The original purpose was actually to provide 230V/50Hz power to my UK configuration Garrard 401, but that table is not ready for prime time, so I set the jumpers for 60Hz and wired it for 115V output.
I have tried it with both my older series TD-124 and my TD-124 MKII.. I am running these tables at 110V which is about as close to a sweet spot as I have encountered.
It was originally intended as a one off to power that Garrard 401, but I am going to build another for one of my other tables.
I did it mostly for the challenge, but it seems to work well and is so far trouble free. I treat it exactly like wall socket power, so it is designed to survive starting loads, load dump, and running open circuit.
In subjective terms if there are improvements they are subtle, mostly I think related to somewhat quieter motor operation. What I can say is there is no negative effect on turntable performance, and no impact on reliability.
The TD-124 has pretty high rotating mass and short term frequency variations which this device is very effective at dealing with are less of a problem with this table than they might be with another lower inertia table.
The mains power here is extremely distorted which results in some noises the motors do not make while powered on this clean sine source, and the very stable output voltage with a fixed load can't hurt.
I would probably choose an output transformer with slightly lower winding resistance, but other than that I am happy with the performance of this design.
I have tried it with both my older series TD-124 and my TD-124 MKII.. I am running these tables at 110V which is about as close to a sweet spot as I have encountered.
It was originally intended as a one off to power that Garrard 401, but I am going to build another for one of my other tables.
I did it mostly for the challenge, but it seems to work well and is so far trouble free. I treat it exactly like wall socket power, so it is designed to survive starting loads, load dump, and running open circuit.
In subjective terms if there are improvements they are subtle, mostly I think related to somewhat quieter motor operation. What I can say is there is no negative effect on turntable performance, and no impact on reliability.
The TD-124 has pretty high rotating mass and short term frequency variations which this device is very effective at dealing with are less of a problem with this table than they might be with another lower inertia table.
The mains power here is extremely distorted which results in some noises the motors do not make while powered on this clean sine source, and the very stable output voltage with a fixed load can't hurt.
I would probably choose an output transformer with slightly lower winding resistance, but other than that I am happy with the performance of this design.
I just decided to boost the output voltage to 117V under load, no difficulties in doing so.
Edit: One other observation is that the strobe on either table is much steadier (dots not moving around "aka jiggling back and forth" at all) so I guess there are minute variations in line frequency that the strobe sees and that the source obviously eliminates.(?)
Edit: One other observation is that the strobe on either table is much steadier (dots not moving around "aka jiggling back and forth" at all) so I guess there are minute variations in line frequency that the strobe sees and that the source obviously eliminates.(?)
Thanks for posting your findings. I was going to ask if this would work for a Garrard 401 but you have already answered that question.
KR try reducing the voltage down to about 90 volts. a lot less cogging in most motors. might have to vary it a bit to find the sweet spot with your motor.
I've tried running at voltages as low as 90V which necessitates disassembly and re-adjustment of the eddy current brake as torque falls drastically, at a certain voltage even fully warmed up there is not enough torque to maintain speed. The motor used in this table is a shaded pole induction motor and it is fairly sensitive to supply voltage.
After all of that effort the table just didn't sound very good, something about all of that motor torque being necessary for the basic performance of the table.
Things start to go south sonically speaking around 105 - 110V based on experience with my two tables. I typically run them around 110 - 112V which seems like the best compromise.
After all of that effort the table just didn't sound very good, something about all of that motor torque being necessary for the basic performance of the table.
Things start to go south sonically speaking around 105 - 110V based on experience with my two tables. I typically run them around 110 - 112V which seems like the best compromise.
The wattage in your example isn't multiplied by the turns ratio, just the voltage; current is reduced by the same factor so power remains roughly the same. The input side will need slightly more power to make up for losses in the xfmr.
As others have pointed out, the turns ratio isn't 10:1 in your case. 12V out is at full load, unloaded the voltage will be ~15V so the turns ratio is closer to 8:1. Which means if you want 120V out (no load) you need to provide 15VAC in (more if you want 120VAC out at full load).
I'm using a 1:12 step up and due to winding losses on both the primary and secondary sides I find it takes slightly more than 10Vrms to produce 120Vrms under load, at my target load currents the discrepancy is about 4%, another way of putting this would be to state that the no load to loaded regulation at 15VA is about -4%, obviously worsens as load current is increased.
To minimize losses and improve regulation under varying load I would probably use a slightly bigger transformer than the 50VA I choose for the step up. Alternately with some additional complexity the output could be enclosed in a secondary feedback loop which I may attempt in a future iteration.
This design is fixed frequency at either 50Hz or 60Hz, but I may at some point look at revising the design to allow a small range of adjustment which of course will come at the cost of considerable additional complexity. For this application it's not needed.
So far no problems.
To minimize losses and improve regulation under varying load I would probably use a slightly bigger transformer than the 50VA I choose for the step up. Alternately with some additional complexity the output could be enclosed in a secondary feedback loop which I may attempt in a future iteration.
This design is fixed frequency at either 50Hz or 60Hz, but I may at some point look at revising the design to allow a small range of adjustment which of course will come at the cost of considerable additional complexity. For this application it's not needed.
So far no problems.
You're probably familiar with the low power PSU we make which uses DDS as the sinewave source. It also has a HV DC supply and uses a directly coupled output amp (no xfmr), so the output has minimum droop under load, but unfortunately, it is limited to 5W motors or less. I'm in the process of prototyping a higher output version (targeting 15W right now), but it will have to use the step up xfmr design that you (and most others) used. It hasn't worked out to badly:120VAC no load and ~115VAC at 16W full load.
DDS chips aren't that expensive and provide the ultimate in frequency control, but for DIY design they have 2 problems: All the chips are very small footprint SMD and they need to be programmed from an embedded controller. But given the complexity of one of the PLL designs posted on this thread, I'm not sure why he wouldn't just take the leap to DDS....
DDS chips aren't that expensive and provide the ultimate in frequency control, but for DIY design they have 2 problems: All the chips are very small footprint SMD and they need to be programmed from an embedded controller. But given the complexity of one of the PLL designs posted on this thread, I'm not sure why he wouldn't just take the leap to DDS....
I have thought to some extent about using a DDS in a future design and am starting the arduous task of learning how to use and write code for the arduino, realistically speaking with all the other stuff currently on my plate it may be a year or more before I get to it.
Anecdotally I think the TD-124 would benefit from a lower source impedance than I am providing based on the noticeable difference in starting performance with the buck transformer box I normally use on the other table. I am probably going to work on a version where the transformer is enclosed inside a control loop. I actually have an instantaneous output capability of >120W and could make use of it to provide higher starting current capability.
My converter performance is very similar to what you mentioned in your post. My target voltage under load is somewhat lower than yours in order to mitigate some well know TD-124 E50 related motor issues.
The unit seems to be reliable, I've been using for a number of weeks now on a regular basis with no issues at all.
Anecdotally I think the TD-124 would benefit from a lower source impedance than I am providing based on the noticeable difference in starting performance with the buck transformer box I normally use on the other table. I am probably going to work on a version where the transformer is enclosed inside a control loop. I actually have an instantaneous output capability of >120W and could make use of it to provide higher starting current capability.
My converter performance is very similar to what you mentioned in your post. My target voltage under load is somewhat lower than yours in order to mitigate some well know TD-124 E50 related motor issues.
The unit seems to be reliable, I've been using for a number of weeks now on a regular basis with no issues at all.
Sounds like an interesting design.
Another thing you can do to reduce the start up torque requirements (therefore power) is to ramp the frequency from a lower starting point (if/when you go the DDS route). With a direct drive output (no xfmrs) this is fairly easy to do all the way down to ~30 Hz (~17 RPM). With a xfmr output, you will be limited to ~45 Hz (25 RPM) which will still reduce the start up requirement significantly. Not sure how an induction motor would respond to that frequency; the AC synch motors vibrate quite a bit more as the phase cap is also way out from optimum value, but it's only short lived at power up (~1.25 sec). The benefit is even more apparent when starting in 45 RPM mode (still starts at 30Hz and ramps to 81Hz).
Another thing you can do to reduce the start up torque requirements (therefore power) is to ramp the frequency from a lower starting point (if/when you go the DDS route). With a direct drive output (no xfmrs) this is fairly easy to do all the way down to ~30 Hz (~17 RPM). With a xfmr output, you will be limited to ~45 Hz (25 RPM) which will still reduce the start up requirement significantly. Not sure how an induction motor would respond to that frequency; the AC synch motors vibrate quite a bit more as the phase cap is also way out from optimum value, but it's only short lived at power up (~1.25 sec). The benefit is even more apparent when starting in 45 RPM mode (still starts at 30Hz and ramps to 81Hz).
All sorts of options are possible with the DDS and an Arduino based controller. My big concern with ramping up frequency with an induction motor is that starting the motor at lower frequencies is going to require a lot more current.
In the case of this design it is actually intended to be a substitute for AC wall power, the table just plugs into it and you use the table as originally intended - a lot of these tables have drive trains that are interlinked with the power switch. The source will run happily into an open circuit and can start a stone cold motor into its nominal mechanical load without issues. (I have heard stories of exploding chip amps doing these things so I erred on the side of caution; the parts are very cheap to implement the required protection.)
In the case of this design it is actually intended to be a substitute for AC wall power, the table just plugs into it and you use the table as originally intended - a lot of these tables have drive trains that are interlinked with the power switch. The source will run happily into an open circuit and can start a stone cold motor into its nominal mechanical load without issues. (I have heard stories of exploding chip amps doing these things so I erred on the side of caution; the parts are very cheap to implement the required protection.)
That is certainly not a good option: from a purely theoretical point of view, you need to ramp voltage and frequency by exactly the same factor. That is necessary to keep the induction in the motor below saturation (going beyond has no practical usefulness anyway, because the available torque to current ratio decreases when the motor saturates).
In practice, you'll probably need some additional derating of the voltage, because these kind of things don't work linearly, and anyway the resistant torque decreases with a decreasing speed (generally with an exponent greater than one), unless you have an excess of dry friction, which is a symptom of serious problems elsewhere.
It will also protect your transformer from unnecessary stress (it saturates in the same way as the motor, just more abruptly)
Anyway, shaded poles work more or less (and rather less than more) properly at a single frequency, which is 50 or 60Hz: outside these limits, things degrade very quickly.
Therefore, ramping for these motors only has very moderate benefits, compared to a real 3-phase asynchronous motor.
If you ramp something, you have to do voltage too, and keep it minimal, because these motors don't work very well outside of their design target
Last edited:
I understand all of that quite well, was responding to the previous post..
A more universal DDS device could easily offer those features for use with synchronous motors, but that is beyond the scope of what I was attempting which performs as intended for the narrow range of application I designed it for.
I do not know the worst case operating frequency range of the E50, but it was designed for operation on 50Hz to 60Hz mains, I have not run one outside of that range.
A more universal DDS device could easily offer those features for use with synchronous motors, but that is beyond the scope of what I was attempting which performs as intended for the narrow range of application I designed it for.
I do not know the worst case operating frequency range of the E50, but it was designed for operation on 50Hz to 60Hz mains, I have not run one outside of that range.
I just picked up a Powertron 1500va AC power source. it is basically 4 class-AB power amps driven by an external oscillator that drives a quad primary toroid output transformer and can output 0-250V. I thought it interesting that these big AC supplies work exactly as the turntable motor controllers!
Oddly, it has no control circuitry at all. no regulation at all! it is just a big amplifier! The output transformer is interesting in that it is made up of four toroid cores. each primary is separate but the secondaries are connected in series. The amp modules run off of +/-45v and have six pairs of mosfets per module. so they are going for very high current but not a lot of voltage on the primary side and stepping up through the transformer. very similar to a TT motor controller.
Note that the latest version of XY amplifier boards no longer have the reference designators, but have otherwise not changed. (Improved) You can refer to the existing pictures for guidance.
I bought a Lenco tt before Christmas. I was actually only intending to buy the MG-1 linear tracking arm that was on it, but the seller encouraged me to take the table as well and listen to it before I took the arm off .... long and short of it is, I fell in love with the table (as he intended) and bought it as well as the arm. My SOTA of 20 years standing has now been retired to its packing box.
So to my point - this table doesn't have any speed control. It runs straight off 240v mains. Then I found Lenco Heaven. Its a nice forum, with a very specific focus. And they have got an interesting thread about motor contollers.
http://www.lencoheaven.net/forum/index.php?topic=13981.0
It is a good read with lots of info, which is relevant to all AC single phase motors (Lenco, Thorens, etc). I've procured a PCB and hope to build a controller soon.
So to my point - this table doesn't have any speed control. It runs straight off 240v mains. Then I found Lenco Heaven. Its a nice forum, with a very specific focus. And they have got an interesting thread about motor contollers.
http://www.lencoheaven.net/forum/index.php?topic=13981.0
It is a good read with lots of info, which is relevant to all AC single phase motors (Lenco, Thorens, etc). I've procured a PCB and hope to build a controller soon.
Nigel's design is discussed in another thread here as well, the most major difference between this one and his is that mine uses a xtal controlled reference to generate very precise 50Hz or 60Hz output and is not adjustable, and is intended for single phase induction motors typically of the sort found in Garrard 301/401, Thorens TD-124 etc. It will work fine with any small synchronous motor, it does lack the flexibility of speed adjustment since the target tables generally have provisions for adjusting speed.
Elvee posted an intriguing synthesizer design that does provide the benefits of crystal stability but also allows for some speed adjustment - as I recall +/- 1% or so, details are a few pages back in the thread; look for his latest implementation.
Elvee posted an intriguing synthesizer design that does provide the benefits of crystal stability but also allows for some speed adjustment - as I recall +/- 1% or so, details are a few pages back in the thread; look for his latest implementation.
- Status
- Not open for further replies.