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60 WPC Amplifier for DIY Turntable Motor Drive
60 WPC Amplifier for DIY Turntable Motor Drive
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Old 25th November 2017, 01:25 PM   #161
Pyramid is online now Pyramid  United States
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Originally Posted by hirscwi View Post
It appears that the original MK154 amp is no longer available. There are many other LM3886 amps available. Do you recommend a replacement of the TDA7492 amp that you mentioned quite a bit earlier in the thread (page 5, I think). It is still available for purchase.
I like the class D TDA7492 solution better than the LM3886. It generates almost no heat and works just as well if not better.

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The Lenco uses a shaded pole induction motor. I understand this to be a single phase motor and would not use the dual phase option that the VPI motor can use. Is this correct?
Correct. You would use only one output transformer and connect the outputs of the amp in parallel (each low voltage secondary winding is connected to one channel L & R). Be sure to observe the polarity markings on the xfmr (each "dot" goes to positive output of the amp).
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Old 25th November 2017, 03:17 PM   #162
hirscwi is offline hirscwi  United States
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60 WPC Amplifier for DIY Turntable Motor Drive
Default Reducing cogging

Thank you for the fast answer. I hope it's OK to ask another.

I have read this thread completely as well as the one on the SG4 generator. I believe that I understand the signal generator has the capability to adjust phasing. Is this adjustment to help reduce cogging on an AC synchronous motor? If so, is there a place I can learn about how to measure cogging? Also, doesn't voltage factor into the cogging reduction? If I have missed the answer to these questions in this thread, I apologize.
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Old 25th November 2017, 03:47 PM   #163
Pyramid is online now Pyramid  United States
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There is a thread where I measured the cogging vibration of Hurst motors using an Analog Devices accelerometer here: Hurst Motors: 300 RPM vs 600 RPM--Upgrade or Myth?

You can also just put the motor in your hand and adjust the phase for minimum vibration or use a stethoscope.

Reduced voltage will reduce cogging but it also reduces the amount of available torque, and some indicate that it has a negative impact on sound if it gets too low: 'Number9' TT AC motor controller web site finally up | Page 3 | pink fish media
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Old 25th November 2017, 04:30 PM   #164
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I've built a couple of Nigel's Speed controller in the past using the TDA7293 bridged mode with 80VA trans outputting 230VAC/50hz to power Lenco L75. I observed it tends to get warmish at normal tropic temperature and much cooler at air-conditioned room. I'm set on implementing a TDA7498 module for my own SG4 build in good time.
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Old 25th November 2017, 05:08 PM   #165
Pyramid is online now Pyramid  United States
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I've seen the design; a bit of overkill IMHO. It actually uses two TDA7293 100W amps in single ended parallel mode (not BTL) and a dual polarity supply. There is no need to use a 200W amp to drive a 15-20W motor. Likewise it does not need an 80VA output xfmr. That being said, they seem easy to build and should be fairly bullet-proof.

The later Eagle PSU (25W version) uses a TDA7492 (50W total) with a 25VA Amgis toroid output xfmr; it will run a Lenco motor all day and barely break 90F (32C).
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Old 26th November 2017, 07:48 AM   #166
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Hi Bill,
I appreciate your honest views. Normally I won't go overkill mode, but its often from where I shop for parts, the price difference is hardly any worry between VA models since we're not into mass production for commercial sale where savings is everything and i'm buying one of each. In previous builds, I followed to the letter on their recommendations which was minimum 80VA. I will use your recommendations in the upcoming build.
Thank you again.
Lee
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Old 29th November 2017, 12:43 AM   #167
hirscwi is offline hirscwi  United States
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60 WPC Amplifier for DIY Turntable Motor Drive
I have built 3 of the Nigel's Speed Controllers. I always felt they might be a bit of overkill. But the build instructions were good and it was the only controller available to semi-literate DIY'ers like myself. Heat dissipation is a problem however.
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Old 29th November 2017, 05:10 AM   #168
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Originally Posted by hirscwi View Post
I have built 3 of the Nigel's Speed Controllers. I always felt they might be a bit of overkill. But the build instructions were good and it was the only controller available to semi-literate DIY'ers like myself. Heat dissipation is a problem however.
Its very essential to buy TDA chips from a legit source where quality is assured. Its scary to experience fakes or lesser grade chips from anywhere and cause havoc later on. I've learned my lessons with one specimen outputting 40V at initial power on (without load). Recently, I had a pair (from legit source) just died from unknown cause. There was absolutely nothing wrong with the circuit, it just died. Replacement was the answer with 1 hour downtime. That's experience for me. I'm waiting for my new Class D module to arrive, wish me luck.
Lee
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