3 Phase Class D amp for DIY BLDC motor Drive

Oh, well.

Hoping someone here can tell me where I went wrong.

My SG4 is putting out the 2.5 volts it is supposed to and doing everything else it is supposed to do but I cannot get the amplifiers down to the suggested 4.2 volts I am seeing 7.4 using an RMS volt meter.

I thought based upon a previously described problem - whose solution was never described - that I got one of those tantalum caps in wrong - but they look like they are oriented correctly. (Who would put pink markings on an ochre colored thing. Extremely cruel, heartless and perverse. AVX must be run by very strange people).

Any obvious problem? All suggestion and counsel will be appreciated.

Thanks, Mr. Carlin,

I had read the instructions one hundred times but managed to completely ignore AC VOLTMETER. Hard to have pole to pole measurements of 12 volts with DC.

All I can say is how lucky I am you are so kind to dumbasses like me.

Now I cannot wait to get home and get this project working.

Thanks, yet again,
Another SG-4 MA-3G Joins the fold

A big thanks to Pyramid for designing and sharing this project and to Ralph for being super supportive re the uP supply

My main TT is a reworked Orpheus Silex.
Unfortunately the rubber surround on the idler is worn, so a new motor system seemed the right way forward.

I'm quite stunned by the improvement, on what I considered was already a great sounding player.
The background is noticeably clearer with a nothingness between the instruments.
Bass is tighter and clearer and the overall rhythm/groove of all music is compelling.
Mids & Treble are just wonderful now - the improvement in detail and timbre is huge. Larry Carlton's album; Last Nite is a cymbol nuance fest and is a goto record whenever I am evaluating change - It is stunning
Imaging and depth was always a strong point on this TT, but is pinpoint focussed now.

Very happy,

@rickmcinnis The 4mm bore 16mm pully runs smoothly and induces with no visible vibrations/oscillations on the platter. This is something that is visibly very evident on my TT because of the floating/sprung system.

I would love to try a multigroove pulley though


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The thing was working fine all along.

Thanks for the help, Mr. Carlin. And of course THANKS for the whole damn wonderful thing!

I am getting the 30 mV @ TP1 - I guess there is no way to reduce this - other than lowering voltages? Of course it is a minimal error - 0.7% but obsession knows no bounds.

One thing for sure this motor vibrates MUCH less than the LENCO motor at 33.33/40 Hz. It surprised me that it vibrates a bit more at 55 Hz - I would have thought the opposite. Now to finally to get it to turn the platter - ran out of daylight yesterday. I do not foresee any problems.

Good thing I got three of those pulleys - the one I installed initially had some wobble to it and the second one was much straighter. I know this is a temporary solution. I should try the third, shouldn't I?

As an aside I used the 3M adhesive tape you mentioned in your turntable plinth thread between the Reinders top plate and OMA slate plinth. Never liked the idea of those fasteners but it never occurred to be to use double sided tape - did not know the 3M stuff existed.

reubster346, I use springs between my platform and the plinth but I have never seen springs like those. I like that large diameter - extremely long torsion arm! Where did you find those? I would like to use something like that but would need them able to support a much heavier load.
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Hi Rick
I built this TT back in the early 1990's. At that time a friend had built something similar. He had specified & custom ordered the springs (IIRC) from a company in Germany and had a few spares which he sold to me
The springs were designed with the weight of platter + tonearm in mind, to tune the vibration to about 1Hz. It works well, you can give the platter a gentle nudge and see it bounce at ~ 1Hz without hearing anything audible effect.
The torsion arms (2) were my idea. They are 5mm perspex strips with bolt+washer counterweights. You can easily swing their positions to get the platter perfectly level. This is something I need to do to compensate for belt tension changes.
Got the motor actually turning the platter last night.

Well even with the idler all the way out as far as it can go towards the edge of the platter at 40Hz the platter is spinning much too fast. Over 45 rpm. I am using a 13 mm ready made pulley.

So I started lowering the frequency and the controller did not seem to like making large changes. Had to do it in stages. Has anyone had that trouble? Not insurmountable.

I am using the R motor. Is there any reason one should not run this motor at 30 Hz? I think that is where it will need to be to run at 33.33. I do not doubt my question sounds dumb but as I have demonstrated I do not know much at all about all of this. I do know with the motor not turning the platter it was absolutely smooth and silent at 30 Hz.

I can assure all those who might have doubts this motor has PLENTY of torque. Far more than the LENCO motor. Even weighted down but without something to fix the motor in place the spindle contacting the idler is enough to push the motor away before I used modeling clay to hold it in place. The mount has to weigh three pounds. I will make it heavier and come up with some king of permanent attachment when the alignment is settled. Temporarily I am using modeling clay to hold all in place.

One interesting thing with the large spindle the idler needs no help to contact the motor and platter. I was using a weight instead of the LENCO spring but none of that is needed at all now.

Never got the thing reassembled to to see what happens with the speed at 30 Hz.

I know all of you are waiting anxiously for tomorrow's report.
Thanks, Mr. Carlin,

I was thinking I needed to reduce the voltage. Much better getting advice from someone who knows what they are doing!

At start up it is like it wants to spin the platter for a round of FRISBEE golf!

I would like to ask another of my pesky questions - I am still looking for the optimum place for the motor idler and think I am close but this is a puzzle - one would think a mechanical problem would have a frequency to it. At least, someone of my limited experience assumes that.

The platter will spin at a "constant speed" for a minute or so and then all of a sudden will lose speed and return to speed within a revolution.

Any ideas?

Not sure which part takes the most credit for reducing the low frequency noise that would drive me crazy - and was not constant with every record, though it was still there - to a whisper of itself. I think the LENCO motor's running speed accentuated groove noise in my odd application. I do think the motor is the bigger contributor

Together with the VHB tape I have a vastly improved turntable - and I thought it had many fine points previously.

Mr. Carlin is Patron Saint of turntable DIY as Mr. Pass is the Patron Saint of amplifier DIY.

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Is anyone here using an ARDIONO to correct speed?

Towards the end of this thread a few fellows, most notably to me, robnick33, since he is using a LENCO table, with help from the man who knows about these things, seemingly all there is to know about making an excellent turntable for lot less than $100,000 dollars,

Digital Tachometer for record player (LCD display)

Not knowing anything about this stuff but always ready to try something to make the thing better.

I asked Bill and he said this simple approach as outlined by robnik will work with out three phase phase motors. I have ordered an ARDUINO and parts to make my first ROADRUNNER sensor. I have knocked the hall effect sensor off a couple of times and was able to get it back on so I hope I can make a complete one. Luckily the SMD parts are just large enough for me to be able to solder them. The boards are available from OSHPARK. No one else does a DIY project like Bill Carlin and that is a shame..

There is mention of needing resistors between SG4 and the ARDUINO but no value was given.

I am hoping Bill will say what value should be used.

As always, thanks very much to Bill Carlin. Yes I will remain in this giddily satisfied state for awhile longer ...
Is anyone else feeling pressure to find parts before they disappear? I am not even planning to start this right away but put in a mouser order for everything they had. They were out of a few things with long lead times- if anyone has found another source will you let me know?

1) 2N7000 --> Digikey 2N7000TA?

2) SN74HC14N
3) LTC-2723E

4) B3F-1000 (less worried about these as I will look for a panel mount alternative)