Wish to get into DIY Vinyl, however some woes

[Shike]

Hello everyone,

I've been researching some of the DIY turntables, however I'm having issues. I'm pretty sure I want a synchronous (stepper?) motor, however beyond that I'm unsure of how to control the actual speed of the platter.

I'm not wanting to use the external CD method of getting the actual frequencies and waves. I rather use an IC to generate the waves, however I'm having trouble figuring out where to start and how I would control that, especially when I need to change the record speed. I know some stepper drivers generate pulses to determine speed, and was thinking a PWM may help control that to determine speed. Is that even possible though, and if so, ideal? I would need it hooked up to a potentiometer or something of the sort I'd think

Is there a reasonable way to accomplish what I'm wanting, or would I be better off buying an entry level player? I presume most use actual micrcontrollers?

Thanks in advance,
Shike

(Forgive any gross misunderstandings of ideas presented, I've just started trying to learn motors in regards to TTs, and in general)

[Mark Kelly]

If you wish to use a synchronous motor, you are best off feeding it with sine waves of appropriate frequency. Two waves 90 degrees apart is ideal, single wave then a phase shifting cap to fake the second is more common.

There are two broad approaches, analogue and digital.

Single phase analogue using something like a Wien bridge is easy and frequency adjustment is simple. Two phase analogue is doable but more complex. In all cases analogue will make very nice sine waves but suffers from imprecise and drift prone frequency which may or may not be acceptable to you.

Digital is easy to do but hard to make adjustable. Frequency precision is excellent, waveform purity can vary from OK to excellent. A digital generator with clean wave forms, easily adjustable frequency and precise (and adjustable) quadrature is not a trivial design exercise.

A hybrid approach is to use a digitally clocked DAC which gives clean sine waves of any frequency depending on the clock and the division ratio. This scheme is used by inter alia by AD in their direct digital synthesis chips but you need to program a microcontroller to run them.

[Shike]

Okay, so I went to (your?) webite that is at the bottom of your post and started looking through somethings. I take it this is the schematic I should follow then? If so, is the variable frequency good for motors that work in 50/60 hz or should it be more/less/ranged different?

Also, I'm curious as to what the "small globe" is. I'm guessing it has to do with the lightbulb traditionally found in the cirucuit? If so, what should I use for it?

Lastly, what's the "PTC Gain Control" and where's it located in the circuit?

Thanks so far, you helps been invaluable

[Mark Kelly]

The small globe is the lamp and is also the PTC element (the tungsten filament of the globe has a strongly Positive Temperature Coefficient of resistance known as a PTC resistance.)

If you build that drive be prepared for speed drift of 1% or more with normal components. With very careful build and a temperature controlled enclosure you can get down to around 0.1%. One good trick is to match the tempcos of the resistors and the capacitors so that they are more or less equal but opposite. If you do this watch the influence of the potentiometer - the tempcos of pots are foten outrageously high and variable.

[Shike]

Well, the question for me is then would this be suitable for my first turntable? Right now I'm in college so cost was the primary concern with quality following only shorty behind.

Will this drift be extremely bad, or within reason overall? I'm just starting to get into it, and most of my equipment is lining up with entry level.

[Mark Kelly]

I can't answer that, it depends on your tolerance for speed variation. I was happy enough when I first built it but my version was held at constant temperature so it didn't drift much.

[kevinkr]

To start use a synchronous motor running off of 120V/60Hz, later you can build something fancier. Many high end tables in the past have used this approach. (Merrill, AR, Gerard to name a few.)

Old AR XA/XB tables are a convenient and inexpensive basis for a custom table, performance can be surprisingly good. Even a stock AR-XA can be surprisingly good with a limited amount of tweaking. The clunky looking arm outperforms the fancy arms on a lot of not so cheap mass market Japanese tables made from the 1970's onward.

I had a Pink Triangle with dc servo control that had such bad drift that the speed changed drastically from the beginning to the end of a single side of a record. I was given a new motor and speed controller along with the table which did nothing to improve the situation. I got rid of it quite quickly.

[cactuscowboy]

Originally posted by Shike
Well, the question for me is then would this be suitable for my first turntable? Right now I'm in college so cost was the primary concern with quality following only shorty behind.

Will this drift be extremely bad, or within reason overall? I'm just starting to get into it, and most of my equipment is lining up with entry level.

I'd be looking for a used turntable in a thrift shop or at garage sales. Definitely the easiest, cheapest and quickest way to start listening to records. Unless you really want to make a DIY machine.

[Shike]

Trust me, I've tried. None of them that I've found uses a decent AC motor, only your basic dime a dozen DC motors. On top of it the platters aren't worthwhile, allowing for massive vibrations that would damage anything worthwhile. And of course, the tonearms themselves are also pretty much garbage. Let's not even get started on the cartridges they come with

[kevinkr]

Originally posted by Shike
Trust me, I've tried. None of them that I've found uses a decent AC motor, only your basic dime a dozen DC motors. On top of it the platters aren't worthwhile, allowing for massive vibrations that would damage anything worthwhile. And of course, the tonearms themselves are also pretty much garbage. Let's not even get started on the cartridges they come with

Try to find an old AR-XA or XB either of them will be surprisingly better than most inexpensive Japanese made tables you are likely to find in a thrift shop. A yard sale might score you one if you are very lucky.

What is your budget? If it is a couple hundred $ there are any number of Thorens, AR and other tables on eBay that will fit the bill very nicely.