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jon tiltman
state registered audiophile
Joined: 30 Dec 2003
Posts: 1433
Location: Bristol Engerland
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 Posted: Mon Nov 02, 2009 3:11 pm Post subject: |
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A few months ago someone linked to a site about how to make a cheap top flight deck. His idea for the motor/psu was to get an AC stepper motor with two sets of windings, digitally create two sinewaves at 90º to each other, convert them to MP3 and power the motor with a cheap integrated amp, using the volume control to trim the voltage back to the minimum it can stand without stalling or at least being affected by stylus drag.
Because you'd be creating the sinewaves digitally you can adjust them to suit the size of your existing pulley rather than vice versa. As soon as I heard of this I wondered why Linn (and the people behind the Hercules) bothered creating their sinewaves with quartz oscillators when it's so much easier and more accurate to just use a digital sampler.
JT |
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LPfan
vinyl addict
Joined: 28 Oct 2007
Posts: 503
Location: Mumbai, India
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| Posted: Mon Nov 02, 2009 5:53 pm Post subject: |
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Hi JT,
You can drive any a/c induction or synchroneous type motor using this concept. Mr. Mark Kelly had shown his ipod driving Garrard 301 motor on his webpage. Unfortunately the link is not working now.
Regards,
LPfan
_________________
Music is a universal language. |
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Edmond123
manufacturer
Joined: 09 Sep 2007
Posts: 93
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| Posted: Tue Nov 03, 2009 4:50 am Post subject: |
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DC voltage applies to DC motor needs filtering, that is capcitors and ferrites. I guess Oracle launched their Turbo PSU has convencing reasons behind.
My point is that audiophile spends big money in tonearm, cartridge ..etc, but they forget the PSU for their turntable.
I know one audiophile use VDH Colibri with ITTOK II in his Valhalla LP12???
As you know, when PSU goes to mass production, and user friendly is required, standarization must be taking into consideration. That is why Quartz Oscillator is one of the options.
"Proof in the Pudding is in the eating". |
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flavio81
contributor
Joined: 16 Sep 2009
Posts: 2030
Location: Lima
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| Posted: Tue Nov 03, 2009 3:15 pm Post subject: Re: Turntable power supplies |
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| duficity wrote: | | What is the difference between all these expensive power supplies that are being sold as upgrades to already very expensive turnables and a regular wall wart 24vdc transformer you can buy at Radio Shack. In an attempt to get my turntable running to check it out, I bought one of the RS ones, hooked it up and to my amazemend, it ran. Checked with the strobe and it was rock solid at both speeds. Played an album and it sounded fine. So what would a $1000 plus power supply do extra and how does it do it? |
For a good DC supply you only need:
1. a transformer to lower down the AC wall voltage
2. a diode bridge
3. a voltage regulator (cheap integrated circuit -- LM7805, etc)
4. some big electrolytic capacitors to smooth the output
5. fuse
6. box
7. connectors
All items are CHEAP. You don't need $1000 to create a DC power supply with noiseless, stable out.
Those $1K+ audiophile DC power supplies are indeed a waste of money.
Now, if we're speaking about a turntable CONTROLLER that has to directly drive and regulate motor speed, it's a different story. But still, it isn't rocket science either. |
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duficity
senior member
Joined: 13 Jul 2002
Posts: 96
Location: florida
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| Posted: Wed Nov 04, 2009 7:17 pm Post subject: |
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| I assume then, that the wall wart DC power supplies simply convert AC to DC at the required voltage and that all the regulation of speed and stability occurs inside the turntable and is then applied to the motor. So if you get a fancy power supply that controls speed and stability, do you bypass the turntable's internal controls and simply wire it into the motor directly. And just how does a power supply regulate speed. Is there a unit which converts AC to DC and can be wired directly to a DC motor and regulate the turntable's platter speed? Sorry to sound so ignorant, but I guess I am on this subject. |
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flavio81
contributor
Joined: 16 Sep 2009
Posts: 2030
Location: Lima
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| Posted: Wed Nov 04, 2009 9:21 pm Post subject: |
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| duficity wrote: | | I assume then, that the wall wart DC power supplies simply convert AC to DC at the required voltage and that all the regulation of speed and stability occurs inside the turntable and is then applied to the motor. So if you get a fancy power supply that controls speed and stability, do you bypass the turntable's internal controls and simply wire it into the motor directly. And just how does a power supply regulate speed. Is there a unit which converts AC to DC and can be wired directly to a DC motor and regulate the turntable's platter speed? Sorry to sound so ignorant, but I guess I am on this subject. |
A DC power supply, by definition, only outputs continuous current.
A motor controller will control speed. And yes, it will have to be wired directly to the motor.
BUT the turntables that use AC synchronous motors (that are directly regulated by the wall socket AC frequency), are by definition externally controlled, and thus they WILL be benefited from a special AC power supply, which then will also be a motor controller.
BUT, still, $1000 for such a supply is excessive. |
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duficity
senior member
Joined: 13 Jul 2002
Posts: 96
Location: florida
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| Posted: Thu Nov 05, 2009 9:13 am Post subject: |
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| ok, to make it simple for my little brain. If I take a DC motor and apply the rated voltage to it, how fast will it spin and what decides that speed. I doubt that all DC motors spin at the same speed and are then just geared down with pulleys. So what does the motor controller do to the motor to raise or lower its rpm? |
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Werner
contributor
Joined: 30 May 2002
Posts: 672
Location: Antwerpen
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| Posted: Thu Nov 05, 2009 10:56 am Post subject: |
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Too bad Mark Kelly's site has disappeared, but an initial
version of his turntable motor and controller primer was published in
Basaudio's DIYMAG:
http://www.basaudio.net/pubs/DIY_2006_1.pdf
Grab it before that one goes too ...
But in short: a brushed DC motor's speed is a function of the applied voltage and load.
For a given load (i.e. the platter with record and tracking stylus) the voltage has to be 1) precise and 2) stable, while the supply delivers the pulsed current to the motor coils.
In other words: a 7805 won't do.
_________________
when did you last get a new drive belt? |
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Conrad Hoffman
senior member
Joined: 01 Aug 2007
Posts: 373
Location: Canandaigua, NY
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| Posted: Thu Nov 05, 2009 12:06 pm Post subject: |
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DC motor systems need some kind of feedback and a controller to utilize it. A PID loop or similar. AC motors, like my Thor-ject, either use the line voltage directly, or have a controller that generates the necessary voltage(s). Those controllers can be AC powered, with the rectifiers and filter caps on the board, or DC powered, hopefully with some regulation on the board. The typical Pro-ject (and Thor-ject) will use a 16 volt *AC* output wall wart, not DC.
BTW, for web pages that have disappeared, try using the Wayback Machine. They've archived a remarkable amount of stuff. Remember, whatever you put on the web is probably out there forever if people know where to look.
Best,
Conrad |
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flavio81
contributor
Joined: 16 Sep 2009
Posts: 2030
Location: Lima
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| Posted: Thu Nov 05, 2009 2:42 pm Post subject: |
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| Werner wrote: | | But in short: a brushed DC motor's speed is a function of the applied voltage and load. (...) while the supply delivers the pulsed current |
You are right when talking about a brushed DC motor, but I think you have mixed more than one type of motor on the same paragraph. "DC (direct current)" not equal to "pulsed current"!
There are many motor designs. For example the best direct drive motors use a special brushless design with many coils in a "star" pattern. Every coil needs a different pulsed current. Etc.
And yes, every decent turntable has a speed sensor and feedback mechanism to correct the speed according to the sensor and make it match with a specified frequency. Example: A hall sensor, a quartz crystal frequency generator, and a PLL to make them match. [Technics]
Or, at the very least, a stable frequency generator that drives the turntable. Example: Wein bridge oscillator [Thorens TD125]
Of course, there are audiophile companies that still sell $1K+ turntables with no such feedback/control mechanism... but that's another story. |
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TNTTNT
senior member
Joined: 21 Sep 2009
Posts: 488
Location: Kent
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| Posted: Thu Nov 05, 2009 3:08 pm Post subject: Re: Turntable power supplies |
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| flavio81 wrote: |
For a good DC supply you only need:
1. a transformer to lower down the AC wall voltage
2. a diode bridge
3. a voltage regulator (cheap integrated circuit -- LM7805, etc)
4. some big electrolytic capacitors to smooth the output
5. fuse
6. box
7. connectors
All items are CHEAP. You don't need $1000 to create a DC power supply with noiseless, stable out.
Those $1K+ audiophile DC power supplies are indeed a waste of money.
Now, if we're speaking about a turntable CONTROLLER that has to directly drive and regulate motor speed, it's a different story. But still, it isn't rocket science either. |
Hi Flavio,
It's wierd timing you posted this, as I was looking into how to make a cheap 21v DC supply for a Technics 1200. The first article I found mirrored your post - Transformer, 4 Diodes, Capacitors and Regulator. They also added a heatsink. They said you need to be careful how on what value you choose the capacitors, so the ripples would be in range of the regulator.
They showed this for 5v DC supply
I am think of learning how to do this. The only barrier is that I have no electrical experience and I am slightly incompetent at most practical tasks. I find running a small country far easier. |
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flavio81
contributor
Joined: 16 Sep 2009
Posts: 2030
Location: Lima
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| Posted: Thu Nov 05, 2009 4:39 pm Post subject: Re: Turntable power supplies |
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| TNTTNT wrote: | | I am think of learning how to do this. The only barrier is that I have no electrical experience and I am slightly incompetent at most practical tasks. I find running a small country far easier. |
Dear Leader,
Yes, that is a cookbook circuit for voltage regulation. Put it inside a gold-plated steel case with golden connectors, and you can sell it for $500 to some audiophile.
There are many websites around for learning basic electronic theory and circuit building. You can start with a basic kit:
- Soldering iron
- Solder tin
- Solder flux (solder paste)
- "Breadboard"
- Prototyping PCB ("perfboard" or "stripboard")
- Wire
- Multimeter
Note that for creating prototype circuits, there are many methods. Check out:
http://www.dartmouth.edu/~sullivan/prototyping.pdf
Within months you'll be building your own RIAA preamp, MC preamp, etc.
Greetings, |
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131east23
junior member
Joined: 18 Oct 2009
Posts: 5
Location: Portland, Oregon
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| Posted: Fri Nov 06, 2009 7:31 am Post subject: |
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| OK, maybe this is a dumb question... but how does the voltage regulator in above diagram know how fast the platter is turning? Doesn't the regulator need an input from the device it's regulating? Speed signal, MPU, voltage? Or is that still just output voltage stepped down, rectified, filtered... is the original line frequency still determining the speed? |
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TNTTNT
senior member
Joined: 21 Sep 2009
Posts: 488
Location: Kent
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| Posted: Fri Nov 06, 2009 10:09 am Post subject: |
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| 131east23 wrote: | | OK, maybe this is a dumb question... but how does the voltage regulator in above diagram know how fast the platter is turning? Doesn't the regulator need an input from the device it's regulating? Speed signal, MPU, voltage? Or is that still just output voltage stepped down, rectified, filtered... is the original line frequency still determining the speed? |
I've proabably asked a lot or naive here, but take the view that all clever people must have started off dumb in the first place.
My understanding is AC is a signal which swings back and forth in direction. The rectifier makes sure the signal points in the one direction; Capacitors smooth out the peaks and fall in the signal; and the regulator makes the aready smoothed signal even flatter. This means a constant uniform power output (21v for a Technics 1200).
This is used to feed a DC motor. A DC motor needs extra circuitry to mantain the correct speed. If more or less power is required (like going from standstill), then the DC supply would provide more current, but maintain 21v.
I am still developing an understanding, so hopefully the more experienced here will correct any errors above. |
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flavio81
contributor
Joined: 16 Sep 2009
Posts: 2030
Location: Lima
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| Posted: Fri Nov 06, 2009 3:13 pm Post subject: |
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| 131east23 wrote: | | OK, maybe this is a dumb question... but how does the voltage regulator in above diagram know how fast the platter is turning? |
The above diagram is for a voltage regulator, not for a turntable controller.
An example of turntable controller will be:
- Platter speed sensor, either hall sensor or magnetic track and magnetic head, or optical.
- Variable frequency generator
- Power amplifier that drives the motor coils
- Frequency standard [quartz crystal oscillator]
- A PLL (phase locked loop) comparator that increases or decreases the motor driving frequency so the sensed speed matches the frequency standard.
That is how most of the quartz-locked turntables work. |
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