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Old 29th December 2012, 09:31 PM   #21
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Roehren-und-Hoeren :: Thema anzeigen - Luxusnetzteil für Synchronmotoren mal anders

There's a decent size thread on a very well regarded implementation of a broadly similar tt-psu (in German). Daniel (Meldano) used to have pcb's available I'm unsure if he still does. Worth a read to find out what counts and what does not in the implementation.
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Old 30th December 2012, 02:24 AM   #22
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Unfortunately I do not speak German :-( I was scrolling through, but I could not find a schematic diagram, that would be interesting. As I see it is microcontroller based, not dds, but just guessing, would be good to see the details. Its a good sign that they used LM3886 with success, I will try that. I will run that from stabilized psu. It is strange, but the power amp really counts at the end. Easy to distinguish between amps. It probably runs the 24V, because I see no output trafo and the LM3886 will not do 110Veff.
JG
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Old 30th December 2012, 08:32 AM   #23
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It's designed for the 24v rega motor, needing a step-up transformer for higher voltage- which is why I don't use mine. The output quality is very good, in fact pretty close to perfect. it's adjustable for voltage in 0.01v increments and frequency in 0.01hz intervals.

If you are interested I can ask the guy gave mine to if he still has the schematic.
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Old 30th December 2012, 12:18 PM   #24
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I would be interested. If not schematic, than a block diagram, especially on what is the source. I do not think I would change from a dds, but curious :-)
On the pictures I do not remember step up transformer.
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Old 30th December 2012, 02:14 PM   #25
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I get some LM3886 PCB from chipamp. Do you know a kit with stabilized PSU?

One thing I know for fact, to supply an old transistor based amp from my agilent programmable power supply gives better result than with a normal not regulated PSU (with quality capacitors). I think it is because the generator supply near 50Hz and the smallest ripple from the mains is interfering with it. (A battery supply would be good to try.)
In the other hand, a regulated PSU designed for the LM3886 would be much more than needed, because from the bench power supply there is no much difference if the motor is connected or not. With this (Leach) amp it was like 300mA without and 450-550mA with the motor.
The LM3886 can work from +-40V, so it should make the 24Veff easy (which is not needed, just about 15% less), so no output step up transformer should be needed.

ÜDV JG

Last edited by Giordano; 30th December 2012 at 02:20 PM.
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Old 30th December 2012, 08:12 PM   #26
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The step-up was only for the 110v motors, not rh 24v Rega.
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Old 31st December 2012, 01:43 AM   #27
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I expect that you need to take extra care to keeep mains 50 Hz fields away from the turntable to avoid beating with the synthesised drive.

I have seen code for generating a PWM sine wave with a cheap Arduino board. It should be easy enough to modify this to get the second quadrature output. Each amplifier is only a few Watts as the motor is typically rated at about 3W. I am planning to use the TDA2050, which is easy to get here.
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Old 31st December 2012, 10:00 AM   #28
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Hello, I would recommend to wait a bit with the TDA2050. I did tried before a TDA20x0 amp with bad result. Not from sound point of view, but it was instable with the motor connected directly, also it has heat issues. It just did not tolerate the inductive load. With a transformer between the motor and the amp (1:1) it was fine, but directly was not good. It may not be a problem if you run through a trafo anyway, but I see from different sources that lm3886 handle it fine. As I get home I check which TDA chip was that.
That was the first amp I tried, than the TA2026 (not sure it is the right number, the "class T" amp), that does not like the motor directly either. Than my old Leach, which works fine and also the best so far for sound. Than another transistor amp, with similar good result. So far the simple complementer output transistor amps worked the best for me. ....but, according to other threads, lm3886 should work as well.

JG

Last edited by Giordano; 31st December 2012 at 10:03 AM.
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Old 4th January 2013, 06:40 PM   #29
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Sorry for the delay, I found out that this proto is not in my lab but a friend is using it. He checked it and it is TDA2040. So, I do not know the 2050, it could be better.
JG
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