My experience is that 90Vac is about right for Premotec motor windings, the sweet spot for torque and vibration. It also avoids core saturation on a "115V" primary winding.
You need some protection on the amplifier chip outputs against back emf, which will be much worse with oversize transformers. Rectifier diodes to the rails is a minimum
You need some protection on the amplifier chip outputs against back emf, which will be much worse with oversize transformers. Rectifier diodes to the rails is a minimum
And if one wanted to go beyond the minimum?
Are the Premotec motors considerably better quality than the Hurst motors?
Are the Premotec motors considerably better quality than the Hurst motors?
for me the TDA amp is only for prototype. As my TT returns I will try with my old and loved Marshall Leach als (what is boxed in the garage now, because the 2A3 PSE replaced it, good job for the leach, I never thought it will run a motor when I made it 🙂. In the other hand, I do not think I will go that far that I make a single ended class A triode amp to run the motor 🙂
I'm curious to hear if it makes a difference, but it is still a month until I get back my TT.
Regards,
JG
I'm curious to hear if it makes a difference, but it is still a month until I get back my TT.
Regards,
JG
In my experience yes. All the Hurst motors I have used have shown considerable reluctance variation with rotor position.
Also they appear to have some quality issues - the shaft diameters are often a long way from the stated specification, so much so that a pulley machined to fit one shaft would be visibly eccentric on the next.
I haven't used as many premotec motors but the ones I have used seemed pretty consistent.
I'm having a hard time envisioning how to rectify back emf for an AC motor. Could someone describe how this is done in greater detail?
For the Premotec and Hurst motors no such protection is required. The back emf consists of a 60 Hz sinewave at about 60 Volts.
Not if a wire to the motor windings goes open. The transformer inductance will throw a large spike back at the amplifier.
Fair enough, I'm sure that I've had similar problems with some induction motors but to this date no problems with Premotec or Hurst synch motors.
That being said, diodes to the supply rails are easy enough to do, they're a standard feature of most digital amp layouts anyway.
For Paul Ebert: the standard thing to do is place two ordinary diodes (1N4004 or similar) between the output and the supply rails, oriented such that in normal circumstances they are reverse biased and therefore don't conduct. If the output rises above the +ve rail the upper diode is forced into conduction and logically the same thing happens (with the other diode) if it drops below the -ve rail. This snubs the output voltage to the rails +/- 0.6 volts.
That being said, diodes to the supply rails are easy enough to do, they're a standard feature of most digital amp layouts anyway.
For Paul Ebert: the standard thing to do is place two ordinary diodes (1N4004 or similar) between the output and the supply rails, oriented such that in normal circumstances they are reverse biased and therefore don't conduct. If the output rises above the +ve rail the upper diode is forced into conduction and logically the same thing happens (with the other diode) if it drops below the -ve rail. This snubs the output voltage to the rails +/- 0.6 volts.
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OK, I think I'm almost there. These diodes would have their cathode attached to the wire connecting the output of the amp to the transformer and their anode attached to the corresponding supply rail being fed into the amp. Is that correct?
I've never known anything...
I almost always go back to "the Art of Electronics" (Horowitz and Hill) if I am looking at starting a project. One of the classic texts in electronics. Or "the AUDIOcyclopedia" (Tremaine, an early book but very helpful none-the-less).
The Horowitz and Hill book is often used in undrgrad courses in electronics (Physics).
I almost always go back to "the Art of Electronics" (Horowitz and Hill) if I am looking at starting a project. One of the classic texts in electronics. Or "the AUDIOcyclopedia" (Tremaine, an early book but very helpful none-the-less).
The Horowitz and Hill book is often used in undrgrad courses in electronics (Physics).
I've got the two (more recent) Ballou-edited editions of Audio Cyclopedia - does the Tremaine edition have substantial amounts of info that was cut out later? Used copies of Tremaine have been in three digits (US$) for over a decade, and I still wonder what one would get for the money.
Sorry for the derail ...
But yes, Paul, (back on topic) that would be a rectifier from the chipamp output to each of the power/voltage rails, connected so they would be reverse-biased in normal operation. It might be good to use Shottkys or other low-forward-voltage-drop rectifiers here, to be sure the diode turns on at a lower voltage than does a parasitic diode inside the chipamp. And make these connections to the chipamp as short and as direct as possible for best protection.
Sorry for the derail ...
But yes, Paul, (back on topic) that would be a rectifier from the chipamp output to each of the power/voltage rails, connected so they would be reverse-biased in normal operation. It might be good to use Shottkys or other low-forward-voltage-drop rectifiers here, to be sure the diode turns on at a lower voltage than does a parasitic diode inside the chipamp. And make these connections to the chipamp as short and as direct as possible for best protection.
While working on speakers for my son and daughter, I happened upon a spare Maxon 110183. So, now I'm thinking I may go the DC motor route to save some expense (I'd only need to buy one additional 110183). So, it's back to the drawing board, just as I was feeling somewhat confident about the AC approach.
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