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#1
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? LP to PC noise artifacts problem
This isn't normal hiss and pop (I'm using a KLH TNE for that).
My current gear is an old Technics SK-1300 direct drive with a new Audio Technca AT440ML/OCC cartridge. My problem is that when I transfer to my computer, there's a pulse added once every revolution of the turntable. It's not noticeable in louder passages, but is really annoying with quieter material. I don't hear this through my computer speakers, but when I play it back on my CD player, it sounds a bit like a typewriter. I have a photo of the sound at http://dude.pawluk.com/ Can anyone determine the cause? Is it fixable, or do I simply need a new turntable? The LPs aren't warped, so that's not it. Or is it in the LP, and my gear somehow amplifies it? I ask because the occasional track, or sometimes channel, comes through without this weird noise. Thanks. |
#2
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My problem is that when I transfer to my computer, there's a pulse added
once every revolution of the turntable. It's not noticeable in louder passages, but is really annoying with quieter material. I don't hear this through my computer speakers, but when I play it back on my CD player, it sounds a bit like a typewriter. I have a photo of the sound at http://dude.pawluk.com/ Can anyone determine the cause? Is it fixable, or do I simply need a new turntable? The LPs aren't warped, so that's not it. Or is it in the LP, and my gear somehow amplifies it? I ask because the occasional track, or sometimes channel, comes through without this weird noise. If it occurs on multiple LPs, then it can't be in the LP. The fact that it occurs once per revolution means that the turntable itself is (99.9%-certainly) the culprit. My guess is that something on the bottom side of the platter is rubbing against, or striking something else, and that this is exciting vibrations in the platter which are travelling through the LP and being picked up by the stylus. It's also possible that the vibrations are being coupled from the point of impact, back through the chassis, into the tonearm, and out to the cartridge and stylus. In either case, the important thing is to figure out what's causing the rubbing or impact, and fix it. It might be something sticking down from the platter - possibly a stick-on label which has come loose? It might be that some obstruction has gotten into the direct-drive motor assembly, or there might be some sort of damage to the platter's spindle which is scraping inside the main bearing. It might even be something as simple as a lack of proper lubrication in the bearing, due to the age of the 'table. The problem may be simple enough to be fixable easily and inexpensively, or might be the result of damage to parts which are no longer available. In the latter case, replacing the 'table may be less expensive... a simple, quiet belt-drive model might be a good choice for LP-CD transcription use. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
#3
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#4
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"Dave Platt" wrote in message ... My problem is that when I transfer to my computer, there's a pulse added once every revolution of the turntable. It's not noticeable in louder passages, but is really annoying with quieter material. I don't hear this through my computer speakers, but when I play it back on my CD player, it sounds a bit like a typewriter. I have a photo of the sound at http://dude.pawluk.com/ Can anyone determine the cause? Is it fixable, or do I simply need a new turntable? The LPs aren't warped, so that's not it. Or is it in the LP, and my gear somehow amplifies it? I ask because the occasional track, or sometimes channel, comes through without this weird noise. If it occurs on multiple LPs, then it can't be in the LP. The fact that it occurs once per revolution means that the turntable itself is (99.9%-certainly) the culprit. My guess is that something on the bottom side of the platter is rubbing against, or striking something else, and that this is exciting vibrations in the platter which are travelling through the LP and being picked up by the stylus. It's also possible that the vibrations are being coupled from the point of impact, back through the chassis, into the tonearm, and out to the cartridge and stylus. In either case, the important thing is to figure out what's causing the rubbing or impact, and fix it. It might be something sticking down from the platter - possibly a stick-on label which has come loose? It might be that some obstruction has gotten into the direct-drive motor assembly, or there might be some sort of damage to the platter's spindle which is scraping inside the main bearing. It might even be something as simple as a lack of proper lubrication in the bearing, due to the age of the 'table. The problem may be simple enough to be fixable easily and inexpensively, or might be the result of damage to parts which are no longer available. In the latter case, replacing the 'table may be less expensive... a simple, quiet belt-drive model might be a good choice for LP-CD transcription use. -- Dave Platt I would add that if it is audible, one should probably see the artifact in the strobe pattern once each revolution. Mark Z. |
#5
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On Tue, 04 Jan 2005 10:22:13 +0000, Laurence Payne
wrote: On Tue, 04 Jan 2005 05:44:28 -0000, (Dave Platt) wrote: The fact that it occurs once per revolution means that the turntable itself is (99.9%-certainly) the culprit. My guess is that something on the bottom side of the platter is rubbing against, or striking something else, and that this is exciting vibrations in the platter which are travelling through the LP and being picked up by the stylus. The waveform picture isn't typical of mechanical noise. Certainly not on a direct-drive table - it may be a problem with 'hunting' in the speed-control servo. On a belt-drive, you'd suspect a cyclic friction problem causing a 'twang' in the belt. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
#6
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Thanks guys, but I don't think it's mechanical.
I don't see anything on the strobe (looks rock solid to these old eyes) and I can't feel anything with my fingertips nor the back of my hand. ( I also don't hear the sound when recording, but that's my crappy computer setup :-) Note that this occurs with two different cartridges, so that's not it either. Looking at the waveforms, what I seem to have is a 433 Hz carrier frequency that's amplitude-modulated at 33-1/3 rpm. Where might the carrier frequency come from? Does anyone have a link to a tech manual for my Technics SL-1300? I'm going to try to find a TT I can borrow to see if it could be something external that's feeding into the signal path, although the 33- 1/3 modulation pretty much says it's the TT, as Dave said. Thanks. |
#7
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Could the magnetic fields of the TT motor somehow be coupling
into the sound electronics? How close is the computer to the TT? Try moving it further away if you can. Just a W.A.G. Interesting problem - I'd like to know what the real reason is when you find out. --RY Anti-spam writes: Thanks guys, but I don't think it's mechanical. I don't see anything on the strobe (looks rock solid to these old eyes) and I can't feel anything with my fingertips nor the back of my hand. ( I also don't hear the sound when recording, but that's my crappy computer setup :-) Note that this occurs with two different cartridges, so that's not it either. Looking at the waveforms, what I seem to have is a 433 Hz carrier frequency that's amplitude-modulated at 33-1/3 rpm. Where might the carrier frequency come from? Does anyone have a link to a tech manual for my Technics SL-1300? I'm going to try to find a TT I can borrow to see if it could be something external that's feeding into the signal path, although the 33- 1/3 modulation pretty much says it's the TT, as Dave said. Thanks. -- Randy Yates Sony Ericsson Mobile Communications Research Triangle Park, NC, USA , 919-472-1124 |
#8
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Anti-spam wrote:
Looking at the waveforms, what I seem to have is a 433 Hz carrier frequency that's amplitude-modulated at 33-1/3 rpm. You seem to be confused between rpm and Hz. That high frequency wave looks like 10Hz or so. Try some more tests: With the turntable stationary, lower the arm onto an old record. Check the output while stomping about on the floor or tapping the plinth to see what resonates at 10Hz or so. Does the turntable play at 45rpm? Try that and see what happens. -- Eiron. |
#9
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#10
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^ writes:
[...] I have a photo of the sound at http://dude.pawluk.com/ Could you by any chance post the actual .wav file there as well? Just a short clip (5 seconds?) would be great. -- % Randy Yates % "Though you ride on the wheels of tomorrow, %% Fuquay-Varina, NC % you still wander the fields of your %%% 919-577-9882 % sorrow." %%%% % '21st Century Man', *Time*, ELO http://home.earthlink.net/~yatescr |
#11
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04 Jan 2005 11:26 AM Eiron wrote:
You seem to be confused between ... Geez, where was my head - the high frequency in the envelope is around 7-1/2 Hz. Stomping on the floor, tapping the platform the TT is on had no effect. The computer is about 4 feet away from the TT. At 45 RPM, the modulations are still there, but there are only about 10 of the high frequency waves inside each (instead of about 13). The higher frequency is still about 7-1/2 Hz. And I'm still totally mystified. |
#12
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^ writes:
This isn't normal hiss and pop (I'm using a KLH TNE for that). My current gear is an old Technics SK-1300 direct drive with a new Audio Technca AT440ML/OCC cartridge. My problem is that when I transfer to my computer, there's a pulse added once every revolution of the turntable. It's not noticeable in louder passages, but is really annoying with quieter material. I don't hear this through my computer speakers, but when I play it back on my CD player, it sounds a bit like a typewriter. I have a photo of the sound at http://dude.pawluk.com/ Can anyone determine the cause? Is it fixable, or do I simply need a new turntable? The LPs aren't warped, so that's not it. Or is it in the LP, and my gear somehow amplifies it? I ask because the occasional track, or sometimes channel, comes through without this weird noise. Thanks. Here's an idea: You say the record isn't warped, but no record is perfectly flat, and since the amplitude is low, what you're seeing IS a warp. You don't hear it over your computer speakers because they have no low-frequency response and most of this energy is in the lower frequencies, and you hear it on the CD player since you're (presumably) playing that on a bigger, better stereo system. If that doesn't sound like it, please put the wave file (or mp3 or whatever) up on your site. -- % Randy Yates % "Midnight, on the water... %% Fuquay-Varina, NC % I saw... the ocean's daughter." %%% 919-577-9882 % 'Can't Get It Out Of My Head' %%%% % *El Dorado*, Electric Light Orchestra http://home.earthlink.net/~yatescr |
#13
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On Tue, 04 Jan 2005 19:24:16 -0800, Anti-spam wrote:
04 Jan 2005 11:26 AM Eiron wrote: You seem to be confused between ... Geez, where was my head - the high frequency in the envelope is around 7-1/2 Hz. Stomping on the floor, tapping the platform the TT is on had no effect. The computer is about 4 feet away from the TT. At 45 RPM, the modulations are still there, but there are only about 10 of the high frequency waves inside each (instead of about 13). The higher frequency is still about 7-1/2 Hz. And I'm still totally mystified. That sounds awfully like the main arm/cartridge resonance, but seriously underdamped in this case. With a heavy arm and a high-compliance cartridge, you could certainly get a 7.5Hz resonance, but it seems to be continuously excited, which is odd. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
#14
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You're right about the speakers and hearing the artifact, but the same
waveform is inserted into other LPs indentically and I find it hard to believe they're all warped precisely the same way :-) I've uploaded a sample as WAV and AIFF files, clipped to 30 seconds/5 meg to make downloading easier (and you wouldn't want ot hear much of Mayall's singing on this cut anyhow). Teh link is http://dude.pawluk.com/ Thanks. Randy Yates wrote: Here's an idea: You say the record isn't warped, but no record is perfectly flat, and since the amplitude is low, what you're seeing IS a warp. You don't hear it over your computer speakers because they have no low-frequency response and most of this energy is in the lower frequencies, and you hear it on the CD player since you're (presumably) playing that on a bigger, better stereo system. |
#15
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Stewart Pinkerton wrote:
but it seems to be continuously excited, which is odd. Yes indeed. |
#16
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You seem to be confused between ...
Geez, where was my head - the high frequency in the envelope is around 7-1/2 Hz. Aha. This suggests to me that the waves you are observing on the scope are a secondary effect... they're the result of a low-frequency mechanical resonance (perhaps the platter suspension, perhaps the tonearm / cartridge compliance resonance). Such low-frequency signals are not going to be audible by themselves. My guess is that you do have some sort of mechanical obstruction which is snagging the platter once per revolution. Each time this happens, the platter is jolted... this causes the low-frequency wobbling you observe on the scope, and the higher-frequency sound created by the impact is being carried through the platter and picked up by the stylus to create the "typewriter-like" sound that you hear. If you run a spectrogram on the leading edge of each 7.5 Hz set, I suspect that you'll see that there's a brief burst of higher-frequency noise included. Stomping on the floor, tapping the platform the TT is on had no effect. The computer is about 4 feet away from the TT. At 45 RPM, the modulations are still there, but there are only about 10 of the high frequency waves inside each (instead of about 13). The higher frequency is still about 7-1/2 Hz. 10 cycles at 7.5 Hz would be 1.3 seconds, which is the period of a 45 RPM rotation. Apparently the low-frequency oscillation isn't having time to damp down all the way before the next impulse re-excites it. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
#17
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Dave Platt wrote:
Aha. My guess is that you do have some sort of mechanical obstruction which is snagging the platter once per revolution. Each time this happens, the platter is jolted... this causes the low-frequency wobbling you observe on the scope, and the higher-frequency sound created by the impact is being carried through the platter and picked up by the stylus to create the "typewriter-like" sound that you hear. Thanks, this sounds reasonable so I guess it's time to take the TT apart and see what's going on. And thanks to all of you, I really appreciate the feedback. |
#19
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Ding! It's a hole-centering problem. The high-frequency oscillation is your
tonearm's natural radial resonant frequency. -- % Randy Yates % "Maybe one day I'll feel her cold embrace, %% Fuquay-Varina, NC % and kiss her interface, %%% 919-577-9882 % til then, I'll leave her alone." %%%% % 'Yours Truly, 2095', *Time*, ELO http://home.earthlink.net/~yatescr |
#20
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Randy Yates wrote:
Ding! It's a hole-centering problem. The high-frequency oscillation is your tonearm's natural radial resonant frequency. Is there any way for me to get rid of that with the equipment I have, an adjustment I can make or some sort of 'tone-arm-natural-radial-frequency-damper'? The SL-1300 arm doesn't look too replaceable, so my other option appears to be a turntable with a less-tone-arm-natural-radial-frequency-susceptible tone arm. Any suggestions, remembering that all I want to do is digitize some LPs then get outta here without spending a bundle :-) Thanks. |
#21
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"Anti-spam" wrote in message ... Randy Yates wrote: Ding! It's a hole-centering problem. The high-frequency oscillation is your tonearm's natural radial resonant frequency. Is there any way for me to get rid of that with the equipment I have, an adjustment I can make or some sort of 'tone-arm-natural-radial-frequency-damper'? The SL-1300 arm doesn't look too replaceable, so my other option appears to be a turntable with a less-tone-arm-natural-radial-frequency-susceptible tone arm. Any suggestions, remembering that all I want to do is digitize some LPs then get outta here without spending a bundle :-) I couldn't load the picture you posted, but it certainly seems like the solution should be obvious without having to resort to a lot of esoteric solutions. Tonearm/cartridge resonance is usually only a big problem when there's a big warp in the record, or if the platter is wobbling, or the unit is being struck or shaken. Or when playing the Telarc recording of Tchaikovsky's 1812 Overture. If the hole-centering problem, referred to above, is what I think it is, I should think tonearm resonance would be the least of your worries. The "wow" factor would be unbearable. Direct-drive turntables are pretty simple, mechanically, and should not be making any noise as severe as you describe if working properly, regardless of tonearm resonance. This sounds as though it's much more severe than anything I've ever seen from a tonearm/pickup compatibility problem. Does the platter turn freely and quietly when the unit is turned off? Have you lifted the platter off to see if any foreign object has gotten lodged between the motor windings and the magnet assembly? Is the thrust bearing still present? If not, the platter will sit too low, and probably scrape on the deck. A drop of heavy machine oil on the spindle might be a good idea if it hasn't had any for a decade or two. You might have a cartridge alignment problem. When a record is playing, is the stylus the only object touching the record (from the top)? Or does the cartridge body occasionally scrape the record's surface? Is the tracking force set correctly? We used to have a bunch of these at a radio station I worked at, and they were not at all temperamental. Just some thoughts... |
#22
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Ding!
If correct, I AM inpressed. I don't remember though if it only did it on the one record. After reading your reply Randy, I was thinking about the OP's jpg. Seems to me that anything which made more of a "tick" rather than a "rub" against the platter might create artifact like that seen. Mark Z. "Randy Yates" wrote in message ... Ding! It's a hole-centering problem. The high-frequency oscillation is your tonearm's natural radial resonant frequency. -- % Randy Yates % "Maybe one day I'll feel her cold embrace, %% Fuquay-Varina, NC % and kiss her interface, %%% 919-577-9882 % til then, I'll leave her alone." %%%% % 'Yours Truly, 2095', *Time*, ELO http://home.earthlink.net/~yatescr |
#23
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"Mark D. Zacharias" writes:
Ding! If correct, Yeah, well that's TBD! I AM inpressed. Don't be until it's proven, because I could (again) be WRONG. I don't remember though if it only did it on the one record. After reading your reply Randy, I was thinking about the OP's jpg. Seems to me that anything which made more of a "tick" rather than a "rub" against the platter might create artifact like that seen. Yes, I take your point. I too realized after posting that a spindle offset would not have so much of an impulsive shape. So again I'm baffled. Note that in my bafflement I'm assuming the OP was intelligent enough and observant enough to see if there were obvious physical defects on the vinyl such as a warped groove and thus am assuming there are no such defects. --RY Mark Z. "Randy Yates" wrote in message ... Ding! It's a hole-centering problem. The high-frequency oscillation is your tonearm's natural radial resonant frequency. -- % Randy Yates % "Maybe one day I'll feel her cold embrace, %% Fuquay-Varina, NC % and kiss her interface, %%% 919-577-9882 % til then, I'll leave her alone." %%%% % 'Yours Truly, 2095', *Time*, ELO http://home.earthlink.net/~yatescr -- Randy Yates Sony Ericsson Mobile Communications Research Triangle Park, NC, USA , 919-472-1124 |
#24
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Karl, I'm with you - after posting I again realized the hole-centering
theory is probably wrong. --RY "Karl Uppiano" writes: "Anti-spam" wrote in message ... Randy Yates wrote: Ding! It's a hole-centering problem. The high-frequency oscillation is your tonearm's natural radial resonant frequency. Is there any way for me to get rid of that with the equipment I have, an adjustment I can make or some sort of 'tone-arm-natural-radial-frequency-damper'? The SL-1300 arm doesn't look too replaceable, so my other option appears to be a turntable with a less-tone-arm-natural-radial-frequency-susceptible tone arm. Any suggestions, remembering that all I want to do is digitize some LPs then get outta here without spending a bundle :-) I couldn't load the picture you posted, but it certainly seems like the solution should be obvious without having to resort to a lot of esoteric solutions. Tonearm/cartridge resonance is usually only a big problem when there's a big warp in the record, or if the platter is wobbling, or the unit is being struck or shaken. Or when playing the Telarc recording of Tchaikovsky's 1812 Overture. If the hole-centering problem, referred to above, is what I think it is, I should think tonearm resonance would be the least of your worries. The "wow" factor would be unbearable. Direct-drive turntables are pretty simple, mechanically, and should not be making any noise as severe as you describe if working properly, regardless of tonearm resonance. This sounds as though it's much more severe than anything I've ever seen from a tonearm/pickup compatibility problem. Does the platter turn freely and quietly when the unit is turned off? Have you lifted the platter off to see if any foreign object has gotten lodged between the motor windings and the magnet assembly? Is the thrust bearing still present? If not, the platter will sit too low, and probably scrape on the deck. A drop of heavy machine oil on the spindle might be a good idea if it hasn't had any for a decade or two. You might have a cartridge alignment problem. When a record is playing, is the stylus the only object touching the record (from the top)? Or does the cartridge body occasionally scrape the record's surface? Is the tracking force set correctly? We used to have a bunch of these at a radio station I worked at, and they were not at all temperamental. Just some thoughts... -- Randy Yates Sony Ericsson Mobile Communications Research Triangle Park, NC, USA , 919-472-1124 |
#25
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Do you have an email address I can use to communicate with you directly?
--RY Anti-spam writes: Randy Yates wrote: Ding! It's a hole-centering problem. The high-frequency oscillation is your tonearm's natural radial resonant frequency. Is there any way for me to get rid of that with the equipment I have, an adjustment I can make or some sort of 'tone-arm-natural-radial-frequency-damper'? The SL-1300 arm doesn't look too replaceable, so my other option appears to be a turntable with a less-tone-arm-natural-radial-frequency-susceptible tone arm. Any suggestions, remembering that all I want to do is digitize some LPs then get outta here without spending a bundle :-) Thanks. -- Randy Yates Sony Ericsson Mobile Communications Research Triangle Park, NC, USA , 919-472-1124 |
#26
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Karl Uppiano wrote:
"Anti-spam" wrote in message ... Randy Yates wrote: Ding! It's a hole-centering problem. The high-frequency oscillation is your tonearm's natural radial resonant frequency. Is there any way for me to get rid of that with the equipment I have, an adjustment I can make or some sort of 'tone-arm-natural-radial-frequency-damper'? The SL-1300 arm doesn't look too replaceable, so my other option appears to be a turntable with a less-tone-arm-natural-radial-frequency-susceptible tone arm. Any suggestions, remembering that all I want to do is digitize some LPs then get outta here without spending a bundle :-) I couldn't load the picture you posted, but it certainly seems like the solution should be obvious without having to resort to a lot of esoteric solutions. Tonearm/cartridge resonance is usually only a big problem when there's a big warp in the record, or if the platter is wobbling, or the unit is being struck or shaken. Or when playing the Telarc recording of Tchaikovsky's 1812 Overture. If the hole-centering problem, referred to above, is what I think it is, I should think tonearm resonance would be the least of your worries. The "wow" factor would be unbearable. Direct-drive turntables are pretty simple, mechanically, and should not be making any noise as severe as you describe if working properly, regardless of tonearm resonance. This sounds as though Does the platter turn freely and quietly when the unit is turned off? Have you lifted the platter off to see if any foreign object has gotten lodged between the motor windings and the magnet assembly? Is the thrust bearing still present? If not, the platter will sit too low, and probably scrape on the deck. A drop of heavy machine oil on the spindle might be a good idea if it hasn't had any for a decade or two. It's all fine. I took the platter off, too, and there are no signs of rubbing, no objects. I did put a drop of light machine oil on the bearing and there's no difference. You might have a cartridge alignment problem. When a record is playing, is the stylus the only object touching the record (from the top)? Or does the cartridge body occasionally scrape the record's surface? Is the tracking force set correctly? No, yes, not even close, absolutely and the cartridge rides like a dream. |
#27
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If correct, I AM inpressed. I don't remember though if it only did it on
the one record. Multiple records in varying degrees. |
#28
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Anti-spam writes:
If correct, I AM inpressed. I don't remember though if it only did it on the one record. Multiple records in varying degrees. Exactly how are you interfacing the TT's L/R outputs to your soundcard? -- Randy Yates Sony Ericsson Mobile Communications Research Triangle Park, NC, USA , 919-472-1124 |
#29
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Randy Yates wrote:
Do you have an email address I can use to communicate with you directly? "dude" and that's at "tude.com" (hate spam). However, your eccentric hole theory may be right. I just tried a quieter LP (Julian Bream plays Bach). The artifact is still there at the beginning, although not quite as strong. It's also worse in the left channel than in the right, unlike with the Mayall record. The artifact essentially disappears by 6 minutes into the record. I can see it since I know what I'm looking for, but can't hear it on the better playback system. 12 minutes into the LP it's almost invisible in the waveform, too. Side thrust from an off-center hole would do that, wouldn't it - more force at the larger distance from the center? I also tried changing the tracking force, doubling it from the recommended "optimal" 1.25 g, but this had no effect. And the funny thing is that I never heard this when I played the LPs directly 15 years ago so maybe there is something else ... |
#30
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Randy Yates wrote:
Exactly how are you interfacing the TT's L/R outputs to your soundcard? I run through a Radio Shack preamp, and have tried two ways from there. My normal setup is through a KLH Transient Noise Eliminator, then a Vidicraft switcher then on to the sound input on my Macintosh. Being a suspicious soul, I tried going directly to the computer from the preamp but this made no difference whatsoever. The turntable also gets it's power from computer back-up power supply that eliminates noise, but bypassing this also had no effect. Surely it couldn't be that cheap Radio Shack box, could it? |
#31
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No, yes, not even close, absolutely and the cartridge rides like a dream.
Hmmm... If tonearm resonance is the issue, you should clearly see "gyrations" of the cartridge with respect to the stylus as it tracks the record. |
#32
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Karl Uppiano wrote:
No, yes, not even close, absolutely and the cartridge rides like a dream. Hmmm... If tonearm resonance is the issue, you should clearly see "gyrations" of the cartridge with respect to the stylus as it tracks the record. How about making a fluid damper from blu-tak, paperclips and honey? Why does the problem disappear after 6 minutes? Is the arm or its wires catching on something at certain positions? -- Eiron. |
#33
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Eiron wrote:
Why does the problem disappear after 6 minutes? Is the arm or its wires catching on something at certain positions? The amplitude of the pulse just gets lower and lower as the arm moves toward the center, which seems reasonable if it is being caused by an off-center hole. The "throwing arm" is longer at the edge of the platter, gets shorter as you move in. Nothing is catching on anything. |
#34
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"Anti-spam" wrote in message ... Eiron wrote: Why does the problem disappear after 6 minutes? Is the arm or its wires catching on something at certain positions? The amplitude of the pulse just gets lower and lower as the arm moves toward the center, which seems reasonable if it is being caused by an off-center hole. The "throwing arm" is longer at the edge of the platter, gets shorter as you move in. Nothing is catching on anything. What off-center hole are we talking about? Because I can practically guarantee a record with an off-center hole will produce unbearable wow long before it begins to excite enough cartridge/tonearm resonance to be a problem. Not every record would exhibit this defect, either. Furthermore, this type of defect would not change with radius. If we're talking about a loose, worn platter spindle (motor shaft), the platter might wobble, causing a periodic "clunk-clunk-clunk". The motion would be mostly vertical, producing out-of-phase noise between the two channels. The "throwing arm" would get shorter with radius in this case. It wouldn't be exactly at the rotational frequency, though. Heavy oil or grease might help a bit, as I suggested earlier. I'm wondering if the noise is being caused by an impending failure in the motor drive electronics. At this age, the motor drive electronics could be failing. If power supply bypass capacitors were starting to go, you might end up with a once-per-revolution pop or click induced into the phono pickup wiring, or even through the power or ground cable (the green or black tonearm ground wire *is* attached to the preamp, right?). Is the noise present when the platter is rotating, but with the tonearm in "cue"? |
#35
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Why does the problem disappear after 6 minutes?
Is the arm or its wires catching on something at certain positions? The amplitude of the pulse just gets lower and lower as the arm moves toward the center, which seems reasonable if it is being caused by an off-center hole. The "throwing arm" is longer at the edge of the platter, gets shorter as you move in. Nothing is catching on anything. Another possibility... perhaps the 'table has a loose spindle bearing, and the platter is able to rock or wobble as it turns? That might produce results similar to an off-center hole in the LP, but would affect multiple LPs. An off-center hole could cause (or excite) the low-frequency oscillations in the suspension or arm/stylus system, but I have difficulty seeing how an off-center hole could cause an audible typerwriter-like "tick" sound in the audio. A loose bearing, with a platter that wobbles with its rotation and then actually rocks from side to side, might do both? Another possibility to consider is that there might be some defect in the direct-drive servo speed-tracking system. Servo-drive 'tables sometimes have a speed sensor, which tracks the rotation rate of the platter by optical or magnetic means. If there were damage to whatever optical or magnetic marking is being sensed, the servo controller might try to make a sudden change in the platter's rotation speed once per revolution. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
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Thanks to you all for trying to help solve my problem.
I finally gave up and am simply processing the weird signal with software. I'm running a piece of Mac software called the Hyper Engine with a module called Ray Gun Pro. This has what seems to be a pretty good "rumble" filter, a low cut filter. I set the cut frequency to 20 Hz and ran my tracks through it with pretty good results. A further benefit is that it also has a noise/click/pop/hiss filter that I set at a mild setting to remove the last of the hiss and pops that my KLH TNE hardware didn't get during the transfer. More than acceptable to me (although my ears aren't what they used to be :-). I'd still, some day, like to find out what is causing the problem, though. Thanks again,all. |
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