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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 7th December 2016, 03:32 PM   #1
Pyramid is offline Pyramid  United States
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Default 60 WPC Amplifier for DIY Turntable Motor Drive

I've identified a great little stereo amp that works well with the SG4 sinewave generator for use as the output stage and motor drive for AC synchronous or AC induction turntable motors. It is based on a pair of the venerable LM3886 chip amps and contains everything needed to boost the SG4 signal up to a level needed to drive a 6V to 115V (or 230V) transformer. The only additional items needed to make a complete motor drive system is the AC input power transformer, the output transformer, the SG4, a heat sink and a slight modification to the amplifier. A complete motor drive can be constructed for ~$100 plus case.

The amp is available on e-Bay for $15.17 including shipping:

60W LM3886TF Sound Audio Amplifier 2-Channel Digital Power AMP | eBay

The amp will need to be modified to reduce the gain for two reasons:

1. The SG4 output is 5VPP and the amp will go into clipping at ~0.75VPP input.
2. With the standard gain, the output waveform becomes quite distorted when connected to the output transformer. With reduced gain, distortion remains very low, even when driving heavy loads and even at 50Hz. If you do not modify the MK-154 gain, the output waveform will look terrible, especially at 50 or 60Hz.

Replace or parallel the two 22K resistors with 2.2K resistors as shown in the attached jpeg (MK-154 Modified.jpeg). With this gain setting, the 5VPP output of the SG4 will drive the output of the transformer to ~125VRMS with very little distortion.

The amp PCB has screw terminals for the AC input, removable connectors for the outputs and both a 3.5mm stereo jack and 3 pin header for the audio inputs.

I've created wiring diagrams for 3 different scenarios:

1. 115VAC input and output single phase.
2. 230VAC input and output single phase.
3. 115VAC input and output dual phase.

The design uses two low cost split bobbin transformers with dual primaries and dual secondaries. The AC input transformer is a Signal LP24-2000 (48W) and the output transformer is a Signal LP12-1900 (24W). Both are available from Mouser ($24 and $19 respectively).

For 115VAC input or output, the high voltage primary windings are connected in parallel. For 230VAC input or output, the high voltage primary windings are connected in series.

Warning: Working with high voltage can be dangerous. Do not attempt to wire these circuits unless you are comfortable and competent to work with high power and high voltage electronics. If wired incorrectly, damage to property and great bodily harm may result.

The wiring diagrams are labeled with the pin numbers on the transformers and are unique to these two parts. If you substitute different transformers you must be aware of the winding polarities of the coils, which are usually indicated with a "DOT". When connecting windings in parallel, the "dots" must be connected together on one side and the non-dot ends must be connected on the other. When connecting windings in series (for 230VAC input or output), the dot on the lower winding must connect to the non-dot end of the upper winding.

When working with AC line voltages, ALWAYS use fuses on both the input and output. The AC input transformer in the attached jpegs has an IEC socket with built in fuse holder for connection to the mains voltage; the fuse should be rated for 1A Slo-Blo type. The AC output should also have a 0.5A Slo-Blo fuse in line with the hot lead. Connect the earth safety ground (third/green wire) from the input connector to all chassis components (and the 3rd terminal on the AC output) to properly ground them.

The MK-154 PCB has detachable connectors on both the L & R outputs. Remove these for easier connection to the output transformer low voltage secondary windings and the transformer will then just plug in for assembly.

For single phase applications, both L & R audio inputs to the MK-154 are connected together and are driven by the 0° output of the SG4. The L & R outputs of the MK-154 are used to drive each winding of the dual low voltage secondary on the output transformer. When wired in phase, they will combine both channels into one output, doubling the current capability.

For dual phase applications, the 0° and 90° outputs of the SG4 drive the L & R audio inputs of the MK-154. Each MK-154 output (L & R) drives its own output transformer with the low voltage secondary windings on each transformer, connected in parallel.

Note that the output connectors on the PCB are mirror images of each other, so the + & - connections are not on the same side of the PCB for each connector. They will be on the same side of each connector that plugs into the PCB.

The MK-154 MUST have an adequate heat sink attached to the two LM-3886 output amps for proper operation. Failure to use a heat sink will result in almost immediate destruction of the amplifier. Use a heat sink with at least 40 square inches (250 cm²) of surface area and at least 2-3 inches deep. The LM3886 chips are in an isolated package so they do not require mica insulators between the chips and the heat sink, however, you will need to use silicone heat sink grease.

If you use the 3.5mm audio input jack to the MK-154, the tip is Right In, Ring is Left In and Sleeve is ground.
Attached Images
File Type: jpg MK154 Modifed.jpg (388.1 KB, 3532 views)
File Type: jpg Input Cabling.jpg (216.2 KB, 3528 views)
File Type: jpg Output Cabling.jpg (205.0 KB, 3456 views)
File Type: jpg SG4 Cabling.jpg (258.7 KB, 3379 views)
File Type: jpg System Interconnect.jpg (221.3 KB, 3395 views)
File Type: jpg Single Phase 115V In-Out.jpg (513.4 KB, 1243 views)
File Type: jpg Single Phase 230V In-Out.jpg (524.9 KB, 1100 views)
File Type: jpg Dual Phase 115V In-Out.jpg (646.3 KB, 1035 views)

Last edited by Pyramid; 9th December 2016 at 05:48 PM.
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Old 7th December 2016, 04:40 PM   #2
Pyramid is offline Pyramid  United States
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Some possible cases to house the amplifier section on e-Bay:

BZ3207S ($50)

2109 ($39.50)

2409 ($43)

WA-5 ($43)

B-2107 ($45)

Unilateral ($39)

Douk Audio ($35)

Last edited by Pyramid; 7th December 2016 at 04:43 PM.
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Old 22nd December 2016, 04:57 PM   #3
jcastellano is offline jcastellano  Spain
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Question For sure a stupid question, but still....

Quote:
Originally Posted by Pyramid View Post
I've identified a great little stereo amp that works well with the SG4 sinewave generator for use as the output stage and motor drive for AC synchronous or AC induction turntable motors. It is based on a pair of the venerable LM3886 chip amps and contains everything needed to boost the SG4 signal up to a level needed to drive a 6V to 115V (or 230V) transformer. The only additional items needed to make a complete motor drive system is the AC input power transformer, the output transformer, the SG4, a heat sink and a slight modification to the amplifier. A complete motor drive can be constructed for ~$100 plus case.

The amp is available on e-Bay for $15.17 including shipping:

60W LM3886TF Sound Audio Amplifier 2-Channel Digital Power AMP | eBay

The amp will need to be modified to reduce the gain for two reasons:

1. The SG4 output is 5VPP and the amp will go into clipping at ~0.75VPP input.
2. With the standard gain, the output waveform becomes quite distorted when connected to the output transformer. With reduced gain, distortion remains very low, even when driving heavy loads and even at 50Hz. If you do not modify the MK-154 gain, the output waveform will look terrible, especially at 50 or 60Hz.

Replace or parallel the two 22K resistors with 2.2K resistors as shown in the attached jpeg (MK-154 Modified.jpeg). With this gain setting, the 5VPP output of the SG4 will drive the output of the transformer to ~125VRMS with very little distortion.

The amp PCB has screw terminals for the AC input, removable connectors for the outputs and both a 3.5mm stereo jack and 3 pin header for the audio inputs.

I've created wiring diagrams for 3 different scenarios:

1. 115VAC input and output single phase.
2. 230VAC input and output single phase.
3. 115VAC input and output dual phase.

The design uses two low cost split bobbin transformers with dual primaries and dual secondaries. The AC input transformer is a Signal LP24-2000 (48W) and the output transformer is a Signal LP12-1900 (24W). Both are available from Mouser ($24 and $19 respectively).

For 115VAC input or output, the high voltage primary windings are connected in parallel. For 230VAC input or output, the high voltage primary windings are connected in series.

Warning: Working with high voltage can be dangerous. Do not attempt to wire these circuits unless you are comfortable and competent to work with high power and high voltage electronics. If wired incorrectly, damage to property and great bodily harm may result.

The wiring diagrams are labeled with the pin numbers on the transformers and are unique to these two parts. If you substitute different transformers you must be aware of the winding polarities of the coils, which are usually indicated with a "DOT". When connecting windings in parallel, the "dots" must be connected together on one side and the non-dot ends must be connected on the other. When connecting windings in series (for 230VAC input or output), the dot on the lower winding must connect to the non-dot end of the upper winding.

When working with AC line voltages, ALWAYS use fuses on both the input and output. The AC input transformer in the attached jpegs has an IEC socket with built in fuse holder for connection to the mains voltage; the fuse should be rated for 1A Slo-Blo type. The AC output should also have a 0.5A Slo-Blo fuse in line with the hot lead. Connect the earth safety ground (third/green wire) from the input connector to all chassis components (and the 3rd terminal on the AC output) to properly ground them.

The MK-154 PCB has detachable connectors on both the L & R outputs. Remove these for easier connection to the output transformer low voltage secondary windings and the transformer will then just plug in for assembly.

For single phase applications, both L & R audio inputs to the MK-154 are connected together and are driven by the 0° output of the SG4. The L & R outputs of the MK-154 are used to drive each winding of the dual low voltage secondary on the output transformer. When wired in phase, they will combine both channels into one output, doubling the current capability.

For dual phase applications, the 0° and 90° outputs of the SG4 drive the L & R audio inputs of the MK-154. Each MK-154 output (L & R) drives its own output transformer with the low voltage secondary windings on each transformer, connected in parallel.

Note that the output connectors on the PCB are mirror images of each other, so the + & - connections are not on the same side of the PCB for each connector. They will be on the same side of each connector that plugs into the PCB.

The MK-154 MUST have an adequate heat sink attached to the two LM-3886 output amps for proper operation. Failure to use a heat sink will result in almost immediate destruction of the amplifier. Use a heat sink with at least 40 square inches (250 cm²) of surface area and at least 2-3 inches deep. The LM3886 chips are in an isolated package so they do not require mica insulators between the chips and the heat sink, however, you will need to use silicone heat sink grease.

If you use the 3.5mm audio input jack to the MK-154, the tip is Right In, Ring is Left In and Sleeve is ground.
If I have a Rega 24v AC motor, I do not need the output transformer after the power amp nor the Rega motor control board that is supplied along with the motor? Or should I install an output transformer at the output of the amplifier and connect there the 220v to 24v rega supplied transformer and then the motor board?

Sorry for the dumb question but sometimes we can not see things that are there in front of us and easy to understand...

Regards

Jorge
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Old 22nd December 2016, 06:01 PM   #4
Pyramid is offline Pyramid  United States
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Jorge-

Not a dumb question at all, a very good one.

If you want to run the Rega motor direct (no output step up transformer), you will need ~68VPP from the amplifier. From a 5VPP source (SG4) you need a gain of ~13.6. The amp comes with a gain of 4.5, so you would need to change each of the two 22K resistors to 82K each; the amp has a 2K resistor in series with 22K and 6K8 to ground for a gain of 1+(24K/6.8K). The new gain will be 1+84K/6.8K or 13.35. You would also need a power supply transformer with two 25VAC secondaries to provide ±35VDC rails. This should give you a ~68VPP or 24VRMS output on the amp. If you go with a dual phase configuration, each phase will be 24VRMS and can directly drive the motor. You would no longer need the Rega interface PCB (in the turntable) but would connect directly to the motor windings. If you do single phase, then you would still need the Rega interface PCB.

If this is to confusing or difficult, then use the diagram for 230VAC input/output and plug the Rega wall adapter into the output of the step up transformer. You will still need to change the 22K resistor to 2K2.

If you are unsure about how to configure this, please seek technical help. If you wire it incorrectly, you could damage the motor or amp.
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Old 22nd December 2016, 09:19 PM   #5
Pyramid is offline Pyramid  United States
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Default Rotary Encoder control for SG4

I've ordered one of the cases above from e-Bay and will build up a number of configurations and document the process. The case I ordered was the #2409 which comes with a front panel on/off switch already mounted and a knob and front panel hole for one control. Rather than carve up the front panel, I came up with a way to operate the SG4 using only 1 rotary encoder control with momentary push button function.

The rotary switch outputs 2 sets of pulses in quadrature, the leading/lagging signal depending upon which way you rotate the switch. I developed a simple circuit using a 4013 dual D flip-flop that converts the 2 quadrature signals into 2 individual pulse trains with each one only active for CW or CCW rotation of the switch. These outputs can then be connected to the UP/DN buttons on the SG4, the momentary switch connected to the Stby button which will allow you to operate all of the normal functions with one control.

There is a short video of the operation Here

The rotary switch was purchased on e-Bay for $3.59 including shipping Here.

I changed the header on the rotary switch to point straight back and wired up the circuit below onto a piece of Radio Shack perfboard. 5 wires connect the circuit to the SG4: 5V, Ground, Up, Down, Stby.

The two 0.47uFd caps are necessary to filter out switch bounce. If you do not add these caps, the outputs will switch almost randomly.
Attached Images
File Type: jpg 4013 Circuit.jpg (266.9 KB, 1059 views)
File Type: jpg DSCN1285.jpg (252.2 KB, 661 views)
File Type: jpg DSCN1286.jpg (253.8 KB, 521 views)
File Type: jpg DSCN1287.jpg (254.4 KB, 468 views)
File Type: jpg DSCN1289.jpg (255.0 KB, 508 views)

Last edited by Pyramid; 22nd December 2016 at 09:47 PM.
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Old 30th December 2016, 05:42 PM   #6
flamethrower1 is offline flamethrower1  United States
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Is the heat sink on the above enclosures sufficient to cool the output amps.
Any chance you could post pics of the components as you mounted them.
My plan is to use the 2409 enclosure and the rotary switch that you have posted above.
Also, thanks for providing this project, appreciated
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Old 30th December 2016, 08:31 PM   #7
Pyramid is offline Pyramid  United States
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I've just built one up with the enclosure #2409, but I haven't done a lot of testing with it. The entire case is thick aluminum with 2 heat sink fins. It should be fine for motors up to 15W, above that you may want to go with more heat sink. I'll post pics soon about the build process.

If you go with the rotary encoder, you might want to purchase the PCB for mounting the switch and parts:

https://www.oshpark.com/shared_projects/AbsVI39H

It uses surface mount parts, but you only need the IC and the 2 caps (0.47uFd) if you use the Arduino rotary switch (3 R's on on the switch already). You can also use the RA header that comes with the switch.
Attached Images
File Type: png Encoder PCB.png (7.6 KB, 494 views)
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Old 30th December 2016, 08:48 PM   #8
flamethrower1 is offline flamethrower1  United States
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Yeah, I ordered the boadrs earlier today.
The encoder you linked was sold out so I ordered this one.
KY-040 Rotary Encoder Module Brick Sensor Development Board Shield for Arduino.
I hope it is the correct one, not much info on the EBAY page
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Old 30th December 2016, 10:38 PM   #9
flamethrower1 is offline flamethrower1  United States
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Sweet, just received conformation of my order from Oshpark.
They have upgraded my order to an expedited service which should only be 5 business days.
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Old 31st December 2016, 01:06 AM   #10
gigigirl is offline gigigirl
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Hi, I am a newbe to electronic circuits. But am just upgrading a Lenco 75. This controller is just what I am looking for as long as it can take the Lenco 75, 25 watt motor requirement.
Is this circuit something a Newbe could build up, on first read it seams a little complicated for me? Cheers
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