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#121
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Low Frequency Mains Noise
"Patrick Turner" wrote in message
John Byrns wrote: In article , Patrick Turner wrote: Denon invented the MC way back in 1949, and the DL103R cart is still available and still well regarded, and I have one. Radio stations preferred the MC because of better noise figures and possibly lower THD and I sure found it better than MM Shure V15. Are you sure the MC cartridge wasn't around before 1949? I built my first MC cartridge as a teenager in the mid 1950s. I am 99% sure that Denon invented the MC. Maybe a google search will proove me wrong though. This google search supports your claim: https://shop.mantra-audio.co.uk/acat...artridges.html "Denon built the world's first stereo moving coil cartridge in 1951 and have been masters of the art of cartridge design ever since." |
#122
Posted to rec.audio.tubes
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Low Frequency Mains Noise
"Arny Krueger" "Patrick Turner" I am 99% sure that Denon invented the MC. Maybe a google search will proove me wrong though. This google search supports your claim: https://shop.mantra-audio.co.uk/acat...artridges.html "Denon built the world's first stereo moving coil cartridge in 1951 and have been masters of the art of cartridge design ever since." ** A Google search also DESTROYS that same, idiotic, unsourced and unsupported claim. " Early LP recordings were monaural, but stereo LP records became commercially available in 1957. " http://en.wikipedia.org/wiki/LP_album ...... Phil |
#123
Posted to rec.audio.tubes
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Low Frequency Mains Noise
flipper wrote: On Wed, 5 Nov 2008 09:36:43 +1100, "Phil Allison" wrote: "Arny Krueger" "Patrick Turner" I am 99% sure that Denon invented the MC. Maybe a google search will proove me wrong though. This google search supports your claim: https://shop.mantra-audio.co.uk/acat...artridges.html "Denon built the world's first stereo moving coil cartridge in 1951 and have been masters of the art of cartridge design ever since." ** A Google search also DESTROYS that same, idiotic, unsourced and unsupported claim. " Early LP recordings were monaural, but stereo LP records became commercially available in 1957. " http://en.wikipedia.org/wiki/LP_album OK, don't ask me who invented or made the first monaural MC cart. I searched awhile, and didn't find who. But my DL103R Denon has been around a long time, and works for me. Patrick Turner. ..... Phil Are you guys arguing about MC or *stereo* MC? Mono MC carts were around before the later. Grado is credited with inventing the stereo MC and I presume that's patent # 3040136 filed Jan 1959 (issued 1962). http://www.pat2pdf.org/ |
#124
Posted to rec.audio.tubes
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Low Frequency Mains Noise
Patrick Turner wrote:
snip 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. One of the potential sources I have discovered is excess noise in the anode resistors. This could account for 20uV or more of the total noise. The solution seems to be to replace metal film resistors with wire wound types. However, I am having trouble finding sources for 100K and 39K wire wound types at anything less than 5W rating which is something of an overkill. Do you know any good sources of high value low wattage wire wound resistors (preferable non-inductive of course)? Cheers Ian |
#125
Posted to rec.audio.tubes
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Low Frequency Mains Noise
"Ian Bell" One of the potential sources I have discovered is excess noise in the anode resistors. This could account for 20uV or more of the total noise. The solution seems to be to replace metal film resistors with wire wound types. ** Where does this LUNATIC get these wacky ideas from ?? Metal film resistors are near as damn it free of voltage noise - noise from the valve will always be waaaay higher . However, I am having trouble finding sources for 100K and 39K wire wound types at anything less than 5W rating which is something of an overkill. Do you know any good sources of high value low wattage wire wound resistors (preferable non-inductive of course)? ** ROTFLMAO ........ Phil Cheers Ian |
#126
Posted to rec.audio.tubes
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Low Frequency Mains Noise
Ian Bell wrote: Patrick Turner wrote: snip 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. One of the potential sources I have discovered is excess noise in the anode resistors. This could account for 20uV or more of the total noise. The solution seems to be to replace metal film resistors with wire wound types. However, I am having trouble finding sources for 100K and 39K wire wound types at anything less than 5W rating which is something of an overkill. Do you know any good sources of high value low wattage wire wound resistors (preferable non-inductive of course)? Cheers Ian Suppose you had 30uV of noise due to the input tube at the output of your amp with gain = 15x. And total noise = 50uV. Say you have Ra of the input tube = 20k, and the load resistor for dc in parallel to the following stage bias R might be 50k. The 50k 20Hz ro 20k noise can be calculated, but the its shunted by Ra = 20k and thus attenuated. The excess noise would also be shunted, but unlikely to be as high as the V1 tube noise, even if its a poor quality R. Its the value of R in ohms which gives rise to noise, and usually 90% of the noise at the output of a mic amp is due to the broadand noise of V1, and all following R and tubes have little contribution unless the output of V1 is a tiny voltage. I think you should just build it and then try things to make it silent. Wire wound would appear to be blameless, and getting a high value one may mean you series a few. A 47k WW type will at least make the predicted amount of noise because its the ohms than make the noise. Any other type of R, metal film, carbon film also will make similar noise you should find unless they are faulty. Read up from RDH4 about noise and equivalent input resistance and noise in R and summing of noise voltages. Patrick Turner. |
#127
Posted to rec.audio.tubes
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Low Frequency Mains Noise
Phil Allison wrote: "Ian Bell" One of the potential sources I have discovered is excess noise in the anode resistors. This could account for 20uV or more of the total noise. The solution seems to be to replace metal film resistors with wire wound types. ** Where does this LUNATIC get these wacky ideas from ?? Metal film resistors are near as damn it free of voltage noise - noise from the valve will always be waaaay higher . Suppose noise generated by the V1 tube as 30uV at the output. If total noise was 50uV, then you have to add far more than 20uV to 30uV to get a total of 50uV, because the total of a bunch of noise sources is the sq.rt of the total of each voltage squared. Interested ppl in such noise problems are advised to study theory more deeply because its impossible for those of us who do manage to make amps with excellent SNR to spend the time to repeat all we have said in the past yet again. However, I am having trouble finding sources for 100K and 39K wire wound types at anything less than 5W rating which is something of an overkill. Do you know any good sources of high value low wattage wire wound resistors (preferable non-inductive of course)? ** ROTFLMAO So impolite Phil, but I can see why you are laughing when there are sources of highish values of wire wound around. And as you say, why not metal film? Patrick Turner. ....... Phil Cheers Ian |
#128
Posted to rec.audio.tubes
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Low Frequency Mains Noise
"Patrick Turner" Phil Allison wrote: "Ian has Bats in his Belfry " One of the potential sources I have discovered is excess noise in the anode resistors. This could account for 20uV or more of the total noise. The solution seems to be to replace metal film resistors with wire wound types. ** Where does this LUNATIC get these wacky ideas from ?? Metal film resistors are near as damn it free of voltage noise - noise from the valve will always be waaaay higher . Suppose noise generated by the V1 tube as 30uV at the output. If total noise was 50uV, then you have to add far more than 20uV to 30uV to get a total of 50uV, because the total of a bunch of noise sources is the sq.rt of the total of each voltage squared. Interested ppl in such noise problems are advised to study theory more deeply because its impossible for those of us who do manage to make amps with excellent SNR to spend the time to repeat all we have said in the past yet again. However, I am having trouble finding sources for 100K and 39K wire wound types at anything less than 5W rating which is something of an overkill. Do you know any good sources of high value low wattage wire wound resistors (preferable non-inductive of course)? ** ROTFLMAO So impolite Phil, but I can see why you are laughing when there are sources of highish values of wire wound around. ** Not what I was laughing at - the bit about " non-inductively wound was very funny. How much L does it take to make a 100 kohm, WW resistor have say 101 Kohms of impedance at 20 kHz ?? The answer is 113 mH !!!!!!! The resistance wire would have to be wound on a Mu-Metal core to get such a value. Do the math. ...... Phil |
#129
Posted to rec.audio.tubes
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Low Frequency Mains Noise
Phil Allison wrote:
"Ian Bell" One of the potential sources I have discovered is excess noise in the anode resistors. This could account for 20uV or more of the total noise. The solution seems to be to replace metal film resistors with wire wound types. ** Where does this LUNATIC get these wacky ideas from ?? Metal film resistors are near as damn it free of voltage noise Are they? Most metal film resistor suppliers that actually bother to spec this usually put a figure of about 0.1uV/V for excess noise. With 150V across an anode resistor that an extra 15uV of noise I can well do without. Can you cite a supplier that quotes a lower figure? Cheers Ian |
#130
Posted to rec.audio.tubes
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Low Frequency Mains Noise
Patrick Turner wrote:
Ian Bell wrote: Patrick Turner wrote: snip 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. One of the potential sources I have discovered is excess noise in the anode resistors. This could account for 20uV or more of the total noise. The solution seems to be to replace metal film resistors with wire wound types. However, I am having trouble finding sources for 100K and 39K wire wound types at anything less than 5W rating which is something of an overkill. Do you know any good sources of high value low wattage wire wound resistors (preferable non-inductive of course)? Cheers Ian Suppose you had 30uV of noise due to the input tube at the output of your amp with gain = 15x. And total noise = 50uV. Say you have Ra of the input tube = 20k, and the load resistor for dc in parallel to the following stage bias R might be 50k. The 50k 20Hz ro 20k noise can be calculated, but the its shunted by Ra = 20k and thus attenuated. The excess noise would also be shunted, but unlikely to be as high as the V1 tube noise, even if its a poor quality R. Its the value of R in ohms which gives rise to noise, and usually 90% of the noise at the output of a mic amp is due to the broadand noise of V1, and all following R and tubes have little contribution unless the output of V1 is a tiny voltage. I think you should just build it and then try things to make it silent. Wire wound would appear to be blameless, and getting a high value one may mean you series a few. A 47k WW type will at least make the predicted amount of noise because its the ohms than make the noise. Any other type of R, metal film, carbon film also will make similar noise you should find unless they are faulty. Read up from RDH4 about noise and equivalent input resistance and noise in R and summing of noise voltages. Patrick Turner. |
#131
Posted to rec.audio.tubes
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Low Frequency Mains Noise
Patrick Turner wrote:
Ian Bell wrote: Patrick Turner wrote: snip 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. One of the potential sources I have discovered is excess noise in the anode resistors. This could account for 20uV or more of the total noise. The solution seems to be to replace metal film resistors with wire wound types. However, I am having trouble finding sources for 100K and 39K wire wound types at anything less than 5W rating which is something of an overkill. Do you know any good sources of high value low wattage wire wound resistors (preferable non-inductive of course)? Cheers Ian Suppose you had 30uV of noise due to the input tube at the output of your amp with gain = 15x. And total noise = 50uV. Say you have Ra of the input tube = 20k, and the load resistor for dc in parallel to the following stage bias R might be 50k. The 50k 20Hz ro 20k noise can be calculated, but the its shunted by Ra = 20k and thus attenuated. The excess noise would also be shunted, but unlikely to be as high as the V1 tube noise, even if its a poor quality R. Its the value of R in ohms which gives rise to noise, and usually 90% of the noise at the output of a mic amp is due to the broadand noise of V1, and all following R and tubes have little contribution unless the output of V1 is a tiny voltage. I think you should just build it and then try things to make it silent. Wire wound would appear to be blameless, and getting a high value one may mean you series a few. A 47k WW type will at least make the predicted amount of noise because its the ohms than make the noise. Any other type of R, metal film, carbon film also will make similar noise you should find unless they are faulty. Read up from RDH4 about noise and equivalent input resistance and noise in R and summing of noise voltages. Thanks for the input Patrick. I know about Johnson noise and in plate resistors it is not much of an issue as it is swamped by other noise sources. What I am concerned about is excess noise which is voltage dependent. In the few places I have seen this specified it is typically 0.1uV/V so with a plate resistor with 150V across it there is possibly 15uV of noise due to this effect - enough to warrant a change of resistor type. Are you saying that regular metal film resistors do not suffer from excess noise? Cheers Ian Patrick Turner. |
#132
Posted to rec.audio.tubes
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Low Frequency Mains Noise
"Ian Bell" Phil Allison wrote: "Ian Bell" One of the potential sources I have discovered is excess noise in the anode resistors. This could account for 20uV or more of the total noise. The solution seems to be to replace metal film resistors with wire wound types. ** Where does this LUNATIC get these wacky ideas from ?? Metal film resistors are near as damn it free of voltage noise Are they? Most metal film resistor suppliers that actually bother to spec this usually put a figure of about 0.1uV/V for excess noise. ** What measurement bandwidth - eh ?? What resistance value - eh ?? Got no ****ig clue - have you. You ****ING **** WIT ........ Phil |
#133
Posted to rec.audio.tubes
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Low Frequency Mains Noise
"Ian Bell" Thanks for the input Patrick. I know about Johnson noise and in plate resistors it is not much of an issue as it is swamped by other noise sources. What I am concerned about is excess noise which is voltage dependent. In the few places I have seen this specified it is typically 0.1uV/V so with a plate resistor with 150V across it there is possibly 15uV of noise due to this effect - enough to warrant a change of resistor type. ** No it is not - you hee hawwwing ASS ...... Phil |
#134
Posted to rec.audio.tubes
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Low Frequency Mains Noise
Phil Allison wrote: "Patrick Turner" Phil Allison wrote: "Ian has Bats in his Belfry " One of the potential sources I have discovered is excess noise in the anode resistors. This could account for 20uV or more of the total noise. The solution seems to be to replace metal film resistors with wire wound types. ** Where does this LUNATIC get these wacky ideas from ?? Metal film resistors are near as damn it free of voltage noise - noise from the valve will always be waaaay higher . Suppose noise generated by the V1 tube as 30uV at the output. If total noise was 50uV, then you have to add far more than 20uV to 30uV to get a total of 50uV, because the total of a bunch of noise sources is the sq.rt of the total of each voltage squared. Interested ppl in such noise problems are advised to study theory more deeply because its impossible for those of us who do manage to make amps with excellent SNR to spend the time to repeat all we have said in the past yet again. However, I am having trouble finding sources for 100K and 39K wire wound types at anything less than 5W rating which is something of an overkill. Do you know any good sources of high value low wattage wire wound resistors (preferable non-inductive of course)? ** ROTFLMAO So impolite Phil, but I can see why you are laughing when there are sources of highish values of wire wound around. ** Not what I was laughing at - the bit about " non-inductively wound was very funny. How much L does it take to make a 100 kohm, WW resistor have say 101 Kohms of impedance at 20 kHz ?? The answer is 113 mH !!!!!!! The resistance wire would have to be wound on a Mu-Metal core to get such a value. Do the math. I've never noticed a hugely worrying amount of L in higher value wire wound R. Then there is is the self capacitance of the wound turns. I have not often used WW R for dc supply loads, but when I have its been with low Ra triodes so the poles caused by reactances have been at fairly high F. I have not experienced problem with stability with use of WW R for anode loads even when GNFB is used. Non inductive WW R are available, with turns wound in two directions to cancel out the inductance, but I've only ever seen low value types, never high values. Let me see now, XL of 0.113H at 20kHz = 0.113 x 20,000 x 6.28 = approx 15kohms. So the Z (R + L) would be only very slightly greater than the 100k at 1 kHz. But there are lots of turns. I've never bothered to measure such things. Patrick Turner. ..... Phil |
#135
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 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. One of the potential sources I have discovered is excess noise in the anode resistors. This could account for 20uV or more of the total noise. The solution seems to be to replace metal film resistors with wire wound types. However, I am having trouble finding sources for 100K and 39K wire wound types at anything less than 5W rating which is something of an overkill. Do you know any good sources of high value low wattage wire wound resistors (preferable non-inductive of course)? Cheers Ian Suppose you had 30uV of noise due to the input tube at the output of your amp with gain = 15x. And total noise = 50uV. Say you have Ra of the input tube = 20k, and the load resistor for dc in parallel to the following stage bias R might be 50k. The 50k 20Hz ro 20k noise can be calculated, but the its shunted by Ra = 20k and thus attenuated. The excess noise would also be shunted, but unlikely to be as high as the V1 tube noise, even if its a poor quality R. Its the value of R in ohms which gives rise to noise, and usually 90% of the noise at the output of a mic amp is due to the broadand noise of V1, and all following R and tubes have little contribution unless the output of V1 is a tiny voltage. I think you should just build it and then try things to make it silent. Wire wound would appear to be blameless, and getting a high value one may mean you series a few. A 47k WW type will at least make the predicted amount of noise because its the ohms than make the noise. Any other type of R, metal film, carbon film also will make similar noise you should find unless they are faulty. Read up from RDH4 about noise and equivalent input resistance and noise in R and summing of noise voltages. Thanks for the input Patrick. I know about Johnson noise and in plate resistors it is not much of an issue as it is swamped by other noise sources. What I am concerned about is excess noise which is voltage dependent. In the few places I have seen this specified it is typically 0.1uV/V so with a plate resistor with 150V across it there is possibly 15uV of noise due to this effect - enough to warrant a change of resistor type. Are you saying that regular metal film resistors do not suffer from excess noise? I've never noticed it in amps i have built. If I'd found that the noise measurements didn't seem to add up, then I'd have been the one to reason why. I've usually used Welwyn or Beyshlag metal film R for most circuits. Noise is negligible. Patrick Turner. Cheers Ian Patrick Turner. |
#136
Posted to rec.audio.tubes
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Low Frequency Mains Noise
Ian Bell wrote: Phil Allison wrote: Metal film resistors are near as damn it free of voltage noise Are they? Most metal film resistor suppliers that actually bother to spec this usually put a figure of about 0.1uV/V for excess noise. With 150V across an anode resistor that an extra 15uV of noise I can well do without. Can you cite a supplier that quotes a lower figure? All the more reason to use solid state circuitry with lower voltages. Graham |
#137
Posted to rec.audio.tubes
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Low Frequency Mains Noise
Eeyore wrote: Ian Bell wrote: Phil Allison wrote: Metal film resistors are near as damn it free of voltage noise Are they? Most metal film resistor suppliers that actually bother to spec this usually put a figure of about 0.1uV/V for excess noise. With 150V across an anode resistor that an extra 15uV of noise I can well do without. Can you cite a supplier that quotes a lower figure? All the more reason to use solid state circuitry with lower voltages. Graham 15uV of noise isn't a heck of a lot to worry about if its after stage 1 of the amp, or at the output. The use of a mic step up transformer should produce a good enough SNR with a tube amp. No need to use all SS. But I like a j-fet at the input to drive a cathode of a grounded grid triode. It is of course an inherently quiet cascode circuit. No drain or cathode resistance to be seen, and gain of such a stage 200. So if input is 1mV, you get 200mV output, and if noise at the output was 20uV, you can work out the SNR at -80dB, unweighted. Patrick Turner. |
#138
Posted to rec.audio.tubes
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Low Frequency Mains Noise
Phil Allison wrote:
"Ian Bell" Thanks for the input Patrick. I know about Johnson noise and in plate resistors it is not much of an issue as it is swamped by other noise sources. What I am concerned about is excess noise which is voltage dependent. In the few places I have seen this specified it is typically 0.1uV/V so with a plate resistor with 150V across it there is possibly 15uV of noise due to this effect - enough to warrant a change of resistor type. ** No it is not - you hee hawwwing ASS Simple negation is no argument. I presently have about 65uV of noise from the circuit under test. Eliminating a 15uV component of it is worthwhile. Cheers Ian |
#139
Posted to rec.audio.tubes
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Low Frequency Mains Noise
Phil Allison wrote:
"Ian Bell" Phil Allison wrote: "Ian Bell" One of the potential sources I have discovered is excess noise in the anode resistors. This could account for 20uV or more of the total noise. The solution seems to be to replace metal film resistors with wire wound types. ** Where does this LUNATIC get these wacky ideas from ?? Metal film resistors are near as damn it free of voltage noise Are they? Most metal film resistor suppliers that actually bother to spec this usually put a figure of about 0.1uV/V for excess noise. ** What measurement bandwidth - eh ?? What resistance value - eh ?? Got no ****ig clue - have you. You ****ING **** WIT Sounds like you are back pedalling, Phil. You of all people will know exactly how excess noise is specified (which includes the bandwidth). I happen to have a 100K resistor in one anode which, from one manufacturers graph, shows its excess noise is 0.1V/V. As a said before, show me a manufacturer that quotes less. CHeers Ian ....... Phil |
#140
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Low Frequency Mains Noise
Patrick Turner wrote:
Phil Allison wrote: "Patrick Turner" Phil Allison wrote: "Ian has Bats in his Belfry " One of the potential sources I have discovered is excess noise in the anode resistors. This could account for 20uV or more of the total noise. The solution seems to be to replace metal film resistors with wire wound types. ** Where does this LUNATIC get these wacky ideas from ?? Metal film resistors are near as damn it free of voltage noise - noise from the valve will always be waaaay higher . Suppose noise generated by the V1 tube as 30uV at the output. If total noise was 50uV, then you have to add far more than 20uV to 30uV to get a total of 50uV, because the total of a bunch of noise sources is the sq.rt of the total of each voltage squared. Interested ppl in such noise problems are advised to study theory more deeply because its impossible for those of us who do manage to make amps with excellent SNR to spend the time to repeat all we have said in the past yet again. However, I am having trouble finding sources for 100K and 39K wire wound types at anything less than 5W rating which is something of an overkill. Do you know any good sources of high value low wattage wire wound resistors (preferable non-inductive of course)? ** ROTFLMAO So impolite Phil, but I can see why you are laughing when there are sources of highish values of wire wound around. ** Not what I was laughing at - the bit about " non-inductively wound was very funny. How much L does it take to make a 100 kohm, WW resistor have say 101 Kohms of impedance at 20 kHz ?? The answer is 113 mH !!!!!!! The resistance wire would have to be wound on a Mu-Metal core to get such a value. Do the math. I've never noticed a hugely worrying amount of L in higher value wire wound R. Then there is is the self capacitance of the wound turns. I have not often used WW R for dc supply loads, but when I have its been with low Ra triodes so the poles caused by reactances have been at fairly high F. I have not experienced problem with stability with use of WW R for anode loads even when GNFB is used. Non inductive WW R are available, with turns wound in two directions to cancel out the inductance, but I've only ever seen low value types, never high values. Let me see now, XL of 0.113H at 20kHz = 0.113 x 20,000 x 6.28 = approx 15kohms. So the Z (R + L) would be only very slightly greater than the 100k at 1 kHz. But there are lots of turns. I've never bothered to measure such things. Patrick Turner. ..... Phil Morgan did these tests and the results are in his book. He concluded that for 10K the inductance is negligible and the equivalent parallel capacitance is about 3pF. Low resistance values have high inductances because of the use of thicker wire. Cheers IAn |
#141
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Low Frequency Mains Noise
Eeyore wrote:
Ian Bell wrote: Phil Allison wrote: Metal film resistors are near as damn it free of voltage noise Are they? Most metal film resistor suppliers that actually bother to spec this usually put a figure of about 0.1uV/V for excess noise. With 150V across an anode resistor that an extra 15uV of noise I can well do without. Can you cite a supplier that quotes a lower figure? All the more reason to use solid state circuitry with lower voltages. Graham All the more reason for you to disappear and go post on a semiconductor news group. What are you doing here, Graham?? Cheers Ian |
#142
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Low Frequency Mains Noise
Patrick Turner wrote:
Ian Bell wrote: Patrick Turner wrote: Ian Bell wrote: Patrick Turner wrote: snip 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. One of the potential sources I have discovered is excess noise in the anode resistors. This could account for 20uV or more of the total noise. The solution seems to be to replace metal film resistors with wire wound types. However, I am having trouble finding sources for 100K and 39K wire wound types at anything less than 5W rating which is something of an overkill. Do you know any good sources of high value low wattage wire wound resistors (preferable non-inductive of course)? Cheers Ian Suppose you had 30uV of noise due to the input tube at the output of your amp with gain = 15x. And total noise = 50uV. Say you have Ra of the input tube = 20k, and the load resistor for dc in parallel to the following stage bias R might be 50k. The 50k 20Hz ro 20k noise can be calculated, but the its shunted by Ra = 20k and thus attenuated. The excess noise would also be shunted, but unlikely to be as high as the V1 tube noise, even if its a poor quality R. Its the value of R in ohms which gives rise to noise, and usually 90% of the noise at the output of a mic amp is due to the broadand noise of V1, and all following R and tubes have little contribution unless the output of V1 is a tiny voltage. I think you should just build it and then try things to make it silent. Wire wound would appear to be blameless, and getting a high value one may mean you series a few. A 47k WW type will at least make the predicted amount of noise because its the ohms than make the noise. Any other type of R, metal film, carbon film also will make similar noise you should find unless they are faulty. Read up from RDH4 about noise and equivalent input resistance and noise in R and summing of noise voltages. Thanks for the input Patrick. I know about Johnson noise and in plate resistors it is not much of an issue as it is swamped by other noise sources. What I am concerned about is excess noise which is voltage dependent. In the few places I have seen this specified it is typically 0.1uV/V so with a plate resistor with 150V across it there is possibly 15uV of noise due to this effect - enough to warrant a change of resistor type. Are you saying that regular metal film resistors do not suffer from excess noise? I've never noticed it in amps i have built. If I'd found that the noise measurements didn't seem to add up, then I'd have been the one to reason why. I've usually used Welwyn or Beyshlag metal film R for most circuits. Noise is negligible. I'll check out Welwyn and Beyshlag specs, thanks Cheers IAn Patrick Turner. Cheers Ian Patrick Turner. |
#143
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Low Frequency Mains Noise
Ian Bell wrote:
Patrick Turner wrote: Ian Bell wrote: Patrick Turner wrote: Ian Bell wrote: Patrick Turner wrote: snip 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. One of the potential sources I have discovered is excess noise in the anode resistors. This could account for 20uV or more of the total noise. The solution seems to be to replace metal film resistors with wire wound types. However, I am having trouble finding sources for 100K and 39K wire wound types at anything less than 5W rating which is something of an overkill. Do you know any good sources of high value low wattage wire wound resistors (preferable non-inductive of course)? Cheers Ian Suppose you had 30uV of noise due to the input tube at the output of your amp with gain = 15x. And total noise = 50uV. Say you have Ra of the input tube = 20k, and the load resistor for dc in parallel to the following stage bias R might be 50k. The 50k 20Hz ro 20k noise can be calculated, but the its shunted by Ra = 20k and thus attenuated. The excess noise would also be shunted, but unlikely to be as high as the V1 tube noise, even if its a poor quality R. Its the value of R in ohms which gives rise to noise, and usually 90% of the noise at the output of a mic amp is due to the broadand noise of V1, and all following R and tubes have little contribution unless the output of V1 is a tiny voltage. I think you should just build it and then try things to make it silent. Wire wound would appear to be blameless, and getting a high value one may mean you series a few. A 47k WW type will at least make the predicted amount of noise because its the ohms than make the noise. Any other type of R, metal film, carbon film also will make similar noise you should find unless they are faulty. Read up from RDH4 about noise and equivalent input resistance and noise in R and summing of noise voltages. Thanks for the input Patrick. I know about Johnson noise and in plate resistors it is not much of an issue as it is swamped by other noise sources. What I am concerned about is excess noise which is voltage dependent. In the few places I have seen this specified it is typically 0.1uV/V so with a plate resistor with 150V across it there is possibly 15uV of noise due to this effect - enough to warrant a change of resistor type. Are you saying that regular metal film resistors do not suffer from excess noise? I've never noticed it in amps i have built. If I'd found that the noise measurements didn't seem to add up, then I'd have been the one to reason why. I've usually used Welwyn or Beyshlag metal film R for most circuits. Noise is negligible. I'll check out Welwyn and Beyshlag specs, thanks Cheers IAn Welwyn MFR5 types specify a maximum excess noise of 0.1uV/v per decade of frequency. I have been unable to find a spec for this parameter on any of type of theirs other than the MFR series. I have looked at several Vishay (Beyschlag) data sheets and the best they can do is to say 'low noise' whatever that means. So I am still unconvinced that metal film resistors do not produce a significant amount of excess noise for low level low noise applications. Cheers Ian Patrick Turner. Cheers Ian Patrick Turner. |
#144
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Low Frequency Mains Noise
"Ian Bell = utterly STUPID ****WIT " One of the potential sources I have discovered is excess noise in the anode resistors. This could account for 20uV or more of the total noise. The solution seems to be to replace metal film resistors with wire wound types. ** Where does this LUNATIC get these wacky ideas from ?? Metal film resistors are near as damn it free of voltage noise Are they? Most metal film resistor suppliers that actually bother to spec this usually put a figure of about 0.1uV/V for excess noise. ** What measurement bandwidth - eh ?? What resistance value - eh ?? Got no ****ing clue - have you. You ****ING **** WIT Sounds like you are back pedalling, Phil. You of all people will know exactly how excess noise is specified (which includes the bandwidth). ** Then YOU need to post the link - ****HEAD. Since that is the ONLY evidence you have. As a said before, show me a manufacturer that quotes less. ** The figure you quoted ( without ANY kind of link or reference ) is simply not a spec at all. ...... Phil |
#145
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Low Frequency Mains Noise
"Ian Bell = LIAR "
Thanks for the input Patrick. I know about Johnson noise and in plate resistors it is not much of an issue as it is swamped by other noise sources. What I am concerned about is excess noise which is voltage dependent. In the few places I have seen this specified it is typically 0.1uV/V so with a plate resistor with 150V across it there is possibly 15uV of noise due to this effect - enough to warrant a change of resistor type. ** No it is not - you hee hawwwing ASS Simple negation is no argument. ** An totally unsupported assertion is NOT a case and requires NO DISPROOF !! I presently have about 65uV of noise from the circuit under test. Eliminating a 15uV component of it is worthwhile. ** Another ****ING RIDICULOUS unsupported assertion = typical Bell puke. FYI, you arrogant ****head: Noise voltages DO NOT ADD !!! ....... Phil |
#146
Posted to rec.audio.tubes
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Low Frequency Mains Noise
Ian Bell wrote: Phil Allison wrote: "Ian Bell" Thanks for the input Patrick. I know about Johnson noise and in plate resistors it is not much of an issue as it is swamped by other noise sources. What I am concerned about is excess noise which is voltage dependent. In the few places I have seen this specified it is typically 0.1uV/V so with a plate resistor with 150V across it there is possibly 15uV of noise due to this effect - enough to warrant a change of resistor type. ** No it is not - you hee hawwwing ASS Simple negation is no argument. I presently have about 65uV of noise from the circuit under test. Eliminating a 15uV component of it is worthwhile. Cheers Ian OK, you have 65uV of noise. I think you said your amp has a gain of about 15. Suppose the input signal was 4.3 mV, then output signal would be 65mV, and SNR = -60dB unweighted. Removing 15uV of the noise won't make a significant SNR improvement. If the output signal is to be fed into a typical power amp needing 1Vrms for clipping at 50W/6 ohms, then the power amp gain = 17.3x, 25dB, and 65uV of applied noise will become 1.124mV not something that would be improved by lowering to 0.87mV if 15uV was removed. 65mV of signal at the power amp becomes 1.124Vrms, enough to make 0.21 watts into a 6 ohm speaker, and if the 6 ohm speaker sensititivity is 90dB for 1 watt with 2.45Vrms, then the 0.21 watts gives about 83dB SPL and is loud enough for most ppl, and allows a considerable headroom. I suggest you work out the whole basic working of your system and amps using a block diagram with signal levels or else quit mucking around theorizing, and just build it and see if its quiet enough. After than you can tweak things to make things more silent. Or raise the signal level before feeding it to a power amp via an attenuator. Patrick Turner. |
#147
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Low Frequency Mains Noise
Ian Bell wrote: Patrick Turner wrote: Phil Allison wrote: "Patrick Turner" Phil Allison wrote: "Ian has Bats in his Belfry " One of the potential sources I have discovered is excess noise in the anode resistors. This could account for 20uV or more of the total noise. The solution seems to be to replace metal film resistors with wire wound types. ** Where does this LUNATIC get these wacky ideas from ?? Metal film resistors are near as damn it free of voltage noise - noise from the valve will always be waaaay higher . Suppose noise generated by the V1 tube as 30uV at the output. If total noise was 50uV, then you have to add far more than 20uV to 30uV to get a total of 50uV, because the total of a bunch of noise sources is the sq.rt of the total of each voltage squared. Interested ppl in such noise problems are advised to study theory more deeply because its impossible for those of us who do manage to make amps with excellent SNR to spend the time to repeat all we have said in the past yet again. However, I am having trouble finding sources for 100K and 39K wire wound types at anything less than 5W rating which is something of an overkill. Do you know any good sources of high value low wattage wire wound resistors (preferable non-inductive of course)? ** ROTFLMAO So impolite Phil, but I can see why you are laughing when there are sources of highish values of wire wound around. ** Not what I was laughing at - the bit about " non-inductively wound was very funny. How much L does it take to make a 100 kohm, WW resistor have say 101 Kohms of impedance at 20 kHz ?? The answer is 113 mH !!!!!!! The resistance wire would have to be wound on a Mu-Metal core to get such a value. Do the math. I've never noticed a hugely worrying amount of L in higher value wire wound R. Then there is is the self capacitance of the wound turns. I have not often used WW R for dc supply loads, but when I have its been with low Ra triodes so the poles caused by reactances have been at fairly high F. I have not experienced problem with stability with use of WW R for anode loads even when GNFB is used. Non inductive WW R are available, with turns wound in two directions to cancel out the inductance, but I've only ever seen low value types, never high values. Let me see now, XL of 0.113H at 20kHz = 0.113 x 20,000 x 6.28 = approx 15kohms. So the Z (R + L) would be only very slightly greater than the 100k at 1 kHz. But there are lots of turns. I've never bothered to measure such things. Patrick Turner. ..... Phil Morgan did these tests and the results are in his book. He concluded that for 10K the inductance is negligible and the equivalent parallel capacitance is about 3pF. Low resistance values have high inductances because of the use of thicker wire. You are not quite correct. Low WW R may have L which can affect circuit performance when used in speaker crossovers or series current FB resistors between source and load or 0V in SS amps. The amount of L for a low value R is lower than for a high value R. The actual R is always taken to be in series with the amount of L, but the full model of a WW R needs your inspection. There are far more turns in a 47k WW R than in a 4r7 resistance. L is higher in the 47k, but the series R is enough so that the L does not significantly increase the load impedance driven by the active device, so the response stays flat at least between dc and 20kHz. In a 0.22 source or emitter resistance in an SS amp, the small amount of L in such a low impedance circuit can mean the impedance at say 500kHz is rising and inductive and can cause oscillations in the circuit. The answer is to use non inductive WW resistances which are sold at many outlets. I've never seen a non inductive 47k R, but probably because there is no need. Patrick Turner. Cheers IAn |
#148
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Low Frequency Mains Noise
Ian Bell wrote: Patrick Turner wrote: Ian Bell wrote: Patrick Turner wrote: Ian Bell wrote: Patrick Turner wrote: snip 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. One of the potential sources I have discovered is excess noise in the anode resistors. This could account for 20uV or more of the total noise. The solution seems to be to replace metal film resistors with wire wound types. However, I am having trouble finding sources for 100K and 39K wire wound types at anything less than 5W rating which is something of an overkill. Do you know any good sources of high value low wattage wire wound resistors (preferable non-inductive of course)? Cheers Ian Suppose you had 30uV of noise due to the input tube at the output of your amp with gain = 15x. And total noise = 50uV. Say you have Ra of the input tube = 20k, and the load resistor for dc in parallel to the following stage bias R might be 50k. The 50k 20Hz ro 20k noise can be calculated, but the its shunted by Ra = 20k and thus attenuated. The excess noise would also be shunted, but unlikely to be as high as the V1 tube noise, even if its a poor quality R. Its the value of R in ohms which gives rise to noise, and usually 90% of the noise at the output of a mic amp is due to the broadand noise of V1, and all following R and tubes have little contribution unless the output of V1 is a tiny voltage. I think you should just build it and then try things to make it silent. Wire wound would appear to be blameless, and getting a high value one may mean you series a few. A 47k WW type will at least make the predicted amount of noise because its the ohms than make the noise. Any other type of R, metal film, carbon film also will make similar noise you should find unless they are faulty. Read up from RDH4 about noise and equivalent input resistance and noise in R and summing of noise voltages. Thanks for the input Patrick. I know about Johnson noise and in plate resistors it is not much of an issue as it is swamped by other noise sources. What I am concerned about is excess noise which is voltage dependent. In the few places I have seen this specified it is typically 0.1uV/V so with a plate resistor with 150V across it there is possibly 15uV of noise due to this effect - enough to warrant a change of resistor type. Are you saying that regular metal film resistors do not suffer from excess noise? I've never noticed it in amps i have built. If I'd found that the noise measurements didn't seem to add up, then I'd have been the one to reason why. I've usually used Welwyn or Beyshlag metal film R for most circuits. Noise is negligible. I'll check out Welwyn and Beyshlag specs, thanks Cheers Noise is mainly the product of the resistance value. It should not matter what the R is made from. If properly made from any resistive material the number of ohms is the main issue, then temperature. I don't expect Welwyn or Beyshlag or Mills or Cadock or anything else from the Vishay Resistor Mafia to be much different. Metal film do have low noise, and noise below old fashioned carbon composition types. I have a box full ot NOS from the mid 1930s which are carbon rods with brass end shells clamped on and painted. They are in good condition but I doubt they will be noiser than later carbon compostion types which were notorious for change of value and moisture ingress and chemical corrosion and decomposition over time. Quad used these horrible R in the Quad-II and 22 control units. All may have been fine when installed. I'm sure Peter Walker would have checked all this out. But maybe they were not so quiet after 55 years... The circuit resistances in most old ancient tube amps including Quad junk and others was always on the high side. EG, Quad 22 volume control is 500k. Using say 100k instead of 1M to bias a tube reduces noise by 1/3.16, but is true only if there isn't anything else shunting such R. Noise in smaller R is proportional to 1 / sq.rt of the reduction of resistance. Or if you had 1uV noise in 1k for a given bandwidth, then noise with 10k = 3.16uV, 100k gives 10uV, and 1M gives 31.6uV. 10M gives 100uV, and is a typical value used to bias a tube with grid leak biasing as in a radio. But there is usually some other R shunting the 10M, like a 1M volume control, so noise is less at the output. Patrick Turner. Patrick Turner. Cheers Ian Patrick Turner. |
#149
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Low Frequency Mains Noise
Ian Bell wrote: Ian Bell wrote: Patrick Turner wrote: Ian Bell wrote: Patrick Turner wrote: Ian Bell wrote: Patrick Turner wrote: snip snip, Read up from RDH4 about noise and equivalent input resistance and noise in R and summing of noise voltages. Thanks for the input Patrick. I know about Johnson noise and in plate resistors it is not much of an issue as it is swamped by other noise sources. What I am concerned about is excess noise which is voltage dependent. In the few places I have seen this specified it is typically 0.1uV/V so with a plate resistor with 150V across it there is possibly 15uV of noise due to this effect - enough to warrant a change of resistor type. Are you saying that regular metal film resistors do not suffer from excess noise? I've never noticed it in amps i have built. If I'd found that the noise measurements didn't seem to add up, then I'd have been the one to reason why. I've usually used Welwyn or Beyshlag metal film R for most circuits. Noise is negligible. I'll check out Welwyn and Beyshlag specs, thanks Cheers IAn Welwyn MFR5 types specify a maximum excess noise of 0.1uV/v per decade of frequency. I have been unable to find a spec for this parameter on any of type of theirs other than the MFR series. I have looked at several Vishay (Beyschlag) data sheets and the best they can do is to say 'low noise' whatever that means. So I am still unconvinced that metal film resistors do not produce a significant amount of excess noise for low level low noise applications. From the data you have seen, what is the worst case amount of noise you coud expect in your circuit? What happens to noise when you change resistance brands/types in your circuit? Ya gotta try things. Patrick Turner. |
#150
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Low Frequency Mains Noise
Phil Allison wrote:
"Ian Bell = utterly STUPID ****WIT " One of the potential sources I have discovered is excess noise in the anode resistors. This could account for 20uV or more of the total noise. The solution seems to be to replace metal film resistors with wire wound types. ** Where does this LUNATIC get these wacky ideas from ?? Metal film resistors are near as damn it free of voltage noise Are they? Most metal film resistor suppliers that actually bother to spec this usually put a figure of about 0.1uV/V for excess noise. ** What measurement bandwidth - eh ?? What resistance value - eh ?? Got no ****ing clue - have you. You ****ING **** WIT Sounds like you are back pedalling, Phil. You of all people will know exactly how excess noise is specified (which includes the bandwidth). ** Then YOU need to post the link - ****HEAD. Since that is the ONLY evidence you have. This is not a trial in court - I don't need to post 'evidence' it was simply a request for information. As a said before, show me a manufacturer that quotes less. ** The figure you quoted ( without ANY kind of link or reference ) is simply not a spec at all. Really, well the Welwyn metal film resistors Patrick recommended can be found he http://www.welwyn-tt.co.uk/products/...&Submit=Search Check out the pdf file for their MFR range which states simply 0.1uV/V max per decade. FInd me one significantly better than that and I'll happily use it. Cheers Ian ..... Phil |
#151
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Low Frequency Mains Noise
Phil Allison wrote:
"Ian Bell = LIAR " Thanks for the input Patrick. I know about Johnson noise and in plate resistors it is not much of an issue as it is swamped by other noise sources. What I am concerned about is excess noise which is voltage dependent. In the few places I have seen this specified it is typically 0.1uV/V so with a plate resistor with 150V across it there is possibly 15uV of noise due to this effect - enough to warrant a change of resistor type. ** No it is not - you hee hawwwing ASS Simple negation is no argument. ** An totally unsupported assertion is NOT a case and requires NO DISPROOF !! I presently have about 65uV of noise from the circuit under test. Eliminating a 15uV component of it is worthwhile. ** Another ****ING RIDICULOUS unsupported assertion = typical Bell puke. FYI, you arrogant ****head: Noise voltages DO NOT ADD !!! No, their powers do. I made no statement either way about how they add. Cheers Ian |
#152
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Low Frequency Mains Noise
Patrick Turner wrote:
Ian Bell wrote: Phil Allison wrote: "Ian Bell" Thanks for the input Patrick. I know about Johnson noise and in plate resistors it is not much of an issue as it is swamped by other noise sources. What I am concerned about is excess noise which is voltage dependent. In the few places I have seen this specified it is typically 0.1uV/V so with a plate resistor with 150V across it there is possibly 15uV of noise due to this effect - enough to warrant a change of resistor type. ** No it is not - you hee hawwwing ASS Simple negation is no argument. I presently have about 65uV of noise from the circuit under test. Eliminating a 15uV component of it is worthwhile. Cheers Ian OK, you have 65uV of noise. I think you said your amp has a gain of about 15. Suppose the input signal was 4.3 mV, then output signal would be 65mV, and SNR = -60dB unweighted. Removing 15uV of the noise won't make a significant SNR improvement. Of course not. But it is just one of two such sources and I am simply taking your recommendation of identifying each source in turn and addressing them in turn. Cheers Ian If the output signal is to be fed into a typical power amp needing 1Vrms for clipping at 50W/6 ohms, then the power amp gain = 17.3x, 25dB, and 65uV of applied noise will become 1.124mV not something that would be improved by lowering to 0.87mV if 15uV was removed. 65mV of signal at the power amp becomes 1.124Vrms, enough to make 0.21 watts into a 6 ohm speaker, and if the 6 ohm speaker sensititivity is 90dB for 1 watt with 2.45Vrms, then the 0.21 watts gives about 83dB SPL and is loud enough for most ppl, and allows a considerable headroom. I suggest you work out the whole basic working of your system and amps using a block diagram with signal levels or else quit mucking around theorizing, and just build it and see if its quiet enough. After than you can tweak things to make things more silent. That is EXACTLY what I have done. The thing is on my bench now and the output noise I quoted is as measured. You recommended I identify each noise source and tackle them in turn which is just what I am trying to do. I have fixed the low frequency noise as described in other posts and now I am looking at other sources. Excess noise is just one of them. From looking at metal film resistor specs it seemed they could be a contributory factor and that wirewound types would be significantly quieter. The only problem is finding them in the high values I need; hence my original question on this topic, to which you and others replied either that metal film resistors are not noisy or that the noise they contribute is not significant. Cheers Ian Or raise the signal level before feeding it to a power amp via an attenuator. Patrick Turner. |
#153
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Low Frequency Mains Noise
Patrick Turner wrote:
Ian Bell wrote: Patrick Turner wrote: Ian Bell wrote: Patrick Turner wrote: Ian Bell wrote: Patrick Turner wrote: snip 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. One of the potential sources I have discovered is excess noise in the anode resistors. This could account for 20uV or more of the total noise. The solution seems to be to replace metal film resistors with wire wound types. However, I am having trouble finding sources for 100K and 39K wire wound types at anything less than 5W rating which is something of an overkill. Do you know any good sources of high value low wattage wire wound resistors (preferable non-inductive of course)? Cheers Ian Suppose you had 30uV of noise due to the input tube at the output of your amp with gain = 15x. And total noise = 50uV. Say you have Ra of the input tube = 20k, and the load resistor for dc in parallel to the following stage bias R might be 50k. The 50k 20Hz ro 20k noise can be calculated, but the its shunted by Ra = 20k and thus attenuated. The excess noise would also be shunted, but unlikely to be as high as the V1 tube noise, even if its a poor quality R. Its the value of R in ohms which gives rise to noise, and usually 90% of the noise at the output of a mic amp is due to the broadand noise of V1, and all following R and tubes have little contribution unless the output of V1 is a tiny voltage. I think you should just build it and then try things to make it silent. Wire wound would appear to be blameless, and getting a high value one may mean you series a few. A 47k WW type will at least make the predicted amount of noise because its the ohms than make the noise. Any other type of R, metal film, carbon film also will make similar noise you should find unless they are faulty. Read up from RDH4 about noise and equivalent input resistance and noise in R and summing of noise voltages. Thanks for the input Patrick. I know about Johnson noise and in plate resistors it is not much of an issue as it is swamped by other noise sources. What I am concerned about is excess noise which is voltage dependent. In the few places I have seen this specified it is typically 0.1uV/V so with a plate resistor with 150V across it there is possibly 15uV of noise due to this effect - enough to warrant a change of resistor type. Are you saying that regular metal film resistors do not suffer from excess noise? I've never noticed it in amps i have built. If I'd found that the noise measurements didn't seem to add up, then I'd have been the one to reason why. I've usually used Welwyn or Beyshlag metal film R for most circuits. Noise is negligible. I'll check out Welwyn and Beyshlag specs, thanks Cheers Noise is mainly the product of the resistance value. It should not matter what the R is made from. If properly made from any resistive material the number of ohms is the main issue, then temperature. I don't expect Welwyn or Beyshlag or Mills or Cadock or anything else from the Vishay Resistor Mafia to be much different. I hear what you say Patrick but Morgan Jones and the manufacturers data sheets I have seen do not support that view. For example the Johnson noise in a 20KHz bandwidth at room temperature for a 39K resistor is ABOUT 3.6uV. If it is in an anode circuit with 150V across it then the excess noise of a typical metal film resistor will be about 15uV per decade. In low voltage circuits I agree Johnson noise predominates but I am not sure it does in anode circuits. Cheers Ian Metal film do have low noise, and noise below old fashioned carbon composition types. I have a box full ot NOS from the mid 1930s which are carbon rods with brass end shells clamped on and painted. They are in good condition but I doubt they will be noiser than later carbon compostion types which were notorious for change of value and moisture ingress and chemical corrosion and decomposition over time. Quad used these horrible R in the Quad-II and 22 control units. All may have been fine when installed. I'm sure Peter Walker would have checked all this out. But maybe they were not so quiet after 55 years... The circuit resistances in most old ancient tube amps including Quad junk and others was always on the high side. EG, Quad 22 volume control is 500k. Using say 100k instead of 1M to bias a tube reduces noise by 1/3.16, but is true only if there isn't anything else shunting such R. Noise in smaller R is proportional to 1 / sq.rt of the reduction of resistance. Or if you had 1uV noise in 1k for a given bandwidth, then noise with 10k = 3.16uV, 100k gives 10uV, and 1M gives 31.6uV. 10M gives 100uV, and is a typical value used to bias a tube with grid leak biasing as in a radio. But there is usually some other R shunting the 10M, like a 1M volume control, so noise is less at the output. Patrick Turner. Patrick Turner. Cheers Ian Patrick Turner. |
#154
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Low Frequency Mains Noise
Patrick Turner wrote:
Ian Bell wrote: Ian Bell wrote: Patrick Turner wrote: Ian Bell wrote: Patrick Turner wrote: Ian Bell wrote: Patrick Turner wrote: snip snip, Read up from RDH4 about noise and equivalent input resistance and noise in R and summing of noise voltages. Thanks for the input Patrick. I know about Johnson noise and in plate resistors it is not much of an issue as it is swamped by other noise sources. What I am concerned about is excess noise which is voltage dependent. In the few places I have seen this specified it is typically 0.1uV/V so with a plate resistor with 150V across it there is possibly 15uV of noise due to this effect - enough to warrant a change of resistor type. Are you saying that regular metal film resistors do not suffer from excess noise? I've never noticed it in amps i have built. If I'd found that the noise measurements didn't seem to add up, then I'd have been the one to reason why. I've usually used Welwyn or Beyshlag metal film R for most circuits. Noise is negligible. I'll check out Welwyn and Beyshlag specs, thanks Cheers IAn Welwyn MFR5 types specify a maximum excess noise of 0.1uV/v per decade of frequency. I have been unable to find a spec for this parameter on any of type of theirs other than the MFR series. I have looked at several Vishay (Beyschlag) data sheets and the best they can do is to say 'low noise' whatever that means. So I am still unconvinced that metal film resistors do not produce a significant amount of excess noise for low level low noise applications. From the data you have seen, what is the worst case amount of noise you coud expect in your circuit? 15uV per decade What happens to noise when you change resistance brands/types in your circuit? Pass, but my original idea was to substitute wirewound types because they have very much lower levels of excess noise, but I found it difficult to find 39K and 100K wirewound types that were not huge - hence my original question about sources of wirewound types. I thought I would buy some wirewound types anyway and try them but thought is was a good idea to cheack the group wisdom before parting with my cash. Cheers Ian Ya gotta try things. Patrick Turner. |
#155
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Low Frequency Mains Noise
"Ian Bell = utterly STUPID ****WIT " One of the potential sources I have discovered is excess noise in the anode resistors. This could account for 20uV or more of the total noise. The solution seems to be to replace metal film resistors with wire wound types. ** Where does this LUNATIC get these wacky ideas from ?? Metal film resistors are near as damn it free of voltage noise Are they? Most metal film resistor suppliers that actually bother to spec this usually put a figure of about 0.1uV/V for excess noise. ** What measurement bandwidth - eh ?? What resistance value - eh ?? Got no ****ing clue - have you. You ****ING **** WIT Sounds like you are back pedalling, Phil. You of all people will know exactly how excess noise is specified (which includes the bandwidth). ** Then YOU need to post the link - ****HEAD. Since that is the ONLY evidence you have. This is not a trial in court - I don't need to post 'evidence' ** Merely asking for a link to the data you are quoting. So we see it in CONTEXT - you dumb ass !!! So we can see if you are MISQUOTING or MISINTERPRETING it. ** The figure you quoted ( without ANY kind of link or reference ) is simply not a spec at all. Really, well the Welwyn metal film resistors Patrick recommended can be found he http://www.welwyn-tt.co.uk/products/...&Submit=Search Check out the pdf file for their MFR range which states simply 0.1uV/V max per decade. ** Which is not what it ACTUALLY says at all. ...... Phil |
#156
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Low Frequency Mains Noise
"Ian Bell = LIAR " I presently have about 65uV of noise from the circuit under test. Eliminating a 15uV component of it is worthwhile. ** Another ****ING RIDICULOUS unsupported assertion = typical Bell puke. FYI, you arrogant ****head: Noise voltages DO NOT ADD !!! No, their powers do. I made no statement either way about how they add. ** Yes you ****ing did !!! Do the math correctly as see what the result is. Then **** OFF - you VILE LYING PIG . ........ Phil |
#157
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Low Frequency Mains Noise
On Sun, 09 Nov 2008 08:07:26 +0000, Ian Bell
wrote: Phil Allison wrote: "Ian Bell" Phil Allison wrote: "Ian Bell" One of the potential sources I have discovered is excess noise in the anode resistors. This could account for 20uV or more of the total noise. The solution seems to be to replace metal film resistors with wire wound types. ** Where does this LUNATIC get these wacky ideas from ?? Metal film resistors are near as damn it free of voltage noise Are they? Most metal film resistor suppliers that actually bother to spec this usually put a figure of about 0.1uV/V for excess noise. ** What measurement bandwidth - eh ?? What resistance value - eh ?? Got no ****ig clue - have you. You ****ING **** WIT Sounds like you are back pedalling, Phil. You of all people will know exactly how excess noise is specified (which includes the bandwidth). I happen to have a 100K resistor in one anode which, from one manufacturers graph, shows its excess noise is 0.1V/V. As a said before, show me a manufacturer that quotes less. CHeers Ian ....... Phil Vishay sells bulk foil resistors http://www.vishay.com/company/press/...08/080507foil/ , and according to "JIS C5202 5.9" method of measurement, they are at -40db, where 0db is 1 uv/v, and I assume it is for 1Hz bandwidth, since I can't find any details of what this standard uses (without paying for it). That means the -40db would give you about .01uv/v (10 nv/v) voltage noise. My guess is that this resistor is as good as you'll get. I've been told that most wirewounds are typically -38db. Metal film resistors often use this spec, and typical values for good resistors (100kohms) are about -20 db using JIS C5202 5.9. From an article promoting Vishay resistors: http://www.planetanalog.com/features...leID=177105460 "Current noise is the bunching and releasing of electrons associated with current flow. The amount of current noise (or lack thereof) depends largely on the resistor technology employed, and it is measurable and is expressed as a function of the input voltage. The magnitude is microvolts per volt applied. A noise index is expressed in decibels, and the equation converting µV/V to dB is: dB = 20 x log (noise voltage [in µV]/DC voltage [in V]). For example, 0 dB equates to 1.0 µV/V, and 15 dB equates to 5.6 µV/V." (end of quotation) Read the article.... it answers a lot of questions, and poses some possible audio nuttyness. Current noise has a 1/f frequency distribution. Bear that in mind when you read the above article.... The frequency of the artifacts is very low, and the oscilloscope pictures suggest a problem that is really not as audibly bad as presented. Carbon resistors have "contact noise", which is an additional very significant noise. You should avoid carbon resistors, especially the composition carbon ones (cheapo resistors). The Johnson noise for the 100K resistor is about 41 nv (bw=1Hz), or about 128 nv for the decade (I don't know why manufacturers specify a decade when 1 Hz is more specific). It is wide band noise, not 1/f noise. The different frequency distributions (1/f and wideband) make judgements difficult, especially with the ear's sensitivity vs. frequency. It's going to take a lot of 1/f noise to be noticed compared to the wideband Johnson noise. Wirewound and bulk film resistors are considered best for noise, even by Phil Allison http://sound.westhost.com/project66.htm "Metal film resistors are about the best only bettered by wire wound which is a bit impractical" You must also be careful of wirewound resistors, since they can inductively pick up AC magnetic fields, especially the precision bobbin types of resistors. The resistor noise voltage generated, is on the anode circuit for your tube, if you use the input noise voltage for a typical low noise tube (12AX7), you have about 450nv (bw=1Hz) effectively at the grid. Considering typical gains of 10-100, that gives a noise (bw=1Hz) at 4.5uv to 45uv at the anode. The tube noise will completely swamp the noise of the resistor! Make sure to use the correct bandwidth when making the comparison. At the very low level signal levels you seem to want, you will probably get more satisfaction by using some of the more recent low noise op-amps, and then amplify to get the voltage levels required by your tube circuits. Vacuum tubes DO have considerable 1/f noise (Johnson, John B, "The Schottky effect in low frequency circuits," Physical Review, July 1925, pg 71.). That's 1925! Not that I have much against tube circuitry.... but they are not appropriate for low level signal amplification (IMHO). Paul G. |
#158
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Low Frequency Mains Noise
"Paul G." Wirewound and bulk film resistors are considered best for noise, even by Phil Allison http://sound.westhost.com/project66.htm "Metal film resistors are about the best only bettered by wire wound which is a bit impractical" ** No way did I suggest " bulk film " resistors had low DC voltage noise - quite then opposite, I warned specifically against them. The full quote is: " Where a resistor has significant DC voltage imposed on it in high gain circuits always use low noise types. Metal film resistors are about the best only bettered by wire wound which is a bit impractical. Avoid cermet, metal glaze, and very old carbon composition types. " FYI Cermet and "Metal Glaze" are thick or " bulk film " resistors - notorious for having high and variable amounts of DC voltage noise. ..... Phil |
#159
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Low Frequency Mains Noise
Phil Allison wrote:
"Ian Bell = utterly STUPID ****WIT " One of the potential sources I have discovered is excess noise in the anode resistors. This could account for 20uV or more of the total noise. The solution seems to be to replace metal film resistors with wire wound types. ** Where does this LUNATIC get these wacky ideas from ?? Metal film resistors are near as damn it free of voltage noise Are they? Most metal film resistor suppliers that actually bother to spec this usually put a figure of about 0.1uV/V for excess noise. ** What measurement bandwidth - eh ?? What resistance value - eh ?? Got no ****ing clue - have you. You ****ING **** WIT Sounds like you are back pedalling, Phil. You of all people will know exactly how excess noise is specified (which includes the bandwidth). ** Then YOU need to post the link - ****HEAD. Since that is the ONLY evidence you have. This is not a trial in court - I don't need to post 'evidence' ** Merely asking for a link to the data you are quoting. So we see it in CONTEXT - you dumb ass !!! So we can see if you are MISQUOTING or MISINTERPRETING it. ** The figure you quoted ( without ANY kind of link or reference ) is simply not a spec at all. Really, well the Welwyn metal film resistors Patrick recommended can be found he http://www.welwyn-tt.co.uk/products/...&Submit=Search Check out the pdf file for their MFR range which states simply 0.1uV/V max per decade. ** Which is not what it ACTUALLY says at all. ..... Phil Very helpful Phil. The sheet I saw read 'Noise. (in a decade of frequency) uV/V' and then under the column labelled 'Max' it said 0.1. Cheers Ian |
#160
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Low Frequency Mains Noise
Phil Allison wrote:
"Ian Bell = LIAR " I presently have about 65uV of noise from the circuit under test. Eliminating a 15uV component of it is worthwhile. ** Another ****ING RIDICULOUS unsupported assertion = typical Bell puke. FYI, you arrogant ****head: Noise voltages DO NOT ADD !!! No, their powers do. I made no statement either way about how they add. ** Yes you ****ing did !!! No I did not. I said eliminating 15uV component was worthwhile. Cheers Ian |
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