With dividing head at your disposal, if you have time, something really cool could be done. Not that much influencing playback, but cool.
What I was thinking to do if I would make precise frequency generator coming from platter is to turn this F signal into voltage by one of available F to V chip converters.
Than I would use one of these vintage mA meters, example from internet:
One side connected to voltage reference of some sort, other to said F to V converter output.
Vibration of instrument needle shows TT speed deviations, in real time and cool way.... If I had all the time in the world I would do this
I have to admit that I do like steampunk art; I saw a wonderful steampunk R2-D2 unit at a model engineering exhibition.
This is how instruments should look: https://blog.balena.io/show-tell-a-steampunk-desktop-background-radiation-monitor/
This is how instruments should look: https://blog.balena.io/show-tell-a-steampunk-desktop-background-radiation-monitor/
Hi, just back from my Winter break walking in the mountains.....
A clarification on the above paragraph - when using more than one optical sensor reflective patches on the platter (setting CP_REV to 2 or 4), it still measures the speed over a single revolution in each case, but the update rate is increased to 2 or 4 per revolution. For example, with 2 patches called A and B, it will measure the speed from A->A again and B->B again. This also means that the spacing of the patches does not have to be exactly even, only approximately so.
Hi Rich, did you test what's giving better measurement, one or more trigger patches for sensor?
If the accuracy of trigger points isn't critical, than it's really easy to paint more of them
If the accuracy of trigger points isn't critical, than it's really easy to paint more of them
'Better' is rather subjective! There is also the averaging function (NR_AVG), and this combined with CP_REV can give you different combinations of responsiveness and stability. I've chosen 2 patches (CP_REV) and an averaging of 4 (NR_AVG), but I'd suggest playing with the settings and seeing what you like the most.
Hi Rich, here is one little thing I don't agree with you, whats supposed to be subjective. Its just to accurately measure platter speed, surely with limitations of time in which we measure.
Since I'm confident in most solutions to make the end to decent TT, I started to craft instead of calculating and testing. Craft is time taking, I understand folks sitting at computer and afterwards ordering PCB-s and prepared chassis just to assemble their design, it is probably smarter way.... for some reason I must cover myself in dust and bleed a finger or two 🙂
- finished front display with control rotary switch. At the end chosen smoked plexiglass. The glass was matched to routed hole in the wood by file and sand paper (later I will turn better knob on a lathe):
On the back side is Supaspin display and rotary encoder, mounted on a piece of pcb board. This OLED has M2 mounting holes, took some time to find adequate M2 distances:
Routed hole in MDF would show some light through smoked glass, to avoid it I hand painted MDF with my kids equipment:
- finished front display with control rotary switch. At the end chosen smoked plexiglass. The glass was matched to routed hole in the wood by file and sand paper (later I will turn better knob on a lathe):
On the back side is Supaspin display and rotary encoder, mounted on a piece of pcb board. This OLED has M2 mounting holes, took some time to find adequate M2 distances:
Routed hole in MDF would show some light through smoked glass, to avoid it I hand painted MDF with my kids equipment:
And on the back side, i finished "drawer" for the preamp, I still did not decide of final preamp configuration as it will be dependent on cartridge I use. That's why I decided to make maximally flexible arrangement to let me change preamp configuration together with cart change. Picture is showing connectors, from left:
Behind this panel with jacks is generous 12 x 23 cm PCB meant to piggyback all that is needed; PS regulator, Front end amp, RIAA EQ and final amp.
The board is kept with all the copper except 2 traces leading back where PS regulators (if needed at all ) will be placed.
You can see on the PCB I still struggle with technology of making it, but after 30 + years not giving up making own in house PCB-s, probably not very smart but what to hack..
- 2 x XLS-s for main output
- XLR to plug in +-18V battery PS
- Aux 4 pin XLR to take out stereo signal before RIAA , for digitalizing or using before RIAA EQ's
Behind this panel with jacks is generous 12 x 23 cm PCB meant to piggyback all that is needed; PS regulator, Front end amp, RIAA EQ and final amp.
The board is kept with all the copper except 2 traces leading back where PS regulators (if needed at all ) will be placed.
You can see on the PCB I still struggle with technology of making it, but after 30 + years not giving up making own in house PCB-s, probably not very smart but what to hack..
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Can you say more about the what type of display and how it's controledl? That looks nice. Is there a processor in there?
Also nice board! What do you use to do the resist and etch?
Also nice board! What do you use to do the resist and etch?
Hi,
The code and motherboard are from Richb; this is his thread about it. It is emphasizing on 2 phase , but it drives 3 phase motors too as I used it. This is his original thread:
The processor is RPI Pico as I use it, but it can also be CytronMaker Nano RP2040
Suitable displays are in posts #36 and #38 of this thread, but more could be chosen from, see original Richb's thread for specificatons...
Don't agree it is nice board, barely ok... I use HCl + H2O2.
For bit complicated boards I use laser print on photo paper, than transfer with iron. For very simple ones like this, just black permanent marker pen.
This is not correct. Poles always come in pairs as there has to be a N at the same time there is a S, same as with a magnet, so the number of poles is always even. Some people use "pole" and "winding" interchangeably and while "technically" correct, it is better to not intermix them for clarity. A 2 pole 3 phase motor will have 6 windings (poles) but it is still a 2 pole motor and the speed will be: RPM=freq*60/pole pairs or in this case, freq*60/1.
For a 24 pole motor, the speed will be: RPM=freq*60/12.
If the motor has 24 windings and is 3 phase, it is an 8 pole motor (4 pole pairs) and the speed will be: RPM=freq*60/4 or 50Hz*60/4=750 RPM.
A better way to express your formula is: # of poles=# of windings/# of phases. # of pole pairs= # of poles/2
Windings/Poles in motors
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Hi Pyramid,
Thank you for correction, I have noticed you digested this subject very much and I'm happy you came on this thread.
Indeed its better to use standard terminology. I refer to Wikipedia which is even bit more friendly in wording:
https://en.wikipedia.org/wiki/Synchronous_motor
Nevertheless, there is one little mystery in this that lead me to forget to divide by 2 to get #of poles. This is not provocative, but honest question:
According:
Thanks!
Thank you for correction, I have noticed you digested this subject very much and I'm happy you came on this thread.
Indeed its better to use standard terminology. I refer to Wikipedia which is even bit more friendly in wording:
https://en.wikipedia.org/wiki/Synchronous_motor
Nevertheless, there is one little mystery in this that lead me to forget to divide by 2 to get #of poles. This is not provocative, but honest question:
- In my post #50 of this thread is preferred motor with picture "No 1, Phillips VCR capstan motor"
- This motor clearly has 24 windings
- It is also very obviously 3 phase machine
- However it runs at 375 RPM @ 50 Hz. This statement I can confirm by dozens of measurements, believe me it is 375 rpm sync speed
According:
it should run double the speed at 750rpm, but it doesn't. Can you see on the picture from post # 50 where are is another set of poles hidden?
Thanks!
That's a good question and I'm not sure what is going on, but I have a hunch:
To further clarify terminology, poles actually refers to the permanent magnet poles of the rotor which always come in pairs (N/S) and alternate as you go around the circumference of the rotor. In most applications, the number of windings will be determined by the number of magnetic poles of the rotor: Windings = # of poles * # of phases. This is consistent with every motor I've worked with and most of the references cited.
It should be possible to double the # of magnetic poles of the rotor while keeping the number of windings the same as before and the result should be that the speed would be cut in half, thus 375 RPM for your motor instead of 750 which the formula would suggest.
I wonder if it is possible to check the PM rotor of your motor using a small magnet to count the number of attractions and repulsions as you move around the perimeter of the rotor. I suspect that you will find 8 North and 8 South magnetic poles (16 poles total or 8 pole pairs) which would yield the correct speed you are seeing according to the formula?
To further clarify terminology, poles actually refers to the permanent magnet poles of the rotor which always come in pairs (N/S) and alternate as you go around the circumference of the rotor. In most applications, the number of windings will be determined by the number of magnetic poles of the rotor: Windings = # of poles * # of phases. This is consistent with every motor I've worked with and most of the references cited.
It should be possible to double the # of magnetic poles of the rotor while keeping the number of windings the same as before and the result should be that the speed would be cut in half, thus 375 RPM for your motor instead of 750 which the formula would suggest.
I wonder if it is possible to check the PM rotor of your motor using a small magnet to count the number of attractions and repulsions as you move around the perimeter of the rotor. I suspect that you will find 8 North and 8 South magnetic poles (16 poles total or 8 pole pairs) which would yield the correct speed you are seeing according to the formula?
Hi Pyramid, thanks again for sharing your experience here.
I took small screwdriver with hard iron tip and walked it slowly around rotor of the motor in question, we have 16 attraction and 16 repulsion points in full circle.
I did the same with another motor that runs much lower speed that # of coils would suggest (motor No 4 from post #50), actually only 6 coils which would suggest 1 pole pair @ 3 phases. However permanent magnet rotor has 24 attraction and 24 repulsion points.
Seems we are missing a part of equation, common truth that number of stator poles should equal number of rotor poles is kind of not so solid any more...
I took small screwdriver with hard iron tip and walked it slowly around rotor of the motor in question, we have 16 attraction and 16 repulsion points in full circle.
I did the same with another motor that runs much lower speed that # of coils would suggest (motor No 4 from post #50), actually only 6 coils which would suggest 1 pole pair @ 3 phases. However permanent magnet rotor has 24 attraction and 24 repulsion points.
Seems we are missing a part of equation, common truth that number of stator poles should equal number of rotor poles is kind of not so solid any more...
To be perfectly honest, most of the motors I work with are internal rotors so counting windings is not so easy and I must admit I've never done it; external rotor motors like the ones you are talking about are easier to count windings. I rely on the mfr's data sheets for the number of poles and the actual speed is always consistent with the formula and the expected speed based on that.
I think the "usual" number of windings is what the formula suggests (magnetic poles x phases); I was struggling with my previous explanation because if you doubled the number of magnetic poles on the rotor, the "usual" number of windings would also double for the speed to be cut in half. It made we wonder if you kept the windings at 24, you would have to quadruple the number of magnetic poles to get half the speed, which would jibe nicely with what you observed (32 poles instead of the expected 8). 32 poles plugged back into the formula would suggest 187.5 RPM at 50Hz so that would indicate to me that the formula for RPM is only accurate if the "usual" winding arrangement is being used (windings=poles*phases). Increasing the number of magnetic poles on the rotor to slow the speed is easy to do, adding additional windings to use the normal formula is not so easy, so I suspect they increased the magnetic poles by 4x while keeping the windings the same to cut the speed in half for cost or performance reasons.
It would be interesting if you could find a spec sheet for the motor, how many poles it would indicate?
I've done a number of Google searches on this, but have been unable to uncover anything relevant to this discussion.
I think the "usual" number of windings is what the formula suggests (magnetic poles x phases); I was struggling with my previous explanation because if you doubled the number of magnetic poles on the rotor, the "usual" number of windings would also double for the speed to be cut in half. It made we wonder if you kept the windings at 24, you would have to quadruple the number of magnetic poles to get half the speed, which would jibe nicely with what you observed (32 poles instead of the expected 8). 32 poles plugged back into the formula would suggest 187.5 RPM at 50Hz so that would indicate to me that the formula for RPM is only accurate if the "usual" winding arrangement is being used (windings=poles*phases). Increasing the number of magnetic poles on the rotor to slow the speed is easy to do, adding additional windings to use the normal formula is not so easy, so I suspect they increased the magnetic poles by 4x while keeping the windings the same to cut the speed in half for cost or performance reasons.
It would be interesting if you could find a spec sheet for the motor, how many poles it would indicate?
I've done a number of Google searches on this, but have been unable to uncover anything relevant to this discussion.
Do you know what speed this motor would run at and what frequency was needed for that speed? It has 24x the number of expected magnetic poles and would give us another data point to further refine or understand the formula.
Hi,
I connected it this morning:
According to established wisdom this should run 3000 RPM @ 50 Hz.
But it runs 750 RPM
By all means please laugh at my measuring device 😎
Contemplating at mismatched number of stator and rotor poles, it is actually very good... If you think of circle with mismatched poles, there is never situation where all poles are aligned (stator to rotor) which distributes torque and reduces ripple by some good factor.
Found this paper about optimizing mismatched windings to rotor poles, quite in depth and still did not see speed formula, but will find it:
https://eprints.whiterose.ac.uk/146189/1/TMAG-18-05-0357-final.pdf
Found this paper about optimizing mismatched windings to rotor poles, quite in depth and still did not see speed formula, but will find it:
https://eprints.whiterose.ac.uk/146189/1/TMAG-18-05-0357-final.pdf