Raka,
I would suggest you try to make frequency variable at least arround the 50Hz instead of going after variable phase. I say this because it seems you already got noise down to accetable levels and because the sonic benefits of getting platter speed right are more than just pitch and are greater than trimming phase (IMO, of course).
Guilherme.
I would suggest you try to make frequency variable at least arround the 50Hz instead of going after variable phase. I say this because it seems you already got noise down to accetable levels and because the sonic benefits of getting platter speed right are more than just pitch and are greater than trimming phase (IMO, of course).
Guilherme.
Thanks for your suggestion, Guilherme. I was also thinking about making provisions for fine tuning the speed, as with a Wien Bridge it seems not so difficult. It's a pitty I can't use the Dhaen pcb... it works fantastic but my tt has bit bigger platter than desired.
Now I'm spending time with the output trafos, and cannot simulate a good solution. Need to study a bit more. Any place to find info about transformers and saturation in step up condition? Should a smaller turn ratio give better results?
Now I'm spending time with the output trafos, and cannot simulate a good solution. Need to study a bit more. Any place to find info about transformers and saturation in step up condition? Should a smaller turn ratio give better results?
Sorry, the only info I can remember is from the book "The Art of Electronics". They show a circuit to do just what you're doing - to step-up a sine through an amp and then a trafo. The amp's feedback loop is taken partially from the transformer's output, so output impedance is improved. If you dont have this book email me privately.
Guilherme.
Guilherme.
Hi.
I think you'll find your answer in this paper:
http://engr.calvin.edu/PRibeiro_WEBPAGE/courses/engr332/Handouts/oscillators.pdf
J.Guilherme.
I think you'll find your answer in this paper:
http://engr.calvin.edu/PRibeiro_WEBPAGE/courses/engr332/Handouts/oscillators.pdf
J.Guilherme.
Well, the oscillator is done and works beautifully. Even less noise than before (can't note if the motor is switched or not, with a sthetoscope). Distortion is less than 0.2%
I fine tuned the speed, and results that my TD requires around 52Hz to achieve 33*1/6.
Sound? Very good indeed. Now I have to work on the power stage, with phase control, to get rid of the cap.
Thanks Guilherme for your link.
I fine tuned the speed, and results that my TD requires around 52Hz to achieve 33*1/6.
Sound? Very good indeed. Now I have to work on the power stage, with phase control, to get rid of the cap.
Thanks Guilherme for your link.
I'm glad you found it useful. 
Now that you can get really close to 33.33, how would you comment the sound ? do you think it's all just about pitch or do you notice other things sort of falling into place ?
You remind me that I really have to get back to my own psu, stuff it inside a box and call it finished.
I've been having a lot of fun with those measurements; the speed meter was improved and I'm actually measuring the effects of stylus drag on platter speed. Of course, that led to more experiments, turning it into a project within a project.
I ordered a wow&flutter meter to complement the experiment's data, once that is done I'll show you the results (and then get back to the psu). It's a subject I see mentioned a lot but without much (any) references to supporting data.
So much to do and so little time available, sometimes it gets frustrating
Best Regards,
J.Guilherme
Now that you can get really close to 33.33, how would you comment the sound ? do you think it's all just about pitch or do you notice other things sort of falling into place ?
You remind me that I really have to get back to my own psu, stuff it inside a box and call it finished.
I've been having a lot of fun with those measurements; the speed meter was improved and I'm actually measuring the effects of stylus drag on platter speed. Of course, that led to more experiments, turning it into a project within a project.
I ordered a wow&flutter meter to complement the experiment's data, once that is done I'll show you the results (and then get back to the psu). It's a subject I see mentioned a lot but without much (any) references to supporting data.
So much to do and so little time available, sometimes it gets frustrating
Best Regards,
J.Guilherme
Well, now things are a bit more crisp, but this has to do with the higher pitch. Anyway, I tested a LP vs a CD, now with same speed and you know who won.
But this afternoon I played a solo piano work (Satie) and there is a not so light wow in sustained notes. I fine tuned the oscillator frequency (I use two pots to equalize the resistance values and 1% cap values) but no big improvings. Later, I compared this PS with the big trafo, and the wow was the same, so the LP pressing is to blame. Anyway, I had no time to do more tests, tomorrow I will play some other piano recordings to see what happens.
Antonio? Vivaldi? are you there? where is your l'estro armonico? in my LP? I hear somethin... you are there!
Sorry, I'm back to my tt, Vivaldi is calling me. See you tomorrow.
But this afternoon I played a solo piano work (Satie) and there is a not so light wow in sustained notes. I fine tuned the oscillator frequency (I use two pots to equalize the resistance values and 1% cap values) but no big improvings. Later, I compared this PS with the big trafo, and the wow was the same, so the LP pressing is to blame. Anyway, I had no time to do more tests, tomorrow I will play some other piano recordings to see what happens.
Antonio? Vivaldi? are you there? where is your l'estro armonico? in my LP? I hear somethin... you are there!
Sorry, I'm back to my tt, Vivaldi is calling me. See you tomorrow.
I'll use soprano voices this evening, thanks again for the suggestion.
What I've thinking about is to change the digital circuit of the dhaen pcb. I've studied the counter, and think how to increase the frequency a bit, as is a 8bit counter, there is space for fine tuning. Besides, I think a digital oscillator is more constant, but I'll test both.
How close do you get this improvement? Has to be 33.33 exact to get that thing you mention?
What I've thinking about is to change the digital circuit of the dhaen pcb. I've studied the counter, and think how to increase the frequency a bit, as is a 8bit counter, there is space for fine tuning. Besides, I think a digital oscillator is more constant, but I'll test both.
How close do you get this improvement? Has to be 33.33 exact to get that thing you mention?
Hi.
When I started using my psu, the initial impression was the obvious change in pitch. Latter, in the many test runs I did, I started to notice the improvement on the 'presence' of the voices.
I don't know how close you need to get to hear it, I can only tell you how close I am. The best I got was 33.333 rpm (average over an entire side of the LP).
But this is an average, stylus drag and other factors will make this number worse when you look at a single lap, still, it gives an idea of where I am.
I do agree with you with going digital.
J.Guilherme
When I started using my psu, the initial impression was the obvious change in pitch. Latter, in the many test runs I did, I started to notice the improvement on the 'presence' of the voices.
I don't know how close you need to get to hear it, I can only tell you how close I am. The best I got was 33.333 rpm (average over an entire side of the LP).
But this is an average, stylus drag and other factors will make this number worse when you look at a single lap, still, it gives an idea of where I am.
I do agree with you with going digital.
J.Guilherme
You are doing an interesting work, indeed.
Well, I've tested my digital ps, and works well, and in 180 minutes, the lp spinned 100 times, so I think the speed is as close as I want to get.
But my final conclusion (final?, what is final? ) is that the digital has deeper and better bass. There is absolutely no wow in the piano recording I mentioned yesterday. Theorically, the wien bridge would do a great job, but is not so stable (the voltage amplitude isn't as constant as the digital oscillator), so despite it sounds good, is not so good as the dhaen one.
Now I'll work on the amp stage, if I managed to stop listening to the Firebird
Well, I've tested my digital ps, and works well, and in 180 minutes, the lp spinned 100 times, so I think the speed is as close as I want to get.
But my final conclusion (final?, what is final?
) is that the digital has deeper and better bass. There is absolutely no wow in the piano recording I mentioned yesterday. Theorically, the wien bridge would do a great job, but is not so stable (the voltage amplitude isn't as constant as the digital oscillator), so despite it sounds good, is not so good as the dhaen one.Now I'll work on the amp stage, if I managed to stop listening to the Firebird
not such a good result
Well,
After reading all those interesting posts about a power supply for an AC synchronous motor I decided to build one myself.
So I made a wien-bridge oscillator, and gainclone power amplifier which I connected to an inverted mains transformer.
This set-up gives me a nice sinus which I can vary in voltage from 0 to 240 volts.
When I hooked this up to my turntable (Thorens TD160 MkII) the sinus stays nice but the results are horrible. I managed to build myself a nice wowing turntable. Back to standard mains give a much better result.
After a lot of searching and measuring I found that my gainclone amp is looking at an impedance (of the transformer) of 68 Ohms. Could this be the problem. Is the motor getting too little current to work well.
And if so, how can this be solved?
any help appreciated, MArco
Well,
After reading all those interesting posts about a power supply for an AC synchronous motor I decided to build one myself.
So I made a wien-bridge oscillator, and gainclone power amplifier which I connected to an inverted mains transformer.
This set-up gives me a nice sinus which I can vary in voltage from 0 to 240 volts.
When I hooked this up to my turntable (Thorens TD160 MkII) the sinus stays nice but the results are horrible. I managed to build myself a nice wowing turntable. Back to standard mains give a much better result.
After a lot of searching and measuring I found that my gainclone amp is looking at an impedance (of the transformer) of 68 Ohms. Could this be the problem. Is the motor getting too little current to work well.
And if so, how can this be solved?
any help appreciated, MArco
Hi Ded,
I tried that;- reduced mains (500mVac) into poweramp (100W into 4r) into inverted 12V 20VA transformer. Adjusted the gain stage to give 90Vac output to the Thorens motor (110Vac) and it ran perfectly. This was phase1 of a crystal referenced two speed electronic drive for the Thorens 150. Never finished the crystal part.
The main difference between your set up & mine was the oscillator.
Is that your problem?
I think the reflected impedance from the low power motor will not affect the quality of the drive signal. The impedance must be high due to the low current draw of the low power motor (150 has 8W motor). As long as the effective impedance is above the safe value for continuous use of the amplifier then I see no problem here ( note CONTINUOUS).
I tried that;- reduced mains (500mVac) into poweramp (100W into 4r) into inverted 12V 20VA transformer. Adjusted the gain stage to give 90Vac output to the Thorens motor (110Vac) and it ran perfectly. This was phase1 of a crystal referenced two speed electronic drive for the Thorens 150. Never finished the crystal part.
The main difference between your set up & mine was the oscillator.
Is that your problem?
I think the reflected impedance from the low power motor will not affect the quality of the drive signal. The impedance must be high due to the low current draw of the low power motor (150 has 8W motor). As long as the effective impedance is above the safe value for continuous use of the amplifier then I see no problem here ( note CONTINUOUS).
Dear AndrewT,
I don't think that's the problem. The sine is looking pretty good on the scope. Even after amplification and the transformer it's still looking good. I've a small amplitude variation of about 0.75 Volts on an average voltage of 95. The sine stays the same when the Thorens (TD 160 mkII with a 2.5 W motor according to the sign on it) is running.
Well I'm afraid that the problem is here because of the perfect looking sine during operation. Is it possible that the motor can't draw enough current from the PS?
Things did improve by bettering the layout and adding a capacitor to counteract oscillation.
greetings, MArco
I don't think that's the problem. The sine is looking pretty good on the scope. Even after amplification and the transformer it's still looking good. I've a small amplitude variation of about 0.75 Volts on an average voltage of 95. The sine stays the same when the Thorens (TD 160 mkII with a 2.5 W motor according to the sign on it) is running.
Well I'm afraid that the problem is here because of the perfect looking sine during operation. Is it possible that the motor can't draw enough current from the PS?
Things did improve by bettering the layout and adding a capacitor to counteract oscillation.
greetings, MArco
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