The pink foam is anti-static material, meaning that it doesn't generate static charge but the properties of the material decays over time. Depending on how long it's been packaged, it's probably ineffective by now if it's original.
As far as whether the lasers are still functional, there needs to be some education.
I once worked in the calibration department for Analog Devices and their failure analysis department was next door. Static discharge can and does cause damage that 'weakens' devices. I have seen microscope images of perfectly functioning chips but they have been weakened by microscopic damage to the substrate caused by static.
The fact is this; Just because a device functions after poor handling or storage, doesn't give any confidence that it's not carrying damage that will affect it long term.
Lasers are particularly susceptible to static and should always be stored and handled with extreme regard for esd and static prevention. I've seen the evidence with my own eyes and I expect we've all had an electronic gadget or article that has failed prematurely and It'd be my considered judgement that it's down to esd damage at some point in the vast majority of such cases.
Of course, it's difficult to prove without specialist equipment such as that which AD had.
As far as whether the lasers are still functional, there needs to be some education.
I once worked in the calibration department for Analog Devices and their failure analysis department was next door. Static discharge can and does cause damage that 'weakens' devices. I have seen microscope images of perfectly functioning chips but they have been weakened by microscopic damage to the substrate caused by static.
The fact is this; Just because a device functions after poor handling or storage, doesn't give any confidence that it's not carrying damage that will affect it long term.
Lasers are particularly susceptible to static and should always be stored and handled with extreme regard for esd and static prevention. I've seen the evidence with my own eyes and I expect we've all had an electronic gadget or article that has failed prematurely and It'd be my considered judgement that it's down to esd damage at some point in the vast majority of such cases.
Of course, it's difficult to prove without specialist equipment such as that which AD had.
Hello db0360
To make things worse they wrapped the diodes into a foil that loads with static (hope that is the correct term) Rubbed the foil against my body and it became "magnetic" - of course after unpacking. Started a return @ebay. Really, really disappointing. Those diodes became precious over time and some idiots who trade with overstock ruin them.
To make things worse they wrapped the diodes into a foil that loads with static (hope that is the correct term) Rubbed the foil against my body and it became "magnetic" - of course after unpacking. Started a return @ebay. Really, really disappointing. Those diodes became precious over time and some idiots who trade with overstock ruin them.
Hi danico,
What I see most people completely losing sight of is the fact that a non-oversampling DAC requires a 7th or 8th order filter to follow behind. To omit that stage is to inject any audio system using that signal to heaps and loads of 44.1 KHz energy. Still low enough to do damage to most tweeters, and output stages won't care for it either.
So,
My machine (Nakamichi OMS-7) also uses the TDA1540 and it sounds excellent. This is more about the filtering and signal treatment that Nakamichi used than it is about this particular DAC. If I am successful, this old warhorse will be using a 24 bit DAC at 192 KHz that sounds in real terms, far superior than the older TDA series of DAC chips. It will also have access to an ovenized 10 MHz reference oscillator, which should go a long way towards reducing the jitter to levels far superior than most clock modified CD players and external DACs. I'm talking about real world performance rather than allowing the math to cause you to lose sight of the real story.
Does a 24 bit, 192 HKz sampling DAC system sound better than any non-oversampling system? Hell yes,and not by a small margin either! Even the 20 bit system that Denon + Burr-Brown used lays waste to the TDA1540 in its x4 application in the OMS-7.
-Chris
What I see most people completely losing sight of is the fact that a non-oversampling DAC requires a 7th or 8th order filter to follow behind. To omit that stage is to inject any audio system using that signal to heaps and loads of 44.1 KHz energy. Still low enough to do damage to most tweeters, and output stages won't care for it either.
How does that work? If you repeat the same sample 4 times, it looks all the world identical to a 44.1 KHz signal, and will therefore require the same filter. The entire oversampling deal works with interpolation that smooths the transitions and then contains the switching energy at the oversampling frequency. This then allows you to relax the constraints on the reconstruction filter to something that has much less of an effect on the audio pass band.
So,
isn't even close to true in practical terms. You either have interpolation, or you do not have oversampling. Repeating the same value for "x" number of times for each sampled value means you divide the effective clock by that amount ("x").
My machine (Nakamichi OMS-7) also uses the TDA1540 and it sounds excellent. This is more about the filtering and signal treatment that Nakamichi used than it is about this particular DAC. If I am successful, this old warhorse will be using a 24 bit DAC at 192 KHz that sounds in real terms, far superior than the older TDA series of DAC chips. It will also have access to an ovenized 10 MHz reference oscillator, which should go a long way towards reducing the jitter to levels far superior than most clock modified CD players and external DACs. I'm talking about real world performance rather than allowing the math to cause you to lose sight of the real story.
Does a 24 bit, 192 HKz sampling DAC system sound better than any non-oversampling system? Hell yes,and not by a small margin either! Even the 20 bit system that Denon + Burr-Brown used lays waste to the TDA1540 in its x4 application in the OMS-7.
-Chris
I don't use filtering at the output. Its just sound more opened and clear.
Never had a problem with Radford STA25 amp (200KHZ) and Infinity (EMIT highs) or KEF speakers, both goes around 30KHz.
But sometimes it can cause oscillation in an amp.
ThorstenL:
"Based on some old documents from Philips I have around, the TDA1541 was intended for up to 8 Times oversampling at 48KHz, in other words, 384KHz sample rate. Anything up to that will be fine, in any CD Player it was routinely run at 44.1KHz X 4 or 176.4KHz."
16bit/192Khz
CMOS based Delta_sigma dacs just never sounded real for me.
The internal CMOS transistors/switches have limitations that start to show up when frequency increases. "high noise 2.5ps"
Until in a R2R dacs CML/ECL 0.2ps noise
And yes you can hear this difference in a properly build dac stage.
We are talking here a CD player with 16/44.1 so I dont see any reason to oversample this .......
Hi danico,
!
Really? You're not pulling my leg are you ???? Please tell me that you aren't doing what you just said you were doing!
Okay, assuming you really are running wide open then ... you do not deserve to have any tweeters any more. At least the EMIT tweeters are robust enough, and the matching transformer probably doesn't have good response at 44.1 KHz. What you are doing is certainly ill-informed and liable to cause trouble somewhere, and certainly to someone. We used to do warranty work for KEF speakers. Those tweeters are not that robust and you may have already damaged them in the form of cooked voice coils. Lightly cooked mind you. If they suddenly start sounding raspy, it's probably because the epoxy holding the voice coils together is beginning to let go. No idea when that might be.
Let's reason this out a little, game? We can assume that manufacturers of audio equipment will generally not use parts that are not required for some reason. Fair? So in the beginning, the bad old days of the Generation 1 CD players (when I started my training), why do you think that a 7th order audio filter was normal on every single CD player made? Give me a guess, just pull something out of the air for me. Immediately, there was a push to raise the sampling frequency in order to be able to relax those filters. Every engineer knows what a steep filter like that is going to do in the audio pass band. There were already complaints about this. That filter was most probably so they could get to market with something in a CD player. If you survey all those early players, you won't find any without that filter - except for possibly a couple flakes selling "high end".
So why were those filters required do you think? To block close to full amplitude output at 44.1 KHz from entering your system. The possible legal implications of this was enough to make certain everyone followed good design practices. Even if the amplifiers didn't blow up, the level could be high enough to burn out the zobel network in the amplifier, making it unstable and poof! Dead amp (if you're lucky!).
The entire N.O.S. movement in DAC design drives me nuts, because it is abundantly clear that the proponents haven't the foggiest clue as to what they are doing. Just because you're "fine" now doesn't mean that you are okay, nor does it mean that others ought to try it. Why? Because no one has taken the time to learn about how this stuff works and what the effects might be on downstream equipment. I know bad things can happen, and so does every single design engineer (real ones).
What would you say to a friend who brought his speakers over to audition for you, and his tweeters get damaged? What if they are very expensive speakers with terribly expensive parts? Would you have warned him about your setup, or would you act surprised and make like you don't know what happened? After all, it is your non-standard setup that could easily cause this.
Oversampling is done specifically to reduce the effects of the filter. There is science and reason behind it, and even the original Philips digital filters in gen 1 equipment over-sampled the audio information (in those units that used the SAA7030). Never did anyone building D to A converters expect or intend their products to be used without a proper filter network. Oversampling takes the 1/2 fs from 22.05 KHz way up and away - taking artifacts and sampling noise up there with it. Now you can use a lower order filter tuned to a higher frequency (away from the audio band). Every educated person who designs with (especially) audio DACs has been careful to keep the switching frequencies out of the audio chain. Switching frequencies? What did you think was going on between samples?
Anyway, I implore you, please read up on how this stuff works (in real electronics literature) so you understand what is going on in your equipment. Ignore literature from audio manufacturers, read the stuff that the people who design and make those D to A converters you are using, and the competition too. Understand too, "white papers" are advertising. You want suggested circuits and application notes.
For me, 2R2 converters sound the best. Especially the BB DACs in the PCM1702 series. The new ones I'll be looking at.
-Chris
!Really? You're not pulling my leg are you ???? Please tell me that you aren't doing what you just said you were doing!
Okay, assuming you really are running wide open then ... you do not deserve to have any tweeters any more. At least the EMIT tweeters are robust enough, and the matching transformer probably doesn't have good response at 44.1 KHz. What you are doing is certainly ill-informed and liable to cause trouble somewhere, and certainly to someone. We used to do warranty work for KEF speakers. Those tweeters are not that robust and you may have already damaged them in the form of cooked voice coils. Lightly cooked mind you. If they suddenly start sounding raspy, it's probably because the epoxy holding the voice coils together is beginning to let go. No idea when that might be.
Let's reason this out a little, game? We can assume that manufacturers of audio equipment will generally not use parts that are not required for some reason. Fair? So in the beginning, the bad old days of the Generation 1 CD players (when I started my training), why do you think that a 7th order audio filter was normal on every single CD player made? Give me a guess, just pull something out of the air for me. Immediately, there was a push to raise the sampling frequency in order to be able to relax those filters. Every engineer knows what a steep filter like that is going to do in the audio pass band. There were already complaints about this. That filter was most probably so they could get to market with something in a CD player. If you survey all those early players, you won't find any without that filter - except for possibly a couple flakes selling "high end".
So why were those filters required do you think? To block close to full amplitude output at 44.1 KHz from entering your system. The possible legal implications of this was enough to make certain everyone followed good design practices. Even if the amplifiers didn't blow up, the level could be high enough to burn out the zobel network in the amplifier, making it unstable and poof! Dead amp (if you're lucky!).
The entire N.O.S. movement in DAC design drives me nuts, because it is abundantly clear that the proponents haven't the foggiest clue as to what they are doing. Just because you're "fine" now doesn't mean that you are okay, nor does it mean that others ought to try it. Why? Because no one has taken the time to learn about how this stuff works and what the effects might be on downstream equipment. I know bad things can happen, and so does every single design engineer (real ones).
What would you say to a friend who brought his speakers over to audition for you, and his tweeters get damaged? What if they are very expensive speakers with terribly expensive parts? Would you have warned him about your setup, or would you act surprised and make like you don't know what happened? After all, it is your non-standard setup that could easily cause this.
Oversampling is done specifically to reduce the effects of the filter. There is science and reason behind it, and even the original Philips digital filters in gen 1 equipment over-sampled the audio information (in those units that used the SAA7030). Never did anyone building D to A converters expect or intend their products to be used without a proper filter network. Oversampling takes the 1/2 fs from 22.05 KHz way up and away - taking artifacts and sampling noise up there with it. Now you can use a lower order filter tuned to a higher frequency (away from the audio band). Every educated person who designs with (especially) audio DACs has been careful to keep the switching frequencies out of the audio chain. Switching frequencies? What did you think was going on between samples?
Anyway, I implore you, please read up on how this stuff works (in real electronics literature) so you understand what is going on in your equipment. Ignore literature from audio manufacturers, read the stuff that the people who design and make those D to A converters you are using, and the competition too. Understand too, "white papers" are advertising. You want suggested circuits and application notes.
For me, 2R2 converters sound the best. Especially the BB DACs in the PCM1702 series. The new ones I'll be looking at.
That isn't what you have. Your DACs are incomplete and dangerous to equipment.
-Chris
I had a used OMS-7 in 1986, swapped it to a OMS-7II. To my ears, the Burr-Brown based OMS7II sounded better...
Now:
Besides building a transport, the second goal is to save SharpLT022 based lasers.
First victim will be a BU-1 mechanism. The Sharp could maybe replaced by a modern laser from Rohm?
Here is the Sharp datasheet:
LT022MC pdf, LT022MC description, LT022MC datasheets, LT022MC view ::: ALLDATASHEET :::
Here are the datasheets of two Rohm Lasers. Single 780nm lasers do not seem to be produced any more:
http://rohmfs.rohm.com/en/products/databook/datasheet/opto/laser_diode/multi_beam/rld2wmnl2-00x.pdf
http://rohmfs.rohm.com/en/products/databook/datasheet/opto/laser_diode/multi_beam/rld2wmnl2-01x.pdf
Could anyone show up the differences in laser power and sensitivity of the
photo diode? What are the optical differences, i.e in astigmatism?
Here is the APC of a CDP502, using the Sharp LT022MC:
Compatibility of pins is the least problem I assume
Now:
Besides building a transport, the second goal is to save SharpLT022 based lasers.
First victim will be a BU-1 mechanism. The Sharp could maybe replaced by a modern laser from Rohm?
Here is the Sharp datasheet:
LT022MC pdf, LT022MC description, LT022MC datasheets, LT022MC view ::: ALLDATASHEET :::
Here are the datasheets of two Rohm Lasers. Single 780nm lasers do not seem to be produced any more:
http://rohmfs.rohm.com/en/products/databook/datasheet/opto/laser_diode/multi_beam/rld2wmnl2-00x.pdf
http://rohmfs.rohm.com/en/products/databook/datasheet/opto/laser_diode/multi_beam/rld2wmnl2-01x.pdf
Could anyone show up the differences in laser power and sensitivity of the
photo diode? What are the optical differences, i.e in astigmatism?
Here is the APC of a CDP502, using the Sharp LT022MC:
Compatibility of pins is the least problem I assume
Attachments
Hi Salar,
As for those lasers, I don't know. I wouldn't think there could be an astig. problem, and I would imagine that sensitivity differences would be minimized with the pick up diodes. Until I can go over those data sheets, I wouldn't say anything more. But my time is taken up with a few things right now. Anyone else can dive in here too.
Looking at this another way, there is nothing that says the CD must be read by a 780 nm laser. Any matched transmitter - receiver pair can be used as long as the bulk material in the CD is transparent at those wavelengths. It's just that the 780 nm red laser is too long to work with the smaller features in a DVD type disc. It needs a shorter wavelength in order to differentiate the smaller pits whereas the 780 nm (red, okay ... infra-red) could not track even. If anything, I can't see why the shorter wavelength wouldn't produce a cleaner eye pattern. I guess it's time to look at a DVD / CD player on the bench. Much later in time, but that will be my approach.
-Chris
I agree with you 100%. I was doing warranty through that period and beyond. The OMS-7 has the best transport, the OMS-7II has a much better D/A.
As for those lasers, I don't know. I wouldn't think there could be an astig. problem, and I would imagine that sensitivity differences would be minimized with the pick up diodes. Until I can go over those data sheets, I wouldn't say anything more. But my time is taken up with a few things right now. Anyone else can dive in here too.
Looking at this another way, there is nothing that says the CD must be read by a 780 nm laser. Any matched transmitter - receiver pair can be used as long as the bulk material in the CD is transparent at those wavelengths. It's just that the 780 nm red laser is too long to work with the smaller features in a DVD type disc. It needs a shorter wavelength in order to differentiate the smaller pits whereas the 780 nm (red, okay ... infra-red) could not track even. If anything, I can't see why the shorter wavelength wouldn't produce a cleaner eye pattern. I guess it's time to look at a DVD / CD player on the bench. Much later in time, but that will be my approach.
-Chris
Hi danico,
Really? You're not pulling my leg are you ???? Please tell me that you aren't doing what you just said you were doing!
Okay, assuming you really are running wide open then ... you do not deserve to have any tweeters any more.
Thast's a funny response, Chris
Of course we know the "theoretical" possibility of running filterless NOSDAC. But we have also empirical knowledge and experience...
I think the old one has Philips TDA1540 and the markII has Burr-Brown PCM54. According to Salar he could hear the sawtooth in the PCM54 (and all other old chips?). Now both of you agree that OMS7-II sounded much better, and Chris thinks that PCM54 is a much better chip than TDA1540...
My empirical experience told me that a complete DC machine cannot show the quality of the DAC chip. Implementation is important. TDA1540 is considered one of the best, so if PCM54 is considered better by both of you then I feel very lucky
(I will try to go all out with this chip, hopefully I wont hear the sawtooth).
Hi Jay,
I have never heard the TDA1540 on its own, but behind the excellent work from the engineers at Nakamichi. So too, the PCM54, but from a different era. Those two designs reflect different approaches only a couple years apart. So you can not make any statements about our preferences with regard to DAC chips only. If you must know, the OMS-4 was also in the mix with the OMS-7 trouncing it, no doubt! Now, those two machines were in the same model lineup.
Currently my favorite DAC resides in my Denon DCD-S10 CD player. It also has external inputs so it acts as a standalone DAC as well. Now, before you get all excited, it uses BB PCM1702 (x2 per channel) and a 20 bit digital filter (1700?). I'm going purely on memory here, so forgive minor errors.
Just because you haven't seen damage due to this silly practice doesn't mean that it isn't sending 44.1 KHz into your system at a relatively high level. Some of you are probably oversampling without knowing it. That will actually work to save you from damage as most amplifiers are limited in HF response due to a filter. Jay, have you had a look at your zobel networks in your amplifier(s)? Are you actually oversampling? The Philips chip set that supported the TDA1540 included the SAA7030 digital filter that over-samples by a factor of 4x, like it or not. I think that this was one of the reasons that the TDA1540 has a good reputation in the better CD players of that time. It allowed a much lower order of reconstruction filter at a higher frequency - as you know.
It is entirely possible that high capacitance cables and low drive current is performing the filter function for some of your group, but I also feel that it is likely not many of you have looked at the signal (with a 'scope), and therefore don't realize what they are sending in to their equipment. Ignorance can be bliss .. or "fat, dumb and happy" to put it another way.
You know, my brother doesn't believe in changing the oil in any of his cars - like it doesn't get changed. However, the car doesn't blow up after a few missed oil changes. It can go on for years like this. One day, the engine will fail at a young age due to the accumulated damage done slowly over time.
Has the group you're in actually had a knowledgeable discussion of what the filters do and what is actually being sent out of their DACs without the filter? I think that the topic should be explored, not doing so is inexcusable if you have the technical knowledge and an understanding. My concern is both real and coming from a standpoint of helping to avoid unnecessary equipment damage. I'm not just laughing, my concern is genuine. For the record, I have looked at the unfiltered audio many times.
-Chris
You're putting words into my mouth. I compared two complete CD players.
I have never heard the TDA1540 on its own, but behind the excellent work from the engineers at Nakamichi. So too, the PCM54, but from a different era. Those two designs reflect different approaches only a couple years apart. So you can not make any statements about our preferences with regard to DAC chips only. If you must know, the OMS-4 was also in the mix with the OMS-7 trouncing it, no doubt! Now, those two machines were in the same model lineup.
Currently my favorite DAC resides in my Denon DCD-S10 CD player. It also has external inputs so it acts as a standalone DAC as well. Now, before you get all excited, it uses BB PCM1702 (x2 per channel) and a 20 bit digital filter (1700?). I'm going purely on memory here, so forgive minor errors.
I'm not familiar with the "sawtooth" you are talking about. If you are speaking of the discrete steps from a multibit DAC chip, please be aware that they are normally over-sampled where the digital filter interpolates between the values, which makes the steps too small to hear after the reconstruction filter has done it's job. So, what on earth are you talking about?
No, you're quite right about that, but a poor choice of DAC chip can sink a good design.
Why would you try such an ancient DAC chip when we don't feel it is the best available? If you wished to compare machines as we originally did, you would find that the OMS-7II does sound better than the OMS-7, which sounds much better than the OMS-4. I had all three machines at one point in time. Two I still have and one was borrowed. I actually have one OMS-7II in for service currently, so I could compare all three again should this interest me.
So do I. I have had some CD players in with this "modification" where the filter has been pulled to "improve the sound". I have had to explain to people why their tweeters are toast after a while, maybe their amp too. Some of them run "wide open". The others are singing into a mike and they had feedback (briefly).
Just because you haven't seen damage due to this silly practice doesn't mean that it isn't sending 44.1 KHz into your system at a relatively high level. Some of you are probably oversampling without knowing it. That will actually work to save you from damage as most amplifiers are limited in HF response due to a filter. Jay, have you had a look at your zobel networks in your amplifier(s)? Are you actually oversampling? The Philips chip set that supported the TDA1540 included the SAA7030 digital filter that over-samples by a factor of 4x, like it or not. I think that this was one of the reasons that the TDA1540 has a good reputation in the better CD players of that time. It allowed a much lower order of reconstruction filter at a higher frequency - as you know.
It is entirely possible that high capacitance cables and low drive current is performing the filter function for some of your group, but I also feel that it is likely not many of you have looked at the signal (with a 'scope), and therefore don't realize what they are sending in to their equipment. Ignorance can be bliss .. or "fat, dumb and happy" to put it another way.
You know, my brother doesn't believe in changing the oil in any of his cars - like it doesn't get changed. However, the car doesn't blow up after a few missed oil changes. It can go on for years like this. One day, the engine will fail at a young age due to the accumulated damage done slowly over time.
Has the group you're in actually had a knowledgeable discussion of what the filters do and what is actually being sent out of their DACs without the filter? I think that the topic should be explored, not doing so is inexcusable if you have the technical knowledge and an understanding. My concern is both real and coming from a standpoint of helping to avoid unnecessary equipment damage. I'm not just laughing, my concern is genuine. For the record, I have looked at the unfiltered audio many times.
-Chris
Sony/Philips specify a 780 +- 10 nm wavelength for CD.
A wavelength of 780 nm and the polycarbonate's refractive index is 1.55. The laser's wavelength in the polycarbonate is equal to 780/1.55 = 503nm. The pit depth is 1/4 of the wavelength 503/4 = 124.75nm.
It is the relationship pit geometry, laser spot size ,wavelength that produces the eye-pattern and make playback possible.
Understanding this part of technology is key to designing the optics.
A wavelength of 780 nm and the polycarbonate's refractive index is 1.55. The laser's wavelength in the polycarbonate is equal to 780/1.55 = 503nm. The pit depth is 1/4 of the wavelength 503/4 = 124.75nm.
It is the relationship pit geometry, laser spot size ,wavelength that produces the eye-pattern and make playback possible.
Understanding this part of technology is key to designing the optics.
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Oops sorry I misinterpreted this:
4x PCM1702-J >> SM5845AF >> YM3623B
It's one of the best. The Mark III uses its brother, PCM1704.
Salar was talking about feeding oscope with -60dB 1kHz sinewave:
Because I have plenty. But the main motivation is when it is considered as good as or even close to TDA1540
But your favorite DAC machine is using ancient chip too It is not just a possibility. Without the downstream filtering "conditions" I will not be so reckless. But no, I don't use zobel, never (only in amplifier design prototyping stage).
I have no group. I have built DAC from chips never been used by others, so yes I know when I went the NOS way. But don't forget that high quality audio is about compromise. A little "risk" is fine (but no, I have never had a problem with my tweeters for having used NOS for more than 10 years) if there is audible sound improvement.
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You already suggested a CD Pro2 that is known to last for 20 years and I think that's true. It has been discussed that many people have moved to higher resolution computer based playback, so some who decide to stay with the old technology can source the second hand transports (the CD itself can become more expensive than the free-to-copy digital music files). So what else can you bring to the table?
I'm trying to use laser player with stable platter for the sake of DIY. Slow progress
Firstly, don't confuse the terms - a stable platter is absolutely beneficial! What you are talking about specifically is achieving that stability via increased inertia and gyroscopic effect.
The speed change during play is very small and is not stepped (well, depends on the motor control).
The only time there is heavy acc/de-acc is during track searching so a heavy platter will cause fractionally longer pauses between play when skipping tracks. Then again, that speed change depends on the torque of the motor used.
Most mechs don't have ANY platter and clamping systems leave much to be desired in terms of accuracy of the clamp and the eccetricity of the magnets in the clamp. They can cause vibration for the laser focus servos work on, although obviously they are better than nothing which wouldn't work at all.
Well, that's what the CD is for, it acts as a 'stable platter' as per your definition of it. That's what it was designed to do by the smart folks that drafted the CD standard. Adding additional weight will not only increase the wear on the motor and bearings, but also cause for longer spin up/down times as you correctly mentioned.
Over the years I've read your posts mentioning the OMS-7 (I have a broken one) and it's great mech. What makes it so good? The cast construction, laser, control circuitry?
And... what are common causes for them not to read? (for me to try to fix mine).
As an aside, your frustration at NOS DAC builders is daft. Why is it of your concern what people do , why choose to be frustrated about it? In some ways your approach is like telling explorers not to sail west too far because they will drop off the end of the earth or meet the big monster - NOS Dac users are taking their chances for the cause of better sound (not lazyness like the car oil example - unless they are deliberately setting out to note the real-world effects of actual wear versus theoretical wear in the context of time scales of other terminal failures). They will discover what they will discover (and I've not heard of a NOS dac user complaining of how their tweeters keep dying either...). Chill out, it is dac experimentation and even "dangerous" experimentation is beneficial even if you can say "I told you so" at the end (but who would be so callous as to do so?).
Besides, NOS is about no digital filter and hence no oversampling - there is no hard and fast rule about analogue filtering so you could well be barking up the wrong tree. A transformer coupled output for example provides filtering.
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