Restoring a Roksan Xerxes (original)... Wow!

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25-03-2016, 16:40
pankon

Restoring a Roksan Xerxes (original)... Wow! And no plinth sag anymore.
I have recently restored my Roksan Xerxes, which I had purchased in the UK during my MSc studies in 1989. The exact model year of the turntable is unknown, but I estimate it to be around 1987.
So what I did is the following:
- Changed the blobs, which were rather stiff, with new Roksan blobs X3bi
- Cleaned and re-lubricated the main bearing with a few drops of oil
- Changed the belt with a new one from Origin Live
- Changed the tonearm (perviously Rega RB300) with an Audiomods Series 5, especially tuned for the new cartridge
- Changed the cartridge (previously Dynavector DV10x4 MkII) to a MusicMaker III
After all that, I sat to listen some of my old records. I have to admit that over the last years, my Roksan was somewhere in a corner, because at some point one of my kids had accidentally damaged the cantilever of my Dynavector cartridge and I had not done anything about it since then. It seems that I had grown accustomed to the ease-of-use of the CD and downloadable music from Spotify and Apple Music.

Well, it took only a few seconds of playing a record on the restored Xerxes again to remember what I had been missing...

Compared to the CD, the soundstage was wider and deeper, more palpable, more real, more convincing, with better separation of instruments and voices. Everything was much better. And the supposedly annoying record pops and clicks were so few that I would simply ignore.

Yes, people who still favor analogue sound are not crazy. And even if they are, I am happy to be one of them. Again!
25-03-2016, 17:28
pankon

One thing that concerns me though is that when I tap the top plinth of the turntable with my finger while a record is playing, I do hear the thump coming through the speakers. I wonder to what extent this is expected or whether I should try to remedy it. Does this mean that my tonearm and cartridge are not properly (acoustically) decoupled from the top plinth and this negatively influences the sound?

Could / should this be improved and if yes, how? I have put a rubber washer at the arm base, but it did not seem to make any real difference. I wonder whether the bearing is too tightly screwed on the top plinth...

Any advice from other Xerxes owners, please?
25-03-2016, 17:46
struth

i got that with the thorens. dont think its anything to worry about; it happens with some decks
25-03-2016, 18:21
pankon

Quote:

Originally Posted by struth

i got that with the thorens. dont think its anything to worry about; it happens with some decks

Hey, Grant.

Thanks for the feedback. I wonder that if I could remedy this, which might mean that there would be better decoupling of the cartridge from the plinth, I would be able to achieve an audible improvement..?
26-03-2016, 07:12
Pete The Cat

I ran an original Xerxes for a while. I wouldn't be concerned that you can hear the tapping, it's hard to see how the design could be materially decoupled further. You've done well with the restoration, I didn't ever get round to replacing the blobs on mine since the basic set-up process on its own was fiddly enough and took me several attempts (and they say LP12s are a pain). An under-rated deck these days, may the enjoyment continue !

Pete
26-03-2016, 07:33
jandl100

sounds good - any chance of a photo or 2? :)
26-03-2016, 07:49
pankon

2 Attachment(s)

Roksan Xerxes photos

Yes, gladly.

Here are a couple of photos of the turntable. It sounds pretty good I can tell you. I just wonder whether it can be further improved...

The drilled holes you can see at the back of the top plinth are due to my effort to fix the notorious plinth sag of the early Xerxes models by bolting a metal shim to level the plinth parts. I eventually ended up running a screw horizontally from the back of the plinth towards the center over the gap (cannot be seen in the photos), so the holes where useless any more.

Attachment 16512 Attachment 16513
26-03-2016, 08:05
jandl100

Thanks for the pics - looks great

Some wood filler for those holes, maybe?

Interesting that you found a fix for the notorious Xerxes plinth sag, I'd got the impression it couldn't be done!
26-03-2016, 08:40
struth

Quote:

Originally Posted by pankon

Hey, Grant.

Thanks for the feedback. I wonder that if I could remedy this, which might mean that there would be better decoupling of the cartridge from the plinth, I would be able to achieve an audible improvement..?

as above, I doubt its gonna leave the deck. It is what it is, design wise. If is sounds great then its not an issue unless you like tapping the deck :eyebrows:
26-03-2016, 08:55
pankon

4 Attachment(s)

Quote:

Originally Posted by jandl100

Thanks for the pics - looks great

Some wood filler for those holes, maybe?

Interesting that you found a fix for the notorious Xerxes plinth sag, I'd got the impression it couldn't be done!

Well as a matter of fact, it seems that it can be done after all. And all is needed is a long (approx. 5cm) screw for wood.

My Roksan suffered from a 3mm sag and now -after the fix- it's completely level for more than 3 months. You can see more details at the attached photos about how I did it.

You can also see the Origin Live DC motor attached on the top plinth with some rubber supports to minimize motor vibration and noise. I now wonder whether it would be worthwhile attaching the motor to the bottom plinth, but I am afraid that this is not such a good idea, because it may yield minute sheer stresses between the two plinths, which will be translated to speed variations (not good).

Attachment 16514 Attachment 16515 Attachment 16516

Initially I used two screws (see photo below with the screws running across the plinth cut, bridging the two parts), but then I realized that just one screw would be enough...

Attachment 16517
26-03-2016, 09:10
YNWaN

Quote:

Originally Posted by pankon

One thing that concerns me though is that when I tap the top plinth of the turntable with my finger while a record is playing, I do hear the thump coming through the speakers. I wonder to what extent this is expected or whether I should try to remedy it. Does this mean that my tonearm and cartridge are not properly (acoustically) decoupled from the top plinth and this negatively influences the sound?

Could / should this be improved and if yes, how? I have put a rubber washer at the arm base, but it did not seem to make any real difference. I wonder whether the bearing is too tightly screwed on the top plinth...

Any advice from other Xerxes owners, please?

I'm not sure which component you are referring to when you say the 'top plinth' as I would say there is the outer plinth and the top plate or chassis. Either way it is inevitable that tapping them whilst playing a record will result in a thump sound coming through the speakers. As you know the outer chassis is only decoupled from the plinth by Roksan's rubber 'blobs' and this only offer a modicum of isolation. If tapping the top plate then one is, in essence, effectively tapping the chassis directly and as this is directly coupled to the arm base and the platter this is bound to be heard as transmitted vibration (vibration very much greater than the stylus is generating). I wouldn't recommend placing anything compliant between the arm base and the chassis either. Unfortunately, I also wouldn't recommend changing the AC motor for the DC Origin Live - but you've already done that :).
26-03-2016, 09:39
pankon

Quote:

Originally Posted by YNWaN

I'm not sure which component you are referring to when you say the 'top plinth' as I would say there is the outer plinth and the top plate or chassis. Either way it is inevitable that tapping them whilst playing a record will result in a thump sound coming through the speakers. As you know the outer chassis is only decoupled from the plinth by Roksan's rubber 'blobs' and this only offer a modicum of isolation. If tapping the top plate then one is, in essence, effectively tapping the chassis directly and as this is directly coupled to the arm base and the platter this is bound to be heard as transmitted vibration (vibration very much greater than the stylus is generating). I wouldn't recommend placing anything compliant between the arm base and the chassis either. Unfortunately, I also wouldn't recommend changing the AC motor for the DC Origin Live - but you've already done that :).

Hi Mark,

thanks for the feedback. As a matter of fact, with respect to the motor, I changed it more than 10 years ago, when the PSU of my Xerxes appeared unable to even start rotating the platter. It must have been a PSU problem, but at that time -living in Greece- I did not have too many options of fixing the PSU. Why are you saying that the Origin Live motor worse than the original AC motor?

I see where you are coming from with respect to the thump and it seems quite reasonable. By 'top plinth' I am referring to the top horizontal, where the main bearing and the platter are supported, not the outer wooden casing.

May I ask why you do not think that placing anything compliant between the area base and the chassis is not recommended? I have done it (can be reversed) and did not hear any improvement with respect to the thump issue, nor any degradation of the sound quality either.

Any suggestions for further improvement, if any, are definitely welcome.
26-03-2016, 10:07
YNWaN

Hi Panos, to be honest there are a whole bunch of potential issues.

With regard to the thump there's nothing you can do and nor is there any need to. If you were to tap the sub-chassis of any turntable during play you will hear some thump through the speakers (unless perhaps if it is extremely heavy and dense but that brings other issues). The chassis is supposed to be isolated from the outer plinth and the rest of the world, as such your tapping of the top plate is not an input it should see (unless you bypass the suspension by deliberately tapping on it :)).

The motor issue is another matter. I'm afraid I'm not overly impressed with the OL speed controller and a friend who had one found its speed stability to be deeply questionable. Attaching it to the top plinth also means that all vibration is effectively coupled directly to the platter and arm. I realise you have added some rubber shims but that is unlikely to be having a significant effect I'm afraid. In addition, one of the primary design features of the Xerxes was the rotating motor and this has obviously been lost in your modification. Further, in general, I'm not convinced by the use of DC motors in turntables and after years of experimentation have settled on AC (but that's another long winded story).

The problem with adding compliance to the arm base is that if it is sufficiently compliant to reduce the transmission of vibration it will be decoupling the arm. The point of the chassis is to act as a drain for vibration emanating from the arm (from the cartridge originally) and adding a rubber washer will work against this. The rubber is also likely to create an uneven level of damping which is also undesirable.

Sorry, it's all a bit negative - if you like it that's cool and all that matters. Unfortunately the Xerxes power supplies have gained rather a reputation for being a bit flaky in the long term so I quite understand why you abandoned it.
26-03-2016, 14:24
rubber duck

Looking at the last set of photos with three screws, and provided I've understood what you've done correctly, I think the three screws that now secure the arm board cutout to the top plate may nullify the purpose of the cutout to break up vibration to the arm from the top plate. I think there are several ways to fix the sagging plinth that preserve the design aim of the cutout, e.g. on pink fish.
26-03-2016, 14:58
pankon

Quote:

Originally Posted by rubber duck

Looking at the last set of photos with three screws, and provided I've understood what you've done correctly, I think the three screws that now secure the arm board cutout to the top plate may nullify the purpose of the cutout to break up vibration to the arm from the top plate. I think there are several ways to fix the sagging plinth that preserve the design aim of the cutout, e.g. on pink fish.

Thanks for the feedback. I searched on the Internet a few months ago and the only proposed solution I found was to bolt a metal shim below the top plinth and across the cut-out, to level the two parts and thus eliminate the sag. I did that initially, hence the six holes you can see on my deck. However then I realized that the horizontal screw across the two parts would provide less contact (and coupling) compared to the metal shim method.

Are you perhaps aware of any other method, which may be preferable?

Thanks for the feedback.
26-03-2016, 15:33
pankon

Quote:

Originally Posted by YNWaN

Hi Panos, to be honest there are a whole bunch of potential issues.

With regard to the thump there's nothing you can do and nor is there any need to. If you were to tap the sub-chassis of any turntable during play you will hear some thump through the speakers (unless perhaps if it is extremely heavy and dense but that brings other issues). The chassis is supposed to be isolated from the outer plinth and the rest of the world, as such your tapping of the top plate is not an input it should see (unless you bypass the suspension by deliberately tapping on it :)).

The motor issue is another matter. I'm afraid I'm not overly impressed with the OL speed controller and a friend who had one found its speed stability to be deeply questionable. Attaching it to the top plinth also means that all vibration is effectively coupled directly to the platter and arm. I realise you have added some rubber shims but that is unlikely to be having a significant effect I'm afraid. In addition, one of the primary design features of the Xerxes was the rotating motor and this has obviously been lost in your modification. Further, in general, I'm not convinced by the use of DC motors in turntables and after years of experimentation have settled on AC (but that's another long winded story).

The problem with adding compliance to the arm base is that if it is sufficiently compliant to reduce the transmission of vibration it will be decoupling the arm. The point of the chassis is to act as a drain for vibration emanating from the arm (from the cartridge originally) and adding a rubber washer will work against this. The rubber is also likely to create an uneven level of damping which is also undesirable.

Sorry, it's all a bit negative - if you like it that's cool and all that matters. Unfortunately the Xerxes power supplies have gained rather a reputation for being a bit flaky in the long term so I quite understand why you abandoned it.

Matt, the point IMHO is not to be positive or negative. I do not mind that at all. It's about sharing experiences and helping each other to do better. So, I really appreciate your sincere feedback, as it highlights points you think could be improved on my deck. Quite right so.

I had at least two failures of the original Roksan Xerxes PSU and the repairs seemed to me rather costly at that time. That's why I decided to go for something else and I stumbled upon the OL DC motor. It was before 2000 when I replaced the motor, if I remember correctly. It seemed like a big improvement to me then. From a reliability point of view I had no issue at all. Recently I upgraded the controller unit with a new 'advanced' controller from OL again. It we me to be able to maintain a very constant speed. But I have used it only for a few tens of hours until now.

I have read also various opinions in favor of both DC and AC motors. I have no personal experience or knowledge on the issue, but the AC case locking on the power network's frequency (50 or 60 Hz) in order to keep rotational speed constant, seems pretty reasonable.

I wonder whether I could try alternative motor solutions on my Xerxes to see if they work better than the OL motor. Perhaps the recent ones from Roksan could be retrofitted to my Xerxes? In any case I am not eager to pay an arm and a leg just out of curiosity.in any case, Roksan's idea of the rotating motor seems rather strange to me. I would expect than at any point the stylus friction increases, the motor will just turn, instead of trying to overcome that friction and keep the speed constant. Am I getting something wrong here?

I will continue experimenting. The method is quite clear. Trial and error... -))
26-03-2016, 22:38
Pete The Cat

Aside from Roksan's own under-platter shim, the other conventional solution to plinth sag is the so-called "Gene Rubin fix" (named after a US retailer, I believe) which involves screwing a small plate underneath the upper plinth, bridging the gap at about 12.30 o'clock - ie supporting the sagging side with the opposite side. This does seem to defeat the object of the decoupling principle that the gap is intended to provide though.

The other hitch with the original Xerxes is the PSU, which seems to be unusually fault-prone albeit they are rather old now. Mine was fine at 33 1/3rd but didn't like singles... I still rate the Xerxes nonetheless.

Pete
27-03-2016, 00:39
legb4rsk

Hi,I have an original Xerxes as well.Purchased new back in the early '90's.I also had problems with the old PSU & have the new smaller XPS 7 which has been ok for many years now.I always 'kick start' the platter when spinning up as it is very heavy.The original motor is mounted on the sub-chassis so was completely decoupled from the platter/arm board and the belt drive poked through a hole in that board.I have replaced the main spindle bearing with a TMS one as it has finer tolerances.
I always remove the old lubricant using alcohol & a cotton bud before adding the new.It's surprising how black & gungy the old stuff gets.I used a short nut & bolt with large washers inserted in the cut out slot to remove the sag.I was drawn to the Xerxes as it has a sense of precision that appeals to me.I still havn't heard a TT that would persuade me to spend a lot of money to replace it.I am using the original Tabriz arm & a 2M Black............must count as my best buy after giving such great service after all these years.My one is the ash black look.I have removed the outer box & added a chrome strip around the lower plinth.I will post some pics when I get the chance.
27-03-2016, 06:32
pankon

Quote:

Originally Posted by legb4rsk

Hi,I have an original Xerxes as well.Purchased new back in the early '90's.I also had problems with the old PSU & have the new smaller XPS 7 which has been ok for many years now.I always 'kick start' the platter when spinning up as it is very heavy.The original motor is mounted on the sub-chassis so was completely decoupled from the platter/arm board and the belt drive poked through a hole in that board.I have replaced the main spindle bearing with a TMS one as it has finer tolerances.
I always remove the old lubricant using alcohol & a cotton bud before adding the new.It's surprising how black & gungy the old stuff gets.I used a short nut & bolt with large washers inserted in the cut out slot to remove the sag.I was drawn to the Xerxes as it has a sense of precision that appeals to me.I still havn't heard a TT that would persuade me to spend a lot of money to replace it.I am using the original Tabriz arm & a 2M Black............must count as my best buy after giving such great service after all these years.My one is the ash black look.I have removed the outer box & added a chrome strip around the lower plinth.I will post some pics when I get the chance.

Yes, it seems that many of the older PSUs were rather unreliable due to excessive heat build up, which could not be dissipated. I understand that newer generation PSUs do not have that problem.

In any case, I am still wondering about the theoretical benefits that the spring-loaded motor placement can bring. The purpose of the motor is to keep the rotational speed constant even at more demanding moments, such as when the cartridge friction ('stylus drag') peaks. At such moments the speed should not be affected and the motor should be there to overcome such resistance, not turn around its axis. From a theoretical perspective I am rather cautious. I wonder whether any one has tried to eliminate this axial self-rotation of the motor and provide an opinion about the improvement/deterioration observed...

Furthermore, it's clear that placing the motor on the bottom plinth provides decoupling from the tonearm and cartridge. However, the possible relative motion of the two plinths makes me think that the motor pull may cause minute horizontal motions of the top plinth, which may end up in audible speed variations. Just my two pence...
27-03-2016, 16:46
legb4rsk

Hi,the motor only spins on it's axis when the platters spins up apparently to compensate for the torque needed to start up the very heavy plater. Once up too speed it stabalises & remains in place.If you put the outer platter on upside down,which Roksan have provided the lip cut-out on the underside exactly for this purpose,you can see the motor spin to it's maximum extent & then gradually return to it's original position, assisted by the return spring, as the platter reaches a stable speed.With the platter on upside down you can also check that the belt is running true.Quite a neat solution.

Apologies if seeming to tell you what you already know but may be of benefit for others less well acquainted with the idiosyncrasies of this design.
29-03-2016, 08:59
pankon

Quote:

Originally Posted by legb4rsk

Hi,the motor only spins on it's axis when the platters spins up apparently to compensate for the torque needed to start up the very heavy plater. Once up too speed it stabalises & remains in place.If you put the outer platter on upside down,which Roksan have provided the lip cut-out on the underside exactly for this purpose,you can see the motor spin to it's maximum extent & then gradually return to it's original position, assisted by the return spring, as the platter reaches a stable speed.With the platter on upside down you can also check that the belt is running true.Quite a neat solution.

Apologies if seeming to tell you what you already know but may be of benefit for others less well acquainted with the idiosyncrasies of this design.

Stewart,
I understand the design reason of placing the motor on the bottom plinth (and not on the top), so that vibrations are not carried over to the cartridge through the tonearm. However, I still remain rather sceptical about the motor rotating around its axis. This may help the platter to start easier, but I wonder whether it is beneficial with respect to the sound quality. Should the motor give in when there is even a momentary increase of resistance due to higher cartridge friction? The answer should be negative, I guess...
By the way, the OL DC motor can easily spin up the platter in a matter of a few (4-5) seconds.
29-03-2016, 09:17
pankon

Motor placement on the bottom plinth of Xerxes

Although Origin Live recommend placing their DC motor on the top plinth with a single screw, and although the OL DC motor is quiet, still there are inevitably vibrations that may be carried from the motor to the cartridge through the tonearm.
So I took the decision to experiment a bit and placed the motor on the bottom plinth, as the original Xerxes (AC) motor used to be. With the only difference that I did not allow the motor to rotate around its axis.
Initially, my impression was that the sound had become somewhat 'smaller' in comparison to when the motor was placed on the top plinth. Then, a few tracks and a few minutes later, I realized that the sound was somewhat cleaner and more precise and that gave the above-mentioned impression. It was perhaps the lack of motor vibrations and hence added energy around each note that made things smaller; but also more precise.
So, I will continue my experiment by having the motor on the bottom plinth, but I think that this is how it is eventually going to stay.
I do not know whether any other fellow forum member has had a similar experience with the two alternative motor placements.
29-03-2016, 09:33
YNWaN

My experience is that reducing the vibration transmitted from the motor and/or main bearing significantly increases the signal to noise ratio and so enhances dynamic range - for the same playback level (as previously used) this can initially give the impression of a 'smaller' sound.

I think mounting the motor on the same mechanical plane as the arm and bearing can work but it requires a lot more care with the motor mounting than just a simple rubber shim/gasket.
29-03-2016, 09:43
pankon

Quote:

Originally Posted by YNWaN

My experience is that reducing the vibration transmitted from the motor and/or main bearing significantly increases the signal to noise ratio and so enhances dynamic range - for the same playback level (as previously used) this can initially give the impression of a 'smaller' sound.

I think mounting the motor on the same mechanical plane as the arm and bearing can work but it requires a lot more care with the motor mounting than just a simple rubber shim/gasket.

Mark,
your feedback confirms my initial impression. Slightly 'smaller' sound but also slightly more detail.
I will keep the motor positioned on the bottom plinth, until my 'experiment' is concluded. It may take a few more weeks. But it seems that the placement on the bottom plinth is better (for now).
29-03-2016, 17:23
YNWaN

Restoring a Roksan Xerxes (original)... Wow!

Quote:

Originally Posted by legb4rsk

Hi,the motor only spins on it's axis when the platters spins up apparently to compensate for the torque needed to start up the very heavy plater. Once up too speed it stabalises & remains in place.

That's not quite right I'm afraid. The rotating motor isn't to do with startup torque - it doesn't help this aspect at all and the AC motor used would have no difficulty overcoming the static inertia of the platter anyway. The actual idea is to compensate for variable stylus drag and momentary variations in motor speed. As you say, once up to speed the motor is held stable, in equilibrium, though the spring holding it is under tension. For the idea to work the strength of the spring must be matched to that of the suspension and drive belt compliance - that is to say that it should be significantly less resistive than either (which it is). The concept is thus; the platter and motor are supposed to stay in a fixed relationship in terms of rpm and linked by the drive belt. However, is the rotation of one alters (due to variation in stylus drag or motor flutter) it will react independently initially, stretching the belt until the belt is able to compensate and regain the equilibrium. The idea is that instead of the forces acting to stretch the belt they will cause the motor to rotate by the same amount so maintaining even belt tension and so even speed. It's rather an interesting, but controversial, idea. Speed stability is one of the foundations upon which the success of the Xerxes was based though and so it certainly doesn't seem to do any harm (which on first thought one would rather expect it to).
29-03-2016, 19:00
pankon

Quote:

Originally Posted by YNWaN

That's not quite right I'm afraid. The rotating motor isn't to do with startup torque - it doesn't help this aspect at all and the AC motor used would have no difficulty overcoming the static inertia of the platter anyway. The actual idea is to compensate for variable stylus drag and momentary variations in motor speed. As you say, once up to speed the motor is held stable, in equilibrium, though the spring holding it is under tension. For the idea to work the strength of the spring must be matched to that of the suspension and drive belt compliance - that is to say that it should be significantly less resistive than either (which it is). The concept is thus; the platter and motor are supposed to stay in a fixed relationship in terms of rpm and linked by the drive belt. However, is the rotation of one alters (due to variation in stylus drag or motor flutter) it will react independently initially, stretching the belt until the belt is able to compensate and regain the equilibrium. The idea is that instead of the forces acting to stretch the belt they will cause the motor to rotate by the same amount so maintaining even belt tension and so even speed. It's rather an interesting, but controversial, idea. Speed stability is one of the foundations upon which the success of the Xerxes was based though and so it certainly doesn't seem to do any harm (which on first thought one would rather expect it to).

Mark,
I see where you are coming from, but I think there is an issue (potential weakness?) with the whole concept. Let's assume the classical case of momentary increased cartridge friction (stylus drag, as you call it). In that case the platter will tend to slow down. Then, if we assume that the belt does not stretch, the motor will tend to slow down as well. If however the motor tended to keep its rotational speed unchanged and overcome the platter deceleration, the fact that the motor is attached to a spring, it will not allow the motor to exert the required extra torque, but just give in instead and rotate around its axis, because -as you say- the spring is more compliant that the inertia of the platter.
So, unless my thinking is wrong, I believe the solution would be to have an extra-strong motor, keep it fixed in terms of self-rotation and also have a belt from a material that cannot stretch.
I am not contradicting your line of thinking just for the sake of it, I just think that the self-rotation principle is questionable.
29-03-2016, 21:49
YNWaN

Restoring a Roksan Xerxes (original)... Wow!

I must tell you that the concept I expounded was not my own but that of Touraj Moghaddam designer of the Xerxes, I just phrased it for the purpose of this thread. Personally I have taken a different path. There is however an issue I am personally aware with with the mechanism that you propose; motor torque is proportional to load - during steady running friction is very low and load is also approaching zero as is torque. When the load does vary there is significant compliance surrounding the magnetic field within the motor, this compliance must be compressed before motor torque can increase and this injects delay into the system.

When you write 'extra strong motor' you presumably mean one capable of developing high torque. However, that torque only exists when under load, when loaded by the static inertia of a heavy platter at startup for example. What few seem to realise is that as load approaches zero so does torque - the maximum potential torque of the motor makes no difference in such a situation and once up to speed a turntable platter does offer very minimal load if the platter is balanced and the main bearing is low friction, the mass of the platter is irrelevant.
30-03-2016, 04:56
pankon

Quote:

Originally Posted by YNWaN

I must tell you that the concept I expounded was not my own but that of Touraj Moghaddam designer of the Xerxes, I just phrased it for the purpose of this thread. Personally I have taken a different path. There is however an issue I am personally aware with with the mechanism that you propose; motor torque is proportional to load - during steady running friction is very low and load is also approaching zero as is torque. When the load does vary there is significant compliance surrounding the magnetic field within the motor, this compliance must be compressed before motor torque can increase and this injects delay into the system.

When you write 'extra strong motor' you presumably mean one capable of developing high torque. However, that torque only exists when under load, when loaded by the static inertia of a heavy platter at startup for example. What few seem to realise is that as load approaches zero so does torque - the maximum potential torque of the motor makes no difference in such a situation and once up to speed a turntable platter does offer very minimal load if the platter is balanced and the main bearing is low friction, the mass of the platter is irrelevant.

I see where you are coming from with respect to requiring minimal torque when the platter is rotating at nominal speed. The issue is what happens when a deceleration force appears ('stylus drag') and how this can be overcome without being audibly noticeable.
By 'extra strong motor' I mean that the motor can provide the required torque so quickly, that any momentary increased cartridge friction will be instantly overcome without allowing for any deceleration and hence audible consequences. I assume that the belt will not be stretched (deformed).
The mass of the platter is relevant, because if properly distributed at the edge, it will create a flywheel effect, i.e. it will have a high angular momentum, and thus be less prone to deceleration (or acceleration).
30-03-2016, 08:24
YNWaN

The absolute torque of the motor is not the same as the speed it can alter its speed. In addition, it can't 'steamroller' through load variations as it is actually running at near zero torque (this is irrespective of the maximum torque the motor can generate when under load).

With regard to the mass of the platter, yes it will form a flywheel but not a very effective one when you consider the very low rotational velocity. I put to you that there is a dilemma in the logic of the drive system, a kind of chicken and egg issue or, more correctly, a master and slave problem. Is the platter inertia supposed to be governing the motor or is the motor supposed to be governing the speed of the platter? Or, as often seems to be the case, are both the platter and motor attempting to work against each other?
02-04-2016, 04:59
pankon

Placement of OL DC motor on the bottom plinth
Well, it is now evident that the placement of the Origin Live DC motor on the bottom plinth (or chassis), instead of the top plinth as proposed by Origin Live, provides the following advantages:
- better fine detail
- lower noise floor
- slightly more realistic overall sound, especially with voices and separate instruments
The only tradeoff is the somewhat 'smaller' sound, but if I had to choose I would go for the motor on the bottom plinth.

I wonder whether there are other users of the OL DC motor or other motors who have made the same experiment of motor placement.
02-04-2016, 09:56
YNWaN

You could, in my experience, have achieved the same result and still kept the motor on the top plinth but it would have meant some considerable surgery to the deck and reinvention of the motor mount.
03-04-2016, 05:01
pankon

Quote:

Originally Posted by YNWaN

You could, in my experience, have achieved the same result and still kept the motor on the top plinth but it would have meant some considerable surgery to the deck and reinvention of the motor mount.

Mark,
how do you imagine the mounting of the motor on the top plinth -with the extensive surgery-, in order to get similar results (or even better?) results than mounting the motor on the bottom plinth? Can you perhaps share a drawing or a photo, in case you have done in reality something like that?
Thanks
04-04-2016, 23:01
YNWaN

I'm sorry, I'm in danger of transcribing into your situation too much of my own thoughts and position regarding turntable design. Congratulations on achieving a great improvement and enjoy your records - that's what it's all about :).