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#1
Posted to rec.audio.pro
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Hi-Z mics? where OH where have they gone!
I'm looking a mic that will work on a hi-z input (12Kohm) without a
preamp or impedance transformer. Two questions: 1) How will a 600ohm mic sound through this input? Will I get a decent signal or do I need a mic with much high impedance? 2) Can anyone recommend a hi-z mic, not more than $100, that is NOT a dinky computer microphone? And where I could get one? I would have thought that some mics I consider to be "cheap", such as a PG58 or even a "Sony dynamic mic" (radioshack style) for $40 would be hi-z, but they are in fact 600ohm. I admit this isn't really "pro" level equipment I'm asking about but it's to accompany the Tascam Pocketstudio 5 that I got for my girlfriend  so come on, help a brother out, eh!Dex |
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#2
Posted to rec.audio.pro
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Hi-Z mics? where OH where have they gone!
wrote:
I'm looking a mic that will work on a hi-z input (12Kohm) without a preamp or impedance transformer. Two questions: You can find one at a truckstop or a place that sells ham radio supplies. Unbalanced high-Z mikes are still standard for communications applications where high frequency response isn't needed. 1) How will a 600ohm mic sound through this input? Will I get a decent signal or do I need a mic with much high impedance? It won't be very loud unless you use a matching transformer. 2) Can anyone recommend a hi-z mic, not more than $100, that is NOT a dinky computer microphone? And where I could get one? I would have thought that some mics I consider to be "cheap", such as a PG58 or even a "Sony dynamic mic" (radioshack style) for $40 would be hi-z, but they are in fact 600ohm. The thing is, if you want a lot of windings around a coil, you are going to have a lot of mass on the coil. So either you get no high end, or you get a transformer with an integral step-up transformer if you want a dynamic high-Z mike. I admit this isn't really "pro" level equipment I'm asking about but it's to accompany the Tascam Pocketstudio 5 that I got for my girlfriend so come on, help a brother out, eh!Pocketstudio? Is this a thing with a 1/8" input that provides plug-in power? If so, you will need a microphone that uses plug-in power and if you use a dynamic mike you will need to add a blocking cap. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
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#3
Posted to rec.audio.pro
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Hi-Z mics? where OH where have they gone!
On Dec 5, 7:33 am, wrote:
I'm looking a mic that will work on a hi-z input (12Kohm) without a preamp or impedance transformer. Two questions: 1) How will a 600ohm mic sound through this input? Will I get a decent signal or do I need a mic with much high impedance? 2) Can anyone recommend a hi-z mic, not more than $100, that is NOT a dinky computer microphone? And where I could get one? I would have thought that some mics I consider to be "cheap", such as a PG58 or even a "Sony dynamic mic" (radioshack style) for $40 would be hi-z, but they are in fact 600ohm. I admit this isn't really "pro" level equipment I'm asking about but it's to accompany the Tascam Pocketstudio 5 that I got for my girlfriend so come on, help a brother out, eh!Dex Go get an Audio-Technica CP8201 Lo-Z to Hi-Z transformer. It will cost around $12. Use this on the Line B input to the PS5. Now use whatever dynamic mic you prefer. bobs Bob Smith BS Studios we organize chaos http://www.bsstudios.com |
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#4
Posted to rec.audio.pro
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Hi-Z mics? where OH where have they gone!
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#5
Posted to rec.audio.pro
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Hi-Z mics? where OH where have they gone!
Scott Dorsey wrote: wrote: I'm looking a mic that will work on a hi-z input (12Kohm) without a preamp or impedance transformer. Two questions: You can find one at a truckstop or a place that sells ham radio supplies. Unbalanced high-Z mikes are still standard for communications applications where high frequency response isn't needed. 1) How will a 600ohm mic sound through this input? Will I get a decent signal or do I need a mic with much high impedance? It won't be very loud unless you use a matching transformer. How can you say that without knowing the sensitivity ? The impedance per se isn't the issue. Graham |
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#6
Posted to rec.audio.pro
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Hi-Z mics? where OH where have they gone!
wrote: I'm looking a mic that will work on a hi-z input (12Kohm) without a preamp or impedance transformer. Two questions: 1) How will a 600ohm mic sound through this input? Will I get a decent signal or do I need a mic with much high impedance? Read the flipping manual ! http://www.tascam.com/i-864-232-128-0-7DF475C0.pdf The 'B' input appears on both a 3.5mm jack designed for 'computer mics' and also a 1/4 inch jack. Use the 1/4" jack. That impedance is perfectly suitable for direct connection of a 200-600 ohm mic but you'll need to have it wired to an unbalanced jack. The sensitivity of -40dBV will be adequate for many applications. Graham |
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#7
Posted to rec.audio.pro
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Hi-Z mics? where OH where have they gone!
Eeyore writes:
[...] the input impedance on the majority of modern professioanl min inputs is typically ~ 2 k ohms. That figure sounds low. I would think these types of inputs are at least 10k ohms. -- % Randy Yates % "She's sweet on Wagner-I think she'd die for Beethoven. %% Fuquay-Varina, NC % She love the way Puccini lays down a tune, and %%% 919-577-9882 % Verdi's always creepin' from her room." %%%% % "Rockaria", *A New World Record*, ELO http://www.digitalsignallabs.com |
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#8
Posted to rec.audio.pro
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Hi-Z mics? where OH where have they gone!
On Dec 5, 10:56 pm, Randy Yates wrote:
Eeyore writes: [...] the input impedance on the majority of modern professioanl min inputs is typically ~ 2 k ohms. That figure sounds low. I would think these types of inputs are at least 10k ohms. The Tascam unit has 2 mic inputs. a 1/4" of 12Kohm and an 1/8th inch of 2.2Kohm. Anyway this is great advice, I'll get one of the cheaper 600ohm mics. I'd get her a more expensive one but in combination with the other stuff I'm buying, I don't wanna freak her out. Over-eager xmas presents = "I'm a serial killer" !! Dex |
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#9
Posted to rec.audio.pro
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Hi-Z mics? where OH where have they gone!
Randy Yates wrote: Eeyore writes: [...] the input impedance on the majority of modern professioanl min inputs is typically ~ 2 k ohms. That figure sounds low. I would think these types of inputs are at least 10k ohms. NO. Graham |
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#10
Posted to rec.audio.pro
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Hi-Z mics? where OH where have they gone!
On Wed, 05 Dec 2007 22:56:52 -0500, Randy Yates
wrote: Eeyore writes: [...] the input impedance on the majority of modern professioanl min inputs is typically ~ 2 k ohms. That figure sounds low. I would think these types of inputs are at least 10k ohms. The input impedance of the typical mic preamp is of the order of 100k or so. This is set by the op amp or discrete transistor stage used for the input amplifier. As long as this figure is high, it won't load a microphone adversely. What determines the optimum source impedance (the actual impedance of the mic) is the way the noise generators in that input amp balance each other. There are separate mechanisms for generating current and voltage noise. The input impedance of the typical mic preamp *system* is generally around 12k, and this is because it has a requirement to be able to supply phantom power to a condenser mic. It does this with a 48 volt supply fed through a pair of 6.2k resistors, each to one arm of the balanced pair. Turning off phantom power for microphones that don't need it generally involves disconnecting the 48V from the ends of the resistors, but leaving them connected to each other, leaving 12.4k across the microphone input. This is usually what defines the input impedance of a mic preamp. The typical preamp is nominally ok from a fairly wide range of microphone impedances, but you need to know the impedance of the mic because that will determine its output voltage level. You need that to know what range of gains the preamp must offer. A high impedance mic will have a greater voltage output, so you need a lower gain figure from the preamp. This doesn't mean that a high impedance, high output mic will offer a better noise performance, because signal to noise ratio is set by the ratio of powers, not voltages. That all gets a bit complex, and determines the nature of the preamp's input circuitry. d -- Pearce Consulting http://www.pearce.uk.com |
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#11
Posted to rec.audio.pro
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Hi-Z mics? where OH where have they gone!
Don Pearce wrote: The input impedance of the typical mic preamp is of the order of 100k or so. NO. The input impedance of the typical mic preamp *system* is generally around 12k, Complete nonsense. Graham |
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#12
Posted to rec.audio.pro
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Hi-Z mics? where OH where have they gone!
Don Pearce wrote: The input impedance of the typical mic preamp *system* is generally around 12k, and this is because it has a requirement to be able to supply phantom power to a condenser mic. It does this with a 48 volt supply fed through a pair of 6.2k resistors, each to one arm of the balanced pair. Turning off phantom power for microphones that don't need it generally involves disconnecting the 48V from the ends of the resistors, but leaving them connected to each other, leaving 12.4k across the microphone input. This is usually what defines the input impedance of a mic preamp. Utter rubbish. You really shouldn't pontificate about stuff you're very clearly totally unfamiliar with. Just a casual glance at any of the many schematics available online for mic input stages gives the lie to your claim. Graham |
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#13
Posted to rec.audio.pro
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Hi-Z mics? where OH where have they gone!
Don Pearce wrote: What determines the optimum source impedance (the actual impedance of the mic) is the way the noise generators in that input amp balance each other. NO. Not 'balance'. The word you're looking for is ADD ! You can't have 'negative noise' with one stage balancing out another. Did you just have a stroke or something ? You're not normally this daft. Graham |
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#14
Posted to rec.audio.pro
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Hi-Z mics? where OH where have they gone!
On Thu, 06 Dec 2007 10:30:04 +0000, Eeyore
wrote: Don Pearce wrote: The input impedance of the typical mic preamp is of the order of 100k or so. NO. Go on then. You are going to have to do better than that. Looking at a few circuits I find that I could revise that upwards in many cases to probably over 1M. I can't find any that are lower. The input impedance of the typical mic preamp *system* is generally around 12k, Complete nonsense. Again - more is needed. Looking round at a few I find Rane MS1B 10k Neve 11k Behringer 12k d -- Pearce Consulting http://www.pearce.uk.com |
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#15
Posted to rec.audio.pro
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Hi-Z mics? where OH where have they gone!
On Thu, 06 Dec 2007 10:35:19 +0000, Eeyore
wrote: Don Pearce wrote: What determines the optimum source impedance (the actual impedance of the mic) is the way the noise generators in that input amp balance each other. NO. Yes. Not 'balance'. The word you're looking for is ADD ! You can't have 'negative noise' with one stage balancing out another. Did you just have a stroke or something ? You're not normally this daft. Graham I mean exactly what I say. When I speak of balance, what I mean is that for high source impedances current noise dominates, and for low source impedances voltage noise dominates. You need to find a balance between these two to optimize the noise performance. You do this by choosing appropriate input devices and setting their operating currents appropriately. Why have you decided to claim that I am saying that the noise from one stage is balancing that of another? That would be stupid. d -- Pearce Consulting http://www.pearce.uk.com |
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#16
Posted to rec.audio.pro
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Hi-Z mics? where OH where have they gone!
Don Pearce wrote: Eeyore wrote: Don Pearce wrote: The input impedance of the typical mic preamp *system* is generally around 12k, Complete nonsense. Again - more is needed. Looking round at a few I find Rane MS1B 10k I'm not familiar with that one. Neve 11k Certainly not when I was there. What product are you looking at ? Behringer 12k So why does the manual say 2.6 k ? http://www.behringer.com/1622FX/index.cfm?lang=eng (model chosen entirely at random). Graham |
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#17
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Hi-Z mics? where OH where have they gone!
Don Pearce wrote: Eeyore wrote: Don Pearce wrote: What determines the optimum source impedance (the actual impedance of the mic) is the way the noise generators in that input amp balance each other. NO. Yes. ********. Not 'balance'. The word you're looking for is ADD ! You can't have 'negative noise' with one stage balancing out another. Did you just have a stroke or something ? You're not normally this daft. I mean exactly what I say. When I speak of balance, what I mean is that for high source impedances current noise dominates, and for low source impedances voltage noise dominates. Well you're not using it with a high source impedance you ****ing clown ! Since when was 200 ohms a high impedance. Jesus H Christ ! STOP talking drivel about stuff you're not familiar with. Graham |
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#18
Posted to rec.audio.pro
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Hi-Z mics? where OH where have they gone!
On Thu, 06 Dec 2007 11:09:58 +0000, Eeyore
wrote: Don Pearce wrote: Eeyore wrote: Don Pearce wrote: The input impedance of the typical mic preamp *system* is generally around 12k, Complete nonsense. Again - more is needed. Looking round at a few I find Rane MS1B 10k I'm not familiar with that one. Neve 11k Certainly not when I was there. What product are you looking at ? Behringer 12k So why does the manual say 2.6 k ? http://www.behringer.com/1622FX/index.cfm?lang=eng (model chosen entirely at random). That is a input maximum level figure with the gain backed off. At high gain where the noise level matters the input impedance is comprised almost solely of the phantom power resistors. This is true of most preamps. d -- Pearce Consulting http://www.pearce.uk.com |
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#19
Posted to rec.audio.pro
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Hi-Z mics? where OH where have they gone!
On Thu, 06 Dec 2007 11:12:35 +0000, Eeyore
wrote: Don Pearce wrote: Eeyore wrote: Don Pearce wrote: What determines the optimum source impedance (the actual impedance of the mic) is the way the noise generators in that input amp balance each other. NO. Yes. ********. Not 'balance'. The word you're looking for is ADD ! You can't have 'negative noise' with one stage balancing out another. Did you just have a stroke or something ? You're not normally this daft. I mean exactly what I say. When I speak of balance, what I mean is that for high source impedances current noise dominates, and for low source impedances voltage noise dominates. Well you're not using it with a high source impedance you ****ing clown ! Since when was 200 ohms a high impedance. Read the title of the thread, will you? And do try to stop swearing - it really doesn't bolster your position any. Jesus H Christ ! STOP talking drivel about stuff you're not familiar with. I am right now looking at a ribbon mic with an impedance of 50k. To make a low noise pre for that I had to use an op amp which you would have slung out as being totally unacceptable for a 200 ohm mic. As I say, you have to look at the source resistance and choose the right balance of voltage and current noise to pin the minimum generated noise power at that impedance. It is very clear that while you may be familiar with this stuff in the sense of having been around it, you haven't actually absorbed the theory. Can you, for instance, tell me the equation you would use to calculate noise figure given specified current noise, voltage noise and source impedance? d -- Pearce Consulting http://www.pearce.uk.com |
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#20
Posted to rec.audio.pro
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Hi-Z mics? where OH where have they gone!
Don Pearce wrote: Eeyore wrote: Don Pearce wrote: Eeyore wrote: Don Pearce wrote: The input impedance of the typical mic preamp *system* is generally around 12k, Complete nonsense. Again - more is needed. Looking round at a few I find Rane MS1B 10k I'm not familiar with that one. Neve 11k Certainly not when I was there. What product are you looking at ? Behringer 12k So why does the manual say 2.6 k ? http://www.behringer.com/1622FX/index.cfm?lang=eng (model chosen entirely at random). That is a input maximum level figure with the gain backed off. Where does it say that ? You're just making it up as you go alomg. At high gain where the noise level matters the input impedance is comprised Very slightly. almost solely of the phantom power resistors. Rubbish. This is true of most preamps. Complete nonsense. The input Z is usually at the worst only very slightly reduced at high gain. The fact of the matter is that you're talking out of your backside. Here's a mic amp schematic I found quickly with Google from an older Souncraft console. The very first thing you can see is that input Z is dominated by R1 which has a value of 2k2. Graham |
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#21
Posted to rec.audio.pro
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Hi-Z mics? where OH where have they gone!
Don Pearce wrote: Eeyore wrote: Don Pearce wrote: Eeyore wrote: Don Pearce wrote: What determines the optimum source impedance (the actual impedance of the mic) is the way the noise generators in that input amp balance each other. NO. Yes. ********. Not 'balance'. The word you're looking for is ADD ! You can't have 'negative noise' with one stage balancing out another. Did you just have a stroke or something ? You're not normally this daft. I mean exactly what I say. When I speak of balance, what I mean is that for high source impedances current noise dominates, and for low source impedances voltage noise dominates. Well you're not using it with a high source impedance you ****ing clown ! Since when was 200 ohms a high impedance. Read the title of the thread, will you? And do try to stop swearing - it really doesn't bolster your position any. When dealing with halfwit posts like yours I find that very difficult. Jesus H Christ ! STOP talking drivel about stuff you're not familiar with. I am right now looking at a ribbon mic with an impedance of 50k. No it hasn't. No ribbon mic has an impedance of 50k. The transformer may however need a load of 50k. To make a low noise pre for that I had to use an op amp which you would have slung out as being totally unacceptable for a 200 ohm mic. That's a completely different subject. And not really 'pro'. Nor anything to do with the OP's psot. As I say, you have to look at the source resistance and choose the right balance of voltage and current noise to pin the minimum generated noise power at that impedance. It is very clear that while you may be familiar with this stuff in the sense of having been around it, you haven't actually absorbed the theory. Can you, for instance, tell me the equation you would use to calculate noise figure given specified current noise, voltage noise and source impedance? In ONE equation. Don't be daft. You'd want to split it up into 2 at least. I know perfectly well how to add noise sources btw and I'm not rising to your silly goads. Graham |
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#22
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Hi-Z mics? where OH where have they gone!
Don Pearce wrote: Read the title of the thread, will you? The OP hasn't got a Hi-Z mic input nor does he need a Hi-Z mic. Graham |
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#23
Posted to rec.audio.pro
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Hi-Z mics? where OH where have they gone!
Eeyore writes:
Don Pearce wrote: The input impedance of the typical mic preamp *system* is generally around 12k, and this is because it has a requirement to be able to supply phantom power to a condenser mic. It does this with a 48 volt supply fed through a pair of 6.2k resistors, each to one arm of the balanced pair. Turning off phantom power for microphones that don't need it generally involves disconnecting the 48V from the ends of the resistors, but leaving them connected to each other, leaving 12.4k across the microphone input. This is usually what defines the input impedance of a mic preamp. Utter rubbish. You really shouldn't pontificate about stuff you're very clearly totally unfamiliar with. Just a casual glance at any of the many schematics available online for mic input stages gives the lie to your claim. Got an example? -- % Randy Yates % "So now it's getting late, %% Fuquay-Varina, NC % and those who hesitate %%% 919-577-9882 % got no one..." %%%% % 'Waterfall', *Face The Music*, ELO http://www.digitalsignallabs.com |
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#24
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Hi-Z mics? where OH where have they gone!
(Don Pearce) writes:
[nice explanation deleted] Makes sense. I thought it might have something to do with phantom powering. Thanks. -- % Randy Yates % "Remember the good old 1980's, when %% Fuquay-Varina, NC % things were so uncomplicated?" %%% 919-577-9882 % 'Ticket To The Moon' %%%% % *Time*, Electric Light Orchestra http://www.digitalsignallabs.com |
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#25
Posted to rec.audio.pro
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Hi-Z mics? where OH where have they gone!
On Thu, 06 Dec 2007 13:49:24 +0000, Eeyore
wrote: Don Pearce wrote: Eeyore wrote: Don Pearce wrote: Eeyore wrote: Don Pearce wrote: What determines the optimum source impedance (the actual impedance of the mic) is the way the noise generators in that input amp balance each other. NO. Yes. ********. Not 'balance'. The word you're looking for is ADD ! You can't have 'negative noise' with one stage balancing out another. Did you just have a stroke or something ? You're not normally this daft. I mean exactly what I say. When I speak of balance, what I mean is that for high source impedances current noise dominates, and for low source impedances voltage noise dominates. Well you're not using it with a high source impedance you ****ing clown ! Since when was 200 ohms a high impedance. Read the title of the thread, will you? And do try to stop swearing - it really doesn't bolster your position any. When dealing with halfwit posts like yours I find that very difficult. Jesus H Christ ! STOP talking drivel about stuff you're not familiar with. I am right now looking at a ribbon mic with an impedance of 50k. No it hasn't. No ribbon mic has an impedance of 50k. The transformer may however need a load of 50k. As it happens, the impedance of this ribbon mic (not the ribbon - you seem to have major problems with boundary points) has a source impedance of 50k. There is a transformer in the mic, and it needs a load resistance of hundreds of k for proper operation. To make a low noise pre for that I had to use an op amp which you would have slung out as being totally unacceptable for a 200 ohm mic. That's a completely different subject. And not really 'pro'. Nor anything to do with the OP's psot. What has the impedance to do with being pro? It was built at a time when valve amps with input impedances in the megohms were the norm, and it is a highly professional mic. As I say, you have to look at the source resistance and choose the right balance of voltage and current noise to pin the minimum generated noise power at that impedance. It is very clear that while you may be familiar with this stuff in the sense of having been around it, you haven't actually absorbed the theory. Can you, for instance, tell me the equation you would use to calculate noise figure given specified current noise, voltage noise and source impedance? In ONE equation. Don't be daft. You'd want to split it up into 2 at least. I know perfectly well how to add noise sources btw and I'm not rising to your silly goads. Well, that last bit tells us that you don't. Have a look here for my calculation that identified the OP207 as the optimum op amp for my ribbon mic - and also why it would be a poor choice for any more modern, low impedance offering. http://81.174.169.10/odds/opanoise And there you will see the one equation that puts current noise and voltage noise together. d -- Pearce Consulting http://www.pearce.uk.com |
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#26
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Hi-Z mics? where OH where have they gone!
Randy Yates wrote: Eeyore writes: Don Pearce wrote: The input impedance of the typical mic preamp *system* is generally around 12k, and this is because it has a requirement to be able to supply phantom power to a condenser mic. It does this with a 48 volt supply fed through a pair of 6.2k resistors, each to one arm of the balanced pair. Turning off phantom power for microphones that don't need it generally involves disconnecting the 48V from the ends of the resistors, but leaving them connected to each other, leaving 12.4k across the microphone input. This is usually what defines the input impedance of a mic preamp. Utter rubbish. You really shouldn't pontificate about stuff you're very clearly totally unfamiliar with. Just a casual glance at any of the many schematics available online for mic input stages gives the lie to your claim. Got an example? I posted a link. Don has totally lost the plot on this. He likes to sound authoritative but his background isn't actually pro-audio so he makes a fool of himself like this from time to time. Silly becasue his technical knowledge is otherwise pretty sound. I suspect audio's mainly just a hobby with him. Graham |
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#27
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Hi-Z mics? where OH where have they gone!
Randy Yates wrote: (Don Pearce) writes: [nice explanation deleted] Shame it was so wrong. Makes sense. I thought it might have something to do with phantom powering. Thanks. The phantom power resistors have to be included in the overal input impedance calculation for sure, but in all other respects Don's COMPLETELY wrong about typical input impedances. Graham |
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#28
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Hi-Z mics? where OH where have they gone!
Don Pearce wrote: Eeyore wrote: Don Pearce wrote: It is very clear that while you may be familiar with this stuff in the sense of having been around it, you haven't actually absorbed the theory. I'm VERY strong on BOTH theory AND practice thank you. Can you, for instance, tell me the equation you would use to calculate noise figure given specified current noise, voltage noise and source impedance? In ONE equation. Don't be daft. You'd want to split it up into 2 at least. I know perfectly well how to add noise sources btw and I'm not rising to your silly goads. Well, that last bit tells us that you don't. **** off. Of course I bloody well do. There's a fairly good treartment of the subject of adding voltage and current noise sources in either (or both) the TI Bifet Manual or Nationals' Audio Hanbook, but in any event any competent designer can do it from first principles. Graham |
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#29
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Hi-Z mics? where OH where have they gone!
On Thu, 06 Dec 2007 14:27:49 +0000, Eeyore
wrote: Don Pearce wrote: Eeyore wrote: Don Pearce wrote: It is very clear that while you may be familiar with this stuff in the sense of having been around it, you haven't actually absorbed the theory. I'm VERY strong on BOTH theory AND practice thank you. Can you, for instance, tell me the equation you would use to calculate noise figure given specified current noise, voltage noise and source impedance? In ONE equation. Don't be daft. You'd want to split it up into 2 at least. I know perfectly well how to add noise sources btw and I'm not rising to your silly goads. Well, that last bit tells us that you don't. **** off. Of course I bloody well do. There's a fairly good treartment of the subject of adding voltage and current noise sources in either (or both) the TI Bifet Manual or Nationals' Audio Hanbook, but in any event any competent designer can do it from first principles. But you evidently couldn't. That tells us all we need to know. We appear to be fundamentally different types of person. You scream and swear and bully, but produce nothing. I will explain rationally and produce the goods. Before you post, you might want to ask yourself "What would Christopher Robin say?". d -- Pearce Consulting http://www.pearce.uk.com |
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#30
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Hi-Z mics? where OH where have they gone!
Don Pearce wrote: Eeyore wrote: Don Pearce wrote: It is very clear that while you may be familiar with this stuff in the sense of having been around it, you haven't actually absorbed the theory. Can you, for instance, tell me the equation you would use to calculate noise figure given specified current noise, voltage noise and source impedance? In ONE equation. Don't be daft. You'd want to split it up into 2 at least. I know perfectly well how to add noise sources btw and I'm not rising to your silly goads. Well, that last bit tells us that you don't. And how many mic amps have you designed to make it into large scale manufacture (at least 1000 units) ? In my own case it most cover around a dozen or more model series. Graham |
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#31
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Hi-Z mics? where OH where have they gone!
Don Pearce wrote: Eeyore wrote: Don Pearce wrote: Eeyore wrote: I know perfectly well how to add noise sources btw and I'm not rising to your silly goads. Well, that last bit tells us that you don't. **** off. Of course I bloody well do. There's a fairly good treartment of the subject of adding voltage and current noise sources in either (or both) the TI Bifet Manual or Nationals' Audio Hanbook, but in any event any competent designer can do it from first principles. But you evidently couldn't. That tells us all we need to know. **** OFF. You're a gesturing idiot. Very few people here (I can think of only about 2) would undertand a detailed noise calculation and they already know you're talking crap. You're obsessing over a calculation that'll be way over the heads of most people here and it's just a subterfuge of yours to cover up your lack of knowledge of real world practice. We appear to be fundamentally different types of person. Yes. I know what I'm talking about and you don't. Here's some more real world schematics for you. http://www.gyraf.dk/schematics/Macki...1604%20VLZ.pdf Input impedance ~ 2k5 http://www.gyraf.dk/schematics/Behri...0_analouge.PDF Input impedance ~ 2k2 Graham |
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#32
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Hi-Z mics? where OH where have they gone!
On Thu, 06 Dec 2007 15:07:32 +0000, Eeyore
wrote: **** OFF. You're a gesturing idiot. Very few people here (I can think of only about 2) would undertand a detailed noise calculation and they already know you're talking crap. You're obsessing over a calculation that'll be way over the heads of most people here and it's just a subterfuge of yours to cover up your lack of knowledge of real world practice. Are you one of those engineers? I thought they died out about 1970. I mean the type that thinks theory is somehow different to practice and should be ignored. I remember the chief engineer at my first job told me that if theory and practice don't agree, you don't have the theory right. Is that how your engineering career worked out? Sorry, but mine was the reverse; the more I understood, the better theory matched practice. d -- Pearce Consulting http://www.pearce.uk.com |
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#33
Posted to rec.audio.pro
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Hi-Z mics? where OH where have they gone!
Eeyore wrote:
Don Pearce wrote: Eeyore wrote: Don Pearce wrote: Eeyore wrote: I know perfectly well how to add noise sources btw and I'm not rising to your silly goads. Well, that last bit tells us that you don't. **** off. Of course I bloody well do. There's a fairly good treartment of the subject of adding voltage and current noise sources in either (or both) the TI Bifet Manual or Nationals' Audio Hanbook, but in any event any competent designer can do it from first principles. But you evidently couldn't. That tells us all we need to know. **** OFF. You're a gesturing idiot. Very few people here (I can think of only about 2) would undertand a detailed noise calculation and they already know you're talking crap. You're obsessing over a calculation that'll be way over the heads of most people here and it's just a subterfuge of yours to cover up your lack of knowledge of real world practice. We appear to be fundamentally different types of person. Yes. I know what I'm talking about and you don't. Here's some more real world schematics for you. http://www.gyraf.dk/schematics/Macki...1604%20VLZ.pdf Input impedance ~ 2k5 http://www.gyraf.dk/schematics/Behri...0_analouge.PDF Input impedance ~ 2k2 Graham Here is a simple schematic for the MPC-3000 card that I manufacture (see page 2): http://www.johnhardyco.com/pdf/MPC3000.pdf This is essentially the same as the M-1, but a simpler approach and easier to look at. The busier M-1 schematic is here (page 7): http://www.johnhardyco.com/pdf/M1_M2_M1p_20031025.pdf Both preamps use the Jensen JT-16-B input transformer which has the lowest impedance ratio of all the Jensen input transformers, 1:2. See the specs for the JT-16-B he http://www.jensentransformers.com/datashts/16b.pdf The typical input impedance is 1.61k, not including anything to do with phantom supply resistors. The more common Jensen JT-115K-E input transformer has the highest impedance ratio of all the Jensen input transformers, 1:10. It has a typical input of impedance of 1.40k, not including anything to do with phantom supply resistors: http://www.jensentransformers.com/datashts/115ke.pdf The Jensen JT-13K7-A is their mid impedance ratio model (1:5). The typical input impedance is 1.54k, not including anything to do with phantom supply resistors. http://www.jensentransformers.com/datashts/13k7a.pdf The impedance ratio is typically chosen to work best with the noise characteristics of the op-amp or vacuum tube that follows the transformer. The JT-16-B is an ideal match to the 990C op-amp that is used in all of my preamps. All of these mic input transformers provide an input impedance or load impedance that is approximately 10X the source impedance or output impedance of the typical 150 ohm mic, which is considered by many people to be an optimum ratio. There are other mic preamps that have much higher input impedances, probably transformerless circuits, and your mileage may vary. Thank you. John Hardy The John Hardy Co. www.johnhardyco.com |
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#34
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Hi-Z mics? where OH where have they gone!
Don Pearce wrote: Eeyore wrote: **** OFF. You're a gesturing idiot. Very few people here (I can think of only about 2) would undertand a detailed noise calculation and they already know you're talking crap. You're obsessing over a calculation that'll be way over the heads of most people here and it's just a subterfuge of yours to cover up your lack of knowledge of real world practice. Are you one of those engineers? I thought they died out about 1970. I mean the type that thinks theory is somehow different to practice and should be ignored Don't be ridiculous. If theory and practice don't agree then you've misunderstood one of them. In your case you've mostly misunderstood the practice. The simple FACT of the matter is that you're COMPLETELY WRONG about typical mic input impedances. FYI Paul Stamler is well known for example for promoting input Z's as low as 600 ohms to get the best perceived performance from certain mics like the SM57 IIRC. Rane would seem to be barking up the wrong tree with the MS1b Graham |
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#35
Posted to rec.audio.pro
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Hi-Z mics? where OH where have they gone!
John Hardy wrote: Eeyore wrote: Don Pearce wrote: Eeyore wrote: Don Pearce wrote: Eeyore wrote: I know perfectly well how to add noise sources btw and I'm not rising to your silly goads. Well, that last bit tells us that you don't. **** off. Of course I bloody well do. There's a fairly good treartment of the subject of adding voltage and current noise sources in either (or both) the TI Bifet Manual or Nationals' Audio Hanbook, but in any event any competent designer can do it from first principles. But you evidently couldn't. That tells us all we need to know. **** OFF. You're a gesturing idiot. Very few people here (I can think of only about 2) would undertand a detailed noise calculation and they already know you're talking crap. You're obsessing over a calculation that'll be way over the heads of most people here and it's just a subterfuge of yours to cover up your lack of knowledge of real world practice. We appear to be fundamentally different types of person. Yes. I know what I'm talking about and you don't. Here's some more real world schematics for you. http://www.gyraf.dk/schematics/Macki...1604%20VLZ.pdf Input impedance ~ 2k5 http://www.gyraf.dk/schematics/Behri...0_analouge.PDF Input impedance ~ 2k2 Here is a simple schematic for the MPC-3000 card that I manufacture (see page 2): http://www.johnhardyco.com/pdf/MPC3000.pdf This is essentially the same as the M-1, but a simpler approach and easier to look at. The busier M-1 schematic is here (page 7): http://www.johnhardyco.com/pdf/M1_M2_M1p_20031025.pdf Both preamps use the Jensen JT-16-B input transformer which has the lowest impedance ratio of all the Jensen input transformers, 1:2. See the specs for the JT-16-B he http://www.jensentransformers.com/datashts/16b.pdf The typical input impedance is 1.61k, not including anything to do with phantom supply resistors. The more common Jensen JT-115K-E input transformer has the highest impedance ratio of all the Jensen input transformers, 1:10. It has a typical input of impedance of 1.40k, not including anything to do with phantom supply resistors: http://www.jensentransformers.com/datashts/115ke.pdf The Jensen JT-13K7-A is their mid impedance ratio model (1:5). The typical input impedance is 1.54k, not including anything to do with phantom supply resistors. http://www.jensentransformers.com/datashts/13k7a.pdf The impedance ratio is typically chosen to work best with the noise characteristics of the op-amp or vacuum tube that follows the transformer. The JT-16-B is an ideal match to the 990C op-amp that is used in all of my preamps. All of these mic input transformers provide an input impedance or load impedance that is approximately 10X the source impedance or output impedance of the typical 150 ohm mic, which is considered by many people to be an optimum ratio. Agreed. There are other mic preamps that have much higher input impedances, probably transformerless circuits, and your mileage may vary. It's always intrigued me that US mics tend to be closer to 150 ohms and European ones 200 ohms. That would explain your slightly lower input Z than I would design for. Graham |
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#36
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Hi-Z mics? where OH where have they gone!
On Thu, 06 Dec 2007 09:42:03 -0600, John Hardy
wrote: Eeyore wrote: Don Pearce wrote: Eeyore wrote: Don Pearce wrote: Eeyore wrote: I know perfectly well how to add noise sources btw and I'm not rising to your silly goads. Well, that last bit tells us that you don't. **** off. Of course I bloody well do. There's a fairly good treartment of the subject of adding voltage and current noise sources in either (or both) the TI Bifet Manual or Nationals' Audio Hanbook, but in any event any competent designer can do it from first principles. But you evidently couldn't. That tells us all we need to know. **** OFF. You're a gesturing idiot. Very few people here (I can think of only about 2) would undertand a detailed noise calculation and they already know you're talking crap. You're obsessing over a calculation that'll be way over the heads of most people here and it's just a subterfuge of yours to cover up your lack of knowledge of real world practice. We appear to be fundamentally different types of person. Yes. I know what I'm talking about and you don't. Here's some more real world schematics for you. http://www.gyraf.dk/schematics/Macki...1604%20VLZ.pdf Input impedance ~ 2k5 http://www.gyraf.dk/schematics/Behri...0_analouge.PDF Input impedance ~ 2k2 Graham Here is a simple schematic for the MPC-3000 card that I manufacture (see page 2): http://www.johnhardyco.com/pdf/MPC3000.pdf This is essentially the same as the M-1, but a simpler approach and easier to look at. The busier M-1 schematic is here (page 7): http://www.johnhardyco.com/pdf/M1_M2_M1p_20031025.pdf Both preamps use the Jensen JT-16-B input transformer which has the lowest impedance ratio of all the Jensen input transformers, 1:2. See the specs for the JT-16-B he http://www.jensentransformers.com/datashts/16b.pdf The typical input impedance is 1.61k, not including anything to do with phantom supply resistors. The more common Jensen JT-115K-E input transformer has the highest impedance ratio of all the Jensen input transformers, 1:10. It has a typical input of impedance of 1.40k, not including anything to do with phantom supply resistors: http://www.jensentransformers.com/datashts/115ke.pdf The Jensen JT-13K7-A is their mid impedance ratio model (1:5). The typical input impedance is 1.54k, not including anything to do with phantom supply resistors. http://www.jensentransformers.com/datashts/13k7a.pdf The impedance ratio is typically chosen to work best with the noise characteristics of the op-amp or vacuum tube that follows the transformer. The JT-16-B is an ideal match to the 990C op-amp that is used in all of my preamps. All of these mic input transformers provide an input impedance or load impedance that is approximately 10X the source impedance or output impedance of the typical 150 ohm mic, which is considered by many people to be an optimum ratio. There are other mic preamps that have much higher input impedances, probably transformerless circuits, and your mileage may vary. Thank you. John Hardy The John Hardy Co. www.johnhardyco.com Yes. Those transformers are specified for use with op amps like the 5534 (the example used by Jensen). This has an optimum source resistance of about 7000 ohms, so it needs a step up transformer to load it optimally from a microphone. The 5:1 ratio of the first example brings a 150 ohm source up to 750 ohms, which is still not good enough, but leaves a noise figure of about 3.6dB. Unfortunately, the resulting 1.5k load on the mic kills the signal by a further 0.8dB, which can't be recovered as SNR - it is gone for good. Finally add in the 1dB of the transformer's insertion loss, and you have a noise figure of about 5.4dB. That 1.5k input impedance is of course nothing to do with the preamp itself. It is caused by the 9.76k and 39k resistors that have to be hung across the output of the transformer, presumably to keep it from ringing. d -- Pearce Consulting http://www.pearce.uk.com |
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#38
Posted to rec.audio.pro
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Hi-Z mics? where OH where have they gone!
Don Pearce wrote: On Thu, 06 Dec 2007 09:42:03 -0600, John Hardy wrote: Eeyore wrote: Don Pearce wrote: Eeyore wrote: Don Pearce wrote: Eeyore wrote: I know perfectly well how to add noise sources btw and I'm not rising to your silly goads. Well, that last bit tells us that you don't. **** off. Of course I bloody well do. There's a fairly good treartment of the subject of adding voltage and current noise sources in either (or both) the TI Bifet Manual or Nationals' Audio Hanbook, but in any event any competent designer can do it from first principles. But you evidently couldn't. That tells us all we need to know. **** OFF. You're a gesturing idiot. Very few people here (I can think of only about 2) would undertand a detailed noise calculation and they already know you're talking crap. You're obsessing over a calculation that'll be way over the heads of most people here and it's just a subterfuge of yours to cover up your lack of knowledge of real world practice. We appear to be fundamentally different types of person. Yes. I know what I'm talking about and you don't. Here's some more real world schematics for you. http://www.gyraf.dk/schematics/Macki...1604%20VLZ.pdf Input impedance ~ 2k5 http://www.gyraf.dk/schematics/Behri...0_analouge.PDF Input impedance ~ 2k2 Graham Here is a simple schematic for the MPC-3000 card that I manufacture (see page 2): http://www.johnhardyco.com/pdf/MPC3000.pdf This is essentially the same as the M-1, but a simpler approach and easier to look at. The busier M-1 schematic is here (page 7): http://www.johnhardyco.com/pdf/M1_M2_M1p_20031025.pdf Both preamps use the Jensen JT-16-B input transformer which has the lowest impedance ratio of all the Jensen input transformers, 1:2. See the specs for the JT-16-B he http://www.jensentransformers.com/datashts/16b.pdf The typical input impedance is 1.61k, not including anything to do with phantom supply resistors. The more common Jensen JT-115K-E input transformer has the highest impedance ratio of all the Jensen input transformers, 1:10. It has a typical input of impedance of 1.40k, not including anything to do with phantom supply resistors: http://www.jensentransformers.com/datashts/115ke.pdf The Jensen JT-13K7-A is their mid impedance ratio model (1:5). The typical input impedance is 1.54k, not including anything to do with phantom supply resistors. http://www.jensentransformers.com/datashts/13k7a.pdf The impedance ratio is typically chosen to work best with the noise characteristics of the op-amp or vacuum tube that follows the transformer. The JT-16-B is an ideal match to the 990C op-amp that is used in all of my preamps. All of these mic input transformers provide an input impedance or load impedance that is approximately 10X the source impedance or output impedance of the typical 150 ohm mic, which is considered by many people to be an optimum ratio. There are other mic preamps that have much higher input impedances, probably transformerless circuits, and your mileage may vary. Thank you. John Hardy The John Hardy Co. www.johnhardyco.com Yes. Those transformers are specified for use with op amps like the 5534 (the example used by Jensen). This has an optimum source resistance of about 7000 ohms, so it needs a step up transformer to load it optimally from a microphone. The 5:1 ratio of the first example brings a 150 ohm source up to 750 ohms, which is still not good enough, but leaves a noise figure of about 3.6dB. Unfortunately, the resulting 1.5k load on the mic kills the signal by a further 0.8dB, which can't be recovered as SNR - it is gone for good. Finally add in the 1dB of the transformer's insertion loss, and you have a noise figure of about 5.4dB. That 1.5k input impedance is of course nothing to do with the preamp itself. It is caused by the 9.76k and 39k resistors that have to be hung across the output of the transformer, presumably to keep it from ringing. d -- Pearce Consulting http://www.pearce.uk.com |
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#39
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Hi-Z mics? where OH where have they gone!
"Don Pearce" wrote in message
... [...] the input impedance on the majority of modern professioanl min inputs is typically ~ 2 k ohms. That figure sounds low. I would think these types of inputs are at least 10k ohms. The input impedance of the typical mic preamp is of the order of 100k or so. This is set by the op amp or discrete transistor stage used for the input amplifier. As long as this figure is high, it won't load a microphone adversely. What determines the optimum source impedance (the actual impedance of the mic) is the way the noise generators in that input amp balance each other. There are separate mechanisms for generating current and voltage noise. The input impedance of the typical mic preamp *system* is generally around 12k, and this is because it has a requirement to be able to supply phantom power to a condenser mic. It does this with a 48 volt supply fed through a pair of 6.2k resistors, each to one arm of the balanced pair. Turning off phantom power for microphones that don't need it generally involves disconnecting the 48V from the ends of the resistors, but leaving them connected to each other, leaving 12.4k across the microphone input. This is usually what defines the input impedance of a mic preamp. Excuse me, but Don has just exposed a remarkable lack of experience in the world of professional audio -- or, at the very least, a lack of reading spec sheets for professional mic preamps. Virtually every mic preamp in the business has a nominal input impedance of 1.0-2.5k. Go look up the specs. If there's a transformer on the input, its secondary is typically loaded with a resistor of 10x the secondary impedance when fed from a 150 ohm source. A 1:10 transformer has a nominal 15k secondary impedance with a 150 ohm source, and is loaded with 150k (plus, perhaps, a Zobel network). Reflected back through the transformer, that's an input impedance of 1.5k. Add a pair of 6.81k resistors (the phantom power standard specifies 6.8k, *not* 6.2k, another error), and the parallel resistance of 13.62k with the transformer's input impedance works out to about 1.35k input Z. Transformerless preamps do the loading with a simple resistor, plus the phantom resistors, and as mentioned before the total typically works out between 1.0k and 2.5k. There are a very few exceptions. Some preamps have begun adding circuits to lower the input impedance, in order to terminate certain microphones (notably the Shure SM57) with a load that adds more damping. That's usually switchable, as in the Universal Audio circuit (which switches taps on the input transformer) or the ADL 600 (which switches in parallel resistors). I've run across a few prosumer devices with input Z of about 600 ohms (the Groove Tubes Brick is the one that springs to mind). The only preamps I am aware of on the commercial market with input impedances as high as Don suggests are specialty items intended for classic ribbon microphones, which were designed to work best into a higher impedance. The most notable of these is from AEA, and I believe its input impedance (set by a load resistor) is about 12k. There's no phantom, since it's intended to be used only with ribbon mics. Don, before you fire back your usual counterblast, go read about a dozen spec sheets for typical mic preamps. Peace, Paul |
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#40
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Hi-Z mics? where OH where have they gone!
On Dec 6, 12:18 pm, "Paul Stamler" wrote:
The only preamps I am aware of on the commercial market with input impedances as high as Don suggests are specialty items intended for classic ribbon microphones, which were designed to work best into a higher impedance. The most notable of these is from AEA, and I believe its input impedance (set by a load resistor) is about 12k. There's no phantom, since it's intended to be used only with ribbon mics. I believe the AEA TRP input impedance is 18k. The Gordon has a very high input impedance, 2 megohms if I recall, which contributes to its version of "clean." I recall seeing a German (some Steinberg relation, I believe) home studio preamp half a dozen or so years ago that had an input impedance of about 3k, and the current Mackie Onyx crop is 2.4k (the 800R has a couple of inputs with switchable resistors). |
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