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

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

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 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.