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.