Maybe you already know about my power supply for the Thorens TD160, with a signal generator from a dhaen pcb.
After so long time, I looked again at it, made some tests and find out that the main advantage was to get rid of the voltage divider 10K resistor, because it's a great noise maker. But I want to develop another ps.
I'm thinking about the second signal, now created with a simple cap, like in a standard synch motor.
My plan to get rid of it: From the output of the signal generator I take the standard signal, and also take other from a cap. So I have two signal 90º phased. Then apply a volumen control for each signal, I amplify with two GC and two output transformers (I can wind my own trafos here, so I'll adapt the impedances for the GC to be looking at a 8ohm impedance), and the trafo wouldn't be looking at the phasing capacitor. Besides, the second signal can be made as high (or low) in volts as required.
Does this look ok?
After so long time, I looked again at it, made some tests and find out that the main advantage was to get rid of the voltage divider 10K resistor, because it's a great noise maker. But I want to develop another ps.
I'm thinking about the second signal, now created with a simple cap, like in a standard synch motor.
My plan to get rid of it: From the output of the signal generator I take the standard signal, and also take other from a cap. So I have two signal 90º phased. Then apply a volumen control for each signal, I amplify with two GC and two output transformers (I can wind my own trafos here, so I'll adapt the impedances for the GC to be looking at a 8ohm impedance), and the trafo wouldn't be looking at the phasing capacitor. Besides, the second signal can be made as high (or low) in volts as required.
Does this look ok?
Hi.
I'm also doing a ps and have done extensive tests measuring vibration and speed in various possible configurations. I don't know about your previous ps, but if I understand you correctly, you want to do the phase shift before the power amps and then feed each motor phase seperatly. If thats so, I think it is a very good move. My tests show that the phase-shifting cap makes the motor more noisy than it needs to be.
Best Regards,
Guilherme.
I'm also doing a ps and have done extensive tests measuring vibration and speed in various possible configurations. I don't know about your previous ps, but if I understand you correctly, you want to do the phase shift before the power amps and then feed each motor phase seperatly. If thats so, I think it is a very good move. My tests show that the phase-shifting cap makes the motor more noisy than it needs to be.
Best Regards,
Guilherme.
You can check the thread called "change in frequency mains " or something like that. You can find useful info there.
I'm interested in your tests, could you please detail?
Better than the cap shifting, I will invert the signal with an inverting output amp, so the shift is always 90º (provided resistive loads, or identical impedance loads, of course).
Have you found any suitable AC motor?
I'm interested in your tests, could you please detail?
Better than the cap shifting, I will invert the signal with an inverting output amp, so the shift is always 90º (provided resistive loads, or identical impedance loads, of course).
Have you found any suitable AC motor?
I'm using the tt's original AC motor. From the brand name it looks like something from the east.
This is a cut from a post I made at the vinyl engine forum a few days ago:
===============
I have been designing a motor controller 'a la VPI's SDS for myself and now that it is a working prototype I have taken the time to test its efects on the performance of the TT by measuring both motor vibration and platter speed. I'm preparing the data to present it in a website dedicated to the project, but in the mean time here's some thoughts based on those tests (figured this might be useful in this thread).
Regarding motor vibration:
I've found that removing the capacitor and feeding the motor with two separate phases will cause the biggest improvement, reducing vibration by a large factor. Next comes reducing voltage, although, from a certain point, the vibration will increase again. My motor (16V) will vibrate the least when fed with 14V even if it can mantain speed with only 6V. The icing on the cake is phase triming, which provides a smaller but still measurable improvement. My motor literaly feels like its stopped with all those above and a phase trimmed to 92.8 deg.
Regarding mains, I measured 4% THD and looking at the scope the peaks were actualy clipped. This, of course, doesn't help the vibration of the motor. I live in an EEC country, so this will probably be similar in other coutries.
[...] I think you should also consider this: mains also has low freq. "noise" (FM, actually) and that will certaily afect TT performance.
Just last night I measured platter speed and found a peak dev. of 0.02 RPM (0.06%) when using mains feed and 0.005 RPM (0.015%) when using my device (over a period of 5 min). This numbers, are, of course, influenced by the wow introduced by the electromechanical system of the TT itself, but that is the same on both measurements. I think my device's figure is actually being influenced by this and if I had a better TT I would probably get even better results (but this is just a guess).
And then there's the absolute mains freq. and platter/pulley tolerances, which, combined, usually make the platter turn at something else than 33.3 RPM. In my case, I was actually surprised by mains freq. ( I remember it hoovered arround 50.0 Hz. ), but that translated into a platter speed of 33.50 RPM. Again using my device, I was able to get 33.333 RPM (average).
===============
To this I should add that speed measurements were made with a record free platter and that taking the same measurements while playing a record worsened the numbers a bit, suggesting that stylus drag does influence speed stability.
Guilherme.
This is a cut from a post I made at the vinyl engine forum a few days ago:
===============
I have been designing a motor controller 'a la VPI's SDS for myself and now that it is a working prototype I have taken the time to test its efects on the performance of the TT by measuring both motor vibration and platter speed. I'm preparing the data to present it in a website dedicated to the project, but in the mean time here's some thoughts based on those tests (figured this might be useful in this thread).
Regarding motor vibration:
I've found that removing the capacitor and feeding the motor with two separate phases will cause the biggest improvement, reducing vibration by a large factor. Next comes reducing voltage, although, from a certain point, the vibration will increase again. My motor (16V) will vibrate the least when fed with 14V even if it can mantain speed with only 6V. The icing on the cake is phase triming, which provides a smaller but still measurable improvement. My motor literaly feels like its stopped with all those above and a phase trimmed to 92.8 deg.
Regarding mains, I measured 4% THD and looking at the scope the peaks were actualy clipped. This, of course, doesn't help the vibration of the motor. I live in an EEC country, so this will probably be similar in other coutries.
[...] I think you should also consider this: mains also has low freq. "noise" (FM, actually) and that will certaily afect TT performance.
Just last night I measured platter speed and found a peak dev. of 0.02 RPM (0.06%) when using mains feed and 0.005 RPM (0.015%) when using my device (over a period of 5 min). This numbers, are, of course, influenced by the wow introduced by the electromechanical system of the TT itself, but that is the same on both measurements. I think my device's figure is actually being influenced by this and if I had a better TT I would probably get even better results (but this is just a guess).
And then there's the absolute mains freq. and platter/pulley tolerances, which, combined, usually make the platter turn at something else than 33.3 RPM. In my case, I was actually surprised by mains freq. ( I remember it hoovered arround 50.0 Hz. ), but that translated into a platter speed of 33.50 RPM. Again using my device, I was able to get 33.333 RPM (average).
===============
To this I should add that speed measurements were made with a record free platter and that taking the same measurements while playing a record worsened the numbers a bit, suggesting that stylus drag does influence speed stability.
Guilherme.
Ah, so you discovered that the cap is the most important thing to avoid... interesting. How did you measure the vibration, just the fingers? I usually use my sthetoscope
I suppose that the deviation from the 90º is caused by the difference in the loads that the not-exact windings represent, was 92.8 the best result by far, or was small difference when compared to 90º?
I have a lot of suitable transformers, so I can try to invert a singal easily in a short time.
I also have a 1KVA 220/110V transformer, so I'll have the chance to compare what fdegrove suggested.
BTW, I've rewired my RB250, but my stylus left me and I'm still waiting for the goldring1042 to listen again to records.
I had a RPM from Pro-ject, and I know your tt
I suppose that the deviation from the 90º is caused by the difference in the loads that the not-exact windings represent, was 92.8 the best result by far, or was small difference when compared to 90º?
I have a lot of suitable transformers, so I can try to invert a singal easily in a short time.
I also have a 1KVA 220/110V transformer, so I'll have the chance to compare what fdegrove suggested.
BTW, I've rewired my RB250, but my stylus left me and I'm still waiting for the goldring1042 to listen again to records.
I had a RPM from Pro-ject, and I know your tt
Not really.I used a non-magnetic piezo binded to the side of the motor so it is measuring lateral movements. The signal is amplified on the spot by a discrete in-amp and sent to the scope/fft.
Speed is measured with an optic sensor measuring platter lap times with a 10Mhz clock and sending results to the pc via rs232.
92.8deg is a small improvement when compared to no-cap and low-voltage, but still measurable and one that you can feel in your hand. I don't remember the exact number, but I can check it.
I do remember the improvement in vibration from going stock to using my device with all features running: -19 dB.
You should hear it while being driven by my device
.Guilherme.
Wow, nice equipment 
, maybe better than my sthetoscope 
19dB seems a big improvement, I think that this could be heard.
I don't have your equipment so I have to keep the analog track, and build an inverting stage with another GC. I think in a week, everything will be at test stage.
Are you planning to publish your design?
, maybe better than my sthetoscope 19dB seems a big improvement, I think that this could be heard.
I don't have your equipment so I have to keep the analog track, and build an inverting stage with another GC. I think in a week, everything will be at test stage.
Are you planning to publish your design?
Yes, it will be public.
A few screenshots I've taken for my website...
Measuring vibration - as I described earlier, a piezo is binded to the side of the motor. As it moves, the piezo slightly bends and produces a voltage. That voltage is what you see on these pics.
This one is from using the stock trafo while playing a record:
You can see an initial "sine" caused by the power being fed to the motor; the second lower one is the system moving to rest - this would continue to decay if nothing else happened. But the second phase kicks in and so the process repeats itself.
If you look close at the peaks you'll notice a slight amplitude modulation. It's arround 5Hz in frequency. The pulley/platter ratio is 1:10 so a platter moving at 33.3 rpm has a frequency of around 0.5 Hz. So the 5 Hz. would be, more or less, the frequency of the rotating pulley. I think that modulation is caused by the pulley not being perfetly centered; as it moves, it very slightly changes the tension and thus causes the modulation.
Next pic is same record, but now with my device driving the motor:
I don't have a pic here, but if I add gain to take a closer look the wave is not perfect anymore but is mixed with spurious repeating noise together with a much more evident 5Hz. modulation. In other words, the tipical buzzing from the AC motors is so down that it is getting at the same level of other types of noises that have nothing to do with the fact of it being AC. I think you get my drift .
Next pic is a bit large, so here's a link instead:
http://www.itonami.com/temp/t3.jpg
The yellow line is platter speed with the stock trafo, the red is using my device. Note that It's not at 33.3 on purpose, so the two would be close. The blue dialog is the software I made to take speed measurements; those stats are for the red line.
The peak stat is actually peak-to-peak, so to be comparable to the standard wow figures shown on datasheets it should really read 0.0034.
By the way, the manufacturer of this tt specs it with a wow/flutter of 0.08% (if memory serves me), that would give a 0.026 peak dev.
The measured frequency coming out of the supply is within +/- 50 ppm. so these deviations are still wider than those of the frequency itself. Therefor, I think they are not caused by the supply but by the rest of system. A better tt should, in principle, give even better numbers. The limit of the speed stability of the tt becames the tt system itself and is not swamped by the crappy mains feed.
Guilherme.
A few screenshots I've taken for my website...
Measuring vibration - as I described earlier, a piezo is binded to the side of the motor. As it moves, the piezo slightly bends and produces a voltage. That voltage is what you see on these pics.
This one is from using the stock trafo while playing a record:
An externally hosted image should be here but it was not working when we last tested it.
You can see an initial "sine" caused by the power being fed to the motor; the second lower one is the system moving to rest - this would continue to decay if nothing else happened. But the second phase kicks in and so the process repeats itself.
If you look close at the peaks you'll notice a slight amplitude modulation. It's arround 5Hz in frequency. The pulley/platter ratio is 1:10 so a platter moving at 33.3 rpm has a frequency of around 0.5 Hz. So the 5 Hz. would be, more or less, the frequency of the rotating pulley. I think that modulation is caused by the pulley not being perfetly centered; as it moves, it very slightly changes the tension and thus causes the modulation.
Next pic is same record, but now with my device driving the motor:
An externally hosted image should be here but it was not working when we last tested it.
I don't have a pic here, but if I add gain to take a closer look the wave is not perfect anymore but is mixed with spurious repeating noise together with a much more evident 5Hz. modulation. In other words, the tipical buzzing from the AC motors is so down that it is getting at the same level of other types of noises that have nothing to do with the fact of it being AC. I think you get my drift
.Next pic is a bit large, so here's a link instead:
http://www.itonami.com/temp/t3.jpg
The yellow line is platter speed with the stock trafo, the red is using my device. Note that It's not at 33.3 on purpose, so the two would be close. The blue dialog is the software I made to take speed measurements; those stats are for the red line.
The peak stat is actually peak-to-peak, so to be comparable to the standard wow figures shown on datasheets it should really read 0.0034.
By the way, the manufacturer of this tt specs it with a wow/flutter of 0.08% (if memory serves me), that would give a 0.026 peak dev.
The measured frequency coming out of the supply is within +/- 50 ppm. so these deviations are still wider than those of the frequency itself. Therefor, I think they are not caused by the supply but by the rest of system. A better tt should, in principle, give even better numbers. The limit of the speed stability of the tt becames the tt system itself and is not swamped by the crappy mains feed.
Guilherme.
Thanks for the pictures, they show an interesting work indeed. The difference between the piezo output is impressive.
I'm happy to hear that you design will be public, thanks in advance for sharing
I'd like to hear your comments about the differences between the standard AC and your supply.
BTW, I didn't know you had a website
I'm happy to hear that you design will be public, thanks in advance for sharing
I'd like to hear your comments about the differences between the standard AC and your supply.
BTW, I didn't know you had a website
I meant the screenshots are for my *future* website.
Besides what I already said, I can add this: that ten-minute yellow line on the graph really doesn't say it all. While debugging this project I've done numerous test runs over several diferent days and I've found that mains does drift a bit with some days being nastier than others. In fact, I'm thinking of logging mains freq over a period of, say, one week just to put some numbers on this. Add 4% thd to this and some voltage fluctuations, and well...
The website I'm making really details all of this with several diferent psu configurations and comparisons among them. I'm planning of putting it online even before the psu project is completly finished.
I noticed your comment about trying a large trafo. I've also made some tests with one of those and I'd like to hear your comments once you've tried it so I can compare with my own impressions.
Best Regards,
Guilherme.
Besides what I already said, I can add this: that ten-minute yellow line on the graph really doesn't say it all. While debugging this project I've done numerous test runs over several diferent days and I've found that mains does drift a bit with some days being nastier than others. In fact, I'm thinking of logging mains freq over a period of, say, one week just to put some numbers on this. Add 4% thd to this and some voltage fluctuations, and well...
The website I'm making really details all of this with several diferent psu configurations and comparisons among them. I'm planning of putting it online even before the psu project is completly finished.
I noticed your comment about trying a large trafo. I've also made some tests with one of those and I'd like to hear your comments once you've tried it so I can compare with my own impressions.
Best Regards,
Guilherme.
GUILHERME said:I meant the screenshots are for my *future* website.
I noticed your comment about trying a large trafo. I've also made some tests with one of those and I'd like to hear your comments once you've tried it so I can compare with my own impressions.
Best Regards,
Guilherme.
OK, until next week I won't be able to test it, since my td160 has no cartridge until next monday (Goldring1042). I also rewired my RB250Expressimo, so I hope I can hear the differences. I'll report as soon as I adjust the tt.
Well, I've made some tests, just for the motor stopped, and running. With my power supply and the motor stopped there is no noise with my sthetoscope if I apply just the voltage required for a proper starting. If I run the motor, there is no additional noise but some mechanical noise, that I have to fix if I knew.
With the 220/120V 1500va trafo, there is the same result. surprisingly with a bit more voltage (120V) there is no noise, but the transformer is very noisy itself.
Not listening tests until tomorrow.
With the 220/120V 1500va trafo, there is the same result. surprisingly with a bit more voltage (120V) there is no noise, but the transformer is very noisy itself.
Not listening tests until tomorrow.
Raka,
I'm not sure I understand you. You talk about a buzz even when the motor is stopped (I read your other thread). Where does this buzz come from ? is there another transformer inside the tt ?
Regarding your test, again I'm a bit lost. When you said trying a large trafo like fdgrove suggested, I thought you meant just the big trafo between your wallsocket and the tt. But since you talk about changing the voltage, I'm wondering if you're using your psu's amp to drive the big trafo.
Guilherme.
I'm not sure I understand you. You talk about a buzz even when the motor is stopped (I read your other thread). Where does this buzz come from ? is there another transformer inside the tt ?
Regarding your test, again I'm a bit lost. When you said trying a large trafo like fdgrove suggested, I thought you meant just the big trafo between your wallsocket and the tt. But since you talk about changing the voltage, I'm wondering if you're using your psu's amp to drive the big trafo.
Guilherme.
Sorry, It seems I didn't explain myself.
No, there is not another trafo inside, is just that the motor has a low buzz when is connected and not running. Yes, maybe it's a bit strange, but it happens. Reducing the voltage it's almost erased, and is comparable to the noise produced by the series resistor, so I think maybe (I'm sure) the cap is to blame.
Yes, I used the 1,5KVA trafo between the wall and tt, so the input to the tt is 120V. I said higher voltage because with my psu the voltage required is only around 90V, that is 30V less. Hence, I'm surprised that with the trafo giving more voltage, there is no noise in the motor.
No, there is not another trafo inside, is just that the motor has a low buzz when is connected and not running. Yes, maybe it's a bit strange, but it happens. Reducing the voltage it's almost erased, and is comparable to the noise produced by the series resistor, so I think maybe (I'm sure) the cap is to blame.
Yes, I used the 1,5KVA trafo between the wall and tt, so the input to the tt is 120V. I said higher voltage because with my psu the voltage required is only around 90V, that is 30V less. Hence, I'm surprised that with the trafo giving more voltage, there is no noise in the motor.
This thread discusses a dc-blocking device together with schematics:
http://www.diyvideo.com/forums/showthread.php?s=&threadid=2080&highlight=
Guilherme.
I've thinking a bit more (not too much ) about the phase shift, and maybe it's good to provide the means to fine tune the 90º. This way, I can try different angles to see which one optimizes the motor vibration.
It could be done with a simple delay circuit, for 5ms (if 50Hz) and a pot regulating the time constant. This is only an opamp and some resistors and caps. Simulates good in my PC.
Sum up : Signal generator (crystal locked) with two outputs. One directly to a GC and the other one delayed and sent to another GC. Both GC feed two stepup trafos (that I have here in my trash bin) if I can't find a low voltage alternative motor. So no cap at the motor terminals.
I haven't implemented yet any Wien Bridge, has anyone got good results with this? I mean regarding from distortion and estability points of view. My tt turns a bit slower, and maybe I need tu build a 52Hz signal generator.
) about the phase shift, and maybe it's good to provide the means to fine tune the 90º. This way, I can try different angles to see which one optimizes the motor vibration.It could be done with a simple delay circuit, for 5ms (if 50Hz) and a pot regulating the time constant. This is only an opamp and some resistors and caps. Simulates good in my PC.
Sum up : Signal generator (crystal locked) with two outputs. One directly to a GC and the other one delayed and sent to another GC. Both GC feed two stepup trafos (that I have here in my trash bin) if I can't find a low voltage alternative motor. So no cap at the motor terminals.
I haven't implemented yet any Wien Bridge, has anyone got good results with this? I mean regarding from distortion and estability points of view. My tt turns a bit slower, and maybe I need tu build a 52Hz signal generator.
Hi Raka
It's great that you are getting seriously interested in the motor PS - you can get serious improvement by optimising it.
FWIW i would rather try building a high voltage direct drive circuit than mess with transformers. It seems the motors prefer a low impedance drive but you are probably better qualified to make this judgement. At least a lot of the bulk and added distortion of the transformers can be avoided. I am not too sure of the minimum voltage requirements of the Thorens but if you're lucky a bridged 3886 powered at the max allowed voltage may just be enough.
You may also find that a microcontroller is ideal for generating variable and repeatable phaseshifts between the waves. I use a 8515 AVR in a very simple setup.
The advantage of using a Wien bridge is that you need not worry about digital noise generated by the PS entering your system. It seems to be a real problem with Linn supplies.
Being at the moment in Zimbabwe I may not be able to follow this (or any other) thread for some time but certainly hope you'll build the very best Thorens possible
It's great that you are getting seriously interested in the motor PS - you can get serious improvement by optimising it.
FWIW i would rather try building a high voltage direct drive circuit than mess with transformers. It seems the motors prefer a low impedance drive but you are probably better qualified to make this judgement. At least a lot of the bulk and added distortion of the transformers can be avoided. I am not too sure of the minimum voltage requirements of the Thorens but if you're lucky a bridged 3886 powered at the max allowed voltage may just be enough.
You may also find that a microcontroller is ideal for generating variable and repeatable phaseshifts between the waves. I use a 8515 AVR in a very simple setup.
The advantage of using a Wien bridge is that you need not worry about digital noise generated by the PS entering your system. It seems to be a real problem with Linn supplies.
Being at the moment in Zimbabwe I may not be able to follow this (or any other
) thread for some time but certainly hope you'll build the very best Thorens possible
Yes, now that Ive finished a good amp, I'm trying to improve my thorens, or at least trying to get the most of it.
I've been looking to bridge configurations, and a bridged 3886 is not enough voltage, as my motor needs around 90V. Besides, the load the amp will see, is not the usual speaker coil, but a 10K winding, so don`t know the impact will have this on the 3886 peace of life. Maybe I have to search or to design an specific design for this requirements.
The transformer thing is not such a big problem, since I can build my own tranies under specification. Knowing the load of the motor I only have to calculate it, and the 3886 will see 8Ohm load, without saturation.
I'd like to see your configuration, is possible to have the scheme?
I've been looking to bridge configurations, and a bridged 3886 is not enough voltage, as my motor needs around 90V. Besides, the load the amp will see, is not the usual speaker coil, but a 10K winding, so don`t know the impact will have this on the 3886 peace of life. Maybe I have to search or to design an specific design for this requirements.
The transformer thing is not such a big problem, since I can build my own tranies under specification. Knowing the load of the motor I only have to calculate it, and the 3886 will see 8Ohm load, without saturation.
I'd like to see your configuration, is possible to have the scheme?
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