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#41
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Low Frequency Mains Noise
Phil Allison wrote: "Patrick Turner" When I measure the "240Vac" here is usually is stable enough to get a nearly constant reading on a DMM, ** Must be a basic 3.5 digit one ( 2000 count) with only 1 volt resolution when reading 240 volts AC. Any DMM with a larger count allows changes of 0.1 volts to be seen - then the last digit is never steady. Indeed, I'll get 240.XX Vac maybe even 24X.XX if the voltage is just either side of 240.0Vac. That's less than 1% Vac change. But it slowly varies between 235Vac on cold winter nights of heavy loadings to 255Vac when load is light. ** What drivel. Not so, this is without changing local loads here in my shed. Rarely does the mains ever bounce rapidly between 235Vac and 255Vac. One has to be careful when setting bias in fixed bias amps when mains Vac is low. When it rises to 255V sometimes, the B+ rails goes high and the Ia of the output tubes rises alarmingly in fixed bias triode amps and also in multigrid output tubes if the screen voltage is not regulated, and rises also with mains rise. It will instantly drop by 7 or 8 volts if you switch a ( 2.4 kW) electric heater on AND jumps up by 6 volts when the ( 2kW) jug turns itself off when it has boiled. Not necessarily so. But the combined efforts of hundreds of people in my suburb all boiling jugs and turning heaters on and off contributes to making the mains jitter up and down in levels we see, and not by the amount you state unless the mains wiring is over a long distance. A heater of 2.4kW draws 10 amps ac, and if the wire has only 1 ohm resistance from street wires to the jug, a 10Vac drop would occur. But my house supply wires are rated for much more than 40 amps, and the shed power supply is an extension off the 40amp stove & laundry circuit and has a sub board in the shed with 6 metres of wire rated at 20A to the outlets. I doubt resistance is much more than 0.1 ohms. When I look at the rectified Vdc, it shows the expected variations of +/- 30mV. ** Complete ********. No. Any unregulated DC supply FOLLOWS all variations in the AC voltage by the same percentage. Agreed. You misunderstand me. I have been trying to say this 3 times now. But the typical B+ rail variations I see is in the form of low F noise below 5Hz and down to Dc and ranging +/- 30mV peak. Occasionally, the peaks are larger when someone turns something on or off that draws severe current, or when 10 people nearby all happen to turn heaters on/off within a very short time. Some places will be much worse than mine. Regulated DC supplies REGULATE against supply voltage and load current variations, not just load current. Indeed they should, unless the input Vdc falls below the level required across the pass device to maintain regulation or if the current output is limited, and the output tries to exceed the limit. Thus regulators have to work with a voltage x current range and power is dissipated in the pass element, or shunt element if its a shunt reg. Both cost time and effort to make and you pay for the power. Not greenhouse friendly either. But then many people use far more energy in their warm cosy houses in winter while I type to you huddled over a 750W heater, or use 9kW air conditioning to prevent being sweaty and smelly in summer. But I digress... LC filters have resonances and can make rail noise at LF *worse*, but don't do as well as RC filters at real low F. Humungous values of C is the simplest solution to B+ rail changes at F above 0.3Hz. But those pesky noise voltages below 0.3Hz will persist. But such noise is easily filtered by regulating the the B+ for the critical stages only, so the power consumption and cost of building the reg for say 20mA is very easy. Perhaps there are ways and means of making a two stage CLCLC filter so that the Fo of each LC section is different, and the first one acts to make a series impedance which critically loads the Q of the second LC section so the final response is without peaks around either Fo of each LC section. Perhaps adding a series L between the center C and 0V of the CLCLC so that its tuned to 100Hz will make a trap for the 100Hz, and keep the size and weight of all chokes to small while C is high because its cheaper than L. There used to be an only passive filter calculator at some pomme university but the guy who wrote the program which couldn't be downloaded died and I have not seen any other program. I'm not much good at calculating passive CLR filters with 6 or more elements. Once established, the CLC type of filter wastes very little power. Patrick Turner. ..... Phil |
#42
Posted to rec.audio.tubes
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Low Frequency Mains Noise
"Ian Bell" wrote in message
Arny Krueger wrote: "Ian Bell" wrote in message Eeyore wrote: Ian Bell wrote: Since there are untold preamp designs with unregulated supplies Bad preamps you mean ? Graham You tell me. I have the schematics for many broadcast consoles and professional music mixers from the 50s that use unregulated supplies. Standards for audio were a lot lower in the 50s, if you didn't ever notice when you listened to a lot of recordings from that time. There are some exceptional recordings that still sound good, but in general, it was not a good time for quality sound reproduction. I would not say they were a lot lower. I lived back then, trust me, the standards were in general far lower. Good sound of sorts did exist, but it was pretty rare. Things perked up a lot in the 60s and 70s. The flat bandwidth extended only from 50Hz to 15KHz ....and that was a joke. Most audio reproduction systems of the day were in trouble at 100 Hz, let alone 50. Today we can take response down to 20 Hz seriously. Note that speakers of that time in general were not capable of much acoustic output by modern standards. Other than a few very expensive microphones, the mics were about as bad as the speakers. but elsewhere the specs were close to today's. An RCA broadcast console achieved a 68dB S/N ratio with a -60dBm input signal which implies an equivalent input noise of -128dBm - and that would not be achievable with the LF noise I am seeing right now. I suspect that you're looking at a transformer-coupled mic input, which says nothing about the dynamic range of the console's output. Furthermore, a transformer-coupled mic input can be made with wonderful specs, since the transformer in essence covers up a lot of the sins of the active components. But, the transformers of the day weren't all that wonderful, either. Maybe they had better conditioned mains supplies for studios or maybe there was just less crap on the mains in those days. As a rule, audio people's standards were a ton lower in those days. For example, I remember the regional 45 of The Righteous Brothers "You've lost that loving feeling". It was hissy, boomy, dull sounding, and had some pretty massive low frequency transients. Listening to original oldies from the 50s, whether classical or pop can be a lot of fun, but you don't do it for the high fidelity. Even the so-called SOTA recordings, RCA Red Seal for example, had a great many clearly audible flaws. I love the playing by the artists of the day, though. Toscanini is one of my favorites, but listening to him conducting is about the music, not the sound quality. |
#43
Posted to rec.audio.tubes
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Low Frequency Mains Noise
Ian Bell wrote: Patrick Turner wrote: Ian Bell wrote: Phil Allison wrote: "Ian Bell" Indeed. However, I would have expected the transformer to attenuate noise in the 1Hz region ** Complete insanity. Ordinary power transformers attenuate nothing coming it unless it is over 5 kHz. ** Complete fallacy. Transformers by definition have a zero at zero Hz. They have a pole at some frequency determined by the transformer inductance and the source and load impedance. From that pole down to zero Hz their response falls by at least 20dB/decade. But you missed the reason why someone said "Complete insanity". Transformers convey *all* the variations of mains amplitude, and its these amplitude variations which are seen on the rectified signal at the resovoir cap of the dc supply. Hence there are *very* low frenquencies seen at the this resovoir capacitor. Try studying the way AM detectors work in radio sets using a diode and RC network. I realise that now. I am really disappointed that some members of this group have to take such an arrogant stance in explaining things. All that was necessary was to point out, as flipper did, that it is low frequency amplitude modulation of the ac mains I am seeing. Asinine remarks like 'try studying the way am detectors work' are singularly unhelpful. And apologies in advance for the rant. There are others than yourself who read the news group. Some wouldn't dare post here. Our questions and answers are informative to all readers and not just for you. Turning up here to ask questions when some of us have had to answer for ourselves through diligent observations and reading books et all is prone to getting a scorching from some of us. I don't set out to flame anyone, but to only to inform, and there *is* a big simularity between the principles in audio detection from AM waves and mains borne noise voltages. Hope you have had a nice sunday. I rode 106km this morning on a bicycle, and pondered the greatness of nature, recovered awhile, then went out to play chess and won more games than I lost against a fat fellow who studies games with several computer programs 7 days a week. I just play, and never study chess openings or games. My rating if I had one would be only 1200. I keep telling this fat fellow he should climb aboard a bicycle again like he used to and pedal his way back to better physical and mental health, and I get away with it because I am jovial about it. And when i lose a game I chuckle, and see the folly of my games. Occasionally I get a draw with the guy here who regularly is local club champion and rated at about 2,000. If I ever see him with a screwdriver in his hand, I snatch it away, and tell him to leave it alone because he's likely to cause a major damage bill. Horses for courses. This guy really hates to loose, which is one reason why he wins so often. But he's a born natural at chess. Has the Chess gene. Hopeless with tools, and understanding relationships, and doesn't follow stories at the movies so I explain them like he explains a complex chess game to me. I'll never be good at chess, and he'll never become a cyclist. I value all my friends whose strengths and weaknesses are different to my own and whose attitude allows some sharing of experience of thought without being overrun by competitive sparing. The fat guy who delves so deeply into openings and forcing a PC with a chess rating of well over 2,000 into drawing a game doesn't realise the human player with little more than crude intuitiveness can outwit a man who tries to copy a computer. This man had a really bad mental breakdown within the last 10 years. Chess is good therapy for him. Being perpetually logical, aware, and able to concentrate isn't easy for all, and I sure could have been better at all 3. I have a life at the keyboard here which augments what happens when I am away from a damn keyboard. I feel glad to be alive, don't you? Patrick Turner. Cheers Ian |
#44
Posted to rec.audio.tubes
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Low Frequency Mains Noise
Ian Bell wrote: Patrick Turner wrote: Ian Bell wrote: Patrick Turner wrote: snip, What is the maximum voltage gain at say 1kHz? 24dB Gee, that's only about 15x no? What is the noise at the amp output with maximum gain and with input grid directly shunted to 0V close to the input? Not possible to measure accurately at the moment as the LF blips whack the meter needle all over the place one you try to see noise below 1mV. That said, looking at it on a scope you can see the broadband noise underneath the LF blips and I would estimate the noise at the output with the input shorted as about 50uV rms. If you have 50uV of noise at the output and gain is 15x, and input is grounded, then you could have a total of 2uV grid input noise if the input tube is a real good one. 2uV gets amplified to make about 30uV at the output, and some of that is LF noise. where does the rest of the noise come from? By observation you should be able to see where the noise is being generated and how, and find ways of stopping it without much complexity and cost. In my MC phono amp without any GNFB with RIAA correction, but using a passive RIAA, the LF gain at 20Hz is MUCH greater than your 24dB yet the LF noise at the output is minimal, and the result using 1 fet in cascode with 1 triode, then 2 triode µ-follower gain stage produces an outcome equal or better than most other phono amps I have tried including SS with opamps. What happens if you temporally connect a spare 1,000uF or more to be in parallel to the last 100uF cap in the filter line up, ie, the filter cap giving the B+ supply to stage 1 of the mic amp? Not tried that yet, I have a spare 470uF or two so I'll try that. Noise should fall a lot with the extra C added where it'll do the most good. Think big, use enormous C values if you cannot bring yourself to make what might be a very simple shunt regulator in your preamp. Yes and no. I was using just a couple of RC stages using 470uF but then I realised the five RC stage of 100Uf each would perform better. I suppose I could go bananas and replace all the 100uF caps with 470uF ones. The cost now of generic 470uF caps rated at 350Vdc is not huge, and far cheaper than the 100uF caps were in real terms back in say 1960 when a 100uF cap was seen as a frivolous extravagance by bean conters in charge of design teams at major manufacturers. Keen diyers will *NEVER* try to emulate the pausity of design by accountants amoung yesterday's people. Beware using simple zener diode based shunt regs close to mic input stages though. The LF noise of the zener will find its way into signal paths. Agreed. I have been looking at the Maida regulator as a means of eliminating the LF noise *prior* to the normal RC string. Using a regulator right after the resevoir C is OK and you can then make RC filters after that to all stages without risk of LF motorboating. And such LF oscillations may not be obvious at first. A PS and amp can be right on the brink of oscillation at LW and the slightest noise will become amplified by a the peak in the response if there is one below 1Hz. Zeners placed across the second cap in an CRCRCRC filter can reduce LF content and any noise the zeners generate is less than the noise which is shunted, and following RC stages filter the noise of all types. Zeners have higher noise at lowish currents. So if you have a +375V B+ rail and held by 5 x 5watt x 75Vdc rated zeners, heatsink the zeners with a wrap around strip of Al aor Cu and bolt to a chassis or sink and allow the pda to be a safe 0.75Watts each, which means you'd have Izener = 10mA at least. And and in a preamp, the simplest shunt reg that isn't a simple zener string is to have the string feed a base of an npn bjt with emitter to 0V and a current limiting R between collector and B+ rail being shunt regged. This shunt eg has much lower output resistance than a plain zener string, and a much "sharper" threshold of turn on, as the current in the zeners gets amplified by the bjt. The bjt needs a high Vce rating, and such bjts have low hfe and a darlington pair is the best solution, and with a limiting series base resistance and filter cap at the base to 0V to filter out the zener noise. Such a shunt reg works only at LF and simply keeps the Vdc stable while your large value electros do the job on higher F. Shunt regs are good for low current preamp supplies and screen voltage supplies in power amps and have the advantage that in the case where the output becomes shorted or over currented, then the regulator doesn't have any current and survives while it is the low cost series R in RC section that cops the heat and fails. I have used such shunt regs in power amps with choke input supplies, so that the shunt reg shunts enough anode supply dc current right after turn on to stop the B+ soaring. As the input stages and output stages turn on the "bleeder" current of the shunt reg reduces to a low level enough to reg the B+ to stage 1. So thus the high current in a permanently connected bleeder resistance is avoided. Patrick Turner. Cheers Ian Patrick Turner. |
#45
Posted to rec.audio.tubes
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Low Frequency Mains Noise
Ian Bell wrote: Arny Krueger wrote: "Ian Bell" wrote in message Eeyore wrote: Ian Bell wrote: Since there are untold preamp designs with unregulated supplies Bad preamps you mean ? Graham You tell me. I have the schematics for many broadcast consoles and professional music mixers from the 50s that use unregulated supplies. Standards for audio were a lot lower in the 50s, if you didn't ever notice when you listened to a lot of recordings from that time. There are some exceptional recordings that still sound good, but in general, it was not a good time for quality sound reproduction. I would not say they were a lot lower. The flat bandwidth extended only from 50Hz to 15KHz but elsewhere the specs were close to today's. An RCA broadcast console achieved a 68dB S/N ratio with a -60dBm input signal which implies an equivalent input noise of -128dBm - and that would not be achievable with the LF noise I am seeing right now. Maybe they had better conditioned mains supplies for studios or maybe there was just less crap on the mains in those days. "Mains conditioning" for audio studios in the 1950s is not something I have ever seen described in any tech journal. There were however mains regulators based around saturable reactors. Much audio gear was made to work OK without excessive filtering, and when being fed by fairly irregular mobile mains power supplies. BBC vans were full of gear that would try to minimise power losses and use only battery power. Not much damn noise with batteries. The BBC could afford batteries. The dc to tubes was at lowish voltages and anode loads were chokes. And mains noise has always been bad. Much quality gear in 1950 had B+ regulation. Countless designs of tubes oscilloscopes had a regulator using a 6080 and a pentode. Much domestic audio gear was atrocious because design was by accountants. The item was not built up to a quality, but down to a price. Cash strapped dudes who wanted perfect audio in 1950 were not able to have the quality they yearned for because they were forced to feed the large families of the time. No Pill. My father's generation knew the Depression of the 1930s, and WW2, and having a few extra mV of noise at an amp output was the least of their concerns. Many used alcohol to overcome all problems, including those of poor audio, hence the drink cabinets supplied in deluxe radio-grams of 1950. Manufacturers knew the best way for punters to accept their terrible creations was to encourage boozing and smoking. Radio and audio manufacturers had cousins in the drinks and smokes supply businesses. Blokes rooted the missus between drinks and smokes and arguments over money, thus creating today's baby boomers. Domestic survival each night in 1950 was a challenge. Bliss was a rarity. Patrick Turner. Cheers Ian |
#46
Posted to rec.audio.tubes
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Low Frequency Mains Noise
Ian Bell wrote: I realise that now. I am really disappointed that some members of this group have to take such an arrogant stance in explaining things. All that was necessary was to point out, as flipper did, that it is low frequency amplitude modulation of the ac mains I am seeing. How bloody obvious does it have to be ? Graham |
#47
Posted to rec.audio.tubes
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Low Frequency Mains Noise
Ian Bell wrote: Eeyore wrote: Ian Bell wrote: Since there are untold preamp designs with unregulated supplies Bad preamps you mean ? You tell me. I have the schematics for many broadcast consoles and professional music mixers from the 50s that use unregulated supplies. 'Professional' has moved on a bit in 50+ years. I doubt they'd match decent cheap domestic kit now. This is one thing that freaks me out about you tubeophiles, you want to recreate the sound of half a century ago. Graham |
#48
Posted to rec.audio.tubes
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Low Frequency Mains Noise
Arny Krueger wrote:
"Ian Bell" wrote in message Arny Krueger wrote: "Ian Bell" wrote in message Eeyore wrote: Ian Bell wrote: Since there are untold preamp designs with unregulated supplies Bad preamps you mean ? Graham You tell me. I have the schematics for many broadcast consoles and professional music mixers from the 50s that use unregulated supplies. Standards for audio were a lot lower in the 50s, if you didn't ever notice when you listened to a lot of recordings from that time. There are some exceptional recordings that still sound good, but in general, it was not a good time for quality sound reproduction. I would not say they were a lot lower. I lived back then, trust me, the standards were in general far lower. Good sound of sorts did exist, but it was pretty rare. I lived back then too. I don't trust you. Things perked up a lot in the 60s and 70s. The flat bandwidth extended only from 50Hz to 15KHz ...and that was a joke. Most audio reproduction systems of the day were in trouble at 100 Hz, let alone 50. Today we can take response down to 20 Hz seriously. Home audio reproduction had trouble, yes, but not pro audio. Note that speakers of that time in general were not capable of much acoustic output by modern standards. Other than a few very expensive microphones, the mics were about as bad as the speakers. Rubbish. Neumann mics were pentiful. but elsewhere the specs were close to today's. An RCA broadcast console achieved a 68dB S/N ratio with a -60dBm input signal which implies an equivalent input noise of -128dBm - and that would not be achievable with the LF noise I am seeing right now. I suspect that you're looking at a transformer-coupled mic input, which says nothing about the dynamic range of the console's output. It is a transformer coupled mic input - that's the only way to achieve a decent noise figure with tubes. The spec quoted from mic input to console output so it says everything about its dynamic range. Furthermore, a transformer-coupled mic input can be made with wonderful specs, since the transformer in essence covers up a lot of the sins of the active components. But, the transformers of the day weren't all that wonderful, either. I expect they were the weakest link in the console and they do help the overall noise figure but that is good design not a sin. Maybe they had better conditioned mains supplies for studios or maybe there was just less crap on the mains in those days. As a rule, audio people's standards were a ton lower in those days. For example, I remember the regional 45 of The Righteous Brothers "You've lost that loving feeling". It was hissy, boomy, dull sounding, and had some pretty massive low frequency transients. Quite possibly, but it is a long chain from the original 3 track recording to the old 45 vinyl you played. Cheers Ian |
#49
Posted to rec.audio.tubes
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Low Frequency Mains Noise
Phil Allison wrote: "Eeysore the Congenital LIAR " Ian Bell wrote: Yes, that's my other problem. The simple CC cascade pair with NFB I am using has a very poor PSRR. Not a problem with solid state you see. PSRRs are typically in the 120dB region. ** Really? On what planet is that ??? TL071 = 86 dB typ NE5532 = 100 dB typ. Both 30+ years old designs. http://www.national.com/pf/LM/LM4562.html " PSRR and CMRR exceed 120dB (typ) " Graham |
#50
Posted to rec.audio.tubes
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Low Frequency Mains Noise
Patrick Turner wrote:
Ian Bell wrote: Patrick Turner wrote: Ian Bell wrote: Phil Allison wrote: "Ian Bell" Indeed. However, I would have expected the transformer to attenuate noise in the 1Hz region ** Complete insanity. Ordinary power transformers attenuate nothing coming it unless it is over 5 kHz. ** Complete fallacy. Transformers by definition have a zero at zero Hz. They have a pole at some frequency determined by the transformer inductance and the source and load impedance. From that pole down to zero Hz their response falls by at least 20dB/decade. But you missed the reason why someone said "Complete insanity". Transformers convey *all* the variations of mains amplitude, and its these amplitude variations which are seen on the rectified signal at the resovoir cap of the dc supply. Hence there are *very* low frenquencies seen at the this resovoir capacitor. Try studying the way AM detectors work in radio sets using a diode and RC network. I realise that now. I am really disappointed that some members of this group have to take such an arrogant stance in explaining things. All that was necessary was to point out, as flipper did, that it is low frequency amplitude modulation of the ac mains I am seeing. Asinine remarks like 'try studying the way am detectors work' are singularly unhelpful. And apologies in advance for the rant. There are others than yourself who read the news group. Some wouldn't dare post here. Our questions and answers are informative to all readers and not just for you. Turning up here to ask questions when some of us have had to answer for ourselves through diligent observations and reading books et all is prone to getting a scorching from some of us. I don't set out to flame anyone, but to only to inform, and there *is* a big simularity between the principles in audio detection from AM waves and mains borne noise voltages. I really don't have a problem with your posts Patrick - that's why I apologised in advance. It is not what people say, it is the way they say it. Manners cost nothing. Hope you have had a nice sunday. Yes I have. It was my 58th birthday yesterday. I rode 106km this morning on a bicycle, and pondered the greatness of nature, recovered awhile, then went out to play chess and won more games than I lost against a fat fellow who studies games with several computer programs 7 days a week. I just play, and never study chess openings or games. My rating if I had one would be only 1200. I keep telling this fat fellow he should climb aboard a bicycle again like he used to and pedal his way back to better physical and mental health, and I get away with it because I am jovial about it. And when i lose a game I chuckle, and see the folly of my games. Occasionally I get a draw with the guy here who regularly is local club champion and rated at about 2,000. If I ever see him with a screwdriver in his hand, I snatch it away, and tell him to leave it alone because he's likely to cause a major damage bill. Horses for courses. This guy really hates to loose, which is one reason why he wins so often. But he's a born natural at chess. Has the Chess gene. Hopeless with tools, and understanding relationships, and doesn't follow stories at the movies so I explain them like he explains a complex chess game to me. I'll never be good at chess, and he'll never become a cyclist. I value all my friends whose strengths and weaknesses are different to my own and whose attitude allows some sharing of experience of thought without being overrun by competitive sparing. The fat guy who delves so deeply into openings and forcing a PC with a chess rating of well over 2,000 into drawing a game doesn't realise the human player with little more than crude intuitiveness can outwit a man who tries to copy a computer. This man had a really bad mental breakdown within the last 10 years. Chess is good therapy for him. Being perpetually logical, aware, and able to concentrate isn't easy for all, and I sure could have been better at all 3. I have a life at the keyboard here which augments what happens when I am away from a damn keyboard. I feel glad to be alive, don't you? Very much so. Cheers Ian Patrick Turner. Cheers Ian |
#51
Posted to rec.audio.tubes
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Low Frequency Mains Noise
Ian Bell wrote: Eeyore wrote: Ian Bell wrote: Yes, that's my other problem. The simple CC cascade pair with NFB I am using has a very poor PSRR. Not a problem with solid state you see. PSRRs are typically in the 120dB region. Only if you use op amps. Well who wouldn't ? The dc coupled triple typical of the Neve class A preamps is just as bad as its tubed version. Except they did at least have regulated power supplies ! Graham |
#52
Posted to rec.audio.tubes
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Low Frequency Mains Noise
Ian Bell wrote: Arny Krueger wrote: Standards for audio were a lot lower in the 50s, if you didn't ever notice when you listened to a lot of recordings from that time. There are some exceptional recordings that still sound good, but in general, it was not a good time for quality sound reproduction. I would not say they were a lot lower. The flat bandwidth extended only from 50Hz to 15KHz i.e. totally crap. but elsewhere the specs were close to today's. ********. An RCA broadcast console achieved a 68dB S/N ratio with a -60dBm input signal which implies an equivalent input noise of -128dBm Cite ? A weighted by any chance ? Graham |
#53
Posted to rec.audio.tubes
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Low Frequency Mains Noise
Patrick Turner wrote:
Ian Bell wrote: Patrick Turner wrote: Ian Bell wrote: Patrick Turner wrote: snip, What is the maximum voltage gain at say 1kHz? 24dB Gee, that's only about 15x no? Correct but there is (will be) a 10:1 mic transformer at the input so the overall gain is 10 times greater. What is the noise at the amp output with maximum gain and with input grid directly shunted to 0V close to the input? Not possible to measure accurately at the moment as the LF blips whack the meter needle all over the place one you try to see noise below 1mV. That said, looking at it on a scope you can see the broadband noise underneath the LF blips and I would estimate the noise at the output with the input shorted as about 50uV rms. If you have 50uV of noise at the output and gain is 15x, and input is grounded, then you could have a total of 2uV grid input noise if the input tube is a real good one. Agreed and that is about -114dBV at the transformer secondary. At the primary it is 20dB lower. 2uV gets amplified to make about 30uV at the output, and some of that is LF noise. where does the rest of the noise come from? By observation you should be able to see where the noise is being generated and how, and find ways of stopping it without much complexity and cost. In my MC phono amp without any GNFB with RIAA correction, but using a passive RIAA, the LF gain at 20Hz is MUCH greater than your 24dB yet the LF noise at the output is minimal, I would be interested to know what the measured broadband noise is at its output. and the result using 1 fet in cascode with 1 triode, then 2 triode µ-follower gain stage produces an outcome equal or better than most other phono amps I have tried including SS with opamps. What happens if you temporally connect a spare 1,000uF or more to be in parallel to the last 100uF cap in the filter line up, ie, the filter cap giving the B+ supply to stage 1 of the mic amp? Not tried that yet, I have a spare 470uF or two so I'll try that. Noise should fall a lot with the extra C added where it'll do the most good. Think big, use enormous C values if you cannot bring yourself to make what might be a very simple shunt regulator in your preamp. Yes and no. I was using just a couple of RC stages using 470uF but then I realised the five RC stage of 100Uf each would perform better. I suppose I could go bananas and replace all the 100uF caps with 470uF ones. The cost now of generic 470uF caps rated at 350Vdc is not huge, and far cheaper than the 100uF caps were in real terms back in say 1960 when a 100uF cap was seen as a frivolous extravagance by bean conters in charge of design teams at major manufacturers. Agreed. You advised me of this about a year ago and I picked up a bunch of 470uF 450 electrolytics as a result. Keen diyers will *NEVER* try to emulate the pausity of design by accountants among yesterday's people. I think there is more to it than that. It is well known that a string of five RC networks is better than a single RC network of five times the capacitance and resistance. Employing that technique AND using much larger caps should bring about a significant improvement. Beware using simple zener diode based shunt regs close to mic input stages though. The LF noise of the zener will find its way into signal paths. Agreed. I have been looking at the Maida regulator as a means of eliminating the LF noise *prior* to the normal RC string. Using a regulator right after the resevoir C is OK and you can then make RC filters after that to all stages without risk of LF motorboating. That's the plan. And such LF oscillations may not be obvious at first. A PS and amp can be right on the brink of oscillation at LW and the slightest noise will become amplified by a the peak in the response if there is one below 1Hz. Zeners placed across the second cap in an CRCRCRC filter can reduce LF content and any noise the zeners generate is less than the noise which is shunted, and following RC stages filter the noise of all types. Zeners have higher noise at lowish currents. So if you have a +375V B+ rail and held by 5 x 5watt x 75Vdc rated zeners, heatsink the zeners with a wrap around strip of Al aor Cu and bolt to a chassis or sink and allow the pda to be a safe 0.75Watts each, which means you'd have Izener = 10mA at least. And and in a preamp, the simplest shunt reg that isn't a simple zener string is to have the string feed a base of an npn bjt with emitter to 0V and a current limiting R between collector and B+ rail being shunt regged. This shunt eg has much lower output resistance than a plain zener string, and a much "sharper" threshold of turn on, as the current in the zeners gets amplified by the bjt. The bjt needs a high Vce rating, and such bjts have low hfe and a darlington pair is the best solution, and with a limiting series base resistance and filter cap at the base to 0V to filter out the zener noise. Such a shunt reg works only at LF and simply keeps the Vdc stable while your large value electros do the job on higher F. Shunt regs are good for low current preamp supplies and screen voltage supplies in power amps and have the advantage that in the case where the output becomes shorted or over currented, then the regulator doesn't have any current and survives while it is the low cost series R in RC section that cops the heat and fails. I have used such shunt regs in power amps with choke input supplies, so that the shunt reg shunts enough anode supply dc current right after turn on to stop the B+ soaring. As the input stages and output stages turn on the "bleeder" current of the shunt reg reduces to a low level enough to reg the B+ to stage 1. So thus the high current in a permanently connected bleeder resistance is avoided. Patrick Turner. Cheers Ian Patrick Turner. Cheers IAn |
#54
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Eeyore wrote:
Ian Bell wrote: I realise that now. I am really disappointed that some members of this group have to take such an arrogant stance in explaining things. All that was necessary was to point out, as flipper did, that it is low frequency amplitude modulation of the ac mains I am seeing. How bloody obvious does it have to be ? Graham If it were obvious I would not have asked. As I said before, it is not what people say, it is the way they say it. Cheers Ian |
#55
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Eeyore wrote:
Ian Bell wrote: Eeyore wrote: Ian Bell wrote: Since there are untold preamp designs with unregulated supplies Bad preamps you mean ? You tell me. I have the schematics for many broadcast consoles and professional music mixers from the 50s that use unregulated supplies. 'Professional' has moved on a bit in 50+ years. Has it really? I doubt they'd match decent cheap domestic kit now. This is one thing that freaks me out about you tubeophiles, Nothing to do with tubeophiles. Neumann tube mics are still much revered by pros (as are many other tube mics), as are tube mic pres (just look at the popularity of the EMI REDD 47) you want to recreate the sound of half a century ago. Quite possibly. Is there something fundamentally wrong with that? Graham Cheers Ian |
#56
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Eeyore wrote:
Ian Bell wrote: Eeyore wrote: Ian Bell wrote: Yes, that's my other problem. The simple CC cascade pair with NFB I am using has a very poor PSRR. Not a problem with solid state you see. PSRRs are typically in the 120dB region. Only if you use op amps. Well who wouldn't ? Lots of people. The dc coupled triple typical of the Neve class A preamps is just as bad as its tubed version. Except they did at least have regulated power supplies ! Yes, but PSRR is important for other reasons too. Graham Cheers IAn |
#57
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Eeyore wrote:
Ian Bell wrote: Arny Krueger wrote: Standards for audio were a lot lower in the 50s, if you didn't ever notice when you listened to a lot of recordings from that time. There are some exceptional recordings that still sound good, but in general, it was not a good time for quality sound reproduction. I would not say they were a lot lower. The flat bandwidth extended only from 50Hz to 15KHz i.e. totally crap. No, just different. I guess you never listend to AM radio either. but elsewhere the specs were close to today's. ********. Is that a technical term? An RCA broadcast console achieved a 68dB S/N ratio with a -60dBm input signal which implies an equivalent input noise of -128dBm Cite ? RCA BC series broadcast consoles. A weighted by any chance ? Not specified. However it is not that hard to achieve 2uV broadband noise at the mic input tube grid which is -114dBV with the tubes of the day. With a 10:1 transformer that's and EIN of around -124dBV or -126dBm if you prefer. As good as the Neve mic pres of the 70s. Graham Cheers Ian |
#58
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Ian Bell wrote: Arny Krueger wrote: Other than a few very expensive microphones, the mics were about as bad as the speakers. Rubbish. Neumann mics were pentiful. And VERY expensive which is what Arny said. Even 32 yrs ago I sold my U87 for £400. They're about £1600 now new IIRC. Graham |
#59
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Ian Bell wrote: Eeyore wrote: Ian Bell wrote: Eeyore wrote: Ian Bell wrote: Since there are untold preamp designs with unregulated supplies Bad preamps you mean ? You tell me. I have the schematics for many broadcast consoles and professional music mixers from the 50s that use unregulated supplies. 'Professional' has moved on a bit in 50+ years. Has it really? Beyond belief ! You're likely to find more Cat5 patch leads in a modern studio than good old fashioned GPO / bantam patch leads. Plus tape recorders (if present) usually sit around gathering dust. I know a studio that has FIVE Studer 24 track A800s and they're almost never used. They also have one of these. http://www.ams-neve.com/Products/Mus...88RS/88RS.aspx I doubt you'd find much of this in the 50s ! http://www.ams-neve.com/Home/Home.aspx This was state of the art in the 60s ! http://vintageking.com/Shop-Used-Cat...I-Console-used Graham |
#60
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Ian Bell wrote: Eeyore wrote: Ian Bell wrote: Arny Krueger wrote: Standards for audio were a lot lower in the 50s, if you didn't ever notice when you listened to a lot of recordings from that time. There are some exceptional recordings that still sound good, but in general, it was not a good time for quality sound reproduction. I would not say they were a lot lower. The flat bandwidth extended only from 50Hz to 15KHz i.e. totally crap. No, just different. No, CRAP. Graham |
#61
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Ian Bell wrote: Eeyore wrote: Ian Bell wrote: An RCA broadcast console achieved a 68dB S/N ratio with a -60dBm input signal which implies an equivalent input noise of -128dBm Cite ? RCA BC series broadcast consoles. A weighted by any chance ? Not specified. There's your answer then. Graham |
#62
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"Ian Bell" wrote in message
Arny Krueger wrote: "Ian Bell" wrote in message Arny Krueger wrote: "Ian Bell" wrote in message Eeyore wrote: Ian Bell wrote: Since there are untold preamp designs with unregulated supplies Bad preamps you mean ? Well, pretty poor. Regulated power supplies were always possible, but they were generally rare, even in professional gear. The only pro gear from the 50s with regulated power supplies that comes quickly to mind were Ampex tape recorders, where controlling parameters like bias despite variations in power line voltage was almost mandatory. Broadcast equipment such as exciters also had regulated power supplies, for similar reasons. You tell me. I have the schematics for many broadcast consoles and professional music mixers from the 50s that use unregulated supplies. Agreed. Standards for audio were a lot lower in the 50s, if you didn't ever notice when you listened to a lot of recordings from that time. There are some exceptional recordings that still sound good, but in general, it was not a good time for quality sound reproduction. I would not say they were a lot lower. I lived back then, trust me, the standards were in general far lower. Good sound of sorts did exist, but it was pretty rare. I lived back then too. I don't trust you. One difference between us being that you have made 1950s technology into your life, while I've been pretty incorrigible about keeping up with the years of valuable developments in technology since then. ;-) Things perked up a lot in the 60s and 70s. Ian has no comment about this, I wonder why? The flat bandwidth extended only from 50Hz to 15KHz ...and that was a joke. Most audio reproduction systems of the day were in trouble at 100 Hz, let alone 50. Today we can take response down to 20 Hz seriously. Home audio reproduction had trouble, yes, but not pro audio. They both ate from the same rather sparsely-set table. Magnetic tape recording was in its infancy as was loudspeaker design. I need not travel down memory lane to remember how things were. I have friends who have set up legacy audio systems using ca. 1950s higher end components. Mac preamp and amps, high end EV and JBL drivers, and professionally designed and built (tube) electronic crossovers, etc. On the one hand it sounds surprisingly good, on the other it is completely substandard compared to modern equipment of a similar nature. Ian has no comment about this, I wonder why? Note that speakers of that time in general were not capable of much acoustic output by modern standards. Ian has no comment about this, I wonder why? Other than a few very expensive microphones, the mics were about as bad as the speakers. Rubbish. Neumann mics were plentiful. Hello? Is there any intelligent life in there? Neumann mics are and were premium-priced and therefore only a tiny fraction of what is and was in actual use. but elsewhere the specs were close to today's. An RCA broadcast console achieved a 68dB S/N ratio with a -60dBm input signal which implies an equivalent input noise of -128dBm - and that would not be achievable with the LF noise I am seeing right now. I suspect that you're looking at a transformer-coupled mic input, which says nothing about the dynamic range of the console's output. It is a transformer coupled mic input - that's the only way to achieve a decent noise figure with tubes. Point being that the electronics of the day were generally noisy and had relatively high amounts of distortion. The spec quoted from mic input to console output so it says everything about its dynamic range. I was thinking of the -123 dBm input noise, but I should take rest of the spec at its word - the console's SNR was 68 dB. Even a cheap modern console's SNR is more like 90 dB, or about 22 dB better. That's a huge difference! BTW I'm presuming that the tube's SNR was referred to 0 dBM or +4 because that is what I am referencing for the modern console. Furthermore, a transformer-coupled mic input can be made with wonderful specs, since the transformer in essence covers up a lot of the sins of the active components. But, the transformers of the day weren't all that wonderful, either. I expect they were the weakest link in the console and they do help the overall noise figure but that is good design not a sin. Going transformerless has a big performance and cost advantage. Maybe they had better conditioned mains supplies for studios or maybe there was just less crap on the mains in those days. As a rule, audio people's standards were a ton lower in those days. For example, I remember the regional 45 of The Righteous Brothers "You've lost that loving feeling". It was hissy, boomy, dull sounding, and had some pretty massive low frequency transients. Quite possibly, but it is a long chain from the original 3 track recording to the old 45 vinyl you played. It was the sort of thing that was not rare in those days, but just wouldn't happen today. Listening to original oldies from the 50s, whether classical or pop can be a lot of fun, but you don't do it for the high fidelity. Even the so-called SOTA recordings, RCA Red Seal for example, had a great many clearly audible flaws. I love the playing by the artists of the day, though. Toscanini is one of my favorites, but listening to him conducting is about the music, not the sound quality. Ian has no comment about this and even trash-canned it, I wonder why? Methinks the truth hurts. :-( |
#63
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Low Frequency Mains Noise
"Eeyore" wrote in
message Ian Bell wrote: Arny Krueger wrote: Standards for audio were a lot lower in the 50s, if you didn't ever notice when you listened to a lot of recordings from that time. There are some exceptional recordings that still sound good, but in general, it was not a good time for quality sound reproduction. I would not say they were a lot lower. The flat bandwidth extended only from 50Hz to 15KHz i.e. totally crap. but elsewhere the specs were close to today's. ********. An RCA broadcast console achieved a 68dB S/N ratio with a -60dBm input signal which implies an equivalent input noise of -128dBm Cite ? A weighted by any chance ? Here you go, Graham. As usual the tubies can't deliver what a few searches with google turned up almost immediately: http://sujan.hallikainen.org/Broadca.../index.php/RCA Click on the manual for the RCA BC 7A. However, being stereo, this was not a product of the 50s but rather one of the late 1960s. The actual spec on page 4 of the PDF is 68 dB below +18 dbm. IOW, only 50 dB below 0 dB. As bad as that is, I would suspect 50-15 KHz (- 3 dB) weighting. The corresponding spec for a modern console would be about twice that, IOW over 100 dB. (!!!!!!!!!!!!!!!!!!). Moving on to component chassic specs, such as those on page 15 (Figure 11) we see the sad truth - noise level was -47 dBm, with THD speced at 1% over a restricted frequency range. A modern component would have noise about -90 dBm, with THD no worse than 0.02%. As usual, we're getting a humongous load of BS dropped on us. :-( |
#64
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"Eeysore the Congenital LIAR " Not a problem with solid state you see. PSRRs are typically in the 120dB region. ** Really? On what planet is that ??? TL071 = 86 dB typ NE5532 = 100 dB typ. Both 30+ years old designs. ** Totally irrelevant. Modern pro-audio gear is CHOCK full of them. You LYING piece of ****. ..... Phil |
#65
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Eeyore wrote:
Ian Bell wrote: Arny Krueger wrote: Other than a few very expensive microphones, the mics were about as bad as the speakers. Rubbish. Neumann mics were pentiful. And VERY expensive which is what Arny said. Even 32 yrs ago I sold my U87 for £400. They're about £1600 now new IIRC. Graham So what? We are talking professional users here. Cheers Ian |
#66
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Eeyore wrote:
Ian Bell wrote: Eeyore wrote: Ian Bell wrote: Eeyore wrote: Ian Bell wrote: Since there are untold preamp designs with unregulated supplies Bad preamps you mean ? You tell me. I have the schematics for many broadcast consoles and professional music mixers from the 50s that use unregulated supplies. 'Professional' has moved on a bit in 50+ years. Has it really? Beyond belief ! You're likely to find more Cat5 patch leads in a modern studio than good old fashioned GPO / bantam patch leads. Plus tape recorders (if present) usually sit around gathering dust. I know a studio that has FIVE Studer 24 track A800s and they're almost never used. They also have one of these. http://www.ams-neve.com/Products/Mus...88RS/88RS.aspx I doubt you'd find much of this in the 50s ! http://www.ams-neve.com/Home/Home.aspx This was state of the art in the 60s ! http://vintageking.com/Shop-Used-Cat...I-Console-used Graham No ,that's no 'moved on' it is simply different. Cheers Ian |
#67
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Eeyore wrote:
Ian Bell wrote: Eeyore wrote: Ian Bell wrote: Arny Krueger wrote: Standards for audio were a lot lower in the 50s, if you didn't ever notice when you listened to a lot of recordings from that time. There are some exceptional recordings that still sound good, but in general, it was not a good time for quality sound reproduction. I would not say they were a lot lower. The flat bandwidth extended only from 50Hz to 15KHz i.e. totally crap. No, just different. No, CRAP. Graham YAWN Cheers Ian |
#68
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"Patrick Turner"
When I measure the "240Vac" here is usually is stable enough to get a nearly constant reading on a DMM, ** Must be a basic 3.5 digit one ( 2000 count) with only 1 volt resolution when reading 240 volts AC. Any DMM with a larger count allows changes of 0.1 volts to be seen - then the last digit is never steady. Indeed, I'll get 240.XX Vac maybe even 24X.XX if the voltage is just either side of 240.0Vac. That's less than 1% Vac change. ** Another completely irrelevant reply. Yawnnnnnnnnnnnnnn ... But it slowly varies between 235Vac on cold winter nights of heavy loadings to 255Vac when load is light. ** What drivel. Not so, this is without changing local loads here in my shed. ** Another irrelevant reply. Rarely does the mains ever bounce rapidly between 235Vac and 255Vac. ** More irrelevance - since I never claimed it did. It will instantly drop by 7 or 8 volts if you switch a ( 2.4 kW) electric heater on AND jumps up by 6 volts when the ( 2kW) jug turns itself off when it has boiled. Not necessarily so. ** Now that IS a blatant lie. Anyone can try it and see what happens to the AC voltage on the same circuit. When I look at the rectified Vdc, it shows the expected variations of +/- 30mV. ** Complete ********. No. ** Another BLATANT lie. Any unregulated DC supply FOLLOWS all variations in the AC voltage by the same percentage. Agreed. ** Then stop posting ****ING STUPID **** that says otherwise. You misunderstand me. ** NO - you completely misunderstand the point. ..... Phil |
#69
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Arny Krueger wrote:
"Ian Bell" wrote in message Arny Krueger wrote: "Ian Bell" wrote in message Arny Krueger wrote: "Ian Bell" wrote in message Eeyore wrote: Ian Bell wrote: Since there are untold preamp designs with unregulated supplies Bad preamps you mean ? Well, pretty poor. Regulated power supplies were always possible, but they were generally rare, even in professional gear. The only pro gear from the 50s with regulated power supplies that comes quickly to mind were Ampex tape recorders, where controlling parameters like bias despite variations in power line voltage was almost mandatory. Broadcast equipment such as exciters also had regulated power supplies, for similar reasons. You tell me. I have the schematics for many broadcast consoles and professional music mixers from the 50s that use unregulated supplies. Agreed. Standards for audio were a lot lower in the 50s, if you didn't ever notice when you listened to a lot of recordings from that time. There are some exceptional recordings that still sound good, but in general, it was not a good time for quality sound reproduction. I would not say they were a lot lower. I lived back then, trust me, the standards were in general far lower. Good sound of sorts did exist, but it was pretty rare. I lived back then too. I don't trust you. One difference between us being that you have made 1950s technology into your life, while I've been pretty incorrigible about keeping up with the years of valuable developments in technology since then. ;-) Not true. I use a 24bit standalone DAW for most of my recording work plus other digital outboard gear. The fact is, I think 50s designs have a place too. Things perked up a lot in the 60s and 70s. Ian has no comment about this, I wonder why? There's nothing to say. I was in the pro audio scene in the 70s. It was great. The big change was multi-tracking and noise reduction. But then Studer brought out the J4 in the 50s, all tubes and sounding great even by today's standards. The flat bandwidth extended only from 50Hz to 15KHz ...and that was a joke. Most audio reproduction systems of the day were in trouble at 100 Hz, let alone 50. Today we can take response down to 20 Hz seriously. Home audio reproduction had trouble, yes, but not pro audio. They both ate from the same rather sparsely-set table. Magnetic tape recording was in its infancy as was loudspeaker design. I need not travel down memory lane to remember how things were. I have friends who have set up legacy audio systems using ca. 1950s higher end components. Mac preamp and amps, high end EV and JBL drivers, and professionally designed and built (tube) electronic crossovers, etc. On the one hand it sounds surprisingly good, on the other it is completely substandard compared to modern equipment of a similar nature. Ian has no comment about this, I wonder why? Do I have to comment on everything? Note that speakers of that time in general were not capable of much acoustic output by modern standards. Ian has no comment about this, I wonder why? It's rubbish. Today's speakers if anything are less efficient. Other than a few very expensive microphones, the mics were about as bad as the speakers. Rubbish. Neumann mics were plentiful. Hello? Is there any intelligent life in there? Neumann mics are and were premium-priced and therefore only a tiny fraction of what is and was in actual use. All pro mics were premium priced and pros bought them. but elsewhere the specs were close to today's. An RCA broadcast console achieved a 68dB S/N ratio with a -60dBm input signal which implies an equivalent input noise of -128dBm - and that would not be achievable with the LF noise I am seeing right now. I suspect that you're looking at a transformer-coupled mic input, which says nothing about the dynamic range of the console's output. It is a transformer coupled mic input - that's the only way to achieve a decent noise figure with tubes. Point being that the electronics of the day were generally noisy and had relatively high amounts of distortion. No, the point being that a NF of 6dB was achievable even then. No matter what future developments bring they cannot possible reduce the noise by more than 6dB. The spec quoted from mic input to console output so it says everything about its dynamic range. I was thinking of the -123 dBm input noise, but I should take rest of the spec at its word - the console's SNR was 68 dB. Even a cheap modern console's SNR is more like 90 dB, or about 22 dB better. That's a huge difference! Rubbish. You clearly do not understand noise calculations. ANY console with 60dB gain and a 200R source cannot possibly have a 20KHz bandwidth output noise below -74dBm. BTW I'm presuming that the tube's SNR was referred to 0 dBM or +4 because that is what I am referencing for the modern console. Furthermore, a transformer-coupled mic input can be made with wonderful specs, since the transformer in essence covers up a lot of the sins of the active components. But, the transformers of the day weren't all that wonderful, either. I expect they were the weakest link in the console and they do help the overall noise figure but that is good design not a sin. Going transformerless has a big performance and cost advantage. Not if you are using tubes. Maybe they had better conditioned mains supplies for studios or maybe there was just less crap on the mains in those days. As a rule, audio people's standards were a ton lower in those days. For example, I remember the regional 45 of The Righteous Brothers "You've lost that loving feeling". It was hissy, boomy, dull sounding, and had some pretty massive low frequency transients. Quite possibly, but it is a long chain from the original 3 track recording to the old 45 vinyl you played. It was the sort of thing that was not rare in those days, but just wouldn't happen today. There is still no shortage of crappy recordings today. Listening to original oldies from the 50s, whether classical or pop can be a lot of fun, but you don't do it for the high fidelity. Even the so-called SOTA recordings, RCA Red Seal for example, had a great many clearly audible flaws. I love the playing by the artists of the day, though. Toscanini is one of my favorites, but listening to him conducting is about the music, not the sound quality. Ian has no comment about this and even trash-canned it, I wonder why? Methinks the truth hurts. :-( # Methinks you talk BS. Cheers Ian |
#70
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Low Frequency Mains Noise
Arny Krueger wrote:
"Eeyore" wrote in message Ian Bell wrote: Arny Krueger wrote: Standards for audio were a lot lower in the 50s, if you didn't ever notice when you listened to a lot of recordings from that time. There are some exceptional recordings that still sound good, but in general, it was not a good time for quality sound reproduction. I would not say they were a lot lower. The flat bandwidth extended only from 50Hz to 15KHz i.e. totally crap. but elsewhere the specs were close to today's. ********. An RCA broadcast console achieved a 68dB S/N ratio with a -60dBm input signal which implies an equivalent input noise of -128dBm Cite ? A weighted by any chance ? Here you go, Graham. As usual the tubies can't deliver what a few searches with google turned up almost immediately: http://sujan.hallikainen.org/Broadca.../index.php/RCA Click on the manual for the RCA BC 7A. However, being stereo, this was not a product of the 50s but rather one of the late 1960s. If you check the my other posts you will see I cited the BC 6 series not the one you chose and it was mono not stereo. The actual spec on page 4 of the PDF is 68 dB below +18 dbm. IOW, only 50 dB below 0 dB. As bad as that is, I would suspect 50-15 KHz (- 3 dB) weighting. The corresponding spec for a modern console would be about twice that, IOW over 100 dB. (!!!!!!!!!!!!!!!!!!). ********. Work out the actual output noise of a 'modern' console with 68dB and show me how you get it to be -100dBm Moving on to component chassic specs, such as those on page 15 (Figure 11) we see the sad truth - noise level was -47 dBm, with THD speced at 1% over a restricted frequency range. A modern component would have noise about -90 dBm, with THD no worse than 0.02%. As usual, we're getting a humongous load of BS dropped on us. :-( As usual you pick an example that suits your argument. Cheers Ian |
#71
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Arny Krueger wrote:
snip Here you go, Graham. As usual the tubies can't deliver what a few searches with google turned up almost immediately: http://sujan.hallikainen.org/Broadca.../index.php/RCA Click on the manual for the RCA BC 7A. However, being stereo, this was not a product of the 50s but rather one of the late 1960s. The actual spec on page 4 of the PDF is 68 dB below +18 dbm. IOW, only 50 dB below 0 dB. As bad as that is, I would suspect 50-15 KHz (- 3 dB) weighting. The corresponding spec for a modern console would be about twice that, IOW over 100 dB. (!!!!!!!!!!!!!!!!!!). Moving on to component chassic specs, such as those on page 15 (Figure 11) we see the sad truth - noise level was -47 dBm, with THD speced at 1% over a restricted frequency range. A modern component would have noise about -90 dBm, with THD no worse than 0.02%. As usual, we're getting a humongous load of BS dropped on us. :-( Are you totally sure about that Arny???? I just checked out the reference you cited above , the RCA BC-7A, that is the right one isn't it? Because it is a TRANSISTOR console you idiot, - on Page 2 it says - 6 plug in transistorized amplifiers. No we know it is YOU who talks BS. Cheers Ian |
#72
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Ian Bell makes MORE dumb errors
"Ian Bell" Lastly, the scope is a Rapid Electronics 7020A 20MHz dual channel (which is a re-branded Pintek) and its -3dB point is quoted as 20Hz. ** Shame how that is just NOT so. The 7020A has its -3dB point at ** 3.4 Hz ** when in "AC" input coupling mode. As is common practice with most scopes, a 47nF 400 volt film cap is placed in series with the 1 Mohm input to each vertical amplifier :- f -3dB = 1 / ( 2.pi.C.R) Here is the schematic for the whole scope. http://www.rapidonline.com/netalogue/specs/85-2200.pdf ....... Phil |
#73
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Ian Bell makes MORE dumb errors
Phil Allison wrote:
"Ian Bell" Lastly, the scope is a Rapid Electronics 7020A 20MHz dual channel (which is a re-branded Pintek) and its -3dB point is quoted as 20Hz. ** Shame how that is just NOT so. The 7020A has its -3dB point at ** 3.4 Hz ** when in "AC" input coupling mode. As is common practice with most scopes, a 47nF 400 volt film cap is placed in series with the 1 Mohm input to each vertical amplifier :- f -3dB = 1 / ( 2.pi.C.R) Here is the schematic for the whole scope. http://www.rapidonline.com/netalogue/specs/85-2200.pdf Pity your comprehension skills are so poor. I quoted the manufacturers spec. Clearly it is conservative. Thanks for the circuit. Cheers Ian |
#74
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"tubegarden" wrote in message ... On Oct 31, 3:55 pm, Eeyore wrote: Junk. Grow up and use solid state. Graham Hi RATs! Eyesore poses proudly as a knowledgeable and clever adult. "Things are seldom what they seem, Skim milk masquerades as cream; Highlows pass as patent leathers; Jackdaws strut in peacock's feathers. Very true, So they do. Black sheep dwell in every fold; All that glitters is not gold; Storks turn out to be but logs; Bulls are but inflated frogs. So they be, Frequently" This extract from the comic opera "HMS Pinafore" by Gilbert and Sullivan seems somehow appropriate. Don't you agree, Al? :-))) Regards Iain |
#75
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Low Frequency Mains Noise
"Ian Bell" wrote in message ... Eeyore wrote: Ian Bell wrote: Eeyore wrote: Ian Bell wrote: Since there are untold preamp designs with unregulated supplies Bad preamps you mean ? You tell me. I have the schematics for many broadcast consoles and professional music mixers from the 50s that use unregulated supplies. 'Professional' has moved on a bit in 50+ years. Has it really? I doubt they'd match decent cheap domestic kit now. This is one thing that freaks me out about you tubeophiles, Nothing to do with tubeophiles. Neumann tube mics are still much revered by pros (as are many other tube mics), as are tube mic pres (just look at the popularity of the EMI REDD 47) you want to recreate the sound of half a century ago. Quite possibly. Is there something fundamentally wrong with that? Nothing at all. As a classical recording engineer with a special interest in baroque music, I want to recreate the sound of 300 years ago! Cheers Iain |
#76
Posted to rec.audio.tubes
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Low Frequency Mains Noise
"Arny Krueger" wrote in message news "Ian Bell" wrote in message Arny Krueger wrote: Other than a few very expensive microphones, the mics were about as bad as the speakers. Rubbish. Neumann mics were plentiful. Correct Hello? Is there any intelligent life in there? Neumann mics are and were premium-priced and therefore only a tiny fraction of what is and was in actual use. Neumann mics were and still are ubiquitous in broadcast and professional studio applications. The fact that the Baptist handcart recordist cannot afford them has no bearing on the matter. Iain |
#77
Posted to rec.audio.tubes
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Low Frequency Mains Noise
"Eeyore" wrote in message ... Ian Bell wrote: Arny Krueger wrote: Other than a few very expensive microphones, the mics were about as bad as the speakers. Rubbish. Neumann mics were pentiful. And VERY expensive which is what Arny said. Even 32 yrs ago I sold my U87 for £400. They're about £1600 now new IIRC. Graham The *really* valuable Neumanns are the original U47, 49 and 50 some of which were supplied with a Telefunken badge for turnkey installations. They still sound wonderful. No-one parts with those. Iain |
#78
Posted to rec.audio.tubes
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Low Frequency Mains Noise
Phil Allison wrote: "Eeysore the Congenital LIAR " Not a problem with solid state you see. PSRRs are typically in the 120dB region. ** Really? On what planet is that ??? TL071 = 86 dB typ NE5532 = 100 dB typ. Both 30+ years old designs. ** Totally irrelevant. Extremely relevant. TLs are rarely seen these days. Graham |
#79
Posted to rec.audio.tubes
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Low Frequency Mains Noise
Ian Bell wrote: Eeyore wrote: Ian Bell wrote: Arny Krueger wrote: Other than a few very expensive microphones, the mics were about as bad as the speakers. Rubbish. Neumann mics were pentiful. And VERY expensive which is what Arny said. Even 32 yrs ago I sold my U87 for £400. They're about £1600 now new IIRC. So what? We are talking professional users here. And £400 for a secondhand but fairly pristine mic was a small fortune in 1976. So, only VERY EXPENSIVE mics from that era were any good. RE-20s weren't cheap either. You are totally talking out of your rectum. Graham |
#80
Posted to rec.audio.tubes
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Low Frequency Mains Noise
Ian Bell wrote: Eeyore wrote: Ian Bell wrote: Eeyore wrote: Ian Bell wrote: Eeyore wrote: Ian Bell wrote: Since there are untold preamp designs with unregulated supplies Bad preamps you mean ? You tell me. I have the schematics for many broadcast consoles and professional music mixers from the 50s that use unregulated supplies. 'Professional' has moved on a bit in 50+ years. Has it really? Beyond belief ! You're likely to find more Cat5 patch leads in a modern studio than good old fashioned GPO / bantam patch leads. Plus tape recorders (if present) usually sit around gathering dust. I know a studio that has FIVE Studer 24 track A800s and they're almost never used. They also have one of these. http://www.ams-neve.com/Products/Mus...88RS/88RS.aspx I doubt you'd find much of this in the 50s ! http://www.ams-neve.com/Home/Home.aspx This was state of the art in the 60s ! http://vintageking.com/Shop-Used-Cat...I-Console-used No ,that's no 'moved on' it is simply different. MORON ! |
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