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Electrical cartridge analysis

In this article, I will walk you through the electrical cartridge analysis report. This report consists of four main measurements: static electrical parameters, frequency response, channel separation, and tracking ability.

I presume most of my readers are familiar with these terms and their implications, but let’s quickly go through them for those who aren’t.

All electrical phono cartridges (yes, there are optical ones!) include coils. Regardless of their construction, there is always one coil for the left channel and another for the right channel. Since the coil is made of wire (commonly enameled copper, but sometimes silver, gold, or other materials), this wire inherently has resistance. When the wire is wound into a coil, it also acquires an electrical property known as inductance. In most simple terms, this coil can be represented as a resistor and an inductor connected in series. Still following along? Great.

Moving Magnet (MM) cartridges have large coils with many windings of wire. Since the resistance of a wire is proportional to its length, and the inductance of a coil increases with the number of turns, MM cartridges exhibit relatively high resistance and inductance.

In comparison, Moving Coil (MC) cartridges use only a few turns of wire. As a result, their resistance and inductance are minimal and can typically be considered negligible when discussing system-level interactions.

Now, think about what we do to listen to a cartridge. We connect it to a phono preamp! But, most importantly, how do we do that? With a cable, of course. This cable isn’t made of thin air – it consists of a conductor wire and a shielding wire, with some form of insulation between them. And guess what? These parts make the cable act like a capacitor. Just like any capacitor, this cable has capacitance and can be represented using the same symbol.

But the story doesn’t end there. We connect this cable to the inputs of our phono preamp. These inputs have an input resistance – essentially a resistor connected across the RCA input terminal (usually). The terminal and its associated circuitry also have some capacitance, but it’s typically quite small and can often be ignored. Some more advanced (and pricier) phono preamps also have the ability to adjust their input resistance and capacitance, a feature known as input loading.

Once we’ve connected all that setup together, we end up with our cartridge’s electrical system model. The more curious among you may have already noticed that this circuit resembles an LRC resonant tank, but with a variable Q factor controlled by resistors. And yes! There will be a resonance.

Using this circuit, we can analyze and predict how all these components interact with each another. This interaction is typically represented by a frequency response graph.

The frequency response graph shows which frequencies will be exaggerated and which will be reduced. It’s usually plotted on a logarithmic scale, with frequency on the x-axis and sensitivity on the y-axis.

What we typically aim for with most audio equipment is a neutral response graph, which ideally appears as a straight line, as shown above. When this happens, we say the system has a flat frequency response. Unfortunately, when dealing with a phono cartridge, things are not so simple.

First and foremost, and this is crucial, we are only discussing the electrical system and electrical resonance of the cartridge. This is not the full picture! A cartridge is a mechanical device, and as such, it has various mechanical resonances – cantilever, suspension, body, etc. Therefore, its frequency response is the sum of all these effects. So, flat is not necessarily best!

Cartridge Frequency Response is SUM of Electrical and Mechanical Resonances.

So our target here is to have final frequency response as flat as we can by changing what we can. Since we cannot influence cartridge mechanical or electrical parameters – we can change the loading.

But first, we need to measure the electrical parameters of our cartridge. This is what the first part of the electrical analysis report is dedicated to.

Static electrical parameters

We continue from where we left off with the optical analysis, using the same B&O cartridge. Bellow is the final report summary table, which compares the cartridge datasheet parameters with the measured ones.

For now, let’s focus on Coil Resistance and Inductance. Unfortunately, these values are not included in the datasheet, so we can’t evaluate how far our sample deviates from the target values. However, we measured coils having a resistance of approximately 760Ω and an inductance of around 240mH on average.

Now comes the fun part! Let’s plug these values into the calculator I wrote below and see what happens.

Cartridge Loading Calculator



If you used 180pF for the total capacitance and 47kΩ for the input resistance, you should see a graph like the one below (make sure to select Fixed Axis). Now, lower the input resistance and observe how the resonance peak shifts downward.

With approximately 25kΩ loading, we can achieve a flat line with a smooth roll-off. Now, let’s see what happens if we increase the loading capacitance! With each increase in capacitance, let’s try to compensate by lowering the input resistance so that our graph stays within the frame.

We see that by increasing loading capacitance we lower the resonance frequency. We went from ~23khz at 180pF to ~13kHz at 580pF. However, we now require a 25kΩ loading to keep the peak within the 6 dB range, whereas previously, this same loading resistance fully dampened the resonance.

This is a really great tool to get a better understanding of the entire loading concept and to develop an intuition for what happens when changing one parameter or another. More information can be found on “Cartridge Loading Calculator” page.

Cartridge frequency response

Now that we have some understanding of what is cartridge frequency response and what it cosist of, lets go and measure one. In order to do that we need four things: test record with frequency sweep, preamp without RIAA , audio capturing device and processing software.

When it comes to test records, there aren’t many options available. During the heyday of vinyl records, CBS produced a series of test records for shops, which were considered the industry standard. While you can still find them second-hand, buying used records is always a dubious deal. After all, how do you test a test record? Exactly.

This leaves us with the Clearaudio Frequency Response Test Record (CA-TRS-1007). You can still buy these new (or at least as NOS), and they’re the closest you’ll get to a reliable test sweep. By “reliable,” I mean within ±0.5dB accuracy—since, with analog, “good enough” is sometimes the best you can achieve.

For a preamp, I use a lab-built 40X preamp along with my USB MV-1 interface. Despite its somewhat sketchy appearance, the preamp works flawlessly and features adjustable input loading, allowing for a close match to factory loading specifications.

These days, my software of choice is usually REW. It’s become excellent not only for acoustic measurements but also for general frequency response analysis. All the equipment is loop-calibrated by generating an equivalent logarithmic digital sweep and running it through the entire chain for accuracy.

One thing to note about this record is the way it was recorded. When cutting this disc, engineers bypassed the last 75 µs time constant filter, so we have an almost flat line in the treble. This is the hardest region to get right when cutting and this clever trick really makes this disc special.

After the sweep is recorded, what is left is to compensate for the 3180 µs and 318 µs constants, which can be done in software like Audacity. Once that is done, I just import the measurements into REW, apply smoothing, and normalize them to 0 dB at 1 kHz.

And here is the frequency response graph that you will get in your report. It doesn’t look right, does it? But that’s because we’ve already established in our optical analysis that this cartridge is absolutely worn out and has no theoretical chance of reproducing flat frequencies above ~11 kHz. I would normally refuse to even put a stylus like that on my test record, but since it’s tracking at only 1 gram and we’re doing this here “for scientific purposes,” it’s fine.

We also can notice that there is about 1.3dB level difference between channels. This is within 2dB of datasheet value and quite normal to see with these mechanical marvels of engineering.

Remember the fun with the loading calculator? Well, it doesn’t end there! You can actually download the generated frequency graph and calculate how different loading would affect your final frequency response. Now, isn’t that cool or what?

With a loading of 480 pF and 47 kΩ, we could even make this worn-out stylus sound bright again. However, don’t do that – it’s a bad idea, as this worn out stylus is harming your records.

More information on how to calculate graphs like that can be found on “Cartridge Loading Calculator” page.

Channel separation

Since the sweep test tracks are for separate left and right channels, we can easily extract the channel separation. It’s the signal on the other “silent” channel.

As we can see above, it’s not that silent after all. But even with a worn stylus, this cartridge is able to keep its separation below -20 dB from the midrange through all the treble. Anything below -20 dB can be considered “good,” and anything below -25 dB is really “excellent” with <-30dB belonging in a zone of “exotics”.

I should also note that channel separation is a parameter for both channels! It’s possible to adjust the azimuth so that one channel has -40 dB and the other has -10 dB at say 1kHz, but what we strive for here is as equal separation as possible. This should be the goal when adjusting the cartridge azimuth. I always make this adjustment before taking a measurement.

Having a low cartridge separation of 10-20 dB in the bass region is very normal. It’s just the way the tracks are cut and these devices operate. It’s a complex issue that we won’t delve into here, but thankfully, psychoacoustics compensates for this, and it’s not a problem for most of us.

The test report also includes a full graph of frequency response and channel separation. This is how cartridge data are usually presented by reputable manufacturers or during reviews. Although convenient, the large logarithmic vertical scale makes small deviations less visible.

All graphs from the report will also be available for download as .txt files in a .zip archive once the order is completed.

Tracking ability

Tracking ability is often overemphasized as the ultimate cartridge test. I remember when the famous (in a wrong way mostly) Hi-Fi News test record came out, and everyone started torturing their poor cartridges with the +18 dB test track, then complaining that they couldn’t track it. That was really funny!

The 300 Hz +18 dB track has a velocity of 40 cm/s, translating to a lateral modulation of ~210 µm peak. No cartridge on this earth can handle that. I’m not even sure it’s physically possible to produce such a thing, but please, prove me wrong!

For this test, I’m using the Ortofon Test Record, which is otherwise pretty useless unless you’re also interested in ultrasonic ranges. However, it does have solid tracking ability test tracks, calibrated for peak lateral modulation ranging from 50 µm to 100 µm.

It’s worth noting that the maximum modulation in the low-frequency 300 to 800 Hz range on real LPs almost never exceeds 50 µm! Additionally, take this measurement with a grain of salt, as this single 315 Hz measurement is just one piece of the bigger picture when it comes to tracking ability.

Cartridge tracking ability should be defined throughout the entire usable frequency range.

Unfortunately, the only test record (Shure TTR-103) that could be used to do that is nowadays as rare as a unicorn at a vinyl convention. And there are no modern reissues with tracks of that sophistication and extension.

Having said all the above, we can define tracking ranges as follows:

  • Budget cartridges: Around 40 µm
  • Mid-range cartridges: 50-60 µm
  • High-end cartridges: 60-70 µm
  • Audiophile-grade cartridges: Up to 80 µm or more

I would also add that a cartridge unable to track 50 µm typically has suspension issues, such as misalignment or stiffened elastomer. Or a really worn stylus! Like the one we test here.

Above is a series of wave forms you will get with your report. As can be seen, this particular cartridge struggles with 60µm. What is more interesting here is that one channel starts it’s departure from groove wall much earlier then the other and no amount of ant-skating will help that. Why? Because we already found in Optical Analysis that Left stylus contact surface has more wear the the Right. 

Also, I’m refraining from using more technical methods of defining tracking limits, as they can be confusing for the end user. We could measure distortion or intermodulation distortion, but then how do you define the limits in a way that everyone will agree on? It’s impossible.

Here, everything is clear – you see a sinusoidal waveform with a glitch, meaning the stylus lost contact with the groove wall. Mistracking has occurred. Simple!

And that is all the information you will receive if  you order an “Electrical Cartridge Analysis” service from our Shop.