• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

How a cartridge works

TG1

Member
Joined
May 20, 2019
Messages
37
Likes
11
It was suggested to me that I begin by trying to understand (when I asked how one could possibly make one's own determination as to what is and is not worth buying), so I have decided to follow that advice.However, what I did not realise when I happened on this site is how out of my depth I was going to be, not just in terms of knowledge but also in terms of capacity to acquire knowledge. I thought I would start with one thing - the cartridge, since I have been told that changing this component can make the biggest difference to the sound.
I found an explanation or two, and now know that the magnet or coil on the end of the stylus cantilever moves in direct correspondence to the vibration of the tip of the stylus in the record groove. It is this movement that generates the signal which then moves down a wire to the phono stage. However, what I cannot find is an explanation of the underlying process, only that this is what happens. I don't know how the movement of a magnet or coil generates the electrical signal. If there are two coils positioned either side of a moving magnet is it that the two things - the magnet and the coil - generate an electro-magnetic field just by virtue of being in proximity to each other and that the movement of one or the other traces a pattern in the field which is then registered at the far end in the phono stage? Ie, is it wrong to think of a signal being transmitted like a letter being posted and right to think of a brain (receiver in phono amp) seeing a hand signal. That's not a good analogy I know, but I am struggling to understand how a signal can be developed, gathered up, and then sent in its way.

It could be that this is really not something that is wanted as a question on this site, so please feel free to ignore it - I will not take it personally. There is no reason anyone should spend time on answering a question like this, and since my level of knowledge is virtually non existent in comparison to what I now understand is the average level of knowledge among members, I fully expect the above to be a wrong, and therefore meaningless, question.
 
OP
T

TG1

Member
Joined
May 20, 2019
Messages
37
Likes
11
Lenz law.

Keep in mind it is all the same if magnet moves (like in MM cartridges) or the conductor moves (like in MC cartridges) - in either way there is a change in magnetic flow in time. Happy reading! :)

Thanks. I suspect that as with all things I will meet a door I can't open. Answers to questions generate more questions, and so on until one reaches the limit of comprehension. Years ago I read The Human Use of Human Beings and thought 'awesome. I'm going to read Cybernetics next'. No, I was not going to read Cybernetics next because for me to add two to two and get four it has to be a good day.
 

sergeauckland

Major Contributor
Forum Donor
Joined
Mar 16, 2016
Messages
3,440
Likes
9,100
Location
Suffolk UK
Before we consider stereo, let's just look at a single channel mono cartridge. The stylus is moved side to side by the record grooves. This moves a magnet attached to the cantilever relative to a fixed coil, and that induces a voltage in coil. Similarly, if a tiny coil is attached to the cantilever and the magnet is fixed, then the same thing will happen, that a voltage is induced in the coil, and that's what gets amplified and eventually drives the loudspeaker.

Now, for stereo, there are the two groove walls, each one carries different channels, so the stylus doesn't only move side to side, but also up and down. The cantilever now has two magnets or coils attached, and arranged at right angles to each other, and at 45 degrees to the plane of the record. The left and right channels now move the cantilever at + and - 45 degrees to the plane of the record, and that generates the two channels.

Hope this makes sense, and do keep asking the questions, as it's the best way to learn.

S
 
OP
T

TG1

Member
Joined
May 20, 2019
Messages
37
Likes
11
Before we consider stereo, let's just look at a single channel mono cartridge. The stylus is moved side to side by the record grooves. This moves a magnet attached to the cantilever relative to a fixed coil, and that induces a voltage in coil. Similarly, if a tiny coil is attached to the cantilever and the magnet is fixed, then the same thing will happen, that a voltage is induced in the coil, and that's what gets amplified and eventually drives the loudspeaker.

Now, for stereo, there are the two groove walls, each one carries different channels, so the stylus doesn't only move side to side, but also up and down. The cantilever now has two magnets or coils attached, and arranged at right angles to each other, and at 45 degrees to the plane of the record. The left and right channels now move the cantilever at + and - 45 degrees to the plane of the record, and that generates the two channels.

Hope this makes sense, and do keep asking the questions, as it's the best way to learn.

S


Thanks. Please correct the errors as I think this out..

So on the record is a v shaped canyon (groove) in which the stylus sits. Each side of the groove has lateral peaks and troughs cut in it, which the stylus traces. If you were to isolate the line of each side of the groove you would get a series of peaks and troughs that would look something like the ones we are used to seeing on those screens (oscilloscopes?). That equates to the frequencies of the different sounds made during the performance.
That doesn't sound right. I suppose what matters is that the shapes in the groove are the encoded representation of the notes made during the live performance.
So the movement of the magnet or coil on the other end of the cantilever is a mirror image of the stylus movement. In an ideal world a perfect image of that movement.

So point 1: presumably one of the reasons for the difference in cartridge price might be the accuracy with which the pattern in the groove is mirrored by that produced by the moving magnet or coil. This is a point at which the signal can degrade.

Anyway, moving on - The moving magnet, or moving coil, induces a voltage in the coil. Which begs more questions. So there is no power supply at all to the tone arm/cartridge (that is all for the motor). All the power is generated purely by the movement of a magnet or coil. Drilling further down, this voltage that is induced - what is the relationship between that voltage and the signal described by the moving magnet or coil. A pattern is created by the movement, so are you saying that the voltage itself takes on the form of that pattern and if so, how? What of this change in magnetic flow in time ( I will follow the link in a bit). Ie. put simply is the electricity shaped by the pattern like a seal imprinting a pattern on soft wax? Does the magnetism take on the form of the pattern and is that what is transmitted? How does the movement generated pattern, which is a pattern in time, get into the electricity going down the wire?
 

DKT88

Active Member
Joined
Feb 26, 2019
Messages
221
Likes
232
Location
South Korea
Thanks. Please correct the errors as I think this out..

So on the record is a v shaped canyon (groove) in which the stylus sits. Each side of the groove has lateral peaks and troughs cut in it, which the stylus traces. If you were to isolate the line of each side of the groove you would get a series of peaks and troughs that would look something like the ones we are used to seeing on those screens (oscilloscopes?). That equates to the frequencies of the different sounds made during the performance.
That doesn't sound right. I suppose what matters is that the shapes in the groove are the encoded representation of the notes made during the live performance.
So the movement of the magnet or coil on the other end of the cantilever is a mirror image of the stylus movement. In an ideal world a perfect image of that movement.

So point 1: presumably one of the reasons for the difference in cartridge price might be the accuracy with which the pattern in the groove is mirrored by that produced by the moving magnet or coil. This is a point at which the signal can degrade.

Anyway, moving on - The moving magnet, or moving coil, induces a voltage in the coil. Which begs more questions. So there is no power supply at all to the tone arm/cartridge (that is all for the motor). All the power is generated purely by the movement of a magnet or coil. Drilling further down, this voltage that is induced - what is the relationship between that voltage and the signal described by the moving magnet or coil. A pattern is created by the movement, so are you saying that the voltage itself takes on the form of that pattern and if so, how? What of this change in magnetic flow in time ( I will follow the link in a bit). Ie. put simply is the electricity shaped by the pattern like a seal imprinting a pattern on soft wax? Does the magnetism take on the form of the pattern and is that what is transmitted? How does the movement generated pattern, which is a pattern in time, get into the electricity going down the wire?
I looked for some articles that explain Farady's Law and electromagnetic induction. https://www.electronics-tutorials.ws/electromagnetism/electromagnetic-induction.html This should help you understand the physics of cartridges which are tiny generators.
 

LTig

Master Contributor
Forum Donor
Joined
Feb 27, 2019
Messages
5,760
Likes
9,442
Location
Europe
Lenz law.

Keep in mind it is all the same if magnet moves (like in MM cartridges) or the conductor moves (like in MC cartridges) - in either way there is a change in magnetic flow in time. Happy reading! :)
It's the same principle how dynamic speakers and microphones work:
  • In the case of the speaker you have a magnet and a coil reaching inside the magnet. When you let current flow through the coil it moves in and/or out of the magnet. The coil is glued to a membrane hence the membrane moves accordingly, and this moves the air accordingly.
  • In the case of the microphone its just the reverse procedure. Sound is changes of air pressure which moves the membrane. The membrane moves the coil inside the magnet and this creates current flowing in the coil. Actually one can use speakers and headphones as microphones.
 

sergeauckland

Major Contributor
Forum Donor
Joined
Mar 16, 2016
Messages
3,440
Likes
9,100
Location
Suffolk UK
Thanks. Please correct the errors as I think this out..

So on the record is a v shaped canyon (groove) in which the stylus sits. Each side of the groove has lateral peaks and troughs cut in it, which the stylus traces. If you were to isolate the line of each side of the groove you would get a series of peaks and troughs that would look something like the ones we are used to seeing on those screens (oscilloscopes?). That equates to the frequencies of the different sounds made during the performance.
That doesn't sound right. I suppose what matters is that the shapes in the groove are the encoded representation of the notes made during the live performance.
So the movement of the magnet or coil on the other end of the cantilever is a mirror image of the stylus movement. In an ideal world a perfect image of that movement.

So point 1: presumably one of the reasons for the difference in cartridge price might be the accuracy with which the pattern in the groove is mirrored by that produced by the moving magnet or coil. This is a point at which the signal can degrade.

Anyway, moving on - The moving magnet, or moving coil, induces a voltage in the coil. Which begs more questions. So there is no power supply at all to the tone arm/cartridge (that is all for the motor). All the power is generated purely by the movement of a magnet or coil. Drilling further down, this voltage that is induced - what is the relationship between that voltage and the signal described by the moving magnet or coil. A pattern is created by the movement, so are you saying that the voltage itself takes on the form of that pattern and if so, how? What of this change in magnetic flow in time ( I will follow the link in a bit). Ie. put simply is the electricity shaped by the pattern like a seal imprinting a pattern on soft wax? Does the magnetism take on the form of the pattern and is that what is transmitted? How does the movement generated pattern, which is a pattern in time, get into the electricity going down the wire?
You're right in your thinking. The pattern engraved in each groove wall is a mechanical replica of the waveform, as you say, like an oscilloscope trace. It's not exactly the same, as it is modified by the RIAA characteristic which boosts the high frequencies on the record and attenuates them on playback, along with the hiss, but in essence, the groove shape is a replica of the waveform. The price and quality of a cartridge is determines by the accuracy by which it recovers this waveform, although as with so much in hifi, a lot of the price of expensive cartridges is to do with hype,, not engineering quality. Nevertheless, a complex stylus shape and a rigid lightweight cantilever cost a lot more than a simple stylus and ordinary cantilever.

All the voltage generated by the cartridge comes from the motion of the stylus, which is measured in microns, so not much, and as coils etc have to be kept small, the voltage generated is very small, of the order of a millivolt. Consequently, the quality of the amplification, especially noise, is very important to the final result.

S
 

LTig

Master Contributor
Forum Donor
Joined
Feb 27, 2019
Messages
5,760
Likes
9,442
Location
Europe
It was suggested to me that I begin by trying to understand (when I asked how one could possibly make one's own determination as to what is and is not worth buying), so I have decided to follow that advice.However, what I did not realise when I happened on this site is how out of my depth I was going to be, not just in terms of knowledge but also in terms of capacity to acquire knowledge. I thought I would start with one thing - the cartridge, since I have been told that changing this component can make the biggest difference to the sound. [..]
This video explains it quite well (except at 4:35 where the coil and magnet of the pickup are shown as if they are at the end of the tone arm):


This is also quite nice:

 

DDF

Addicted to Fun and Learning
Joined
Dec 31, 2018
Messages
617
Likes
1,355
I thought I would start with one thing - the cartridge

Audio magazine was the golden standard of its day for consumer audio information. In these issues you'll find good, consumable, explanations:

"Understanding Phono Cartridges": https://www.americanradiohistory.com/Archive-Audio/70s/Audio-1979-03.pdf
"Understanding Tonearms": https://www.americanradiohistory.com/Archive-Audio/80s/Audio-1980-06.pdf
Turntable/Tonearm Design articles by Joe Grado: https://www.americanradiohistory.com/Archive-Audio/70s/Audio-1977-06.pdf , https://www.americanradiohistory.com/Archive-Audio/70s/Audio-1977-07.pdf , https://www.americanradiohistory.com/Archive-Audio/70s/Audio-1977-08.pdf

If you decide to go down that rabbit hole, there are many other articles on turntable topics (line stylus, radial tonearms vs pivot, cartidge suspensions...) never mind electronics, speakers, and psychoacoustics: https://www.americanradiohistory.com/Audio-Magazine.htm
 

RayDunzl

Grand Contributor
Central Scrutinizer
Joined
Mar 9, 2016
Messages
13,198
Likes
16,981
Location
Riverview FL
It is this movement that generates the signal which then moves down a wire to the phono stage. However, what I cannot find is an explanation of the underlying process, only that this is what happens.


Watch this interesting demonstration:

"In this video I experiment with Lenz's Law And Faraday's Law of Induction to generate electricity and magnetic force fields in copper. "

 
Last edited:

Krunok

Major Contributor
Joined
Mar 25, 2018
Messages
4,600
Likes
3,065
Location
Zg, Cro
Anyway, moving on - The moving magnet, or moving coil, induces a voltage in the coil. Which begs more questions. So there is no power supply at all to the tone arm/cartridge (that is all for the motor). All the power is generated purely by the movement of a magnet or coil. Drilling further down, this voltage that is induced - what is the relationship between that voltage and the signal described by the moving magnet or coil. A pattern is created by the movement, so are you saying that the voltage itself takes on the form of that pattern and if so, how? What of this change in magnetic flow in time ( I will follow the link in a bit). Ie.

Exactly, no power supply, because none is needed. The process in the cartridge is basically the same as a process in electric generators where the kinetic energy of water or wind is converted into electric energy. Lenz law is saying that generated voltage is proportional to the change of magnetix flux that cundoctor is experiencing, and here is not important if magent is fixed and conductor is travelling or vice versa. So yes, the voltage itself takes on the form of moving pattern. I don't think anybody really knows why is that happening, but we do know how, so we are using it. :D

Does the magnetism take on the form of the pattern and is that what is transmitted? How does the movement generated pattern, which is a pattern in time, get into the electricity going down the wire?

As I said, I don't think we know why is that happening - all we know is that generated voltage is proportional to the speed and direction of movement of either magnet or the coductor.

Btw, here you should also know that matrix for the gramophone record is generated by the opposite process. Generator and motor are basically the same device: one is used to produce electrictity from the kinetic energy (movement) and the other produces movement from the electric energy. So, the matrix for the graophone record (which is used in a pressing process to maker records) is produced in a motor-like fashion: music is played via amplifier which produces enough voltage to shake the needle proportionaly to the voltage pattern which then leaves the same pattern imprinted into a soft material of the matrix, which hardens afterwards. Process of playing the record is a reverse of the process of making a matrix for the record. :)
 
Last edited:

RayDunzl

Grand Contributor
Central Scrutinizer
Joined
Mar 9, 2016
Messages
13,198
Likes
16,981
Location
Riverview FL
A pattern is created by the movement, so are you saying that the voltage itself takes on the form of that pattern and if so, how?

Thinking about this:

The voltage is generated as the coil/magnet move relative to each other, and the magnetic field "moves" through the electron field.

No voltage is generated when the coil and magnet are at rest relative to each other, even if "deflected" at that time.

Push the stylus and hold - there should be a hump of voltage coming back to zero, as the coil and magnet move relatively and come to rest.

Push the stylus and release - there should be a hump of voltage coming back to zero at the peak of the movement (at rest again) and then an opposite hump of voltage.

1560490207079.png


Sorry, I don't sketch well with a friggin' mouse.

The groove of the record may not look like what you would see on an oscilloscope, rather, it encodes the motion required to create what is seen on a scope.

On the other hand, when you graph digital, what you see are the voltage levels - what you see in a digital wave is what should be seen on the 'scope.

Someone else can likely explain this better, or tell me I'm all wet, or have some better visual examples.
 
Last edited:

Krunok

Major Contributor
Joined
Mar 25, 2018
Messages
4,600
Likes
3,065
Location
Zg, Cro
Thinking about this:

The voltage is generated as the coil/magnet move relative to each other, and the magnetic field "moves" through the electron field.

No voltage is generated when the coil and magnet are at rest relative to each other, even if "deflected" at that time.

Push the stylus and hold - there should be a hump of voltage coming back to zero, as it they coil and magnet move relatively and come to rest.

Push the stylus and release - there should be a hump of voltage coming back to zero at the peak of the movement (at rest again) and then am opposite hump of voltage.

View attachment 27670

Sorry, I don't sketch well with a friggin' mouse.

The groove of the record may not look like what you would see on an oscilloscope, rather, it encodes the motion required to create what is seen on a scope.

On the other hand, when you graph digital, what you see are the voltage levels direction - what you see in a digital wave is what should be seen on the 'scope.

Someone else can likely explain this better, or tell me I'm all wet, or have some better visual examples.

Maybe not to complicate too much and stick to the statement that the voltage looks like the slope of the groove - at points of the groove where slope is low the voltage is low, where the slope is high the voltage is also high.
 

RayDunzl

Grand Contributor
Central Scrutinizer
Joined
Mar 9, 2016
Messages
13,198
Likes
16,981
Location
Riverview FL
the voltage looks like the slope of the groove

Yes...

I'm mathematically declined but that's a proper description.
 
OP
T

TG1

Member
Joined
May 20, 2019
Messages
37
Likes
11
You're right in your thinking. The pattern engraved in each groove wall is a mechanical replica of the waveform, as you say, like an oscilloscope trace. It's not exactly the same, as it is modified by the RIAA characteristic which boosts the high frequencies on the record and attenuates them on playback, along with the hiss, but in essence, the groove shape is a replica of the waveform. The price and quality of a cartridge is determines by the accuracy by which it recovers this waveform, although as with so much in hifi, a lot of the price of expensive cartridges is to do with hype,, not engineering quality. Nevertheless, a complex stylus shape and a rigid lightweight cantilever cost a lot more than a simple stylus and ordinary cantilever.

All the voltage generated by the cartridge comes from the motion of the stylus, which is measured in microns, so not much, and as coils etc have to be kept small, the voltage generated is very small, of the order of a millivolt. Consequently, the quality of the amplification, especially noise, is very important to the final result.

S

Thanks. Picking up on that point, does it then follow that it is a good idea to keep the cable from the deck to the phone stage as short as possible, given the voltage is so tiny? Is this another point at which signal degradation could occur? Presumably it is less of a problem once the signal has been significantly amplified.
 
OP
T

TG1

Member
Joined
May 20, 2019
Messages
37
Likes
11
This video explains it quite well (except at 4:35 where the coil and magnet of the pickup are shown as if they are at the end of the tone arm):


This is also quite nice:



Thanks very much - very interesting. Looking at that first video one would think - despite what he says about digital and vinyl being the pretty much the same - that digital would outperform vinyl just because there are fewer (as far as i currently know) gaps in the chain to bridge. Wouldn't it be the case that every time the signal has to be translated it is bound to suffer some loss of integrity?

On the other hand digital sampling does not reproduce the pure waveform (it seems) but only a computer generated waveform based on the limited sampling. So the programme must predict what is in the gaps between samples. I know he said the human ear can't distinguish between the two once a certain frequency of sampling is used, but it surely remains a fact that the two waveforms are not identical,and therefore the music listened to is not the same.
I know I am working my way through a thought process long since settled among members here, so thanks for the tolerance.
 
OP
T

TG1

Member
Joined
May 20, 2019
Messages
37
Likes
11
Audio magazine was the golden standard of its day for consumer audio information. In these issues you'll find good, consumable, explanations:

"Understanding Phono Cartridges": https://www.americanradiohistory.com/Archive-Audio/70s/Audio-1979-03.pdf
"Understanding Tonearms": https://www.americanradiohistory.com/Archive-Audio/80s/Audio-1980-06.pdf
Turntable/Tonearm Design articles by Joe Grado: https://www.americanradiohistory.com/Archive-Audio/70s/Audio-1977-06.pdf , https://www.americanradiohistory.com/Archive-Audio/70s/Audio-1977-07.pdf , https://www.americanradiohistory.com/Archive-Audio/70s/Audio-1977-08.pdf

If you decide to go down that rabbit hole, there are many other articles on turntable topics (line stylus, radial tonearms vs pivot, cartidge suspensions...) never mind electronics, speakers, and psychoacoustics: https://www.americanradiohistory.com/Audio-Magazine.htm


Cheers. Looks like I am in for a fair bit of reading. Good. As for rabbit holes, happening on this site was to trip down one rabbit hole, and now I see that lining it are doors into other rabbit holes. All I want to do is understand one thing at a truly fundamental level, but I suspect that while I will not run out of rabbit holes I will run out of time.
 

sergeauckland

Major Contributor
Forum Donor
Joined
Mar 16, 2016
Messages
3,440
Likes
9,100
Location
Suffolk UK
Thanks. Picking up on that point, does it then follow that it is a good idea to keep the cable from the deck to the phone stage as short as possible, given the voltage is so tiny? Is this another point at which signal degradation could occur? Presumably it is less of a problem once the signal has been significantly amplified.
Yes, short and well screened to avoid noise pickup. Cable length doesn't have any significant effect on signal strength, unless very long, say hundreds of metres, but noise pickup and, in the case of moving magnet cartridges, cable capacitance, are important, so keeping cables short is a Good Thing.

S
 
Top Bottom