Here but not here


Just thought I would send out a quick note that I am currently away, out of country, for an extended period on a work project.  No time for my favourite hobby nor much time to add anything to the blog.  To those who continue to check in and follow me, be assured that when I return I will resume the project and bring it to termination.  So check in every now and then for new posts and in the meantime thanks for your patience.


I sure hope I remember how I built this thing when I get back !!


Have a great summer.
SoundBound

First Dry Run - Ariston RD11 and Bi-Onda Controller

Since I am getting ready for my extended trip for work, I don't have a lot of time to devote to the Bio-Onda controller project.  Even worse is that I am having to pack everything away, which is making my wife very happy of course, but me sad.  Before I packed everything I did want to do a full dry run, that is to connect the controller to the Ariston RD-11 turntable and see everything turning in beautiful harmony as driven by the controller.

But before I could that, I did need to do a little bit of work on the Ariston's motor.  I heard a definite cyclic clicking noise coming from the motor and a bit more motor noise than would be considered normal.  Remember I had bought this turntable from a guy on a local internet classified, I have not done and servicing or reconditioning of the table yet. Suffice it to say for the moment that I did put some time into caring for the motor, after all it has a good 30 or more years of service under it's belt, definitely time for a little TLC!  I will not describe what I did with the motor in this posting, I will reserve that for another post later on.  I did get the motor working fine, much quieter.  So stay tuned for that info at a later date.

I did remount the motor and put the turntable together with the Bi-Onda controller driving the motor fully.  It worked great, sped the platter up no problem, spun nicely.  I tried out the 33.3 rpm and 45 rpm, the acceleration of the motor/platter looked good with the 'basic' values I had programmed before.  Speed was good.  I was especially curious to see how it ran at 45 rpm and was very happy with that.  I did notice that the speed, as per my default setting was a bit slow, but increasing the sine frequency by about 0.3 Hz brought it nicely up to 45 rpm, on the nose.  Me happy.  I did not spin any vinyl though, the table mounts an SME 3009 Improved and I have not set it up yet.  A full turntable reconditioning is slated for this unit, hope to make that into another series.

So far so good.  That was all the time I had for testing, I had to start putting all the equipment neatly and safely away until my return.  Geese, just when it was getting so close and running so well, now I will have to wait to finish it.  Sorry I could not include any pictures, was just too pressed for time.

SoundBound

Forced Break

Well, just as everything was coming together and I was close to the end of this project I am now having to delay it.  It looks like I will be away and tied up with work for a few months and so will have to delay this project.  Bummer.

If I can work on anything while I am gone, then great otherwise continuation of the project will have to wait for my return.

I hope that I can still post something to the blog every now and then, maybe on some other topics other than the motor controller.

Feature Review

Since the first version of the software is now complete I was thinking this might be a good occasion to summarize the features and functions of the Bi-Onda TT motor controller as they are now implemented.  I must admit I had an idea for a new feature last night but I will keep this on the back burner for now.  Gotta stop somewhere.

So let's take a look at the feature list.

Characteristics

• Dual DDS sine wave generation.
• Adjustable frequencies with a resolution up to 0.01 Hz.
• Micro controller DDS generation, 16MHz quartz clock, interrupt driven
• Chebyshev low pass filters
• Power Op-amp amplification up to +-15V with transformer boost to 120+VAC
• Adjustable output levels
• LCD 16x2 character backlit display
• 33.3 & 45 RPM speed generation
• EEPROM storage of calibration settings
• Remote expansion header to allow incorporation of all, or some, operating buttons into the turntable, parallel to the buttons on the Bi-Onda.

Operating Modes

User selectable operating modes:

• Continuous always-on mode with single or dual sine wave out as mains source
• Switchable on-off mode with dual sine wave, phase shifted for direct drive of motor coils

Features

Run Mode

• Calibrated sine output for 33.3 and 45 RPM operation
• Speed selection
• Speed adjust with selectable resolution: 1.0Hz, 0.1Hz, 0.01Hz (during play and in CAL mode)
• Incr Decr speed buttons
• Motor acceleration startup (spin-up)

Calibration Modes

• 33.3 RPM Calibration
• 45 RPM Calibration
• Phase Shift adjustment (1.4 degree steps)
• Operating Mode selection
• Acceleration Mode (on or off)
• Acceleration Parameter Adjust (start frequency, frequency step, step delay)

This should pretty much cover most needs as a power source upgrade or for custom turntables.  The one thing left to do is determine the total power handling capacity based on the components (op-amps, transformers, etc.) currently in use and possible alternatives to drive motors with lower voltage requirements or motors with higher wattage ratings.

Firmware Finito

(that means finished !)

Now that the hardware is behaving as it should, I decided to get back to the firmware and see about giving it some necessary cleanup.  There were features to add and unnecessary/debug code to clean out.

The main feature I needed to add, and the one that I was hesitant to tackle, was the acceleration feature.  I knew I needed to add an option to spin up the motor gradually rather than the full-on power up I have been using.  The main idea of course is to compensate for the inertia of the platter and belt system, the heavier the platter, the more important this feature is.  In fact, on my Ariston RD11 they designed the motor pulley with a slip clutch to deal with the inertia problem (you will find this on many Thorens turntables as well).

The way the acceleration needed to work is that when the user started up the turntable, the Bi-Onda controller would have to start spinning at a much lower frequency than 60Hz and slowly, or quickly, ramp up to the final frequency set by the user for their turntable.  I concentrated on acceleration and felt that deceleration was not as big an issue and decided to omit a deceleration routine.

My problem was trying to figure out how I would shoehorn this feature into the existing software without having to re-write the existing code or change the overall structure.  While writing a post on a blog for assistance, the ideas became clear to me and I was able to figure out a relatively simple way to implement it that would only require modification of one function subroutine and would work with any action that started up the turntable (calibration modes, 33 and 45 rpm etc.).  That also reminds me that another reason to implement acceleration is the feature that allows the controller to increase the motor speed to reach 45 RPM, this higher drive frequency can cause difficulty in these motors to start turning from 0 to the high frequency of the 45 RPM mode.  Accelerating from a lower speed usually works well in dealing with this issue.

I made the acceleration feature flexible to anyone's needs.  In calibration mode you are able to turn acceleration on or off and you can set your own parameters for: starting frequency, frequency step in Hz and the delay time between steps.  These are all stored in eeprom and only need to be set once.  So you can pretty much set up your own acceleration ramp (linear).

So now I will need to build an enclosure for this unit and put it in operation.

SoundBound

Dang! It's Working!

The basic electrical tests and scoping show that the new PCB layout is working fine.  Time to hook it up to an AC motor for the real deal.  First of all I wanted to take a look at the stock configuration of my Ariston RD11 turntable, so here is a picture of the 'underbelly' and we can see the phasing cap (yellow) that feeds the second coil of the AC motor.  I took the oscilloscope to the motor to see what the two phases looked like as per stock.

Close up of phase capacitor

Ariston RD11 showing AC motor

Here in the picture you can see that the phase shift is fairly decent by the cap but the waveforms themselves are not the best looking sine waves ever seen.  This is off the 120VAC line voltage.  You can see that the capacitor does affect the quality of the waveforms to some degree, both being affected.

AC at motor coils without TT controller

Time to remove the motor and connect it to the Bi-Onda controller.  I first calibrated both sine waves at the tranformer outputs to 119VAC rms as measured on my multimeter.  I then connected each channel to a coil as per the Ariston configuration: AC direct coil to sine A and the cap shifted second coil to sine B outputs.  When I started up the controller and ran the motor, beauty, turning perfectly.  The motor runs nicely.  I then scoped the outputs to the motor like I did before and here is the photo, the waveforms are very nice and clean sine waves.  Me happy.

AC at motor driven by the BiOnda Controller - clean!

I did check the output and it looks like the voltage dropped about 9VAC with the motor connected and running.  Since the power supply is unregulated, I expected some voltage drop and am happy with that and a small drop should not affect the overall performance.  Now this of course is a no load condition, no platter is being turned so I will have to check it again when the TT is assembled and running the platter.  One very nice thing that I did notice, is an improved torque.  With the motor in stock condition off of the AC I noted how easily I could stop the motor from turning by gripping it with a particular amount of pinch of the spindle.  When driven by the motor controller I noticed that it was still possible, but I had to exert more pressure, thus increased torque.  Nice, not sure I was going to have more torque, but looks like I do.

I also tried changing the sine frequency to alter the RPMs and the motor responded nicely.  I did notice however in 45RPM mode the motor had a problem in starting it's rotation.  As soon as I gave it a bit of a spin it would run nicely.  This likely means that I should add an acceleration routine to the controller software to help the motor spin up, especially for the 45 RPM mode.  I also noted that the motor was spinning backwards, no big problem, just reverse the hookup of sine A & B outputs, but I will look into the software too, could be I incorrectly calculated the direction of phase shift of sine B, which would easily be corrected by changing the subtraction to addition or vice versa, which ever is currently in the code.  Will test that in the next couple of days.

I did play with the phase change too and was able to sense a slight change in the motor's vibrations as I went far off the 90 degree mark in either direction. In the end it felt like a phase shift of 91.4 degrees seemed to provide the least amount of vibration in my hand. 


Next, will have to improve the heatsink, I have been holding off on getting a good one together but I did notice the small aluminum plate I was using getting a bit too warm, so will have to find an appropriate one.  Then I just need to hook it up fully and spin some vinyl.  I do want to do some restoration and upgrading of the Ariston at this point too, so I may do this before putting the unit back into full operation.


Thanks for tuning in, keep checking back!
If you have any questions, feel free to leave it in the comments.
SoundBound

Ver. 2 PCB on test bed.

Update on Testing

 
Just a brief update on the tests with PCB Ver. 2 for those following.  I have fully connected the op-amps and output transformers and the waveforms look excellent.


They are very clean, stable and no signs of noise or ripple.  So far thumbs up. You can see the new layout in the photo above. 

Scope shot of dual sine waves at 60Hz

It is still using the hand wired button panel, not expecting too much trouble from the PCB for that. Here is the first posting of a picture of my oscilloscope output of the two sine waves.  This is during a run at 60Hz with 90 degree phase shift.  All in all, looks ok.  The waveforms have been scoped at the output of the boost transformers, so this is what would be feeding the motor.

I will now have to proceed to rewiring my turntable for dual power, for each coil, and drive the turntable motor.  May take a few days, I have to clear some space on my makeshift bench.

So far no tweaking of any components was necessary, so values look acceptable, at least before load and current testing starts.

SoundBound

PCBs and Happy Times !!

So here is a sneak peek to the new PCBs.  They look good even though it is only the standard green, but once they are in an enclosure, well, you don't see them much anymore.


The switch and LED board is up top and you can see the main PCB here.  I started populating the boards a couple of days ago.  I only hooked up the power supply section, the microcontroller section and the low pass filters.  Thus leaving the power op-amps out so I could verify stage by stage.  The power supply was built up but I left out a series resistor that feeds the power to the board so that I could check it out before powering up the rest of the circuit.  The power supply looked to be working very well, with very low ripple.  Happy there.  Then I checked out the microcontroller section by powering it from it's USB connector first.  No problems here either, the LCD and buttons worked great.

New PCB layout with fatter traces and ground fill.

So I checked the sine wave outputs on the low pass filter section and happiness here too, the waves looked really nice and clean.  I replaced the single turn output amplitude adjustment pots with nice multi-turn trim pots.  This made the adjustment of precise amplitude easy and worked great.  So far so good.

Next step was to power the microcontroller with the PCB mounted supply.  I placed a pop-out wire jumper for the series resistor (this resistor is only needed in case you are going to install the zener diode voltage clamp which was not needed with the transformer I am using), I used a wire I can remove so that I can measure current draw later on. Measuring all voltages I confirmed that the board was working fine off the on-board power supply.

At this point I am very happy with the unit and next step will be plugging in the op-amps and testing the amplification and output transformer stages.  Coming soon, so check back to see the results.

Soundbound

        Boards are IN !!

  

The PCBs have arrived and they look pretty good.  Solder mask is standard green, which is ok but not as cool as the purple ones of my first version.

So I will be heating up the soldering iron and assembling the board.  I will do this in stages so that I can check each stage before moving on to the next one so that I can verify functionality stage by stage.

Will keep you posted and will add some pics.

SoundBound

Tonearm NOT TONED ARM !!

  

     Tonearm Lust

My second version of the motor PCB is out awaiting return from the fab house (been notified they are on their way, yay), so I thought it could be an opportunity to add a post that is outside the controller project.

Browsing the web for turntable information on motors and bearings etc., I could not help coming across the images and information for various tonearms.  I am now lusting over some nice shiny Linn tonearms like the Ittok or the out-of-reach Ekos series.  The best tonearm I have is an SME 3009 arm.  A well engineered, super nice to look at, tonearm.  It is serving me well at the moment on my modified Thorens TD160.  The SME however is one of the 'J' type designed arms and I would like to have a straight arm design, probably to eventually mount on my Ariston RD11.  Now the RB300 type arms are nice and well respected but the Linn looks great, and enjoys hefty praise.   These Linn arms are fetching some serious prices on the used market (Ebay or other) and is keeping me at bay for the moment.

The arms are easily going from $800 to well over four digits for ones in good shape.  Recently I went into a music instrument store, to look for a guitar pick made from 'lignum vitae' (boy, did I get a confused look from that question!) to be cut for a thrust plate for a turntable bearing.  I looked around at the instruments while I was there and could see that you can buy a beautiful, new, shiny, saxophone for less than $1000.  Now considering all the work and parts that go into making that sax, I started wondering how some tonearms get the prices they do. ( I recently read a very interesting comment on the web by someone similarly comparing the cost of some very high priced speakers to a lower costing, new, baby grand piano).  I know that high end tonearms are carefully manufactured using top notch materials but seriously, have you looked at how many parts and how much work must go into making a saxophone?

The thought of making a tonearm has crossed my mind but you need a bit of a machine shop to make one and in any case the effort versus the results obtained may not be worth considering.  So I will continue to dream and peruse the used market for a nice arm like the Ittok or better.  Hmmm maybe I can buy the sax, or some other complex instrument, and strip it for parts.  Should be enough bits and pieces there to hobble together a tonearm or two!

Anyone out there who owns a Linn arm?  What do you think, let me know your opinions on them.

SoundBound

 

The Motor Spins and a New Layout

 

So, as mentioned last time, I had my Franken-prototype working again and I wanted to connect it up to a turntable motor to see if it will do as promised.  I made a simple connection of just one sine output to drive the motor's AC cord as per normal capacitor configuration (single supply, cap generated shift).  I connected it to a stock Ariston RD11 turntable.  It worked! the single channel could drive the motor no problem.  I left it connected for awhile to see how my small heat sink would do, it got kind of hot, so as I thought, a better heat sink will be needed.

New PCB Layout

Feeling happy and confident that the unit is working, I set out to re-design the PCB to include the added components and changes needed to fix my noise problems with the original PCB.  The new PCB is slightly larger and I took care to layout the sections differently.  The power supply is closer to the op-amp sections, the transformer hookups are all along the back.  I think this layout is better but the PCB is larger, now measuring 5x5 inches.  I also took care to increase the size of all traces carrying the power rails and the outputs from the op-amps.  You can see a picture of the 3D mock up of the PCB included here.  Also designed a small PCB for the front panel buttons and the RPM indicator LEDs (the fab house had a really good sale price for 5cmx5cm boards).

Button / LED Panel

So designing this new PCB was fun, it took some time as I tried being very careful with all traces, layout and hole sizes.  Now I just have to wait for them to come back from the fab house, and that is the hard part.

SoundBound

The Turntable Motor Controller Project - Part 5 - The Project Gets a Name

I was really happy with the result of the prototype PCBs when they arrived, nicely made, awesome silkscreen colour.  So it was time to populate the board and see if it was going to work, fingers crossed.  Here is a block diagram of the system, pretty self evident from the diagram of how it is meant to work (you can click on the images to see them larger).  When I was designing the PCB, I wanted to label the board so I realized I did not have a name other than turntable motor controller, so giving it some thought I decided to call it the Bi-Onda  TT Motor Controller.  Since this is a dual sine wave generator and 'wave' in Italian is onda, I named it Bi-Onda, which if you know Italian, bionda means blonde, as is my darling wife.  Sounds ok too.

Test Bed for the Bi-Onda

In order to hold the whole prototype system together I decided to make a wooden base to hold all the bits and facilitate connections.  You can see in the picture the brackets for the LCD and the button panel I wired up.  While all this took extra time, the advantage of keeping everything neatly together, and easy to modify, is really worth it and keeps the frustration factor down when testing.  

However, it did not keep the frustration totally at bay.  I first populated the PCB with all the parts up to, but not including, the output op-amp stages.  This way I would be able to test the power supply, the signal generator and low pass filters.  This worked like a charm, while the supply rail voltages were a bit higher than I liked, it worked fine and I could get two very nice sine waves at the output of the filters.  The LCD looked good and the debounce components worked well for the tactile buttons I chose.  So I thought, ok, lets put in the power op-amps.

Back to the drawing proto board !

Problem city, the waveforms looked horrible and the op-amps were overheating badly!  Now, I know that the heatsink I made was a bit small, but the over heating seemed way too high.   I thought it was a problem with the supply rails being higher than spec so I ordered a lower voltage transformer and put it in, but that did not resolve the problem.  The issue was getting serious, I had to go back to more basic prototyping to find the problem.  This meant removing the op-amps from the PCB and wiring them on the breadboard to see what I could find.  You can see the picture here of what it looked like when I re-wired the whole thing. The potentiometer flying off the right side of the PCB is for LCD contrast.


So after a bunch of trial and error, here is what I found to be the problems with the system fully put together as per the initial design:

1. Power supply capacitors need to be of much larger value.
2. Additional bypass capacitors have to be installed on both inverting and non-inverting inputs of the op-amps to stabilize the signals.
3. Some minor component value changes and circuit improvements.

So, overall not too many changes, but the whole thing really threw me considering everything looked pretty good as per design on the breadboard version.  Just goes to show you can not be confident until the whole thing is really put together, completely.  So I will look to use a better heat sink in the final unit and I will probably have to design a new PCB to accommodate the changes, but I should be able to make these PCBs work with a few 'flying' components.


Next, hook up both output transformers and try driving the turntable motor!
That will do it for now, 'til next time.


SoundBound

The Turntable Motor Controller Project - Part 4 - Prototyping and Hair Pulling

Initial Testing Prototype

Here is a picture of the earliest prototyping stage, it was minimal to test the most basic functions and critical stages.  The wooden base is a general prototyping box I made some time ago, it has a place for the mounted micro controller (left) the prototyping board (right) and a bank of switches, buttons and pots that are prewired and easily connected to the protoboard with wires popping up through the slot just above them.  Helps keep everything in place when doing projects.

So the micro controller is an Atmel based board with built in USB interface and various I/O ports including the all important PWM ports needed in the generation of the sine waves, serial communications.  It has analog input ports too, but I have not used them for anything on this project, yet.  On the protoboard is mounted one channel of the filter network, part of the op-amp circuit and the power supplies. You can see off to the left the power op-amp mounted to a heat sink.  The op-amps I used need hefty heat sinks as they can handle a fair amount of current and also generate pretty good heat in the process, without the heat sink, they would fry fast.

My first steps involved finding a method of generating the sine waves with the micro controller.  Browsing around for ideas and clues I came across a technique that I really liked laid out by a guy at the University of Koln in Germany.  After checking the program out and seeing it would be great for my purposes I wrote the author of the code for permission to use some of it in my project.  Nice guy, he gave me his blessings.  So I set out altering the code (by the way, the whole thing is programmed in C ) to meet my needs and add all the code necessary to operate the unit.  My first test codes generated a very nice sine wave, oh yeah I thought, this can work!  So once I verified the basic sine wave generation, I had to get my fingers dirty generating all the code to make it a dual sine wave generator with the features I wanted in it.  Dang, I have not programmed in a long time, simply due to a lack of any specific project or purpose needing coding. So it was a bit of work brushing the 'rust' off my coding skills.  But hey, like riding a bike they eventually came back, wobbly, but came back.  That is where the hair pulling came in, debugging code and programming all the bits and pieces.  As mentioned this was the basic test bed, so no fancy LCD displays, minimal functions.

The area that did cause me headaches was the op-amp circuit, getting it to behave and produce a clean sine wave was a bit of battle with components, values and dealing with the heat issues (first prototyping took place without a heat sink, that was dumb) a lot of the instability was because the op-amp chip was overheating.  I did eventually get to a good working stage, so I designed the schematic according to the configuration on the protoboard.  

3D Rendered Model of the PCB

So, next phase was to layout a complete schematic for a working board on my computer to advance to the next stage of designing the complete working PCB with everything needed to generate and amplify two independent sine waves, connect the LCD display and button panel and the power supplies.  That was fun to do, a very zen thing.  There is some great software out there for hobby, and professional, board design and layout.  To the right you can see the 3D model of the board I designed with the micro controller mounting to the bottom (gray part at bottom centre).  I liked the look of how it came out, so I checked and re-checked and re-checked again and again before finally sending out an order for 3 prototype boards to get made up for me.  I was really excited and all I could do was wait the month or so it took to get the boards back.  That was a painful wait.

So, my next blog I will go into my adventures with the second prototyping phase, the full build. 
 

The Turntable Motor Controller Project - Part 3 - Design Goals

Enough of the motor stuff, let's get to the controller and what I want it to accomplish.  There are other manufacturers that have AC motor controllers out there, they seem to fall into what I feel are two product categories, the more basic model that is intended to only generate a single precise AC sine wave and still have a capacitor to generate the second shifted AC waveform and the higher end category that generates two separate AC waveforms driving each coil independently and not using the capacitor.  Products like the Linn Valhalla fall into the first category, as for the second category there are a couple out there and they don't come cheap.

With this one I am shooting for the stars and will look to make a unit that doesn't pull any punches, go big or go home.  So here is what it should have:

1. Precise digital generation of the sine wave
2. Dual independent sine wave generation
3. Generation and selection of frequencies for 33.3 rpm and 45 rpm
4. Frequency adjustment with a precision of 0.01 Hz
5. Adjustable phase shift of the two sine waves
6. Calibration mode to adjust output for any specific turntable/motor combination
7. Ability to adjust frequency during play
8. The ability to turn off or dim the lights that will be on the unit
9. Be able to run high or low voltage motors

That should do it.  No tall order here.  Well, I have to be honest, I am cheating a bit, as I right this blog I am writing post development, so it will be easy to meet my spec list as it's already in prototype stage.  Thought I would come clean, don't want a James Fry/Oprah moment here. 

Here is what I have put together and am currently working on.  It's a micro controller based unit that is used to digitally synthesize two AC sine waves, the focus for the micro controller is that the sine waves are precise and stable and finely adjustable by digital means.  So there are no analog components used in the actual generation of the waves.  This is important to assure that there is no drift or alteration due to component drift or tolerances or heat etc.  The analog components only come in to play after the signals are generated and are for filtering and amplification of the sine waves.  The precision of the micro controller assures a stable and precise wave form.  The micro controller also serves to control the system and the user adjusts all parameters digitally with buttons via an LCD display (except for amplification calibration which is by potentiometers).

So I have prototyped a system with a micro controller unit, more on that later, a 16x2 LCD display and only four buttons to manage all the functions.  There will also be a power switch, a contrast control pot and maybe the odd switch to turn off LED's etc.  Oh, and a couple of LED's that display selected RPMs (45 or 33.3).  My analog circuits have filter stages and a cal pot that then feeds the power op amps.  If running a low power motor, it should be possible to drive it directly off the op amps but for 110V based motors I use step up transformers to bring the voltages up to the proper levels.

A first generation circuit board has already been designed ( and will already need to be modified! ) and is in prototype stage.  I will elaborate on some of my experiences with prototyping the unit in another blog, there is enough material there for it's own space. The software has been written that covers all the major functions and operations and seems to be working nicely.

Next I will be describing some of my experiences during the early design/prototyping stages.  Thanks for tuning in.

SoundBound

The Turntable Motor Controller Project - Part 2 - A Bit More About Synchronous Motors

Before describing my controller design goals let's talk a bit more about AC synchronous motors and what makes them spin.  The AC motor needs voltage delivered in alternating current but unlike a DC motor which only needs to be fed a single DC current into two wires, an AC motor needs multiple sets of wires (coils) to be fed the AC current, most AC synchronous motors have either 2 or 3 sets of coils, 2 phase and 3 phase respectively.  The thing is that these AC waveforms have to be fed into the motor out of phase from each other, ie, slightly shifted in time (technically in degrees) from each other in order for the motor to rotate.

3 Phase AC

Now in terms of pure performance, a 3 phase motor is better, it has smoother rotation if not a bit more torque.  The downside is mainly the cost of the motor and especially the complexity of driving the 3 separate AC phases.  Most turntables that use AC motors use 2 phase ones, they are cheaper and the two shifted phases are easily generated by simply adding a capacitor to the second coil which will phase shift the AC by the degrees needed for it to work (90 degrees, 3 phase motors require AC feeds each shifted by 120 degrees).  You can see the different waveforms in the pictures.  The thing about using a capacitor to introduce the phase shift is that it is cheap and simple to implement, but not likely very precise, usually close enough that the motor rotates as expected.  If the phase shift is not precisely 90 degrees the motor may be subject to increased vibration, so you want it as close as possible to 90 degrees. 

The motors used in turntables can be either low voltage (20-30V AC) or line power driven (110V) so this has to be considered when I design the controller.  The turntables I mentioned previously use line power level motors (110V here, 220V in other countries).

So I am going to be dealing with 2 phase motors for my project, they are easy to come by and are inexpensive and work well enough.  Interestingly, stepper motors are basically AC synchronous motors that if driven by AC waveforms as above will also work.  Stepper motors can be found in all kind of computer devices such as printers, scanners and some disk drives.  So it is conceivable, with a good controller, to scavenge some of these motors and use them to drive a turntable !  Nice and cheap (usually free if you hunt for discarded printers by the curbside as I have been known to do) but maybe we will see how that works out some other time.  Most of these steppers are low voltage ranging from 5-24V so that needs to be considered.

So this is not a very deep description on AC motors, but hopefully is enough to  understand where I am heading on this project.

The Turntable Motor Controller Project - Intro

 

OK, so there are a few motor choices for turntables within the two major categories; direct drive and non direct drive.  We will not be dealing with the direct drive motors, they are not the most popular choice for turntable aficionados even if there may be good ones out there.  I want to address indirect drive turntables and these fit into two major categories, belt drive and idler wheel drive.  In driving the platter these models can use either an AC synchronous motor or a DC motor.

My turntables of preference use AC synchronous motors, with their benefit being that the rotational speed is strictly controlled by the AC frequency it is fed.  A typical AC synchro motor is displayed in the photo above from an Ariston RD11.  A DC motor has it's frequency determined by the voltage it is driven at (or pulse width driven, another method of altering average voltage).  So I find the use of the AC motor easier to control as one only needs to modify the frequency and needs not pay attention to controlling the level of voltage applied (usually the motor is driven at it's full specified voltage).  A DC motor can be prone to rotation speed drift should the voltage level not be correct for the desired speed.  It is not my desire to get into too much description of all these drive types, methods of control and benefits or limitations, there is plenty out there on the web if you search for the info.  Suffice it to say that I will be working with AC motors and my project will serve to drive these precisely and optimally for best speed control.

Most of the AC motor turntables are speed controlled by the frequency of the AC coming into your home from the electrical utility (60Hz here, 50Hz used in many other countries).  The electrical utilities are usually pretty good at maintaining a constant 60Hz for which these motors are typically rated for their speed spec, but there is no guarantee that it will not drift or change.  If it does change from 60 Hz, your motor speed will also change.  So delivering a good steady 60Hz is important.  However, depending on the precision of your turntable's other parts (pulley, platter diameter etc.) even with exact 60Hz driving your motor, these other components have an effect on the rotational speed and so your turntable may not be rotating at a precise 33.3 rpm.  Being able to slightly adjust the 60 Hz up or down would allow us to dial in the right frequency so that we are getting exactly 33.3 Hz.  An added benefit is also that by adjusting the AC frequency we could even get the motor-platter to spin at 45 rpm for us without switching the drive pulley of the turntable.

So this is where my project leads me, the ability to adjust the 60 Hz to my desired value for precise speeds of 33.33 rpm or 45 rpm.  Another reason for doing this project is that I also have in mind at some time to build my own turntable, having a motor controller that is adjustable will free me from having to have a very precisely dimensioned drive pulley for the platter.  As long as I am close, I should be able to adjust the motor speed for spot on platter rotation speed.

So in my next entry I will describe the goals and general design ideas I have for the motor speed controller.
 

Welcome to this blog on audio, me and my projects

So, here I go, thinking I am going to start blogging.  What about? My audio hobby of course.  Maybe other stuff might find it's way in here but as I see things now I am more likely to write about the things I do in audio and the discoveries I make.  So, if you stumbled across this or have followed a link here, welcome one and all.

I have been messing with audio stuff since I was in my early teens, caught the bug early on and it never let me go, although there are numerous periods where I did not do much, either taking interest in other things or just being busy, but always made my way back.

Never been a big spender on audio like some, I have always looked to spend reasonably and not go too crazy with this hobby.  I have owned several systems over the years and the quest, to find what I felt was true in the music and the experience of listening, has led me from a purchaser to a tinkerer, modifier and builder of audio bits.  Also this turned out to be the best way to get what I wanted out of the audio experience without dishing out a lot of cash.

In future blogs I may elaborate a bit more on the things I have owned or still own, my impressions and the chain of events that lead to my current system.  At this time though the blog will likely be dealing with my current projects.  Right now I am designing / building a turntable motor controller for AC based turntables like the Thorens, Ariston and Linn types.  Pretty much any turntable using an AC motor.  Other projects on the list awaiting their turn on my bench is an Ariston RD11 turntable rebuild (the predecessor to the Linn LP12) a tube based preamplifier with motorized volume control among other projects.

So if you join me on this journey, welcome aboard, and let's see how this all turns out.

If you are a frequenter of some of the audio forums out there you might have seen the odd comment from me as SoundBound, if not as is most likely, don't worry about it.

SoundBound

(Rick)