Hi there
I have searched the forum for similar discussions of a valid design but all has been a bit hazy.
Basic unit specs:
Two vari frequencies (for 33.3 and 45 rpm)
Stable operation
High current capability without strain
Output voltage adjustable
One-box solution (no odd pieces of amps and iPods
)
This is what I have come up with. I am no electro guru but this is my best guess for a PSU to fit the above requirments.
Wien-bridge oscillator with two fixed cap banks as per each speed for selection. Fed by a regulated PSU.
TDA7249 IC Op-Amp as driver stage for motor/transformer - at least 5 amps capability.
A super advanced PSU with processor control is not really nessesary (display etc). You want a stable supply to the motor (especially frequency).
Anybidy care to expand on this and comment/make suggestions on the schematic. Like I said - I am no expert but this is my best guess.
Dewald
I have searched the forum for similar discussions of a valid design but all has been a bit hazy.
Basic unit specs:
Two vari frequencies (for 33.3 and 45 rpm)
Stable operation
High current capability without strain
Output voltage adjustable
One-box solution (no odd pieces of amps and iPods
)This is what I have come up with. I am no electro guru but this is my best guess for a PSU to fit the above requirments.
Wien-bridge oscillator with two fixed cap banks as per each speed for selection. Fed by a regulated PSU.
TDA7249 IC Op-Amp as driver stage for motor/transformer - at least 5 amps capability.
A super advanced PSU with processor control is not really nessesary (display etc). You want a stable supply to the motor (especially frequency).
Anybidy care to expand on this and comment/make suggestions on the schematic. Like I said - I am no expert but this is my best guess.
Dewald
Attachments
If you are looking to run a single phase (induction) motor, don't use a class AB power op amp as the power amplifier. You will have a devil of a time compensating it due to the effect of the motor inductance on the feedback loop. T amps and their ilk are a far easier solution.
If you are looking to run a two phase (synchronous) motor splitting the two phases and establishing quadrature correctly is very important to optimal performance.
I once used Wien bridge and then some more complex analogue oscillators (modified Fraser multiple phase shift) but the drift is difficult to control. Yes square waves are difficult to filter but Direct Digital Synthesis gets around that very neatly.
Is the "one box solution" allowed to have multiple components inside?
PS (or battery) > frequency generator > output amplifier(s) > transformer(s)
There are good reasons for keeping the sections separate.
If you are looking to run a two phase (synchronous) motor splitting the two phases and establishing quadrature correctly is very important to optimal performance.
I once used Wien bridge and then some more complex analogue oscillators (modified Fraser multiple phase shift) but the drift is difficult to control. Yes square waves are difficult to filter but Direct Digital Synthesis gets around that very neatly.
Is the "one box solution" allowed to have multiple components inside?
PS (or battery) > frequency generator > output amplifier(s) > transformer(s)
There are good reasons for keeping the sections separate.
Mark
I did not realize that the amp in the schematic is class A/B - the data sheet doesnt mention it.
What is needed is a class B amp for best efficiency.
Also looking at doing this oscillator solution than the above unit: http://www.maxim-ic.com/appnotes.cfm/an_pk/3846
A dual phase unit is not needed as the phase shift for AC Synch motors is done by a cap (but you knew that).
I want a PSU with a single phase that will enable me to use it on a varety of AC motor turntables. Converting these tables to DC motor is not an option. The PSU must also have Low Voltage (12 - 24vac) and High Voltage (110v - 220v) output, selectable by a toggle switch. (Look at the puny "Speedboxes" from Pro-Ject)
Last night I tried my 12vdc-to-230vac inverter on my turntable and the results were quite impressive! This is what I want - no need for an over-fancy device.
A single box solution is also a must - clutter is not an option. Mains operated also a must.
I think the inclution of an analogue voltage and frequency meter on the front could be a good idea. Maybe a ammeter as well.
Dewald
PS - Any tips for a high power class B amp in Chip form?
I did not realize that the amp in the schematic is class A/B - the data sheet doesnt mention it.
What is needed is a class B amp for best efficiency.
Also looking at doing this oscillator solution than the above unit: http://www.maxim-ic.com/appnotes.cfm/an_pk/3846
A dual phase unit is not needed as the phase shift for AC Synch motors is done by a cap (but you knew that).
I want a PSU with a single phase that will enable me to use it on a varety of AC motor turntables. Converting these tables to DC motor is not an option. The PSU must also have Low Voltage (12 - 24vac) and High Voltage (110v - 220v) output, selectable by a toggle switch. (Look at the puny "Speedboxes" from Pro-Ject)
Last night I tried my 12vdc-to-230vac inverter on my turntable and the results were quite impressive! This is what I want - no need for an over-fancy device.
A single box solution is also a must - clutter is not an option. Mains operated also a must.
I think the inclution of an analogue voltage and frequency meter on the front could be a good idea. Maybe a ammeter as well.
Dewald
PS - Any tips for a high power class B amp in Chip form?
I repeat: Do not use a class AB (or class B) power op amp for an induction motor, the inductance causes huge problems. Class D gives you better efficiency than Class B anyway.
I didn't say that a two phase supply was necessary, I said it was important to optimal performance. It is of course up to you what compromises in performance you will accept.
I didn't say that a two phase supply was necessary, I said it was important to optimal performance. It is of course up to you what compromises in performance you will accept.
bigwill said:
No please - simplicity and efficiency is very important. It must be a sleek black box that does the job it is made for - to make a turntable run smooth and true.
You may certainly experiment with a tube PSU but I would rather go SS. I think Mark Kelly made a tube PSU for a Garrard 301...?
D
Here is a block diagram of the idea I have in my head:
R1 & R2 - PSU Regulators
T1 - Mains IN transfo
T2 - AC signal OUT transfo
A1 - Gain stage
A2 - Power Amplifier
WB VFO - Wien-Bridge Vari Frequency Oscillator
UI C - User Interface Controller
D
An externally hosted image should be here but it was not working when we last tested it.
R1 & R2 - PSU Regulators
T1 - Mains IN transfo
T2 - AC signal OUT transfo
A1 - Gain stage
A2 - Power Amplifier
WB VFO - Wien-Bridge Vari Frequency Oscillator
UI C - User Interface Controller
D
Lets study a very important PSU (IMHO) of a great turntable. The PSU of a Thorens TD125 mkI.
I used this table for an exstended time and is impressed by its speed stability and easy of adjustment.
We can distill the essence from this circuit and build on that to create a good PSU. Dont you think so?
First of all - we only need one phase.
Second - more power (better amp section)
D
I used this table for an exstended time and is impressed by its speed stability and easy of adjustment.
We can distill the essence from this circuit and build on that to create a good PSU. Dont you think so?
First of all - we only need one phase.
Second - more power (better amp section)
D
Attachments
It is considerably easier to go ground up, rather than adapt.
Especially if you are looking for precision.
There are 3 distinct challenges.
1/ Precise generation of a 50 (60, or switchable) sine wave with no / low harmonics
2/ applying 'gain' to the sine wave with as little distortion as possible to take it to the 110/220/240 Vrms required
3/ Stepping up the current capability to provide 100 or so watts of power.
1 is a challenge thanks to the precision required - you are in the realms of the capacitance of a switch possibly adversely impacting the output
2 is more straightforward, except that the gain will be of the order of 50+
3 take high voltage, low current to high voltage, high current...
I'd suggest tubes for 3, a good transformer for 2, and a *nice* oscillator (or dedicated sine generator chip) for 1.
This is not inexpensive, and not without difficulty, but the results will be worth it. Most specifically, elimination of the ULF oscillations on the mains power circuits (sub 1 Hz, that are like subtly varying DC)
An alternative route is
1/ a great oscillator
2/ a great amp - to provide gain and current
3/ a huge transformer to step up to the correct voltage.
This is challenging, because many amps are not happy driving inductively coupled loads, and low loads
Welcome to the fun
Owen
Especially if you are looking for precision.
There are 3 distinct challenges.
1/ Precise generation of a 50 (60, or switchable) sine wave with no / low harmonics
2/ applying 'gain' to the sine wave with as little distortion as possible to take it to the 110/220/240 Vrms required
3/ Stepping up the current capability to provide 100 or so watts of power.
1 is a challenge thanks to the precision required - you are in the realms of the capacitance of a switch possibly adversely impacting the output
2 is more straightforward, except that the gain will be of the order of 50+
3 take high voltage, low current to high voltage, high current...
I'd suggest tubes for 3, a good transformer for 2, and a *nice* oscillator (or dedicated sine generator chip) for 1.
This is not inexpensive, and not without difficulty, but the results will be worth it. Most specifically, elimination of the ULF oscillations on the mains power circuits (sub 1 Hz, that are like subtly varying DC)
An alternative route is
1/ a great oscillator
2/ a great amp - to provide gain and current
3/ a huge transformer to step up to the correct voltage.
This is challenging, because many amps are not happy driving inductively coupled loads, and low loads
Welcome to the fun
Owen
I'm about to make a supply for a turntable. I'm afraid almost all the motors made for turntables are rubbish. The bearings and pole pieces in the Philips/Airpax/Premotec 24 pole synchronous motor used by Linn, Rega etc are poor. The Garrard 301 and 401 motors have nice bearings but there's little you can do electronically to help the motor. Brushed DC motors are a recent inexplicable fad. However...
The brushless DC motors in 5 1/4" floppy drives have superb bearings and can be driven as a three-phase synchronous motor from the sort of voltage that can be produced directly by a TDA2030 (ultra-cheap 20W audio amplifier IC), and a three-phase analogue oscillator is not too difficult.
Start looking for 5 1/4" drives.
The brushless DC motors in 5 1/4" floppy drives have superb bearings and can be driven as a three-phase synchronous motor from the sort of voltage that can be produced directly by a TDA2030 (ultra-cheap 20W audio amplifier IC), and a three-phase analogue oscillator is not too difficult.
Start looking for 5 1/4" drives.
Old flopy drives are obviously rare now and mostly found as landfill... I dis assembled a HP CD rom last week. Expected a brushed DC motor like most CD mechs but no sir, uses something far more eloquent and advanced with what feels like lovely bearings. Would that not be a hoot. Best TT motor ever salvaged from CD ROM? I think it is the same/simillar type as in the 5 1/4 drive.
Yes, I had wondered about a CD drive as the required speed is about the same. Trouble is, the ones I've seen have nasty little motors more akin to a child's toy. (Cue rude comments about CD.)
Another possibility is the motors intended for electric flight. These are very powerful very small BLDC motors that can be run as synchronous motors. They wouldn't have any trouble starting a large platter...
Another possibility is the motors intended for electric flight. These are very powerful very small BLDC motors that can be run as synchronous motors. They wouldn't have any trouble starting a large platter...
How about one of these...
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXLBS1&P=0
Combined with one of these...
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXUA39&P=0
Should do the job very nicely
Owen
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXLBS1&P=0
Combined with one of these...
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXUA39&P=0
Should do the job very nicely
Owen
Add one of these to mount
http://www3.towerhobbies.com/cgi-bin/wti0093p?&C=GHK
And you're good to go
Owen
http://www3.towerhobbies.com/cgi-bin/wti0093p?&C=GHK
And you're good to go
Owen
Yes, that's the idea. Ideally, you want an outrunner motor because the outer rotor gives a much better flywheel effect and helps screen the stray magnetic field from the windings. I was looking at these:
http://www.jperkinsdistribution.co....ght items&subcatname=Brushless motors - E-Pro
I will use three TDA2030 (IC power amplifier chips costing just over £1 each) to drive the motor.
http://www.jperkinsdistribution.co....ght items&subcatname=Brushless motors - E-Pro
I will use three TDA2030 (IC power amplifier chips costing just over £1 each) to drive the motor.
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