Some vinyl users use a SUT to enhance the signal of the MC cartridge so that it can be used in the MM input of a phono stage. Although I don't understand the theory behind it, I realize that a SUT should be matched individually to a particular cartridge, depending on the internal impedance of the MC, among other things.
Assuming an appropriately / ideally matched SUT and MC, What are the inherent advantages or disadvantages of inserting a SUT after the MC in the audio chain? Does the SUT theoretically enhance or degrade the sound quality? What does the SUT actually do to the sound quality?
As @intactaudiopoints out, loading is another aspect of the SUT, and this is where, based on my limited reading, things seem to start to get complicated. Here is what Rothwell Audio's website says about transformer loading:
"transformer loading
The idea that optimum performance comes from matching the impedance of the load to the cartridge's impedance (shown above to be somewhat hit-and-miss) also gives rise to another fallacy – that of transformer loading. The misguided theory, sometimes advocated on websites and forums, says that a loading resistor on the transformer's secondary winding can be used to “correctly load the cartridge” or to “match the transformer to the cartridge”. This is a very dubious theory indeed, so lets analyse what is really happening. Take as an example the Ortofon Vivo Red cartridge examined above (5 ohm source impedance, 0.5mV output voltage). As has already been determined, a 1:10 transformer will give us the voltage we require for an MM phonostage, but the advocates of “correct loading” may be convinced that the cartridge performs best with a particular load, despite the manufacturer's recommended load being anything over 10 ohms. So what is “the correct load”? Often, it is claimed to be the same as the cartridge's source impedance, hence “matching” is achieved. As shown above, a turns ratio of 1:97 will present a 5 ohm load to the cartridge, but what if such a transformer cannot be found? What if the nearest transformer available is 1:36? Can that be made to “match the cartridge correctly”? The transformer with a normal 47k load would give the cartridge a load of 36 ohms (and produce an output voltage of 15.8mV). In order to make this transformer match the cartridge with a load impedance at the primary of 5 ohms, a load on the secondary of 6480 ohms could be employed instead of the 47k normally found on an MM phonostage. This would not only produce a load impedance for the cartridge of 5 ohms, it would also reduce the output voltage to 9mV. Has the additional loading resistor now made the system optimal? No, it hasn't. The cartridge is now seeing half the minimum impedance which the manufacturer recommends and the signal voltage into the MM phonostage is still enough to reduce its headroom significantly. Clearly, this isn't optimal, but it is a lot better than it was with a 1:36 transformer and no additional loading resistor. Anyone who is taking an empirical approach to optimising their system and experimenting with loading resistors based on the idea of “impedance matching” as advocated on some websites would conclude (understandably) that their system now sounds better because “the cartridge is loaded correctly”. In fact it sounds better because the phonostage is being overdriven less than it was before. It would be better still if a 1:10 transformer was used instead of trying to make a transformer with far too high a turns ratio “match” anything by fudging it with resistors.
The “correct loading” or “load matching” myths are fuelled further by a fortuitous by-product of loading the transformer with an additional resistor – damped ringing, analysed in more detail below.."
That's a very thorough, well-considered assessment of the advantages and disadvantages of SUT. Thanks for taking the time to share your knowledge with me / us!
I’m not sure that I completely understand the matter, but it seems that there are two options in cartridge signal amplification in or before the phono stage: either 1. an SUT before the phono stage, or 2. a transistor in the phono stage.
If that’s the case, then the sound quality would depend on how linear the electric signal is transmitted by either the SUT or the transistor. Then, I suppose both approaches have certain weaknesses, but under near ideal circumstances, both would sound nearly identical.
Are there any inherent weaknesses in a SUT versus a transistor, or vice versa?
I think a course in English comprehension would benefit you immensely, and allow you to contribute more positively to these forum discussions:
Firstly, the thread in April was a thread about phono stages for a particular turntable, and only peripherally and incidentally touched on SUT's, and did not go into the theory or discussion of what SUT's do to audio signal / SQ in any detail.
Secondly, you hijacked that April thread on phono stages and ceaselessly posted about power amplifiers, which I surmise is due to your inability to comprehend what is written in English.
Thirdly, I am still enjoying the CH Precision P1 with X1 power supply, and have no intention of changing that component, but I am intellectually curious about other approaches to phono signal, and why one approach is chosen over another, and @atmasphere was kind enough to share a very thorough explanation yesterday.
In the future, I may get an SUT to use to plug into the MM input of the CH Precision P1, just to compare the SQ from the MC current input and the MC voltage input, or perhaps I'll get a second phono stage to compare SQ with. This is just a fun hobby for me.
With your extensive experience and knowledge, I think you really could contribute positively to these audiogon threads, but somehow, I think you just do not comprehend the details of what is being discussed. No, I never said, nor is there a "problem" with the Ypsilon monoblocks, and so far I’ve yet to hear anything that is as transparent, delicate, and detailed, with proper timbre as the passive Ypsilon pre-amplifier. . . but let’s not hijack another thread into another topic, as this is just for SUT discussion.
Now discussion of how signal is actually transmitted through a SUT would be quite interesting: does the signal actually move through the wound wire? As we know, the electrons in a wire don’t travel. . . do you think that the signal is rather transmitted via the core, and not the wires? What really happens to the signal? I don’t know if anyone really knows (but I’m not an electrical engineer), but I do know the limitations of human knowledge. Now, how much of the signal is purely electrical, and how much is magnetic, and can they even be separated? I suppose now it gets into a "religious" argument, where our minds may not be able to comprehend the exact way that everything works.
A brief internet search pulled up this basic, but informative article:
Audio Transformers are electromagnetic devices that transmit and modify input electromagnetic signals into output signals via inductive coupling. They isolate an input circuit from an output circuit and filter signals; operating on the audible band of the frequency spectrum (20Hz to 20kHz). As such they can have applications in the input stage (microphones), output stage (loudspeakers), as well as coupling and impedance matching of amplifiers. In all cases, the frequency response, primary and secondary impedances and power capabilities all need to be considered.
Materials and Structure
A transformer is an electrical device which allows an input signal (such as an audio signal or voltage) to produce an output signal or voltage without the input side and output side being physically connected to each other. This coupling is achieved by having two (or more) wire coils (called windings) of insulated copper wire wound around a soft magnetic iron core. Audio transformers are typically composed of copper wire windings around a steel or nickel-iron alloy core. Each core material transmits electromagnetic signals differently. Steel has a higher degree of hysteresis (magnetic signal lag), making it better for lower frequency transfer. The higher permeability of nickel makes it ideal for transmitting higher frequencies. The windings around the core determine the impedance level, which increases, decreases, or maintains the signal level as it passes through the transformer.
Figure 1: Audio Transformer Structure
When the signal enters the transformer via the input (primary winding), it then gets transferred to the output secondary winding due to the inductive coupling of the soft iron core. The ratio between the number of coil turns on the primary winding (NP) to the number of coil turns on the secondary winding (NS) is called the “turns ratio”. The turns ratio between the input and output wire coils provides either an increase or a decrease of the applied signal as it passes through the transformer. More windings around the core correspond with a higher impedance, so if the primary winding has more than the secondary, the signal will decrease (step down). Conversely, if the secondary winding impedance is greater than the primary, the signal will increase (step up).
The number of turns on each winding determines whether the transformer provides a gain or loss of the signal:
If there are more turns on the input winding, the signal will decrease or step down.
More turns on the output winding will result in a step up.
Audio transformers are produced for a range of specific audio functions; many are similar in construction to power transformers and they often perform several functions at once. They can be considered as either a step-up or step-down type, but rather than being wound to produce a specific voltage output, audio transformers are mainly designed for impedance matching, isolation, and a variety of applications (see Data/Voice Coupling Transformers).
Impedance Matching
Transformers can step impedance up or down in the same way they do with voltage and current. Whereas they change voltage by the turns ratio and current by the inverse of the turns ratio, audio transformers change impedance by the square of the turns ratio. The same amount of voltage is induced within each single coil turn of both windings. The primary to secondary voltage ratio (VP/VS) will therefore be the same value as the turns ratio (NP/NS). Impedance matching audio transformers always give their impedance ratio value from one winding to another by the square of their turns ratio. That is, their impedance ratio is equal to its turns ratio squared and also its primary to secondary voltage ratio squared:
Impedance is determined by the efficiency of the conversion from voltage into magnetic flux. Audio transformers are ideal for balancing amplifiers and loads together that have different input/output impedances in order to achieve optimal power transfer, as in the case of a transformer at the amplifier input to match the impedance between microphones, connecting cables and the amplifier input. The input and output impedance levels are matched to create efficient power transfer without distortion or signal overload. Impedance matching transformers are similar in design to low frequency voltage and power transformers, but they operate over a much wider range of frequencies (for example, 20Hz to 20kHz voice range).
Isolation or Unity Transformer
Transformers have another very useful property, isolation. Since there is no direct electrical connection between their primary and secondary windings, transformers provide complete electrical isolation between their input and output circuits and this isolation property can also be used between amplifiers and speakers. A transformer with a turns ratio of 1:1 does not change the voltage or current levels but instead isolates the primary circuit from the secondary side. This type of transformer is commonly known as an isolation transformer.
Figure 3: Isolation Transformer
As the impedance is identical for the primary and secondary, the signal level does not change. The transformer allows an audio signal to pass unmodified from the primary to the secondary while blocking DC voltage and radio frequency interference (RFI). Since the primary and secondary circuits are insulated from each other, the transformer will electrically isolate different pieces of equipment. This can solve hum problems by isolating or "lifting" the grounds of different devices. Other unity transformer applications include providing multiple outputs from a single mic input by using multiple secondary windings, and changing balanced signals to unbalanced signals or vice-versa.
Audio transformers are designed to operate over the audio frequency range, or much higher for radio-frequency (RF) transformers. Due to this wide frequency band, one of the main disadvantages of audio transformers is that they can be somewhat bulky and expensive. This is because a transformer's core size increases as the supply frequency decreases. Smaller designs can be achieved by using special core materials. Audio transformers have played an important role since the birth of audio electronics. When compared to modern miniaturized electronics, transformers seem large and heavy but they continue to be the most effective solution in many audio applications. The usefulness of a transformer lies in the fact that electrical energy can be transferred from one circuit to another without direct connection, and in the process the energy can be readily changed from one voltage level to another.
Perhaps this blurb from a manufacturer sums it up more concisely: they say the signal is tranferred "via electromagnetic induction" and creates "power transfer without distortion"
Audio transformers are typically composed of copper wire windings around a steel or nickel-iron alloy core. Each core material transmits electromagnetic signals differently. Steel has a higher degree of hysteresis (magnetic signal lag), making it better for lower frequency transfer. The higher permeability of nickel makes it ideal for transmitting higher frequencies.
The windings around the core determine the impedance level, which increases, decreases, or maintains the signal level as it passes through the transformer. When the signal enters the transformer via the input (primary winding), it then gets transferred to the secondary winding via electromagnetic induction. More windings around the core correspond with a higher impedance, so if the primary winding has more than the secondary, the signal will decrease (step down). Conversely, if the secondary winding’s impedance is greater than the primary, the signal will increase (step up).
Impedance matching is one of the primary uses of audio transformers. Impedance is determined by the efficiency of the conversion from voltage into magnetic flux. In addition to stepping signals up or down, audio transformers can match the input and output impedance levels to create efficient power transfer without distortion or signal overload. Impedance-matching transformers will not necessarily boost or attenuate the signal but will create balance for an optimal energy transfer.
You quote another post above: “A phono cartridge is a voltage generator (Vs)”
To me, that sounds like a premise, and from my very limited knowledge base, it sounds like it could very well be a false premise, as phono cartridges generally produce very low voltages, which would imply that they are indeed better classified as current generators….
if that’s the case, then all conclusions based on that premise are also potentially false.
Here’s my current assessment, which has been nicely summarized by @intactaudio : basically, the cartridge is naturally developed as a current generator, however for the past decades, phono stages were created to unnaturally transform the cartridge into a voltage generator by adding the load in the phono stage. However, when the cartridge operates as a current generator, no external arbitrary loading needs to be added to the signal created by the cartridge. So, it seems, based on my limited knowledge, that the current based phono stages would be most naturally associated with phono cartridges.
It seems like we maybe venturing slightly off topic with respect to SUT and SQ, but perhaps it is related, as SUT are magnetic-electrical devices, as are cartridges, which seems to be primarily magnetic and secondarily electrical devices (if electromagnetism can even be split up like that), but here is an interesting overview of magnetism, which seems to indicate that current is more directly related to magnetic devices, as opposed to voltage, although both current (I) and Voltage (V) are related by ohms law V = IR:
“Magnetic flux and current go hand in hand, and they have the differences. When current is induced in an area there will be magnetic flux and this magnetic flux will be opposite to that of the normal flux.
Now there will be a coil where we will induce current into it and then we can see the production of a magnetic flux. we see that when there is current induced there will automatically be an electric field and magnetic field produced inside the coil. So now when there is both magnetic and electric field there will also be flux lines.
Magnetic flux is simply the quantity which measures the amount of magnetic force that passes through a unit area per unit time. The magnetic flux is generally the number of lines which usually pass through the given unit area.
Simplest terms, a magnetic flux is comparable with electrical current as well as a magnetization in which current plays a major role is comparable with electrical voltage.
Although there are significant distinctions, a magnetic circuit is comparable to an electrical circuit. Magnetomotive force is equivalent to electromagnetic force inside of an electrical circuit.”
I was about to ask details about the transimpedance phono stages, such as exactly how the current is converted to voltage, and where / if a load is added, and how it automatically detects how to do the voltage conversion, but maybe that's a college course, so I decided to do a simple google search, and found this seemingly very informative video reviewing the advantages of the current mode phono stages, which apparently is getting a better signal to noise ratio, amongst other things. . . and he does recommend a cartridge with an internal impedance under 10 ohms, but maybe he doesn't know everything. . .
You say that "the best SUT is no SUT at all." What structure(s) in your ideal phono stage replaces the gain that the SUT provides, and how is that necessarily better than an SUT?
"A SUT is not a passive device because any audio signal passing trhough those transformers makes that the " hundreds " of meters on each transformer react to that signal and starts the degradation and you have to think that the signal has a " long trip " inside each transformer wires and at each mm. the audio signal is degrading by that SUT.
In the other side a good SS active high gain design say ith bipolar active devices the signal must pass only trhough a matched pair of transistors in that first critical gain stage and degradation is at minimum way lower that in a SUT."
However, a signal in a SUT doesn't pass through meters of wire, nor does it necessarily have more degradation than transistors. . .unless you can point me to scientific papers. . .
Thanks for the detailed response. So, just to clarify, you are most concerned about the bandwidth limitations in a SUT. I could agree with that; however, I'm not certain that actual signal degradation is any better or worse in a transistor, just different.
I think this video from Veritasium does a rather informative job of explaining how current actually travels: no it doesn't travel in the wires but in the surrounding electromagnetic fields, and electrons don't "flow" in the wires, either in AC or DC, and in a wire with no resistance, the current flow is instantaneous, whether 0.001 m long or 100,000 m long. I suppose the magnetic properties of the silver and copper account for the difference in sound, and while I really don't know all the details, I don't know that the method by which a signal is transmitted in a transistor is any better than a transformer.
Your latter post about preferring an integrated "phonolinestage" over separate phono and pre-amplifier would also logically favor an integrated pre-amplifier / amplifier over separate components, so I'm not so sure that your ideal preference holds true to real life experience.
One user recommended a particular search, and it supplied the following website, which I found very informative. Here is a copy from the first two paragraphs from a transformer manufacturer, Rothwell Audio Products:
“the cartridge operating principle
Moving magnet cartridges, as their name implies, contain magnets which are moved by the stylus’ cantilever, and the movement induces the signal voltage in fixed coils in close proximity to the magnets. In moving coil cartridges the roles are reversed, so now the magnets are fixed and the coils move. The big advantage of moving coils is that the coils are much lighter than the magnets, so they are much more responsive to the motion of the stylus.
The big disadvantage is that the output voltage of moving coil cartridges is about 20dB lower than that of moving magnets, so an extra 20dB of gain is required. The extra gain can be provided by the phonostage amplifier, by an external device called a headamp, or by a transformer. The most commonly found solution is to increase the gain in the phonostage, but step-up transformers are still the best solution where cost is no object.
why use a transformer at all?
It used to be the case that a good signal-to-noise ratio was impossible to achieve from a moving coil cartridge without a step-up transformer. An extra 20 or 30 decibels of gain wasn’t a problem, but doing so with low noise using valves, transistors or op-amps was a problem. Modern transistors and op-amps can now offer much better signal-to-noise ratios but valves still usually need transformers to work successfully with low output moving coil cartridges. An alternative to the step-up transformer is the headamp (or pre-preamp). This is a transistor or op-amp amplifier which raises the output of moving coil cartridges up to moving magnet level. Rothwell offer the Headspace as a high quality, low noise headamp.
Apart from the issue of noise, the sound quality of transformers is something their advocates swear by. The distortion produced by audio transformers is of a completely different nature to that produced by a transistor amplifier. The harmonic distortion in transformers is greatest at the lowest frequencies and falls rapidly as the frequency rises, whereas in transistor amplifiers distortion more usually rises as the frequency rises. More importantly, intermodulation distortion tends to be lower in transformers than it is transistor amplifiers. The outcome is that although transformers aren't absolutely free of distortion (nothing is), the distortion is very benign compared to the distortion produced by many transistor amplifiers. This explains why the sound produced when a moving coil cartridge is used with a good transformer is so sublime and can create an open and spacious soundstage with amazing separation between instruments.
The case against transformers is simply one of cost. Transistors can be as cheap as a few pennies (or less when bought in sufficient quantities) whereas transformers always cost a lot more, by as much as a factor of several thousand, due to the expensive materials used in the core and the cost of the copper windings in terms of both material and labour.”
….but, Rothwell Audio Products explanations also go into further detail in the next section, which would definitely imply caution against SUT use in a current based phono stage, due to geometrically increasing impedance:
”the transformer turns ratio and impedance ratio
The turns ratio of a transformer is the ratio of the number of turns of wire on the primary winding to the number of turns of wire on the secondary winding, and the voltage on the primary is stepped up (or down) by the same ratio as the turns ratio and appears on the secondary. A transformer with a 1:10 turns ratio for example will step up a voltage at its primary by a factor of ten. However, since transformers are totally passive devices with no power supply to draw energy from, no extra power can be produced by a transformer and an increase in voltage will be accompanied by a corresponding decrease in current. This is what gives rise to the concept of the impedance ratio. The impedance ratio is the square of the turns ratio and makes an impedance on the secondary winding of a transformer appear to a source feeding the primary as that impedance transformed by the square of the turns ratio. The transformer itself doesn’t have an impedance, rather an impedance on one side of it will look like a different impedance from the other side (it works in both directions). In the case of, for example, a 1:10 step-up transformer, a 20k impedance on the secondary winding will appear to be a 200 ohm impedance on the primary winding (20,000 divided by 10 squared equals 200). A 1:2 step-up transformer with a 100k load on the secondary would appear to have an input impedance to a source driving the primary as 25k (100k divided by 2 squared equals 25k).
So, it would seem logical that a cartridge with an output voltage of, for example, 0.5mV, when used with a step-up transformer with a 1:10 turns ratio, would produce 5mV at the transformer’s output. Yes, it would if the cartridge’s source impedance (also known as its internal impedance or its coil impedance) was zero. In practice, with low impedance cartridges of about 10 ohms or less and low ratio transformers (less than about 1:20), the transformer’s output voltage is very close to the cartridge’s output voltage multiplied by the turns ratio and can be safely used as a good first order approximation for guidance. However, the cartridge’s source impedance may be low but it is never zero, and the transformed secondary load needs to be considered for a more accurate analysis. Consider as an example a transformer with a 1:10 ratio and a cartridge with a 10 ohm coil. If the load on the transformer secondary is an MM phonostage with a 47k impedance, that load appears to the cartridge as 470 ohms (47,000 divided by 10 squared) and must be driven by the 10 ohm coil. The 470 ohm load and the 10 ohm source form a potential divider (the “pre-set volume control” described in the previous section) with some of the cartridge’s voltage dropped across its own internal 10 ohm impedance. The proportion dropped internally is 10/(470+10) = 0.0208, which is not very much at all – just 0.2dB. The deviation from the first order approximation is small and probably not worth worrying about, but it is there. It’s when higher turns ratios are used with higher source impedances that the potential divider effect becomes significant. Consider a cartridge with a 40 ohm coil and a transformer with a 1:30 ratio. The 47k load on the secondary now appears as 52 ohms from the primary side. When driven by a 40 ohm source the voltage divider is formed by 52 ohms and 40 ohms. Therefore the proportion of signal dropped across the cartridge’s coil is 40/(40+52) = 0.43, which is very significant – nearly half the voltage produced by the cartridge is lost internally. Whereas only 0.2dB was lost in the previous example, here the signal loss is 5dB, and instead of achieving a signal voltage at the output of the transformer of 30 times the cartridge’s output, the output is only 0.43x30 times the cartridge’s output, ie a voltage step-up of effectively just 13 times, not 30 times. Clearly, increasing the transformer turns ratio by a factor of X doesn’t increase the output voltage by the same factor. As the turns ratio increases, the increase in the output voltage gets less and less as the load on the cartridge becomes more and more significant until a point is reached where increasing the turns ratio further actually causes the output voltage to drop.
The point at which the maximum possible voltage at the transformer’s output is achieved occurs when the transformed load is equal to the source impedance. In the case of a 47k secondary load (the usual load impedance of an MM phonostage) and a 40 ohm MC cartridge, the turns ratio would have to be 1:34.28 to get the absolute maximum output voltage. This is because 40x34.28x34.28 = 47000
It’s this that gives rise to the misguided notion that the transformer must “match” the cartridge impedance. Yes, it may be true that matching the impedances gives the maximum possible voltage at the transformer’s output, but in a hi-fi system we’re not looking for the absolute maximum voltage from the transformer, we’re looking for a voltage suitable to be fed into the following MM phonostage and we’re looking for maximum fidelity. This rarely (if ever) achieved by matching the impedances. The signal voltage suitable for an mm phonostage to handle is about 5mV. A higher voltage into the phonostage will reduce headroom and increase distortion. A lower voltage will compromise the signal-to-noise ratio. Trying to achieve 5mV into the phonostage (with maximum fidelity) should be the aim of a step-up transformer.
The big mistake most often made when selecting a transformer for a moving coil cartridge is to overlook the voltage required at the phonostage’s input and instead try to make the impedances match so that, for example, a cartridge with a 5 ohm source impedance sees a 5 ohm load at the transformer’s input. This approach takes the cartridge’s impedance as the most important factor when in reality it should be the cartridge’s output voltage.
To demonstrate how far wrong the “matched impedance” approach can be, take as an example an Ortofon Vivo Red cartridge with a 5 ohm source impedance. In order to "match the impedance”, the 47,000 ohms on the secondary side of the transformer would have to appear as 5 ohms on the primary side. That means that the impedance ratio must be 9400 (because 47,000 divided by 5 equals 9400) and therefore the turns ratio must be the square root of 9400, which is 97. So we must find a step-up transformer with a turns ratio of 1:97. However, the Vivo Red’s output voltage is 0.5mV and the voltage fed to the phonostage by a 1:97 transformer would 24mV. That would be enough to overload most phonostages and would be a long way from optimal. A much better approach to finding a suitable transformer ratio would be to work with the cartridge’s output voltage. The Vivo Red has an output of 0.5mV and the phonostage requires about 5mV for the best performance, therefore a ratio of 1:10 would appear to be much better. The first order approximation suggests a 1:10 ratio would give us 5mV. Does that still hold true if we also consider the cartridge’s 5 ohm source impedance and the load impedance presented by the transformer? Yes. A 1:10 transformer with a 47k load on its secondary winding presents a load of 470 ohms to the cartridge. The voltage divider formed by the 5 ohm source impedance and the 470 ohm reflected load means that only 5/(470+5) is dropped across the cartridge’s internal impedance and the actual voltage at the transformer’s output is 4.95mV, ie extremely close to the estimate using the approximate method. The 470 ohm load seen by the cartridge is perfectly compatible with Ortofon’s recommended load of >10 ohms. The “impedance matching” method of using a 1:97 ratio transformer would give the cartridge a 5 ohm load impedance, which is outside the manufacturer’s recommendation. Also, for the reasons explained below, a 1:97 transformer would have a seriously compromised performance compared to a 1:10 transformer.
Now consider a different cartridge, the Dynavector Karat17D3 with a 38 ohm coil. Using the impedance matching approach to find the best transformer ratio we end up with a ratio of 1:35 and the cartridge’s 0.3mV output becomes 5.25mV at the the transformer’s output. This time, the “impedance matching” approach appears to have worked out well, but is is really the best turns ratio? Maybe not, because Dynavector’s recommended load is 100 ohms and a 1:35 transformer would give the cartridge a 38 ohm load. In this instance a lower turns ratio would be better. For example, a 1:20 transformer would give the cartridge a load of 117.5 ohms and have an output of 4.5mV. Also, a 1:20 transformer is likely to have better performance than a 1:35 transformer, as explained below.”
Yes, Rothwell Audio website seemingly very clearly and concisely explains even the basics of audio, as evinced by the next paragraph on impedance loading of cartridges, which can be applied to any component matching:
”cartridge loading
Before considering how to match a moving coil cartridge with a transformer, it is worthwhile considering the effects of different loads on moving coil cartridges.
When any signal source is connected to any load impedance a potential divider is formed by the source's output impedance and the load impedance. (The output impedance is also know as the source impedance or internal impedance. The load impedance is also known as the input impedance.) The signal source could be a phono cartridge, microphone, CD player, mixer etc., it doesn't matter. The load could be a phonostage, mixer, transformer, or simply a resistor – again, it doesn't matter. The potential divider formed by the source and load impedances acts as an attenuator or a pre-set volume control. If the load impedance is very much bigger than the source impedance the attenuation is low and the effective pre-set volume control is near maximum. The usual rule for audio equipment in general is to feed the signal into a load at least ten times greater than the source impedance to avoid any significant signal loss, and this is applies to moving coil cartridges as much as to anything else. If the load impedance is 10 times greater than the source impedance the signal lost by the “pre-set volume control” is less than 1dB, ie nearly all the signal generated by the source is available to the following amplifier. Any loss of signal at the source/load interface is usually considered a bad thing as it compromises the signal-to-noise ratio. More signal is lost, ie the pre-set volume control is turned down more, if the load impedance isn't significantly higher than the source impedance. When the source and load impedances are equal the signal loss is 6dB. When the source impedance is 9 times greater than the load impedance the signal loss is 20dB. Most modern moving coil cartridges have a source impedance of about 10 ohms and the “load impedance ten times the source impedance” rule suggests 100 ohms is a good choice for load impedance and causes less than 1dB of signal loss. This is well in line with the recommendations from many cartridge manufacturers (see the table of data below). Anything above 100 ohms should be equally suitable.
Does the cartridge's tonal balance change with load impedance? It certainly does if the cartridge is a moving magnet type, but low output moving coil cartridges are much less sensitive to changes in the load impedance. Users sometimes claim that higher load impedances produce a brighter sound than lower ones, but cartridge manufacturers tend be non-specific about recommended load impedances, often recommending a wide range or simply anything above a minimum impedance.
The recommendation of Rothwell Audio Products is in line with Ortofon, Audio Technica and most other cartridge manufacturers - that 100 ohms is a good value for most cartridges, and that the exact value is not critical as long as it is well above the cartridge's source impedance.
One thing is certain, and that is that the load impedance should not be equal to the cartridge's source impedance. That would produce a 6dB loss of signal (when there's often only a few hundred microvolts to start with) and seriously compromise the signal-to-noise ratio. The idea that having the load impedance equal to the source impedance achieves perfect "matching" is wrong and is the most commonly held myth about moving coil cartridges. It also gives rise to most of the confusion surrounding step-up transformers and how to select the correct one for any given cartridge. The reasons for the “matched impedance” myth are examined below.}”
For those who don’t mind clicking links, and are interested in reading more, here is the link to the informative, educational page from Rothwell Audio Products, and they do mention use of different materials, such as copper vs silver somewhere on the page, although their experience may differ from others:
While I'm not certain, I think @dovermay be referring to the reaction of the square wave to various loading, resistance, and capacitance properties, when dealing with SUT, which is found on that same Rothwell Audio Products site:
"
figure 1a
figure 1b
figure 1c
figure 1d
Transformer ringing
All transformers have limitations due to the inevitable capacitance between windings, leakage inductance etc. and these determine the transformer’s bandwidth and can produce “ringing”. Ringing can be seen as overshoot at the corners of a squarewave, as illustrated in the figures above. A lower load impedance on the transformer's secondary winding has two effects: reduced output and damped ringing. This perhaps explains why people attempting to tune their system by ear have reported that loading resistors (intended to load the cartridge correctly) have a beneficial effect. However, in reality the improvement in sound quality isn't due to the cartridge being loaded correctly, it's due to the phonostage being overdriven less, and due to transformer ringing being damped.
A much better approach to optimising sound quality would be to separate the two issues and deal with them individually. Overloading the phonostage would be addressed by using a transformer with a lower turns ratio, and that alone would have the added benefit of better performance. Ringing can be dealt with by employing a suitably chosen resistor-capacitor network without the penalty of excessive signal loss. In the case of the Ortofon Vivo Red in the example above, a reduction in output voltage is a benefit, but more often than not it isn't a benefit. With cartridge's such as the Denon DL-304 with its feeble 0.18mV output, any loss of signal voltage caused by attempting to damp ringing with a resistor is unwelcome. Achieving the correct signal level is one issue and damping transformer ringing is another. Trying to treat both issues with one cure isn’t advised. Fortunately, ringing can be damped by a suitably chosen resistor-capacitor network without the penalty of a reduction in output.
The oscilloscope screen shots in figure 1 above illustrate ringing and the effects of different loads on the transformer's secondary winding.
Figure 1a shows the output with a 47k ohm load on the secondary of a fairly modest transformer. The slope on the top and bottom of the waveform is caused by the low frequency limit of the transformer due to inadequate primary inductance. The peaks at the corners of the waveform are due to transformer ringing, also known as overshoot. Figures 1b, 1c and 1d show what happens to the waveform when the secondary load is reduced to 22k, 10k and 5k1 respectively. The slope of the waveform straightens out as the impedance is reduced and the corners lose the unwanted peaks, but the overall signal level also drops significantly. The level with the 5k1 load is about 10dB less than the level with the 47k load. This shows that although the performance of the transformer can be improved by reducing the load impedance, the benefit comes at the expense of a serious loss of signal level. Since the point of using a step-up transformer with a moving coil cartridge is to gain an extra 20dB or so of signal level, any loss due to incorrectly loading the transformer is unacceptable.
The transformer ringing which can be seen as peaks at the corners of the waveform in figure 1 is a common problem and arises from inductive and capacitive elements (leakage inductance and inter-winding capacitance) combining to produce resonance. The capacitance of the cable connecting an mc step-up transformer to the following phonostage also plays a part, which is why the interconnecting cable should be a low capacitance design and kept as short as is practical. Ringing can be found in many commercial moving coil step-up transformers, regardless of price. Sometimes the ringing occurs at very high frequencies and is reasonably well damped and therefore quite benign, but often it occurs at a much lower frequency or rings for such a long period that it can cause quite audible effects. Even expensive transformers from well-known audiophile brands often exhibit poor performance as regards ringing.
Figure 2 below shows oscilloscope screen shots of a step-up transformer from a manufacturer of expensive valve amplifiers. The input signal is again a 1kHz square wave from a 10 ohm source. Figure 2a shows the transformer's output when there is no load and the overshoot is quite clear to see. Figures 2b to 2e show the 1kHz waveform with different loads on the transformer's secondary. A 47k load has barely any effect on ringing, but as the load is reduced through 22k, 10k and 5k1, the ringing is progressively damped. At 5k1, the ringing is gone but the signal level is reduced. With this particular transformer, the signal loss with the 5k1 load is not as bad as the signal loss suffered by the first transformer, but any loss of signal should be avoided. Note however that the top and bottom of the waveform are very flat, indicating that this transformer has very good low frequency performance. Figure 3 is a closer look at the corner of the waveform and shows clear ringing which lasts for several cycles before subsiding. The frequency of the ringing is about 100kHz - well above audibility - so there's no chance of actually hearing a ringing sound, but it is clear that the signal produced by the signal generator is being severely deformed. Figure 4 shows the output from a 10kHz square wave input. The waveform is hardly recognisable as a square wave at all and it is not difficult to imagine what effect such deformation could have on a music signal. The leading edges of crash cymbals, ride cymbals and snare drums or the attack of plucked strings could easily lose integrity and become a confused jumble of sound. When several percussive instruments are playing together, as is very common, separation between the instruments will not be helped by the severe ringing shown in figure 4.
figure 2a
figure 2b
figure 3
figure 2c
figure 2d
figure 4
figure 2e
Fortunately, ringing can be totally eliminated without sacrificing signal level by loading the secondary winding correctly with a resistor-capacitor network, not a simple resistor (though far too many commercial step-up transformers totally neglect this). Although lower values of resistive load on the secondary do tend to reduce ringing, as illustrated above, loading with a correctly optimised resistor/capacitor network will produce far superior results. Since different transformers are constructed with different core materials, wire thickness, number of turns and winding techniques, the optimum load network will be different for each, and the only way to determine the correct network is through measurement.
Figure 5 below shows the transformer of figures 2 and 3 after an optimised load network has been applied, again with a 1kHz square wave input. The ringing has been eliminated and the signal level available into a 47k load has been maintained.
Figure 6 shows the effect of applying a non-optimum loading network. In this case the incorrect component values (out by only a few nanofarads and a few kilohms) have resulted in quite a peculiar deformation of the waveform. This illustrates the need to get the loading network right rather than copying a network which is optimised for a different transformer.
As an aside, the use of silver wire for the windings might appear impressive but does little or nothing for performance due to the fact that silver has only marginally less resistance than copper and the limiting factors in transformer performance are due to the finite size and permeability of the core, leakage inductance and inter-winding capacitance, none of which are improved by the use of silver wire. However, it does have a significant impact on cost. It should go without saying that elaborate cases with 3D milled aluminum front panels or gold plated turrets, while very nice to look at, also have no benefit for audio performance but, again, do have an impact on cost.
Well, my overall assessment is that there are several commenters who always have a positive contribution to just about every thread that they participate in: @atmasphere@antinn almost always have significantly positive contributions to every thread. I think @pindac also has a thoughtful, philosophical insight into matters. I also appreciate others' contributions to the educational aspect of SUT's, as @intactaudiohas done.
On the other extreme, @rauliruegascan occasionally have a positive contribution, but I find most of his posts to be mostly irrelevant to the topic at hand, and mostly just arguing to support his perspective, whether its relevant to the thread or not. Optimistically, I attribute this to his lack of English comprehension. Regardless, I wish him the best with his interests, and I hope he can learn to take constructive criticism, and contribute more positively in the future.
I'm not following this thread too closely at present, because I thought that most of the practical aspects of SUT that I didn't understand was addressed in the links to the Rothwell Audio Products that one commenter ( @larryi) posted early on, and one other user suggested to visit.
The details of transient response of SUT's may ultimately prove to be interesting, as @holmz@lewmmay demonstrate, but at this time, I don't know if it will matter or not, but if those who know more than I do are persuaded that it is relevant, then I would be interested in seeing their hypothesis, methods, data, and conclusion.
I think that @pindachas the correct approach: when children are misbehaving in order to get attention, it's best to ignore them; this approach is colloquially known as "don't feed the trolls" on the internet.
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