Hi folks,
I hear what you say about the low voltage, but the OL kits must run their motors at low voltages given the pulley/sub-platter ratios involved. Looking at the torque/speed curves for the maxon motor it appears that they maintain torque at low speeds (ie low voltage). I think the Teres kit uses a 36volt motor run at a much lower voltage also. If you use a low nominal rated voltage motor the problem of low drive voltage is worse as the speed at rated voltage is several thousand rpm, so you would be running the motor at fractions of a volt to keep the speed down.
TTFN
Matt
I hear what you say about the low voltage, but the OL kits must run their motors at low voltages given the pulley/sub-platter ratios involved. Looking at the torque/speed curves for the maxon motor it appears that they maintain torque at low speeds (ie low voltage). I think the Teres kit uses a 36volt motor run at a much lower voltage also. If you use a low nominal rated voltage motor the problem of low drive voltage is worse as the speed at rated voltage is several thousand rpm, so you would be running the motor at fractions of a volt to keep the speed down.
TTFN
Matt
Bobken said:
Hi,
That is a good way to go. But be careful, Loctite comes in many flavours. Never use the thin fast curing one. It will for sure creep into the motor bearing and then you have a big problem. Use the thick slow curing variety and one with a not so permanent bond, so you can remove the pulley when needed. But even with the thick variety use extreme care the glue does not reach the motor bearing, so keep the motor always upside and the pulley downside when assembling this way.
Cheers
Hi Matt,
Not trying to rain on anyone's parade, but offering (hopefully) some cautious advice here.
At a quick glance, I don't see anything in the ref. you show which indicates that torque is maintained (or otherwise) with any lower than nominal voltages. Maybe I need to look at the specs some more, but no time just now.
Are you certain you are reading that graph correctly, or is there some more info elsewhere, perhaps, which I haven't seen yet?
The lowest voltage motor shown in the specs seems to be about nominal 7-ish V, and reducing this to 1.4 V is a huge reduction.
Running at 2/3rds nominal V should be fine, but running at 20% or less (7/1.4) is another matter altogether.
I am only going from general experiences with DC motors here, and maybe the manufacturer of your motor has come up with something different, but, for your own sake, please make certain.
Not trying to rain on anyone's parade, but offering (hopefully) some cautious advice here.
At a quick glance, I don't see anything in the ref. you show which indicates that torque is maintained (or otherwise) with any lower than nominal voltages. Maybe I need to look at the specs some more, but no time just now.
Are you certain you are reading that graph correctly, or is there some more info elsewhere, perhaps, which I haven't seen yet?
The lowest voltage motor shown in the specs seems to be about nominal 7-ish V, and reducing this to 1.4 V is a huge reduction.
Running at 2/3rds nominal V should be fine, but running at 20% or less (7/1.4) is another matter altogether.
I am only going from general experiences with DC motors here, and maybe the manufacturer of your motor has come up with something different, but, for your own sake, please make certain.
Hi Harwoodspark
This is rather confusing! I think I have the same premotec motor running my Linn with a 10mm pulley. My regulator has to be set for about 1.4v to give 33.33 platter speed. Looking at the data for the motor it has a figure of 3.16volts per 1000rpm. Given that the diameter of the sub-platter is 160mm and the pulley is 10mm, thats 1:16 which gives about 533 rpm for the pulley (@33.33rpm).
So I calculate that the motor voltage should be about 1.7v which close to what I've found in practice. Is your 7.5 volts at the motor terminals or what's going into the regulator?
Matt
This is rather confusing! I think I have the same premotec motor running my Linn with a 10mm pulley. My regulator has to be set for about 1.4v to give 33.33 platter speed. Looking at the data for the motor it has a figure of 3.16volts per 1000rpm. Given that the diameter of the sub-platter is 160mm and the pulley is 10mm, thats 1:16 which gives about 533 rpm for the pulley (@33.33rpm).
So I calculate that the motor voltage should be about 1.7v which close to what I've found in practice. Is your 7.5 volts at the motor terminals or what's going into the regulator?
Matt
Hi Bobken
Maybe I'm not understanding the graph correctly, but the red portion is labelled as recommended operating range. However the torque at low rpm is not clear, so you may be right. However as I said before others seem to be using higher volatge motors at lower speeds with success.
Matt
Maybe I'm not understanding the graph correctly, but the red portion is labelled as recommended operating range. However the torque at low rpm is not clear, so you may be right. However as I said before others seem to be using higher volatge motors at lower speeds with success.
Matt
Hello again!
Looking again at the maxon motor data (REMax226756), the speed constant is 185rpm/v which gives an operating voltage of 2.88v for 33.33rpm and the torque gradient is 33.1rpm/mNm which gives about 16mNm at this voltage. So the question is, is this sufficient torque to maintain constant speed?
Matt
Looking again at the maxon motor data (REMax226756), the speed constant is 185rpm/v which gives an operating voltage of 2.88v for 33.33rpm and the torque gradient is 33.1rpm/mNm which gives about 16mNm at this voltage. So the question is, is this sufficient torque to maintain constant speed?
Matt
Hi Matt,
I'm afraid I don't know the definitive answers to these questions. You would need to check with the motor manufacturers about this, as I am going by personal experience of other motors and intuition here. So far, I haven't seen much to indicate the torque of these motors at lower voltages in the info you mention, though.
What I do know is that now you have specified the motor you have in mind, the concerns I have already advised in this respect have increased dramatically.
Now you make it clear that the proposed motor is nominally 36v, quite frankly I would be astounded to learn that it would drive a TT adequately at a voltage somewhere in the region of merely 5% of its nominal rating.
I know of others (and indeed I do it myself to help reduce motor vibrations etc.) who run at somewhat reduced voltages, but I don't know of anyone who runs them at merely a few % of 'nominal'. The starting torque will be much higher than that needed to maintain motion, and this is what particularly concerns me, as already mentioned.
If you are looking at the red portion on the graph you referred to, I think (I regret I don't know for sure, though, and you do need to check with the makers) that this merely refers to the 'safe operating area', where no harm should come to the motor providing you remain within these guidelines.
I tend to read the comment as "*maximum* recommended operating range" here, I regret to say, but again I could be wrong.
This looks to me to be very similar to the 'SOA' graphs for transistors, which only indicate *maximum ratings* for safety ( i.e. voltage & current), but do not indicate that the transistors will work at their best (or even at all!) in the lower ranges.
I have not played about much with Linn TTs (except to set them up for others) and therefore don't know what their 'running' voltages are, but many years ago I believe their AC motors were powered somewhere in the region of 12V.
I will certainly be amazed to hear that any TT is powered with a voltage as low as the 1.4 or 1.7 volts you mention, but I am always happy to learn something which is new to me.
I'm afraid I don't know the definitive answers to these questions. You would need to check with the motor manufacturers about this, as I am going by personal experience of other motors and intuition here. So far, I haven't seen much to indicate the torque of these motors at lower voltages in the info you mention, though.
What I do know is that now you have specified the motor you have in mind, the concerns I have already advised in this respect have increased dramatically.
Now you make it clear that the proposed motor is nominally 36v, quite frankly I would be astounded to learn that it would drive a TT adequately at a voltage somewhere in the region of merely 5% of its nominal rating.
I know of others (and indeed I do it myself to help reduce motor vibrations etc.) who run at somewhat reduced voltages, but I don't know of anyone who runs them at merely a few % of 'nominal'. The starting torque will be much higher than that needed to maintain motion, and this is what particularly concerns me, as already mentioned.
If you are looking at the red portion on the graph you referred to, I think (I regret I don't know for sure, though, and you do need to check with the makers) that this merely refers to the 'safe operating area', where no harm should come to the motor providing you remain within these guidelines.
I tend to read the comment as "*maximum* recommended operating range" here, I regret to say, but again I could be wrong.
This looks to me to be very similar to the 'SOA' graphs for transistors, which only indicate *maximum ratings* for safety ( i.e. voltage & current), but do not indicate that the transistors will work at their best (or even at all!) in the lower ranges.
I have not played about much with Linn TTs (except to set them up for others) and therefore don't know what their 'running' voltages are, but many years ago I believe their AC motors were powered somewhere in the region of 12V.
I will certainly be amazed to hear that any TT is powered with a voltage as low as the 1.4 or 1.7 volts you mention, but I am always happy to learn something which is new to me.
Loctite
Pjotr is quite right to advise caution if you use this method to secure pulleys, but it does solve the offsetting by a grub-screw problem quite well.
Don't use Engineering Grades of Loctite (Studlock or its equivalent) here unless you know you will not need to remove the pulley ever. This grade of adhesive can be overcome with applied heat, but this is not ideal for motors, of course.
Of the weaker grades of Loctite, Screwlock is the least strong, and this, or Nutlock (which is the next up in strength) will be more than strong enough.
It is a good idea to leave the parts upside down for a while after assembly, also as Pjotr states, but more importantly, make sure you oil the end bearing well before assembly, as this will prevent any possible creepage into the bearing.
Also, don't apply the adhesive to the shaft, itself, as when you push the pulley onto the shaft, this will force the adhesive down towards the bearing, because the pulley scrapes it off the shaft on its way down into position.
Instead, apply the adhesive (perhaps with a coctail stick, or whatever suits the hole size) all over the inside bore of the pulley, only. Then, when the pulley slides down the shaft, any excess adhesive is merely pushed out of the hole in the top of the pulley, and can be cleaned up with some tissue etc.
Pjotr is quite right to advise caution if you use this method to secure pulleys, but it does solve the offsetting by a grub-screw problem quite well.
Don't use Engineering Grades of Loctite (Studlock or its equivalent) here unless you know you will not need to remove the pulley ever. This grade of adhesive can be overcome with applied heat, but this is not ideal for motors, of course.
Of the weaker grades of Loctite, Screwlock is the least strong, and this, or Nutlock (which is the next up in strength) will be more than strong enough.
It is a good idea to leave the parts upside down for a while after assembly, also as Pjotr states, but more importantly, make sure you oil the end bearing well before assembly, as this will prevent any possible creepage into the bearing.
Also, don't apply the adhesive to the shaft, itself, as when you push the pulley onto the shaft, this will force the adhesive down towards the bearing, because the pulley scrapes it off the shaft on its way down into position.
Instead, apply the adhesive (perhaps with a coctail stick, or whatever suits the hole size) all over the inside bore of the pulley, only. Then, when the pulley slides down the shaft, any excess adhesive is merely pushed out of the hole in the top of the pulley, and can be cleaned up with some tissue etc.
Hi,
Here I posted a model of a DC motor. Speed is set by the difference of the back EMF voltage (as a result of the speed and the voltage constant) and the driving voltage. This difference causes a current through the DC resistance of the motor and depends on the torque needed. So if the requested torque is virtually constant so the speed is. The stabilization of the speed depends on the size of the DC resistance and the torque constant. IMO running the motor at low speed is no problem when driven from a low voltage if the torque requested is low compared to the available torque.
The Maxon Remax motors require very low current at no load which is an indication that the mechanical motor losses are quite low. That 15W Remax motor has plenty torque available to keep the platter spinning at the correct speed I think, even when driven from a simple LM317 adjustable regulator.
Cheers
Here I posted a model of a DC motor. Speed is set by the difference of the back EMF voltage (as a result of the speed and the voltage constant) and the driving voltage. This difference causes a current through the DC resistance of the motor and depends on the torque needed. So if the requested torque is virtually constant so the speed is. The stabilization of the speed depends on the size of the DC resistance and the torque constant. IMO running the motor at low speed is no problem when driven from a low voltage if the torque requested is low compared to the available torque.
The Maxon Remax motors require very low current at no load which is an indication that the mechanical motor losses are quite low. That 15W Remax motor has plenty torque available to keep the platter spinning at the correct speed I think, even when driven from a simple LM317 adjustable regulator.
Cheers
Hi Pjotr,
This is interesting, and I have no qualms over using generally reduced voltages here, as it can help to reduce motor vibrations etc.
However, Matt is talking about merely using (less than) 5% of this motor's rated voltage, and I question the sense in going as low as this.
An acquaintance brought his DIY TT set-up to listen to in my system some years ago. I don't recall the precise figures, but I believe he was running at about 20/25 % of the motor's rated voltage, and this would not even 'start up' without being assisted by turning the platter by hand.
Also, I could clearly hear pitch changes during heavily modulated passages, caused by stylus-drag induced motor-braking, although the owner said he was not so sure about this, himself!
Obviously it will depend on many factors here, including:
The motor's torque, how this torque is affected at lower voltages, what the rotating mass of the platter is, and how sensitive the listener's ears are to pitch changes, etc.
However, if you are entirely satisfied that this chosen (36v) motor will perform satisfactorily with merely 1.7v (less than 5%), I wouldn't argue with you.
I am rather puzzled, though, by your comment "plenty of torque"....."when driven from a simple LM317 adjustable regulator", as *how* the voltage is regulated doesn't have much to do with the torque available from any motor, loaded in a particular way, and with a specified voltage being fed to it.
Regards,
This is interesting, and I have no qualms over using generally reduced voltages here, as it can help to reduce motor vibrations etc.
However, Matt is talking about merely using (less than) 5% of this motor's rated voltage, and I question the sense in going as low as this.
An acquaintance brought his DIY TT set-up to listen to in my system some years ago. I don't recall the precise figures, but I believe he was running at about 20/25 % of the motor's rated voltage, and this would not even 'start up' without being assisted by turning the platter by hand.
Also, I could clearly hear pitch changes during heavily modulated passages, caused by stylus-drag induced motor-braking, although the owner said he was not so sure about this, himself!
Obviously it will depend on many factors here, including:
The motor's torque, how this torque is affected at lower voltages, what the rotating mass of the platter is, and how sensitive the listener's ears are to pitch changes, etc.
However, if you are entirely satisfied that this chosen (36v) motor will perform satisfactorily with merely 1.7v (less than 5%), I wouldn't argue with you.
I am rather puzzled, though, by your comment "plenty of torque"....."when driven from a simple LM317 adjustable regulator", as *how* the voltage is regulated doesn't have much to do with the torque available from any motor, loaded in a particular way, and with a specified voltage being fed to it.
Regards,
Hi Bob,
The torque gradient is set by (torque constant)*(driving voltage)/Rdc at zero speed and at the other end by the no load speed at the driving voltage. As long as the torque gradient of the load, that is from the belt, platter and stylus/groove drag, crosses the torque gradient close to the no-load speed (say between 3/4 no load speed and full no load speed) I don’t see any problems.
No load speed in this case is the speed set by voltage constant and the driving voltage. NOT the nominal no load speed as stated in the data sheet.
Note that most commercial TT’s are driven from a 3W motor and deliver enough torque then, so that 15W Remax will do anyway me think.
Cheers
The torque gradient is set by (torque constant)*(driving voltage)/Rdc at zero speed and at the other end by the no load speed at the driving voltage. As long as the torque gradient of the load, that is from the belt, platter and stylus/groove drag, crosses the torque gradient close to the no-load speed (say between 3/4 no load speed and full no load speed) I don’t see any problems.
No load speed in this case is the speed set by voltage constant and the driving voltage. NOT the nominal no load speed as stated in the data sheet.
Note that most commercial TT’s are driven from a 3W motor and deliver enough torque then, so that 15W Remax will do anyway me think.
Cheers
dc motors.
Hello Matt. You are correct in your assumption. I am feeding the regulator with 7.5 volts not the motor itself. I've dug out the O/L paperwork for my dc motor conversion and it states that for the O/L turntable which has an inner hub of 164 mm. the dc voltage at the motor will be 1.98v for 33 rpm and 2.6v for 45 rpm. So the voltages you give for your O/L motor on your Linn must be correct.
I apologise for my mistake. Si.
Hello Matt. You are correct in your assumption. I am feeding the regulator with 7.5 volts not the motor itself. I've dug out the O/L paperwork for my dc motor conversion and it states that for the O/L turntable which has an inner hub of 164 mm. the dc voltage at the motor will be 1.98v for 33 rpm and 2.6v for 45 rpm. So the voltages you give for your O/L motor on your Linn must be correct.
I apologise for my mistake. Si.
DC motor controller
Hi patriz,
I have only just seen your query.
Unfortunately I don't have any links which I know would help you here, but I have seen several schematics over the years on the Internet, so I think you will need to search for yourself.
I am not at liberty to post my own design here, which has been the result of several years in development, as I sold the rights to a TT manufacturer a while ago.
What I can say is that it is a straightforward two-stage voltage regulator, starting off with an over-specified toroidal t'former, soft recovery diodes, and non-polarised Blackgate smoothing caps.
This leads on to the pre-regulator, which is a 3 terminal LT device, again using Blackgates and Vishay bulk foils for further smoothing and output voltage setting etc. before the main regulator, so that the voltage 'dropout' in the main reg. can be tightly controlled.
This then feeds a very well-smoothed, low-noise discrete regulator of my own design (using an LM329 voltage reference as the control element) and, again, using all Vishay & Blackgate components, with a Vishay bulk foil 20 turn preset for accurately setting the final voltage used for the motor.
Whilst under development, I initially used 'lesser' components in several iterations, and none of these performed as well as the final version. Therefore, I have no doubts that its excellent performance in final form is due to using these very low noise/low tempco etc parts, which initially might seem like overkill.
I have never needed to re-adjust the output voltage in the prototype since initially setting it up, and I know this is mainly due to the lack of drift in specs of these carefully chosen parts.
Personally, it is my belief that using a very good non-feedback design which produces a clean and stable voltage at all times with an adequate current reserve, is more important for good sound than using any tacho style arrangements.
I appreciate that this is a contentious subject, but as with power amps etc., no feedback arrangement can ever be truly instantaneous, and this can lead to 'flutter' occurring, which I don't care for. Also, as time goes by, I have enjoyed better results throughout with my own electronic circuits, the more I have managed to simplify them.
What happens in reality with feedback circuits is, the TT begins to slow down as a result of varying stylus drag, caused by differing modulations in the recordings. This then needs to be 'sensed' via (in my case) an elastic belt by the motor (either through its back EMF, or maybe a separate tacho coil) and this braking effect then needs to be transmitted via a cable to the PS sensing circuit, before any reaction can even be contemplated by the PS electronics.
Having sensed this additional drag, the PS circuit reacts to increase the voltage accordingly, this is then transmitted back down the cable to the motor, which then needs to overcome its inherent inertia and speed up, and then transmit this speed increase via the same elastic band back to the TT, which again needs to overcome its own inertia (often quite high) before regaining its correct speed.
Although the electronics will react quickly (but certainly not instantaneously!) my experiences suggest that the other variables do not, and this inevitable 'time-lag' is a problem which all such circuits will suffer from, to some degree or other.
In other words, the correcting 'signal' will always be too late to be fully effective, and hence the hunting effects I have seen and measured do occur.
The only way of successfully avoiding this potential, is if one could 'read ahead' somehow, and anticipate any changes in TT speeds *before they actually occur*, and then applying the correcting forces at the right time so there is no net change in TT speed at any time. However, although this procedure might be easy in digital cases, I simply haven't come up with any effective way of doing this in the analogue domain, unfortunately.
Incidentally, even the quality of wiring used between the motor and TT will affect the overall sonic results, so, as I have said before, this area is more sensitive than many people appear to appreciate.
I hope this helps.
Hi patriz,
I have only just seen your query.
Unfortunately I don't have any links which I know would help you here, but I have seen several schematics over the years on the Internet, so I think you will need to search for yourself.
I am not at liberty to post my own design here, which has been the result of several years in development, as I sold the rights to a TT manufacturer a while ago.
What I can say is that it is a straightforward two-stage voltage regulator, starting off with an over-specified toroidal t'former, soft recovery diodes, and non-polarised Blackgate smoothing caps.
This leads on to the pre-regulator, which is a 3 terminal LT device, again using Blackgates and Vishay bulk foils for further smoothing and output voltage setting etc. before the main regulator, so that the voltage 'dropout' in the main reg. can be tightly controlled.
This then feeds a very well-smoothed, low-noise discrete regulator of my own design (using an LM329 voltage reference as the control element) and, again, using all Vishay & Blackgate components, with a Vishay bulk foil 20 turn preset for accurately setting the final voltage used for the motor.
Whilst under development, I initially used 'lesser' components in several iterations, and none of these performed as well as the final version. Therefore, I have no doubts that its excellent performance in final form is due to using these very low noise/low tempco etc parts, which initially might seem like overkill.
I have never needed to re-adjust the output voltage in the prototype since initially setting it up, and I know this is mainly due to the lack of drift in specs of these carefully chosen parts.
Personally, it is my belief that using a very good non-feedback design which produces a clean and stable voltage at all times with an adequate current reserve, is more important for good sound than using any tacho style arrangements.
I appreciate that this is a contentious subject, but as with power amps etc., no feedback arrangement can ever be truly instantaneous, and this can lead to 'flutter' occurring, which I don't care for. Also, as time goes by, I have enjoyed better results throughout with my own electronic circuits, the more I have managed to simplify them.
What happens in reality with feedback circuits is, the TT begins to slow down as a result of varying stylus drag, caused by differing modulations in the recordings. This then needs to be 'sensed' via (in my case) an elastic belt by the motor (either through its back EMF, or maybe a separate tacho coil) and this braking effect then needs to be transmitted via a cable to the PS sensing circuit, before any reaction can even be contemplated by the PS electronics.
Having sensed this additional drag, the PS circuit reacts to increase the voltage accordingly, this is then transmitted back down the cable to the motor, which then needs to overcome its inherent inertia and speed up, and then transmit this speed increase via the same elastic band back to the TT, which again needs to overcome its own inertia (often quite high) before regaining its correct speed.
Although the electronics will react quickly (but certainly not instantaneously!) my experiences suggest that the other variables do not, and this inevitable 'time-lag' is a problem which all such circuits will suffer from, to some degree or other.
In other words, the correcting 'signal' will always be too late to be fully effective, and hence the hunting effects I have seen and measured do occur.
The only way of successfully avoiding this potential, is if one could 'read ahead' somehow, and anticipate any changes in TT speeds *before they actually occur*, and then applying the correcting forces at the right time so there is no net change in TT speed at any time. However, although this procedure might be easy in digital cases, I simply haven't come up with any effective way of doing this in the analogue domain, unfortunately.
Incidentally, even the quality of wiring used between the motor and TT will affect the overall sonic results, so, as I have said before, this area is more sensitive than many people appear to appreciate.
I hope this helps.
Hi Bobken,
Keep in mind that the motor is kind of a feedback system by itself. In the motor the back EMF is in fact a speed sensor that is subtracted from the driving voltage and as such giving an error signal to set the motor current. This feedback is not instantaneous, but delayed by the inductance of the motor winding.
IMO the only optimum way to control the speed of the platter is by using a controlled braking mechanism at the platter itself like an controlled eddy current brake as suggested somewhere else in one of these threads.
But I agree that at good simple voltage drive can give very good results with a high quality motor.
Cheers
Keep in mind that the motor is kind of a feedback system by itself. In the motor the back EMF is in fact a speed sensor that is subtracted from the driving voltage and as such giving an error signal to set the motor current. This feedback is not instantaneous, but delayed by the inductance of the motor winding.
IMO the only optimum way to control the speed of the platter is by using a controlled braking mechanism at the platter itself like an controlled eddy current brake as suggested somewhere else in one of these threads.
But I agree that at good simple voltage drive can give very good results with a high quality motor.
Cheers
DC motor control.
I have read bobken's post with great interest and have to agree with what he says. As I see it, which ever method of speed regulation you choose, there will always be some delay in speed correction.And what about the belt? This will be expanding and contracting in sympathy with the change in loads on the platter and making matters worse. Maybe a direct drive TT is not such a bad idea after all. Therefore the only way to deal with this problem is to have a platter of sufficient mass that stylus drag is not an issue, use a motor with just enough torque to keep that mass revolving at the required speed and use a psu that maintains a rock steady output without any other external interference. Does this make sense? Si.
I have read bobken's post with great interest and have to agree with what he says. As I see it, which ever method of speed regulation you choose, there will always be some delay in speed correction.And what about the belt? This will be expanding and contracting in sympathy with the change in loads on the platter and making matters worse. Maybe a direct drive TT is not such a bad idea after all. Therefore the only way to deal with this problem is to have a platter of sufficient mass that stylus drag is not an issue, use a motor with just enough torque to keep that mass revolving at the required speed and use a psu that maintains a rock steady output without any other external interference. Does this make sense? Si.
Hi Pjotr,
Yes, these are some more sensible comments, although I have not really found the need to consider this suggested "controlled braking system" you mention, so far.
By whatever means the desirable accelerating or braking effects needed to maintain absolute speed control are carried out (to overcome the inevitably varying drag) it seems to me that there will always be some inherent delays in its operation.
Until the platter actually slows down, and then allowance also needs to be made for the stretchy driving band to 'catch up' and similarly affect the motor's speed (which initially will attempt to maintain speed due to its own inertia, anyway), the 'sensing element' will not know that some correction is needed.
This is so even if this sensing is done directly at the motor, itself, of course.
By this time, it is already too late, unfortunately, and this completely disregards the additional 'reverse' delays with the need for the motor to subsequently react (against its present established inertia, commensurate with its then slightly reduced speed) and via the same stretchy belt speed up the platter again, and overcome the platter's then established inertia, due to its also then lower speed.
It appears to me to be a "no-win" situation, unless, as I said, one could somehow ideally 'read ahead' and anticipate these speed changes, which would be another matter, altogether.
It is much the same with the amplifier analogy I mentioned, except that, with purely electronics circuits, their 'reaction' time is many orders of magnitude faster than that of quite high mass rotating physical bodies, with their also inherently quite high inertial effects.
Perhaps I have misunderstood you here, but I am guessing you refer to some kind of controlled 'magnetic influence' working against the (possibly speed-varying) magnetic forces of the motor, itself, which are probably caused by its back EMF.
I have certainly heard of magnetic 'brakes' to control TT speeds, but if I recall correctly, these are 'static' rather than 'active' devices, simply used for overall speed control.
On a slightly different note, I well recall some of the early Bang & Olufsen decks which I looked at for repair/modification, over 30 Yrs ago.
Their speed was adjusted/controlled by a very crude arrangement of a felt pad which was forced against a ring which rotated along with the platter, and by way of a knob for adjustment, the felt pad was pressed harder or softer against this ring to control the speed!
I imagine they might have described this in their impressive and colourful brochures at the time, as a "Controlled Braking System", but this is rather different from what you have in mind.
Yes, these are some more sensible comments, although I have not really found the need to consider this suggested "controlled braking system" you mention, so far.
By whatever means the desirable accelerating or braking effects needed to maintain absolute speed control are carried out (to overcome the inevitably varying drag) it seems to me that there will always be some inherent delays in its operation.
Until the platter actually slows down, and then allowance also needs to be made for the stretchy driving band to 'catch up' and similarly affect the motor's speed (which initially will attempt to maintain speed due to its own inertia, anyway), the 'sensing element' will not know that some correction is needed.
This is so even if this sensing is done directly at the motor, itself, of course.
By this time, it is already too late, unfortunately, and this completely disregards the additional 'reverse' delays with the need for the motor to subsequently react (against its present established inertia, commensurate with its then slightly reduced speed) and via the same stretchy belt speed up the platter again, and overcome the platter's then established inertia, due to its also then lower speed.
It appears to me to be a "no-win" situation, unless, as I said, one could somehow ideally 'read ahead' and anticipate these speed changes, which would be another matter, altogether.
It is much the same with the amplifier analogy I mentioned, except that, with purely electronics circuits, their 'reaction' time is many orders of magnitude faster than that of quite high mass rotating physical bodies, with their also inherently quite high inertial effects.
Perhaps I have misunderstood you here, but I am guessing you refer to some kind of controlled 'magnetic influence' working against the (possibly speed-varying) magnetic forces of the motor, itself, which are probably caused by its back EMF.
I have certainly heard of magnetic 'brakes' to control TT speeds, but if I recall correctly, these are 'static' rather than 'active' devices, simply used for overall speed control.
On a slightly different note, I well recall some of the early Bang & Olufsen decks which I looked at for repair/modification, over 30 Yrs ago.
Their speed was adjusted/controlled by a very crude arrangement of a felt pad which was forced against a ring which rotated along with the platter, and by way of a knob for adjustment, the felt pad was pressed harder or softer against this ring to control the speed!
I imagine they might have described this in their impressive and colourful brochures at the time, as a "Controlled Braking System", but this is rather different from what you have in mind.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.