Thanks, Mark. So, steppers aren't the best approach, but a TPA 3122 driven by some signal source plus a step up transformer and an AC sync motor can work well. What, besides avoiding the short circuit, is the step up doing? Any suggestions on a relatively inexpensive and available sync motor?
Would this approach be better and/or cheaper than a DC motor?
This is definitely more involved than I thought it would be.
Would this approach be better and/or cheaper than a DC motor?
This is definitely more involved than I thought it would be.
Stepping up, natch. Not many amps are capable of 110V AC output. This arrangement is also safer.
Sorry, no. If you find one tell us.
They have different strengths and weaknesses. See previous posts on topic in this thread.
I have one dual sine generator now (actually 3 channel, because it is made for 3 phase motors), but I think the beauty of this now is that I can finetune the phase shift. It is not exactly 90 degrees where the motor is the most silent/free of vibrations. A few degrees makes signisicant change. This is true for amplitude also, but that is easy to control.
Regards,
JG
Regards,
JG
Mr. Kelly, some clarification on my part...(and Jeff how are the speakers?)
. How are you finding the dMarKeN primes? (or whatever they get called now....)
Mark Kelly:
Mr. Kelly, I'd be the first one to admit that I am certainly capable of confusing things. Up until now I have never seen your underlying reasoning.
For folks in North America, you can do much worse than Hurst motors. They provided the original motor for the AR turntables, and to my knowledge still offer a version at a very reasonable price (under USD $60 last time I checked). The Airpax/Thompson/Premotec (They are all the same motor, but Phillips had sold Airpax to Premotec, then Premotec to Thompson) are more expensive and a little tougher to get. Apparently Thompson and Hurst are now owned within the same group.I purchased a higher torque "industrial" version which should work nicely, but that cannot be disassembled and modified as per Merrill. I found that out the hard way
And as a Linnie, you would know...Another overpriced Linn upgrade. At least they're consistent.
jeff
. How are you finding the dMarKeN primes? (or whatever they get called now....)Mark Kelly:
Mr. Kelly, I'd be the first one to admit that I am certainly capable of confusing things. Up until now I have never seen your underlying reasoning.
For folks in North America, you can do much worse than Hurst motors. They provided the original motor for the AR turntables, and to my knowledge still offer a version at a very reasonable price (under USD $60 last time I checked). The Airpax/Thompson/Premotec (They are all the same motor, but Phillips had sold Airpax to Premotec, then Premotec to Thompson) are more expensive and a little tougher to get. Apparently Thompson and Hurst are now owned within the same group.I purchased a higher torque "industrial" version which should work nicely, but that cannot be disassembled and modified as per Merrill. I found that out the hard way
I've had a number of TT some with DC motors and some with AC. Bluntly I prefer ac operated motors whether line operated or using a power weinbridge oscillator like in my Thorens TD-125.
Most of the dc motor tables (dd and belt) I've owned had less than stellar speed stability.
Incidentally at the physical level there is no such thing as a dc motor, the commutation is handled either electronically or with brushes as found in a lot of dc servo motors by Panasonic. (Technics and the notorious Pink Triangle) The Technics TT could at least maintain a more or less constant speed across one side, the PT absolutely could not -even with a new motor and controller..
Also I believe all motors except for the possible exception of some slotless coreless types cog to some degree. I think this more of an issue with DD tables whether ac or dc servo types.
Hi Kevin,
I think that Pink Triangle (latterly the Funk Firm) have finally sorted out their reliability and stability issues. About four years ago I had my PT TOO modified by them to full Vector status, involving replacement of the bog-standard AC motor by a current-feedback DC system and the addition of a couple of extra idler pulleys. The speed at 33RPM is still spot on, and the subjective speed stability is excellent. I have heard no reports of problems with this system from other users.
My only complaint is a slight amount of audible whirring noise from the motor, but I can only hear this when I am standing next to the deck.
PT's DC decks (the original PT1 and the Anniversary) did have a pretty poor reputation for reliability: the Annie in particular had a reputation for huge sample variation, with one working fine and the next one out of the factory suffering all sorts of objectionable speed changes. When they did work properly, though, they were outstanding.
Alex
And as a Linnie, you would know...
LOL....I'm sure the local dealer would love to sell me something, but that ain't gonna happen. I've been using a Hercules II for a while now, which works quite well, and is way cheaper than a used Lingo I. I recently made another armboard with the correct S-P distance, the sonic improvement is not subtle. Other than a tiny amount of motor noise, the deck sounds good.
They are very nice with the big amp, but don't like my new amp at all. No surprise, as the amp has a distinct distortion sig. in one channel caused by mismatched driver tubes, which I'll sort out this week.
jeff
Looks like it would to me. It looks exactly (electrically, anyway) like the motors on BIC belt-drive turntables. Calculate the pulley ratios you would need for 33 1/3 and 45 for both the 300 and the 600RPM to help you decide which one to get. I'm thinking the slower running one would make less noise (or the noise would be more subsonic), but that's just a offhand guess.
Look on ebay for BIC turntable motor. I see four entries - the one with the mat also has the pulley for the different speeds, AND the run capacitor. If you get one of those it might be a good idea to get the "motor rebuild kit" as well.
Look on ebay for BIC turntable motor. I see four entries - the one with the mat also has the pulley for the different speeds, AND the run capacitor. If you get one of those it might be a good idea to get the "motor rebuild kit" as well.
AR motor...
Paul Ebert: yup, that's the one...part number 3001-001.
Much easier to get your hands on than the Premotec type (in North America), and much cheaper too. Obviously not a torque monster by any means. Includes the correct capacitor if purchasing a 115 VAC type. I bought a 42115D, as it has superior torque numbers but appears to be constructed differently. This is the motor that I killed taking apart. But it is cheap enough that you could buy 3 of them and mount them on a single turntable and pay for the shipping and not hit the USD $60 price of the 3001-001.
benb:: The 3001-001 motor is the correct one. Any turntable that uses a 300 RPM motor can use it as long as the correct capacitor is used (the 115 volt versions come with the correct capacitor to attain 300 RPM) .I don't know if the BIC motor is the same, but it could be reasonably close.
Jeff:
Jeff which amplifiers are you talking about ?(PM me or email me direct so as not to hijack this thread)
Paul Ebert: yup, that's the one...part number 3001-001.
Much easier to get your hands on than the Premotec type (in North America), and much cheaper too. Obviously not a torque monster by any means. Includes the correct capacitor if purchasing a 115 VAC type. I bought a 42115D, as it has superior torque numbers but appears to be constructed differently. This is the motor that I killed taking apart. But it is cheap enough that you could buy 3 of them and mount them on a single turntable and pay for the shipping and not hit the USD $60 price of the 3001-001.
benb:: The 3001-001 motor is the correct one. Any turntable that uses a 300 RPM motor can use it as long as the correct capacitor is used (the 115 volt versions come with the correct capacitor to attain 300 RPM) .I don't know if the BIC motor is the same, but it could be reasonably close.
Jeff:
. I think that the Linn guys have gotten the short end for some time. Almost all LP12s I've seen could benefit from this. Many times when a new armboard is made, it hasn't been taken into consideration to positively locate it with a (an) additional screw(s). So even if the board is cut to correct dimensions it may not get mounted where it should be. Wait till you see my mockup of a LP12 style turntable. It'll make you laugh. I may even mount an AkitoII on it
Jeff which amplifiers are you talking about ?(PM me or email me direct so as not to hijack this thread)
Yes, I do it this way.
I have a 3.6VA 230V/2*12V trafo. I feed on of the 2 "secunder" with 11V and get 130V on the "primer".
I have tried 3 kind of transformer, a small toroid (about 30VA) worked fine, than a small and cheap (3.6VA) pcb trafo, it was terrible, when loaded the waveform was not really sinus, than a good (Gerth) 3.6VA small pcb trafo, it works fine now. The waveform in nice sinus on the secondary also, also loaded with the motor.
One thing I do not know, why I get only 130V (loaded and not loaded is nearly the same) when I feed the 12V sec with 11V. It does not matter if I connect the 2 secondary parallel or not. For the premotec I need to decrease the amplification a bit, I do not remember what is the input eff. voltage for the trafo, but something like 9V.
TDA2040s are driving the trafos for me, the PSU of the amps has a 2*15V secondary. The amp see about +- 19V DC, it starts clipping at about 11.6Veff.
You should be able to set the 2 amp driving signal level individually, for two reasons : to set the level you need for the motor, to finetune one level to the other to minimize motor vibration.
ÜDV JG
I have a 3.6VA 230V/2*12V trafo. I feed on of the 2 "secunder" with 11V and get 130V on the "primer".
I have tried 3 kind of transformer, a small toroid (about 30VA) worked fine, than a small and cheap (3.6VA) pcb trafo, it was terrible, when loaded the waveform was not really sinus, than a good (Gerth) 3.6VA small pcb trafo, it works fine now. The waveform in nice sinus on the secondary also, also loaded with the motor.
One thing I do not know, why I get only 130V (loaded and not loaded is nearly the same) when I feed the 12V sec with 11V. It does not matter if I connect the 2 secondary parallel or not. For the premotec I need to decrease the amplification a bit, I do not remember what is the input eff. voltage for the trafo, but something like 9V.
TDA2040s are driving the trafos for me, the PSU of the amps has a 2*15V secondary. The amp see about +- 19V DC, it starts clipping at about 11.6Veff.
You should be able to set the 2 amp driving signal level individually, for two reasons : to set the level you need for the motor, to finetune one level to the other to minimize motor vibration.
ÜDV JG
if using a transformer...
I would over-size it for an AC motor. Make yourself a DIY Armegeddon . Look for a 300-500 VA transformer suitable for the voltage for the Premotec, (not sure the voltage, some say 24VAC while I have seen 115-120 VAC versions) or whatever AC motor you get (if not line voltage), For example: if 24 VAC is required for a turntable motor get a transformer with a 115-120 VAC , 3A or better primary and a 24 V secondary. In this case bigger is much better than smaller. Your current will increase, thus torque should not be an issue starting.
If a DC motor, then a temperature compensated circuit should be employed to minimize speed drift (please refer to Mark Kelly in this regard). Power supplies can be purchased that are quite smooth, so using one should be quite easy as long as the output has suitable voltage. An old linear computer supply can provide 12 VDC or 5 VDC , so salvaging one (or buying a new one) is easy enough. I am very unsure of the suitability of a SMPS (switching mode power supply) for use with DC motors, again perhaps Mark Kelly could contribute here. Smoothing caps and/or filters may be required. Again, I always prefer to have a current "resevoir" available from the power supply.
I would over-size it for an AC motor. Make yourself a DIY Armegeddon . Look for a 300-500 VA transformer suitable for the voltage for the Premotec, (not sure the voltage, some say 24VAC while I have seen 115-120 VAC versions) or whatever AC motor you get (if not line voltage), For example: if 24 VAC is required for a turntable motor get a transformer with a 115-120 VAC , 3A or better primary and a 24 V secondary. In this case bigger is much better than smaller. Your current will increase, thus torque should not be an issue starting.
If a DC motor, then a temperature compensated circuit should be employed to minimize speed drift (please refer to Mark Kelly in this regard). Power supplies can be purchased that are quite smooth, so using one should be quite easy as long as the output has suitable voltage. An old linear computer supply can provide 12 VDC or 5 VDC , so salvaging one (or buying a new one) is easy enough. I am very unsure of the suitability of a SMPS (switching mode power supply) for use with DC motors, again perhaps Mark Kelly could contribute here. Smoothing caps and/or filters may be required. Again, I always prefer to have a current "resevoir" available from the power supply.
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Yeah, I too thought that 3.6 VA is too small. Also, I think you'd need to put the two secondaries in series and feed them with the 24 VAC to get 230 VAC out, though I'm not sure about that. I believe it's normal usage would be that you put 230VAC in and you get +12volts on one secondary and -12 volts on the other.
The reference I was making was to the Premotec style AC motors as used in the Linn style turntables (or specifically the AR style tables of which the Linn is one of...). The Hurst motors requires 115V so surely you could get a 100 VA toroid cheap enough. As I stated, I like to have reserve torque available, therefore reserve current.
The Premotec motors don't require very much power either, but there is a significant improvement in sound using an Armegeddon with a standard issue LP12 (do they call this a "Basic" now?). Since Naim continues to sell these, I must believe there is a significant improvement. DIY versions can be made pretty inexpensively.
The Premotec motors don't require very much power either, but there is a significant improvement in sound using an Armegeddon with a standard issue LP12 (do they call this a "Basic" now?). Since Naim continues to sell these, I must believe there is a significant improvement. DIY versions can be made pretty inexpensively.
300-500VA ? 3,6VA is already 4 times as what is required. With larger trafo you get more distorsion at zero cross. I would not recommend that at all.
Unfortunately some of the ready made transformators are saturating near the limits of the core material. When I order a toroid for what I specify, I always ask for under saturating it with 10-15% to the normal spec. I do not get that much power out of the trafo, but I get less problems in audio circuits.
Same thing, I had two trafo with the same phisical size. One is 3.6VA the other is 4,5VA. The 4,5VA one makes ugly waveform at the output. Even when not loaded at all. If I go well under the specified voltage, than it gets right, but than I do not get the voltage on the output what I want.
I think the best is to get a small toroid (where I order it is 30VA, it is too big I think) but with a right specs.
I think right now for me it is more important to get the TDA amps replaced with a discrete amp, running from stabilized PSU.
ÜDV JG
Unfortunately some of the ready made transformators are saturating near the limits of the core material. When I order a toroid for what I specify, I always ask for under saturating it with 10-15% to the normal spec. I do not get that much power out of the trafo, but I get less problems in audio circuits.
Same thing, I had two trafo with the same phisical size. One is 3.6VA the other is 4,5VA. The 4,5VA one makes ugly waveform at the output. Even when not loaded at all. If I go well under the specified voltage, than it gets right, but than I do not get the voltage on the output what I want.
I think the best is to get a small toroid (where I order it is 30VA, it is too big I think) but with a right specs.
I think right now for me it is more important to get the TDA amps replaced with a discrete amp, running from stabilized PSU.
ÜDV JG
this is a good quality trafo : http://kepfeltoltes.hu/111221/gerth3_6VA_www.kepfeltoltes.hu_.jpg
this one was the first, it was cheap, but bad : http://kepfeltoltes.hu/111221/makrai4_5VA_www.kepfeltoltes.hu_.jpg (bought in an amateur shop I told several time I will never ever shop again
Both has the same size, shape, housing. For the cheap one, I had to decrease input voltage to get something like sinus on the output. It is loaded on the screenshot.
I just checked, a commercial PSU made for Rega also use 3.6VA trafo on the output, but just one. That is just a 110V sinus generator. I'm using two, for the two phase.
Regards,
JG
this one was the first, it was cheap, but bad : http://kepfeltoltes.hu/111221/makrai4_5VA_www.kepfeltoltes.hu_.jpg (bought in an amateur shop I told several time I will never ever shop again
Both has the same size, shape, housing. For the cheap one, I had to decrease input voltage to get something like sinus on the output. It is loaded on the screenshot.
I just checked, a commercial PSU made for Rega also use 3.6VA trafo on the output, but just one. That is just a 110V sinus generator. I'm using two, for the two phase.
Regards,
JG
I've noted a very small improvement by oversizing the trafo, possibly due to better regulation, possibly due to my imagination. The kit I used to sell used two 6VA trafos, one per phase. If you go way oversize the magnetisation current becomes too high and many problems arise.
Two things to watch for: small trafos have poor regulation, often 20% or more. Because you are using the trafo backwards, the regulation is also reversed. To counter this you'll need a trafo that is designed to produce a lower voltage than your expected feed voltage.
An example might make this clearer. Let's say your amp puts out say 12V AC and you want to step that up to 120V so you buy a 120V / 12V trafo with 20% regulation. What this means is that the trafo produces about 15V unloaded but the load drags it down to 12V, so in fact the trafo has windings of 8:1 not 10: 1. If you wire it in reverse it will step up the voltage x 8 so you'll get 96 V unloaded. The load will drag it down further, perhaps to 80V. This is an extreme example but the effect is real, you'd be better off with a 9V trafo. If that's too low you can always turn the amp output down and it will usually produce a better waveform at a lower voltage anyway.
This unfortunately exacerbates the secondary inductance problem. Mains trafos are designed to have adequate primary inductance, the secondary inductance is proportional to this divided by the square of the turns ratio so a lower voltage rating corresponds to a lower inductance.
Two things to watch for: small trafos have poor regulation, often 20% or more. Because you are using the trafo backwards, the regulation is also reversed. To counter this you'll need a trafo that is designed to produce a lower voltage than your expected feed voltage.
An example might make this clearer. Let's say your amp puts out say 12V AC and you want to step that up to 120V so you buy a 120V / 12V trafo with 20% regulation. What this means is that the trafo produces about 15V unloaded but the load drags it down to 12V, so in fact the trafo has windings of 8:1 not 10: 1. If you wire it in reverse it will step up the voltage x 8 so you'll get 96 V unloaded. The load will drag it down further, perhaps to 80V. This is an extreme example but the effect is real, you'd be better off with a 9V trafo. If that's too low you can always turn the amp output down and it will usually produce a better waveform at a lower voltage anyway.
This unfortunately exacerbates the secondary inductance problem. Mains trafos are designed to have adequate primary inductance, the secondary inductance is proportional to this divided by the square of the turns ratio so a lower voltage rating corresponds to a lower inductance.
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