that gap. I realize it's probably something I'm not going to be able to grasp over night, I'm just looking for some kind of direction. If anyone knows of any resources that would help me, I'd appreciate it. The first thing you need to know with mic pre-amps is how to design with discretes. Has your course covered that in any depth ? Relatively unlikely I'll guess. That's the first hurdle. A good understanding of differential circuitry, feedback methods and noise calculations takes you further. Then you get into understanding device parameters. Does rbb mean anything to you for example ? Graham |
#4
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preamp design
On Mon, 1 Dec 2003 18:02:05 -0500, "David Grant"
wrote: If anyone knows of any resources that would help me, I'd appreciate it. There's also some excellent general info at: http://www.rane.com/library.html Good fortune, Chris Hornbeck "That is my Theory, and what it is too." Anne Elk |
#5
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preamp design
"Pooh Bear" wrote in message ... David Grant wrote: I hope this is an appropriate news group to post this (I apologize if not) Well first of all I'll say a bit about myself... I'm an electrical engineering student with an interest in audio electronics. In the third year of my program we covered basic amplifier design, which I loved, and I've been considering a career in this field since. At the moment I'm particularly interested in microphone preamplifiers since I'm a poor student who has his own project studio, but doesn't own (and can't afford) a nice preamp like the Great River. I'm having a good bit of trouble finding any info on design strategies that are specific to microphone preamps. I've found some schematics on the net but there's rarely any very detailed explanation given about why they were designed the way they were, and what considerations were made. I understand all the basic principles like CMRR, slew rate, etc... but there seems to be some sort of understanding gap, and I'd like to bridge that gap. I realize it's probably something I'm not going to be able to grasp over night, I'm just looking for some kind of direction. If anyone knows of any resources that would help me, I'd appreciate it. The first thing you need to know with mic pre-amps is how to design with discretes. Has your course covered that in any depth ? Relatively unlikely I'll guess. We've never used the term "discrete" anywhere, but am I correct in assuming it means "not in IC form" (i.e BJT amps versus op amp ICs)? If that's the case then we've done a good bit. That's the first hurdle. A good understanding of differential circuitry, feedback methods and noise calculations takes you further. Then you get into understanding device parameters. Does rbb mean anything to you for example ? We've covered differential BJT amps, cascode configuration, some frequency response, feedback (shunt/series sampling) and some stability. I remember some stuff on calculating CMRR if that's what you mean by noise calculations. As for the device parameters, I'm not sure. Rbb sounds like the symbol one of my proffs used to denote the base resistance used for biasing a BJT, but otherwise it doesn't mean anything to me. We did all the derivations of gain, in/out resistance for most of the amps we discussed in class, and usually everything simplified down to something neat and tidy. I've tried to do small signal analysis on some of the mic-pre schematics I've looked at, but I always end up with huge long expressions that turn very messy. I also never end up with the quoted specs in the end! It seems like there must be some simplification that I'm missing. Common mode gain control for example... what on earth is that (apart from a gain control)? Maybe I just need more experience with this stuff, but I'm not sure where to find that. Thanks for the help Dave Graham |
#6
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preamp design
"David Grant" wrote in message
If anyone knows of any resources that would help me, I'd appreciate it. I think a reasonable first step would be to figure out how to reliably and relevantly determine the effectiveness and performance of a mic preamp. Both technical tests and listening tests seem relevant. Tests with various microphones and microphone techniques and/or simulations of them seem relevant. Then, apply those evaluation techniques to a number of commercial products at various price levels, as well as various technological implementations (tubes, discrete solid state, ICs). Identify good things, bad things, peculiarities, foibles, desirable features, and good baseline performance in terms that are comparable across products and implementations. Then, design, build and evaluate a mic preamp that maximizes as many of the high priority desirable properties as possible. |
#7
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preamp design
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#8
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preamp design
David Grant wrote:
I'm having a good bit of trouble finding any info on design strategies that are specific to microphone preamps. I've found some schematics on the net but there's rarely any very detailed explanation given about why they were designed the way they were, and what considerations were made. I understand all the basic principles like CMRR, slew rate, etc... but there seems to be some sort of understanding gap, and I'd like to bridge that gap. I realize it's probably something I'm not going to be able to grasp over night, I'm just looking for some kind of direction. If anyone knows of any resources that would help me, I'd appreciate it. Hi Dave, you may be interested in an article I wrote for, and which was published in Electronics and Wireless World – June 1989, p628, about designing low noise audio amplifiers or more specifically: designing for low audio front-end noise with real semiconductor devices. Reprints of this article which includes numerous references are available from http://www.softcopy.co.uk. Enjoy! Wilfried Adam |
#9
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preamp design
David Grant wrote:
That's the first hurdle. A good understanding of differential circuitry, feedback methods and noise calculations takes you further. Then you get into understanding device parameters. Does rbb mean anything to you for example ? We've covered differential BJT amps, cascode configuration, some frequency response, feedback (shunt/series sampling) and some stability. I remember some stuff on calculating CMRR if that's what you mean by noise calculations. As for the device parameters, I'm not sure. Rbb sounds like the symbol one of my proffs used to denote the base resistance used for biasing a BJT, but otherwise it doesn't mean anything to me. Okay, your typical preamp is a differential BJT amp, with something after it to give it a little bit more gain. OR, it's a transformer with some single-ended gain stages. We did all the derivations of gain, in/out resistance for most of the amps we discussed in class, and usually everything simplified down to something neat and tidy. I've tried to do small signal analysis on some of the mic-pre schematics I've looked at, but I always end up with huge long expressions that turn very messy. I also never end up with the quoted specs in the end! It seems like there must be some simplification that I'm missing. Common mode gain control for example... what on earth is that (apart from a gain control)? Basically you throw out all the small terms.... the input stage noise floor is so high that it swamps everything else. There was a paper by Marshall Leach in the JAES a decade ago which went through all the noise floor math for a dozen different preamp configurations, in a clear and concise way. You need to read it. Everybody needs to read it. Maybe I just need more experience with this stuff, but I'm not sure where to find that. Go to your school library, get old copies of the JAES, and read through them. Also get the RCA Radiotron Handbook, which is thoroughly obsolete and talks about tubes, but the math is the same and the circuits can generally be stolen outright and implemented with FETs. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#10
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preamp design
David Grant wrote:
I'm having a good bit of trouble finding any info on design strategies that are specific to microphone preamps. I've found some schematics on the net but there's rarely any very detailed explanation given about why they were designed the way they were, and what considerations were made. I understand all the basic principles like CMRR, slew rate, etc... but there seems to be some sort of understanding gap, and I'd like to bridge that gap. I realize it's probably something I'm not going to be able to grasp over night, I'm just looking for some kind of direction. If anyone knows of any resources that would help me, I'd appreciate it. John Hardy has an excellent literature package that he sends out on request; some elements of it are available for download as PDFs on his Web site at http://www.johnhardyco.com/products.html--see in particular the PDF about the 990 discrete op amp--but make sure to request the whole package. Also be prepared (not at all with John Hardy, but with some other product lines) to see a fair amount of mysticism and hand-waving that parades as engineering--but you probably noticed that already. |
#11
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preamp design
"Scott Dorsey" wrote in message
Basically you throw out all the small terms.... the input stage noise floor is so high that it swamps everything else. There was a paper by Marshall Leach in the JAES a decade ago which went through all the noise floor math for a dozen different preamp configurations, in a clear and concise way. You need to read it. Everybody needs to read it. That would probably be: Noise Analysis of Transformer-Coupled Preamplifiers 746047 bytes (CD aes5) Author(s): Leach, Jr., W. Marshall Publication: Volume 40 Number 1/2 pp. 3·11; January 1992 Abstract: Noise analyses of input stages of typical transformer-coupled preamplifiers are presented. Conditions are derived for which the transformer improves the signal-to-noise ratio of the circuits. Examples are presented which are typical for microphone preamplifiers Also relevant: Designing Low-Noise, High-Linearity and High-Speed Preamplifiers for Magnetic Transducers 409166 bytes (CD aes10) Author(s): Ogwang, D. Okel Publication: Preprint 1829; Convention 70; October 1981 Abstract: An ultra-low-noise preamplifier front end configuration is determined through the analysis of the noise behaviour of a bipolar transistor, current mirror and an FET in relation to the noise performance of various preamplifier configurations. A design for Hi-Fi performance, in accordance with the demand for a low-noise, high-linearity and high-speed preamplifier for use with a magnetic transducer, is then presented. |
#12
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preamp design
"David Satz" wrote in message
om John Hardy has an excellent literature package that he sends out on request; some elements of it are available for download as PDFs on his Web site at http://www.johnhardyco.com/products.html--see in particular the PDF about the 990 discrete op amp--but make sure to request the whole package. Also be prepared (not at all with John Hardy, but with some other product lines) to see a fair amount of mysticism and hand-waving that parades as engineering--but you probably noticed that already. This one seems to be highly informative and purely orthodox: http://www.johnhardyco.com/pdf/990.pdf . |
#13
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preamp design
"Arny Krueger" wrote in message ... "David Grant" wrote in message If anyone knows of any resources that would help me, I'd appreciate it. I think a reasonable first step would be to figure out how to reliably and relevantly determine the effectiveness and performance of a mic preamp. Both technical tests and listening tests seem relevant. Tests with various microphones and microphone techniques and/or simulations of them seem relevant. Then, apply those evaluation techniques to a number of commercial products at various price levels, as well as various technological implementations (tubes, discrete solid state, ICs). I assume I'd need to know how the commercial products I'm comparing are designed for this to be of most benefit. Are there schematics available somewhere for commercial units (I wouldn't expect there to be) or is it practical to reverse engineer their design? |
#14
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preamp design
David Grant wrote:
I'm having a good bit of trouble finding any info on design strategies that are specific to microphone preamps. I've found some schematics on the net but there's rarely any very detailed explanation given about why they were designed the way they were, and what considerations were made. I understand all the basic principles like CMRR, slew rate, etc... but there seems to be some sort of understanding gap, and I'd like to bridge that gap. I realize it's probably something I'm not going to be able to grasp over night, I'm just looking for some kind of direction. If anyone knows of any resources that would help me, I'd appreciate it. I'm not really touting myself, but recently on my forum, there was an interesting discussion among a lot of the leading preamp designers. Take a look he http://recpit.prosoundweb.com/viewtopic.php?t=7774 Harvey Gerst Indian Trail Recording Studio http://www.ITRstudio.com/ |
#15
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preamp design
"David Grant" wrote in message
"Arny Krueger" wrote in message ... "David Grant" wrote in message If anyone knows of any resources that would help me, I'd appreciate it. I think a reasonable first step would be to figure out how to reliably and relevantly determine the effectiveness and performance of a mic preamp. Both technical tests and listening tests seem relevant. Tests with various microphones and microphone techniques and/or simulations of them seem relevant. Then, apply those evaluation techniques to a number of commercial products at various price levels, as well as various technological implementations (tubes, discrete solid state, ICs). I assume I'd need to know how the commercial products I'm comparing are designed for this to be of most benefit. Are there schematics available somewhere for commercial units (I wouldn't expect there to be) or is it practical to reverse engineer their design? The schematic publication policies of equipment manufacturers range from high levels of secrecy to easy disclosure . Here's some examples of easy disclosu http://www.johnhardyco.com/pdf/990.pdf http://www.rane.com/pdf/ms1bsch.pdf http://www.rane.com/pdf/dms22sch.pdf http://www.rolls.com/data/mp13man.pdf You've got google, right? ;-) |
#16
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preamp design
It might also be useful to get hold of the Jensen transformer data book,
including all of the application notes. That'll give some insight into the design problems to be solved. Peace, Paul |
#17
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preamp design
In rec.audio.pro, "David Grant" wrote:
I hope this is an appropriate news group to post this (I apologize if not) Well first of all I'll say a bit about myself... I'm an electrical engineering student with an interest in audio electronics. In the third year of my program we covered basic amplifier design, which I loved, and I've been considering a career in this field since. At the moment I'm particularly interested in microphone preamplifiers since I'm a poor student who has his own project studio, but doesn't own (and can't afford) a nice preamp like the Great River. I'm having a good bit of trouble finding any info on design strategies that are specific to microphone preamps. I've found some schematics on the net but there's rarely any very detailed explanation given about why they were designed the way they were, and what considerations were made. I understand all the basic principles like CMRR, slew rate, etc... but there seems to be some sort of understanding gap, and I'd like to bridge that gap. I realize it's probably something I'm not going to be able to grasp over night, I'm just looking for some kind of direction. If anyone knows of any resources that would help me, I'd appreciate it. As others here have indicated, there's some good info out there, you just have to dig a bit for it. Arny posted some commercial schematics - the Rane uses the INA163 - I've used it as well as the older (and slightly better and available in DIP thru-hole package) INA103. Get the datasheets for these at http://www.ti.com. I've got a design using it on my website. These are 'basic' chips - Analog Devices have similar ones in there SSM line. To get better performance (lower noise) requires discrete transistors on the input, as I'm sure you know. The LM194/LM394 datasheet has a "High performance instrumentation amplifier" schematic. I don't know how good it would be for a mic pre, though with three of these devices for one amp, it looks like it's designed to sell a large quantity of LM194's. There's this Usenet post from John Hardy concerning the LM194 as used in the 990: http://groups.google.com/groups?q=+%...tbi.com&rnum=1 or: http://makeashorterlink.com/?M2E8222B6 I've yet to ask him for his "data package," I suppose I should. Thanks, Dave ----- http://mindspring.com/~benbradley |
#18
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preamp design
Arny Krueger wrote:
"Scott Dorsey" wrote in message Basically you throw out all the small terms.... the input stage noise floor is so high that it swamps everything else. There was a paper by Marshall Leach in the JAES a decade ago which went through all the noise floor math for a dozen different preamp configurations, in a clear and concise way. You need to read it. Everybody needs to read it. That would probably be: Noise Analysis of Transformer-Coupled Preamplifiers 746047 bytes (CD aes5) Author(s): Leach, Jr., W. Marshall Publication: Volume 40 Number 1/2 pp. 3·11; January 1992 Abstract: Noise analyses of input stages of typical transformer-coupled preamplifiers are presented. Conditions are derived for which the transformer improves the signal-to-noise ratio of the circuits. Examples are presented which are typical for microphone preamplifiers This is later than the paper I am thinking of, I think. But this is also well worth reading. Designing Low-Noise, High-Linearity and High-Speed Preamplifiers for Magnetic Transducers 409166 bytes (CD aes10) Author(s): Ogwang, D. Okel Publication: Preprint 1829; Convention 70; October 1981 Abstract: An ultra-low-noise preamplifier front end configuration is determined through the analysis of the noise behaviour of a bipolar transistor, current mirror and an FET in relation to the noise performance of various preamplifier configurations. A design for Hi-Fi performance, in accordance with the demand for a low-noise, high-linearity and high-speed preamplifier for use with a magnetic transducer, is then presented. Wow, I don't remember this at all. I'm going to have to go look it up now... --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#19
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preamp design
David Grant wrote:
I assume I'd need to know how the commercial products I'm comparing are designed for this to be of most benefit. Are there schematics available somewhere for commercial units (I wouldn't expect there to be) or is it practical to reverse engineer their design? Until about 1985 or so, everything came with schematics in the manual. And a lot of products still do. Without the schematics, you can't fix it. I won't buy anything I cannot fix. For a good adventure, get out the schematics for the Mackie 1202, the 1202 VLZ, and the latest generation, and compare them. The successive refinements are very interesting. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#20
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preamp design
Have a look at:
http://www.forsselltech.com/schematics.htm for some usefull information..... Rgds: Eric Weber www.webermusic.com |
#21
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preamp design
David Grant wrote:
"Pooh Bear" wrote in message ... David Grant wrote: I hope this is an appropriate news group to post this (I apologize if not) Well first of all I'll say a bit about myself... I'm an electrical engineering student with an interest in audio electronics. In the third year of my program we covered basic amplifier design, which I loved, and I've been considering a career in this field since. At the moment I'm particularly interested in microphone preamplifiers since I'm a poor student who has his own project studio, but doesn't own (and can't afford) a nice preamp like the Great River. I'm having a good bit of trouble finding any info on design strategies that are specific to microphone preamps. I've found some schematics on the net but there's rarely any very detailed explanation given about why they were designed the way they were, and what considerations were made. I understand all the basic principles like CMRR, slew rate, etc... but there seems to be some sort of understanding gap, and I'd like to bridge that gap. I realize it's probably something I'm not going to be able to grasp over night, I'm just looking for some kind of direction. If anyone knows of any resources that would help me, I'd appreciate it. The first thing you need to know with mic pre-amps is how to design with discretes. Has your course covered that in any depth ? Relatively unlikely I'll guess. We've never used the term "discrete" anywhere, but am I correct in assuming it means "not in IC form" (i.e BJT amps versus op amp ICs)? If that's the case then we've done a good bit. That's academia for you - lol. Been ages since I heard anyone use the term Bipolar Junction Transistor. Had to stop and think. Real engineers just call the bipolars as opposed to mosfet etc. :-) Most op-amps have bjt inputs btw - they're just 'invisible' to the user. That's the first hurdle. A good understanding of differential circuitry, feedback methods and noise calculations takes you further. Then you get into understanding device parameters. Does rbb mean anything to you for example ? We've covered differential BJT amps, cascode configuration, some frequency response, feedback (shunt/series sampling) and some stability. I remember some stuff on calculating CMRR if that's what you mean by noise calculations. Nope. CMRR is purely rejection of signal. A thorough understanding of noise sources and how to add them is required. Are you familiar with the equation for thermal noise for starters ? En ( the noise voltage ) = sqrt ( 4.K.t.R.Bw) K=Boltzmann's constant ( 1.37.10^-23), t = absolute temp in Kelvin, R=the resistor whose noise you want to know, Bw=bandwidth of interest ( 20kHz for audio ) It's also helpful to know about things like flicker noise (some transistors are better than others). Remember to sum noise sources as RMS ! As for the device parameters, I'm not sure. Rbb sounds like the symbol one of my proffs used to denote the base resistance used for biasing a BJT, but otherwise it doesn't mean anything to me. Damn close, it's the 'intrinisic' base resistance of the transistor itself and appears in series with the source, degrading the noise performance. Select a transistor with low Rbb. Same is true for Ree too, but I've never seen that on a datasheet, prolly to low to be of interest., although the dynamic emiiter impedance is very important. Most mic stages don't run input transistors at around 2.5mA Ic by accident. We did all the derivations of gain, in/out resistance for most of the amps we discussed in class, and usually everything simplified down to something neat and tidy. I've tried to do small signal analysis on some of the mic-pre schematics I've looked at, but I always end up with huge long expressions that turn very messy. Yeah, what they teach you is over-complicated. You need to strip it to the bare essentials and concentrate on what's important. I saw the light when I read a series of articles in the UK's Wireless World about 30 yrs ago. Written by a lecturer who wanted to make to topic of transistor amplification understandable on a practical level. For example - a simple 'common emitter' single transistor gain stage with a collector load R and an un-bypassed emitter R. Theory would have you go into untold complexities. For all practical purposes though, the voltage gain = collector load R / emitter R. I also never end up with the quoted specs in the end! It seems like there must be some simplification that I'm missing. Common mode gain control for example... I've no idea where you would see that in practice. Where did you come acros it ? what on earth is that (apart from a gain control)? Maybe I just need more experience with this stuff, but I'm not sure where to find that. Experience is the key. Keep at it. Graham |
#22
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preamp design
Scott Dorsey wrote:
Arny Krueger wrote: "Scott Dorsey" wrote in message Basically you throw out all the small terms.... the input stage noise floor is so high that it swamps everything else. There was a paper by Marshall Leach in the JAES a decade ago which went through all the noise floor math for a dozen different preamp configurations, in a clear and concise way. You need to read it. Everybody needs to read it. That would probably be: Noise Analysis of Transformer-Coupled Preamplifiers 746047 bytes (CD aes5) Author(s): Leach, Jr., W. Marshall Publication: Volume 40 Number 1/2 pp. 3·11; January 1992 Abstract: Noise analyses of input stages of typical transformer-coupled preamplifiers are presented. Conditions are derived for which the transformer improves the signal-to-noise ratio of the circuits. Examples are presented which are typical for microphone preamplifiers This is later than the paper I am thinking of, I think. But this is also well worth reading. Designing Low-Noise, High-Linearity and High-Speed Preamplifiers for Magnetic Transducers 409166 bytes (CD aes10) Author(s): Ogwang, D. Okel Publication: Preprint 1829; Convention 70; October 1981 Abstract: An ultra-low-noise preamplifier front end configuration is determined through the analysis of the noise behaviour of a bipolar transistor, current mirror and an FET in relation to the noise performance of various preamplifier configurations. A design for Hi-Fi performance, in accordance with the demand for a low-noise, high-linearity and high-speed preamplifier for use with a magnetic transducer, is then presented. Wow, I don't remember this at all. I'm going to have to go look it up now... --scott Lol ! On the commercial front, there's some good stuff too from some of the semiconductor manufacturers. It doesn't go into 'ultra low-noise' applications, but the theory is identical and you get some worked examples. The 'Bifet Design Manual' from Texas is still available I think and I also found National's 'Audio Handbook' useful - not sure of that's still around though. Blow me ! It's been re-issued ! Not hard to see why. http://www.audioxpress.com/bksprods/books/bkaa59.htm TI have an excellent site actually - literally stuffed with info. Check out their 'knowledgebase'. Although most of the stuff is about ICs, the noise theory ( and other stuff ) is universal. If you are planning a career in audio, get TI's 'Op amps for Everyone'. Available online as a pdf. Publication # SLOD006B. A mere 464 pages ! Also, do a google on SSM2019 and get the data sheet. See how an integrated mic pre is made. You can do better with a discrete front end though. Graham |
#23
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#24
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preamp design
In article znr1070416326k@trad, Mike Rivers wrote:
In article writes: Until about 1985 or so, everything came with schematics in the manual. And a lot of products still do. Before 1985, there wasn't a product-of-the-month and competition between manufacturers, so it was OK to openly publish a schematic without a non-disclosure agreement. Today much of our gear is pretty much unfixable even if you had a schematic, and the manufacturers don't want to hint at trade secrets. True. And more recently, we have cases where the people selling the products in the US are just importers who don't know what is inside it and don't care themselves, and the factory won't tell them anyway. I don't see any reason why a mic preamp doesn't come with a schematic though, other than that far more of them are sold to people who don't read manuals (much less keep track of them) so it would be an unjustified publishing expense. I think it's a good thing. I learned an awful lot reading through the Principles of Operation section in the Orban and CBS Labs manuals when I was younger. People should look inside things. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#25
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preamp design
Mike Rivers wrote:
In article writes: Until about 1985 or so, everything came with schematics in the manual. And a lot of products still do. Before 1985, there wasn't a product-of-the-month and competition between manufacturers, so it was OK to openly publish a schematic without a non-disclosure agreement. Today much of our gear is pretty much unfixable even if you had a schematic, and the manufacturers don't want to hint at trade secrets. Uhuh. There's a few things I won't disclose. When you find out how to improve something and it's taken a while, you don't want to give it all away. I've had my design ideas 'copied' through sloppy management of the client company and I don't intend to see it recur. I don't see any reason why a mic preamp doesn't come with a schematic though, other than that far more of them are sold to people who don't read manuals (much less keep track of them) so it would be an unjustified publishing expense. In my experience these days, very few ppl bother with reading the manual. See some of the questions here. Their loss, I say. Graham |
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