MM vs. MC: What Happens When People Jump Into MC Too Early? 

Dear @colossalsound  : I dont know if @kennyc  knows why existe the SUT, the true behind SUT. I already explained in this forum at least 5 or 6 times in the last 10 years, so I don't repeat again.

Ypsilon, why  if for you so good SUT whe is FR is a -3db 8hz to 60/70khz, heavy limitation down there to say the least.

Next information could help any one to understand about SUT role with LOMC cartridges:

" Some of you may find that I’m using some inappropriate terms. The aim of this paper is to understand the way step-up transformers function, and the rules you should follow to select the appropriate step-up to use with your MC cartridge (if you want to obtain a happy marriage).

The characteristics you should take care of for this kind of cartridge to be correctly exploited by your system are:

• The output level, measured in millivolts
• The internal impedance, measured in ohms
• The load impedance, measured in ohms too

In this paper, we’ll ignore high output MC cartridges that can be used with a MM input and concentrate on MC cartridges with an output of less than 1 mV. (The output level of MM cartridges is between 2.5 and 7 mV).

The job of a step-up transformer is to raise the output of the MC cartridge in order for that output to be correctly handled by a MM phono section. At the same time, the step-up transformer adapts the impedance of the signal produced by the MC cartridge to an impedance that can be “read” by your MM input. You must understand that step-ups all have different characteristics that we’re about to explore. These characteristics are such that if you select a step-up and a MC cartridge at random, your probability of obtaining a happy marriage is close to zero.

So please, don't make a definitive judgment of a step-up or a MC cartridge. Before saying “this step-up is pure BS” or ”this cartridge is pure BS”, check the compatibility of your MC / step-up combo. Most of the time, if the sound isn't good it’s because of a compatibility problem.

So, you need to amplify the signal output from a MC cartridge? In fact, you use can two different kind of devices to do that job:

active devices : head amplifier of MC section on a phono section

passive devices : step-up

How can you tell that a device is active or passive? Very simple, on active devices, there is a plug! On step-up, no plug (so, it’s passive since there is no power supply).

Another difference, that makes things unclear for a newbie, is that on active devices the load impedance is indicated (100 ohms, for instance), on passive devices you don’t have a load impedance but an internal impedance; rather than a manufacturer giving a load impedance figure you will get a statement such as: “this step-up is designed for use with cartridges with an internal impedance of 40 ohms". We’ll ignore active devices. There is no fun there; cartridge manufacturers generally specify a load impedance, so you set up your active device (head amp, MC phono section) to that load impedance and listen; game over. 

By reading this paper you will find that some cartridges cannot be used with a step-up, whatever its characteristics. For these cartridges you’ll have to use an active device.

Now, on a step-up you’ll find internal impedances indicated: for instance, take a look at a DENON AU320, two positions are possible: 3 ohms and 40 ohms. So this step-up should be good with cartridges of internal impedance of 3 ohms and 40 ohms. Now the problem is, that for the moment, the load impedance used in that step-up is not known (but we’ll soon know this very important information!). We’re only sure that this load impedance is superior to the internal impedance. And secondly, the load impedance given by a manufacturer for its cartridge is the one you should use on active devices; the one you should use on passive devices is not generally the same and is superior to the load impedance given by the manufacturer.

How can you tell that the impedance indicated on a step-up is not the load impedance?

Let’s do some calculus! If a step-up has a gain of say 1:10, this means that the output of the cartridge will be multiplied by 10. If the output out of the cartridge is 0.3 mV, you’ll have, after the step-up, 3 mV, perfect for a MM input. Now, your MM input has its own impedance generally equal to 47 Kohms. The signal emitted by the MC cartridge must be in accordance to that 47 Kohms. A step-up modifies the impedance of the output by a factor equal to the square of the amplification ratio. This is known as ‘natural impedance’. A word of caution: by itself, a step-up doesn’t have any impedance. The natural impedance is directly linked to the impedance of your MM entry and to the amplification ratio.

So, a step-up with an amplification ratio of 10 has a natural impedance and load impedance of 470 ohms (if your MM input impedance is 47 kohms: 470=47000/10²). Now, let’s go back to our DENON AU320: on the 40 ohms position, since the amplification ratio is 1:10, the load impedance is 470 ohms.

You’re not convinced? Let’s do more calculus. If your load impedance was 40 ohms, your amplification ratio, in that case should be equal to (47000/40)^0.5 = 34.3. With a cartridge output of 0.3 mV, you are sending 0.3*34.3 = 10.28 mV to your MM input. This is important; you may be overloading your MM input. Let’s do the same calculus on the 3 ohms setting. If it were your load impedance, the gain in that case should be (47000/3)^0.5=125.16. Again, with a 0.3 mV output cartridge, you’re about to send 37.5 mV in your MM input: this IS overload! A MM input is generally designed to accept an output between say 2.5 and 10 mV, not 37.5 mV! And the amplification ratios calculated here have nothing in common with the step-up specs given by manufacturers (as we’ll see in a few moments).

So, for one channel, there are two coils: a primary (the ‘input’: the signal emitted by the cartridge arrives at this one) and a secondary (the ‘ouput’: the amplified signal will go out to your MM amplifier stage from this one). You will see that there are less turns on the secondary than on the primary. This is not a strange idea from the designer of this scheme. Your amplification ratio is a direct result of the turns ratio (primary/secondary) (ok, I know, I know, a perfect transformer doesn’t exist and things are not that simple but the rule indicated here is a good proxy). This explains why, on a step-up that can be used with several internal impedances cartridges, the gain differs according to the internal impedance you’re selecting. On the audio technica step-up represented by the scheme, the gains are 23, 26 and 34 db for respective internal impedances of 40, 20 and 3 ohms.        

In a perfect transformer: N2/N1 = V2/V1 = x

Another « detail »: the grounding of the step-up. This is very important. If you’re having grounding problems, or shielding problems, you’ll probably have “hum”.

But, why are only internal impedances indicated on a step-up?

The main reason is certainly the fact that, as I already indicate, natural impedances are not constant: they are a function of the impedance of your MM input. For instance, if your MM input has a 10 Kohms impedance, with a 1:10 amplification ratio step-up, the natural impedance (and your load impedance) is 100 ohms (10000/10^2).

What step-up for my cartridge?

This is THE question. If you’re looking for a step-up you can buy second hand step-up transformers, brand new (most Mc cartridge manufacturers produce step-up transformers) or build them yourself using parts from manufacturers like Lundhal, Sowtek, Hashimoto, Jensen.. (See links to those manufacturers at the end of this paper).

To make things clearer, we’re going to take a look at the specifications of available products. Why? Because these products were designed by MC manufacturers, let’s assume that they knew what they where doing.  Specs shown here are compiled from various sources (internet or vinylengine inmates like Yosh (Hi Yosh!). if you have data relating to other products, contact me and I’ll add them to the table. All I need to know is the gain (measured in db or in amplification factor 1:x)  and the recommended internal impedance of the cartridges to use with that step-up.

Data in bold type are manufacturers specs, other data was recalculated this way:

X factor = 10^[(gain in db)/20]
Gain in db = 20*ln(x factor)/ln(10)
Natural impedance = 47000/[(x factor)^2]

* ortofon T30 : the natural impedance is certainly used for 48 and 12 ohms position and is reduced by “resistor tuning” – if someone here can read the value of the resistors inside the T30, that could help us a lot!

Part 2

What is there to understand here?

Let’s imagine I have a 3 ohms internal impedance cartridge. What are the devices I should buy?

Some devices from this table have a 3 ohms setting: FRT-4, Denon AU 320, Denon AU 340, AT700T, Ortofon T2000, FR-X1L, EAR MC4. What we can see is that the natural impedance of these devices (respectively 37,3 - 36 - 43 - 18,7 – 14.9 – 11.8 and 52,2 ohms) can be separated in two groups: Some of them have very low natural impedance (between 11.8 and 18.7 ohms). I think these figures are really too low and will limit this kind of step-up for use with very low internal impedance cartridges (1-2 ohms) especially the Ortofon T 2000. The remaining step-ups have a natural impedance between 36 and 52.2 ohms.

We will consider this range as a good range for loading a 3 ohms internal impedance MC cartridge. The amplification ratios associated with these step-ups are between 30 and 36 (gain is between 29.5 and 31 db).

Now, there are some other step-ups in my table that have a natural impedance between 36 and 52 ohms:  EAR MC3 (4 ohms position), Ortofon T3000 (2-10 ohms position), FR XF-1 (4-18 ohms position),  FR X1-M (4-18 ohms position), FRT-3 (10 ohms position). Conclusion: you can use that step-up at the position indicated with your 3 ohms cartridge. 

One could add to this list the Ortofon T10, T20 and T30. The natural impedance is equal to 30 ohms (a little low for me – I would couple those transformers with very low impedance cartridges of say 1 - 2 ohms). On one hand you could say “come one, this is Ortofon, worldwide specialist of low impedance cartridges, they know what they doing”. But on the other hand I must add a very important point to understand why Ortofon may have changed their minds. These models are rather old (70’s 80’s). It seems that manufacturers realised in the 80’s that designing a high gain step-up transformer is really difficult. The more gain you have, the more difficult it is to have a flat frequency response. The difficulty of producing a quality high gain step-up with a linear response is translated in the actual price of these step-ups: for instance, the price of an Ortofon T3000 is 1625 euros (are you sure you really want to buy a low impedance cartridge?)

But, from this table, you can find some other transformers that are said to treat correctly a 3 ohms internal impedance cartridge. In fact, for these transformers, manufacturers provide a range of possible internal impedances for the transformers.  

Things are now a little more complicated and one could ask if we can really trust the manufacturers’ recommendations? Let’s take a look at the Denon AUS1, Ortofon SPU-T100, Ortofon T1000, FR XG5, Ortofon T5, Nakamichi MCB100, Sony HA-T110, Ortofon T20MKII, Ortofon T10 MK2 and Supex SDT 3300.

The natural impedance for these transformers is between 66.4 ohms (Supex SDT 3300) and 278 ohms (Denon AUS-1) : there must be a problem for the Denon unit. A 3 ohms internal cartridge plugged into a Denon AUS-1 is certainly producing very amplified highs. So, when a range is indicated for your step-up, there is always some kind of compromise since they cannot be good everywhere. The risk is to have a too high a load impedance for a cartridge with an internal impedance equal to the minimum of the range (too bright sounding) or too low a load impedance for a cartridge with an internal impedance equal to the maximum of the range (no high frequencies in this case).

The Denon AUS-1 should work well with a 40 ohms internal impedance cartridge but no good with a 3 ohms internal impedance cartridge. The Ortofon T5 might not work very well with a 40 ohms internal impedance cartridge or a 3 ohms internal impedance cartridge, but may be good with say, a 10 ohms internal impedance cartridge.   Let’s take a look now at what is proposed for 40 ohms internal impedance cartridges: there is a consensus on a natural impedance of 470 ohms (biased by the fact that we’re having a lot of Denon products in the table). Now, from the table, you can see that the FRT-4 (100 ohms position) and the Ortofon T30 (48 ohms position) will give you the same natural impedance. With transformers proposing a range of internal impedance including 40 ohms, the natural impedance is generally lower, from 118 ohms (Sony HA-T110, Ortofon T5) to 296 ohms (FR XG-5) – for the Briston TF1, 40 ohms is the minimum of the range : the natural impedance (and then the load impedance) is much to high (1052 ohms).

Let’s assume that the loading of a MC cartridge with a transformer is not an exact science.

Loading a MC cartridge is not an exact science? Why? Simply because manufacturers never produce a unique load impedance for a given internal impedance and because, for a given natural impedance, there is frequently a range of internal impedances that suit the transformer. Now, for a given internal impedance, we should propose a range of load impedance. What I’m proposing now is just a starting point – by following my rules, I’m not telling you that you will obtain the perfect load impedance, I’m just telling you that you won’t make stupid mistakes.

So please, don’t contact me to insult me about my rule!

For this rule, we’ll use a spec given by the manufacturer: the load impedance. We’ll take this load impedance as meaning a load impedance recommended for active transformers (and not for passive devices). This data certainly includes things relavent to important characteristics of the cartridge we don’t know, but that must be considered.

A manufacturer generally gives you a minimum load impedance for active devices (or a range, but it’s less common).

If the load impedance (for active devices) is said to be > or equal to 20 ohms, the internal impedance is 3 ohms, you should try to load your cartridge at load impedances between:

1. the load impedance given by the manufacturer (20 ohms)
2. the load impedance given by the manufacturer + 10*internal impedance (50 ohms)

Now, for a 40 ohms internal impedance cartridge with load impedance for active devices of 100 ohms, you should try load impedances between 100 and 500 ohms. If your system is too bright (suppose you’re having triangle loudspeakers…), you will certainly be happy with something that will “cool down” your sound, so try something close to 100 ohms. On the contrary, you may be happier with something closer to 500 ohms.

Now, my opinion: I never hear satisfactory results when the load impedance on a passive device is equal to the load impedance indicated by the manufacturer (we understand as load impedance on an active device). You’ll try and you’ll tell me. We’ll see later the way to test different load impedances but you don’t need to test 100 values between 100 and 500 ohms : something like 3 or 4 value is enough and in our case, you could try 100 ohms (and you’ll tell me), 200 ohms, 300 ohms and 470 ohms (with a 1:10 transformer).

If the manufacturer is proposing a range of load impedance (say between 20 and 200 ohms), follow that range by testing say, 50 ohms, 100 ohms and 150 ohms.   

Do you think things are over? No, they aren’t! The load impedance is an important thing BUT it’s only the first important thing to consider. Remember that the natural impedance is directly linked to the gain of your step-up. In the next table, you will see the maximum gain of your step-up to have a desired load impedance.  "

The information is to long but suffice is to say that each model of LOMC cartridge needs a DEDICATED SUT for that cartridge to works fine. This is another huge limitation of the SUT otherthat is limited FR range at both frequncy extremes.

ASs I said the best SUT is not SUT. It does not matters system price or owner kind of money because exist active high gain units for any owner level of money .

R.

Btw, I owned too the AT1000T too because Audio Technica manufactured here in Mexico for 8 years his microphones and headphones through a joint venture with a Mexican bussiness man that was and is a close fiend of mine.

Through him I owned all MM/MC cartridges, SUT, Telarc LPs and the like. 

That AT1000T was made expresely for the AT MC1000 in the 3ohms  seccion that's dedicated to that cartridge a NO other one. That's why the AT1000T came with 4 transformers.

R.

Raul,

One of the things I used to like to do was step out from behind my kit and go out into the audience to hear what it sounded like in front of the stage, mid hall, at the back of the hall and so forth.  Of course the sound is different in all of these locations.  Every musician learns what the performance is supposed to sound like from his/her seat.  You have learned to know what the music is supposed to sound like from your seat.  You need to recognize what you are doing and what the advantages are, but also what the limitations are from your methodology.  Please do not take my observation as criticism, no quite the contrary, I commend you!  At the same time just as there are other seats in the orchestra that will hear the same music differently, so too, with music reproduction there will be differences based on the choices that are made for equipment.    

@colossalsound   : I forgot: classical, Jazz or Rock recordings is the same because in the recording we don’t know which instruments are using the orchestra players, we don’t know which microphone/amp are using for the recording, we don’t know the attitude/mood or what the players or orchestra Director has on his brain, we don’t know nothing about the whole proccess recording and not know what is looking the recording engineers and reacording producer and the ones that make the mastering and everything.

The " don’t know " is exacatly the same for any LP/CD recording and with any kind of MUSIC. Nothing is totally different because the recording is for Jazz or rock at the end we have a recording and it's from here ( LP/CD) that we can make our each one work/modification or the fine tunning. We have no control of anything in the recording proccess and where we can have some control level is only in the whole playbac proccess at home. Tha's all.

R.

@billstevenson   : I already posted: nothing is prefect and all have to deal with that characteristic, me too.

R