Bra beskrivelse av Radikal/DC-motoren sakset fra ThomasOK på Linn-forum:
Some good posts on here (on both the Keel and the Radikal). If you put together the info from Colin's informative post with that from The Flatearther you will get most of the reason for the superiority of the Radikal. Here are a couple of other things worth pointing out.
One big advantage of the AC motor is that it is a Synchronous device meaning it is synchronized with the AC line frequency so its rotation is quite accurate and free from drift. The big advantage to it initially, as can be seen from the earliest LP12s (not to mention most current Regas and any number of other turntables both current and historic) is that it requires NO control circuitry to keep a steady speed as the line frequency keeps it in line. However, it does pick up noise from our ever noisier AC power lines which translates into more vibrations and it is true that it performs with minimal vibration at relatively low voltages but ones low enough they would have a hard time starting the turntable. (Note that Nottingham Analog overcomes this problem by having you spin the platter to start the turntable and holding the platter to stop it as it doesn't have enough torque to start itself. Hence they have no on/off switch - not that elegant but it works for them.) When the LP12 came out this was the best way to insure speed accuracy as the servo controls of the time (and the vast majority even now) had musically deleterious problems.
Over time Linn developed the Valhalla and then the Lingo to filter out AC problems, ensure even more accurate frequency control of the motor, run the motor at the voltage where it had the lowest vibration combined with enough torque to overcome the friction from any level of groove modulation and to allow convenient switching from 33.3RPM to 45RPM. The Lingo 2 and 3, while musically improved over the original Lingo are essentially the same design but with the improvements brought about by going to a mainly surface mount layout and some other fine tuning.
So it is easy to see the reason the AC motor was used initially (and why it is still used by very many others) and why Linn continually developed improved ways to drive it.
Brushed DC motors, such as the one Linn uses, have the advantage of not having a fluctuating magnetic field as bot AC and brushless DC motors do. So one of the immediate advantages is getting rid of this fluctuating magnetic field, and its effects on the cartridge - which is basically a magnetic vibration sensor. But a number of things needed to be improved from early DC motor technology to make it really useable by Linn. As Colin mentioned one is the ability to run the motor slower to reduce vibration and allow the larger pulley to beter control the belt. I have seen a number of other DC motor turntables from companies like Teres, Origin Live and others as well as "upgrade" motors from OL and they all have pulleys about the size of a pencil. But another problem with brushed motors is that the brushes wear out. Having a life of three or five or seven years was just not acceptable to Linn. Third is the problem of maintaining constant short and long term speed. This is one of the detriments to a DC motor system in that the speed is dependent on the voltage applied. Send more voltage and it goes faster, send less and it goes slower. Other companies have used various methods from servo controls to batteries and I have found none of them to product a musical performance at the level of the AC motor LP12. Servos, with their constantly hunting for the proper speed tend to blur the pitches and render the fine musical nuances harder to hear. Batteries get rid of that problem but have to be regularly recharged and those I have seen have noticeable drift. The worst are the motor drive systems I have seen from Origin Live which drift so bad you can notice that the pitch is off within a single track! This observation comes from similar OL drive systems in three different turntables including an LP12 and an Origin Live table.
So how has Linn overcome this problem? First off for the motor Linn worked with Maxon, considered the pinnacle of DC motor manufacturers, to come up with a low speed, very low vibration and long lasting DC motor. Part of the solution is that the brushes are precious metal and so should last 20 to 30 years of normal usage. And, as mentioned, they have a motor that runs at a speed that allows the pulley to be the same size as on the AC motor. But then Linn takes that motor and surrounds it in a vibration absorbing plastic foam and fits that into a custom machined outer sleeve and mounting fixture of a dense and hard but vibrationally dead plastic material. This motor and mounting system allows very smooth rotation with minimal vibration and again the elimination of the fluctuating magnetic field. The complexity of the motor and its mounting system can be hinted at by the difference in price between the cost for the replacement motors: in the US approximately $170 for the AC and a bit over $1400 for the DC!
But the motor by itself still isn't free from drift - this is where the control system is needed. Linn investigated the alternatives such as battery drive and other simple voltage control circuits and found it virtually impossible to meet a worst case drift target of under .1 percent. But again existing servo systems, which often measure and adjust speed 50 or 250 times per revolution, had unacceptable musical deficiencies as well. So Linn developed a unique control system for the Radikal - a very slow servo. Linn took an extremely accurate clock circuit, from the same family as that used to clock the digital data in the Klimax DS, and use it as a reference. Then they developed an optical sensor system using an infrared LED and an optical sensor to read the speed of the platter and compare it to the clock. Any difference is adjusted by sending more or less voltage to the motor to correct the speed. So far this is similar to most servo systems although the use of the optical sensor may be unusual and the accuracy of the reference clock is certainly well above what others have used. But the devil is in the details, and that is where Linn's system is brilliantly different. Since the main speed problem of a motor as good as Linn is using is not short, quick variations but long term drift, Linn made the servo operate very slowly. The optical sensor only measures the rotation speed of the platter once per revolution so it also only corrects once per revolution. So the constant, quick fluctuations of speed the typical fast servos have are missing from the Radikal. And even the way the sensor works is quite clever as it really doesn't care about the exact placement of the little light-absorbing felt strip as long as the light is interrupted once per revolution it knows what it needs to know. Furthermore, the servo system is designed such the maximum speed change it will make in one revolution is .03%. Yep, 3 hundredths of a percent! Anyone have pitch that perfect? So if the speed were wrong it would take quite a while for it to correct itself hence the recommendation to run the Radikal for 10 minutes on first installing it so it can calibrate itself. Also the reason the dealers have a strobe LED that plugs into the Radikal power supply to verify correct speed with the Linn speed checker disk. But since you don't want to wait 10 minutes for calibration every time you play a record Linn also built in a memory. Every time you turn the LP12 off from the turntable mounted switch the Radikal stores the last voltage setting used. When you turn it back on it starts at the same setting and continues to monitor the platter rotation and fine tune as necessary. This system is what allows the motor to maintain exceptional speed accuracy and timbral purity while the very low vibration motor and the lack of the fluctuating magnetic field means that the cartridge has much less interference in its ability to turn the vibrations engraved in the grooves into electrical signals via a magnetic vibration sensor system.
So this is why this system wasn't used 40 years ago - the technology literally wasn't there. And despite the fact that Linn has done it and made this huge stride forward in musical performance you don't see everybody out there copying it because it is difficult to achieve and required a tremendous amount of R&D to accomplish (not to mention Linn likely have patents pending or granted on the technology).
Will Linn adopt a yet different drive system 35 years from now? Who knows how technology might change and materials science could improve by then? But I think it is safe to say that Linn evaluated all the possible drive systems available currently. And they obviously evaluated them not just for their performance as currently used but for their POTENTIAL performance if they were developed beyond what others were doing. Personally, I'm just glad they spent the time and energy to develop the Radikal as it has literally given me a whole new record collection and brought the musicians and their musical message more forcefully into my room. If they can make another such substantial improvement in 5, 10, 20, or 30 years I say bring it on! (and just hope I can still hear it then).
[HR][/HR]
Some good posts on here (on both the Keel and the Radikal). If you put together the info from Colin's informative post with that from The Flatearther you will get most of the reason for the superiority of the Radikal. Here are a couple of other things worth pointing out.
One big advantage of the AC motor is that it is a Synchronous device meaning it is synchronized with the AC line frequency so its rotation is quite accurate and free from drift. The big advantage to it initially, as can be seen from the earliest LP12s (not to mention most current Regas and any number of other turntables both current and historic) is that it requires NO control circuitry to keep a steady speed as the line frequency keeps it in line. However, it does pick up noise from our ever noisier AC power lines which translates into more vibrations and it is true that it performs with minimal vibration at relatively low voltages but ones low enough they would have a hard time starting the turntable. (Note that Nottingham Analog overcomes this problem by having you spin the platter to start the turntable and holding the platter to stop it as it doesn't have enough torque to start itself. Hence they have no on/off switch - not that elegant but it works for them.) When the LP12 came out this was the best way to insure speed accuracy as the servo controls of the time (and the vast majority even now) had musically deleterious problems.
Over time Linn developed the Valhalla and then the Lingo to filter out AC problems, ensure even more accurate frequency control of the motor, run the motor at the voltage where it had the lowest vibration combined with enough torque to overcome the friction from any level of groove modulation and to allow convenient switching from 33.3RPM to 45RPM. The Lingo 2 and 3, while musically improved over the original Lingo are essentially the same design but with the improvements brought about by going to a mainly surface mount layout and some other fine tuning.
So it is easy to see the reason the AC motor was used initially (and why it is still used by very many others) and why Linn continually developed improved ways to drive it.
Brushed DC motors, such as the one Linn uses, have the advantage of not having a fluctuating magnetic field as bot AC and brushless DC motors do. So one of the immediate advantages is getting rid of this fluctuating magnetic field, and its effects on the cartridge - which is basically a magnetic vibration sensor. But a number of things needed to be improved from early DC motor technology to make it really useable by Linn. As Colin mentioned one is the ability to run the motor slower to reduce vibration and allow the larger pulley to beter control the belt. I have seen a number of other DC motor turntables from companies like Teres, Origin Live and others as well as "upgrade" motors from OL and they all have pulleys about the size of a pencil. But another problem with brushed motors is that the brushes wear out. Having a life of three or five or seven years was just not acceptable to Linn. Third is the problem of maintaining constant short and long term speed. This is one of the detriments to a DC motor system in that the speed is dependent on the voltage applied. Send more voltage and it goes faster, send less and it goes slower. Other companies have used various methods from servo controls to batteries and I have found none of them to product a musical performance at the level of the AC motor LP12. Servos, with their constantly hunting for the proper speed tend to blur the pitches and render the fine musical nuances harder to hear. Batteries get rid of that problem but have to be regularly recharged and those I have seen have noticeable drift. The worst are the motor drive systems I have seen from Origin Live which drift so bad you can notice that the pitch is off within a single track! This observation comes from similar OL drive systems in three different turntables including an LP12 and an Origin Live table.
So how has Linn overcome this problem? First off for the motor Linn worked with Maxon, considered the pinnacle of DC motor manufacturers, to come up with a low speed, very low vibration and long lasting DC motor. Part of the solution is that the brushes are precious metal and so should last 20 to 30 years of normal usage. And, as mentioned, they have a motor that runs at a speed that allows the pulley to be the same size as on the AC motor. But then Linn takes that motor and surrounds it in a vibration absorbing plastic foam and fits that into a custom machined outer sleeve and mounting fixture of a dense and hard but vibrationally dead plastic material. This motor and mounting system allows very smooth rotation with minimal vibration and again the elimination of the fluctuating magnetic field. The complexity of the motor and its mounting system can be hinted at by the difference in price between the cost for the replacement motors: in the US approximately $170 for the AC and a bit over $1400 for the DC!
But the motor by itself still isn't free from drift - this is where the control system is needed. Linn investigated the alternatives such as battery drive and other simple voltage control circuits and found it virtually impossible to meet a worst case drift target of under .1 percent. But again existing servo systems, which often measure and adjust speed 50 or 250 times per revolution, had unacceptable musical deficiencies as well. So Linn developed a unique control system for the Radikal - a very slow servo. Linn took an extremely accurate clock circuit, from the same family as that used to clock the digital data in the Klimax DS, and use it as a reference. Then they developed an optical sensor system using an infrared LED and an optical sensor to read the speed of the platter and compare it to the clock. Any difference is adjusted by sending more or less voltage to the motor to correct the speed. So far this is similar to most servo systems although the use of the optical sensor may be unusual and the accuracy of the reference clock is certainly well above what others have used. But the devil is in the details, and that is where Linn's system is brilliantly different. Since the main speed problem of a motor as good as Linn is using is not short, quick variations but long term drift, Linn made the servo operate very slowly. The optical sensor only measures the rotation speed of the platter once per revolution so it also only corrects once per revolution. So the constant, quick fluctuations of speed the typical fast servos have are missing from the Radikal. And even the way the sensor works is quite clever as it really doesn't care about the exact placement of the little light-absorbing felt strip as long as the light is interrupted once per revolution it knows what it needs to know. Furthermore, the servo system is designed such the maximum speed change it will make in one revolution is .03%. Yep, 3 hundredths of a percent! Anyone have pitch that perfect? So if the speed were wrong it would take quite a while for it to correct itself hence the recommendation to run the Radikal for 10 minutes on first installing it so it can calibrate itself. Also the reason the dealers have a strobe LED that plugs into the Radikal power supply to verify correct speed with the Linn speed checker disk. But since you don't want to wait 10 minutes for calibration every time you play a record Linn also built in a memory. Every time you turn the LP12 off from the turntable mounted switch the Radikal stores the last voltage setting used. When you turn it back on it starts at the same setting and continues to monitor the platter rotation and fine tune as necessary. This system is what allows the motor to maintain exceptional speed accuracy and timbral purity while the very low vibration motor and the lack of the fluctuating magnetic field means that the cartridge has much less interference in its ability to turn the vibrations engraved in the grooves into electrical signals via a magnetic vibration sensor system.
So this is why this system wasn't used 40 years ago - the technology literally wasn't there. And despite the fact that Linn has done it and made this huge stride forward in musical performance you don't see everybody out there copying it because it is difficult to achieve and required a tremendous amount of R&D to accomplish (not to mention Linn likely have patents pending or granted on the technology).
Will Linn adopt a yet different drive system 35 years from now? Who knows how technology might change and materials science could improve by then? But I think it is safe to say that Linn evaluated all the possible drive systems available currently. And they obviously evaluated them not just for their performance as currently used but for their POTENTIAL performance if they were developed beyond what others were doing. Personally, I'm just glad they spent the time and energy to develop the Radikal as it has literally given me a whole new record collection and brought the musicians and their musical message more forcefully into my room. If they can make another such substantial improvement in 5, 10, 20, or 30 years I say bring it on! (and just hope I can still hear it then).
[HR][/HR]
