I was cautioned by a Mod (fair enough! 
) for what I posted on a thread started by someone who wanted to know how to get the best loading for his LOMC, when he was using a SUT in front of his tube MM phono stage.
The mod suggested - given I have some firm views on this subject - I might like to start a thread to discuss the advantages and disadvantages of SUTs vs. active head amps (aka phono pre-preamps). After thinking about this for a while, I have decided to accept the Mod's suggestion. To me, this is almost a 'religious' argument (ie. people hold faith-based views which means they have no rational mechanism for letting go of these views ... rather than views which might have resulted from experimentation) and so any discourse might not progress very far.
But let the discourse begin.
My own views have come from over 40 years of listening to vinyl, through tube and ss components. I've also experimented with SUTs vs. active head amps - one phono stage I bought about 15 years ago used SUTs for the LOMC input (English brand - can't remember the name) and when I removed these and upped the gain (after consultation with the designer) by changing a resistor value ... I got a significant increase in sound stage width. Which to me was a good thing!
At one stage, I owned a well thought of tube head amp from the 80s ... it sounded lovely but had a noise floor which was far too high for me to be able to cope with. So I sold it and bought an SLA-powered, JFET-based head amp (the AKSA 'Paris', designed by Hugh Dean). This is completely noiseless - in effect, to borrow Peter Walker's comment ... "a straight wire with gain"! (Noise was measured by a reviewer in Germany at 141dB down.) So that confirmed to me that JFETs are the go - rather than tubes - when it comes to amplifying LOMC signal levels to MM signal levels with an active device. And, while there are positives ... I am not aware of any negative impact on SQ.
But sure, a SUT is another way of increasing the output of a LOMC to the level needed for an MM phono stage - whether tube or ss.
But raising the signal level is not the only thing required for a LOMC ... IMO, it is critical to get the right loading for the cart - and I see it as a tragedy that so few people get to listen to their cart at its optimal loading.
And this is where those who use a SUT before a MM phono stage ... miss out; they simply do not have the same flexibility for loading that an active (ss) head amp can provide. The default loading for an MM phono stage is 47K ohms ... a few (some classic Japanese phono stages, for example, and my own 'Muse') have 100K load.
Now, tube lovers automatically reach for a SUT instead of an ss head amp ... in my view because, as a philosophical principle, they cannot accept a ss device in their signal chain! If you use a 1:10 SUT then the 47K default loading becomes 470 ohms as seen by the cart (divide the load by the square of the turns ratio). That is fine for a cart which has an optimal loading of 470 ohms - and also, carts which have a lower optimal loading like 60 or 100 ohms can be accommodated (additional parallel resistors on the output of the SUT).
But for a cart which has an optimal load of 4K7 ... this cannot be achieved using a SUT. (Sure, theoretically, you could replace the 47K input load on the phono stage with a 470K resistor - but you cannot just arbitrarily increase the shunt resistor in front of the first (or only) gain stage in a phono stage without having a sonic impact.)
Oh, and what is the "optimal" loading for a cart? Well, there certainly isn't an absolute figure ... it is a preference as to how you like the sound of the cart at different loads. For instance, the specs for my Benz LP say "470-47K" ... so a 1:10 SUT in front of a MM phono stage will deliver the minimum! But I - and several others who have the ability to play with loading - think the LP sounds best at several Kohms; I use 4K7 ohms. This cannot be achieved using a SUT.
So, my opinion is that tube lovers who refuse to countenance a ss head amp are leaving themselves short. Sure, if they have a cart whose optimal load is 470 ohms or less, they can end up with the right load ... but - given the thread on loading which, as I said, I strayed into - this is not a simple matter. (Spoiler alert - you need to take the resistance of the transformer windings into account! )
Whereas with the right headamp they:
* will introduce no noise into their system, and
* can get a simple method of arriving at the optimal cart load ... by using parallel RCA load plugs (plugs loaded with load resistors).
Andy
) for what I posted on a thread started by someone who wanted to know how to get the best loading for his LOMC, when he was using a SUT in front of his tube MM phono stage.The mod suggested - given I have some firm views on this subject - I might like to start a thread to discuss the advantages and disadvantages of SUTs vs. active head amps (aka phono pre-preamps). After thinking about this for a while, I have decided to accept the Mod's suggestion.
To me, this is almost a 'religious' argument (ie. people hold faith-based views which means they have no rational mechanism for letting go of these views ... rather than views which might have resulted from experimentation) and so any discourse might not progress very far. But let the discourse begin.
My own views have come from over 40 years of listening to vinyl, through tube and ss components. I've also experimented with SUTs vs. active head amps - one phono stage I bought about 15 years ago used SUTs for the LOMC input (English brand - can't remember the name) and when I removed these and upped the gain (after consultation with the designer) by changing a resistor value ... I got a significant increase in sound stage width. Which to me was a good thing!
At one stage, I owned a well thought of tube head amp from the 80s ... it sounded lovely but had a noise floor which was far too high for me to be able to cope with. So I sold it and bought an SLA-powered, JFET-based head amp (the AKSA 'Paris', designed by Hugh Dean). This is completely noiseless - in effect, to borrow Peter Walker's comment ... "a straight wire with gain"! (Noise was measured by a reviewer in Germany at 141dB down.) So that confirmed to me that JFETs are the go - rather than tubes - when it comes to amplifying LOMC signal levels to MM signal levels with an active device. And, while there are positives ... I am not aware of any negative impact on SQ.
But sure, a SUT is another way of increasing the output of a LOMC to the level needed for an MM phono stage - whether tube or ss.
But raising the signal level is not the only thing required for a LOMC ... IMO, it is critical to get the right loading for the cart - and I see it as a tragedy that so few people get to listen to their cart at its optimal loading.
And this is where those who use a SUT before a MM phono stage ... miss out; they simply do not have the same flexibility for loading that an active (ss) head amp can provide. The default loading for an MM phono stage is 47K ohms ... a few (some classic Japanese phono stages, for example, and my own 'Muse') have 100K load.
Now, tube lovers automatically reach for a SUT instead of an ss head amp ... in my view because, as a philosophical principle, they cannot accept a ss device in their signal chain!
If you use a 1:10 SUT then the 47K default loading becomes 470 ohms as seen by the cart (divide the load by the square of the turns ratio). That is fine for a cart which has an optimal loading of 470 ohms - and also, carts which have a lower optimal loading like 60 or 100 ohms can be accommodated (additional parallel resistors on the output of the SUT).But for a cart which has an optimal load of 4K7 ... this cannot be achieved using a SUT. (Sure, theoretically, you could replace the 47K input load on the phono stage with a 470K resistor - but you cannot just arbitrarily increase the shunt resistor in front of the first (or only) gain stage in a phono stage without having a sonic impact.)
Oh, and what is the "optimal" loading for a cart? Well, there certainly isn't an absolute figure ... it is a preference as to how you like the sound of the cart at different loads. For instance, the specs for my Benz LP say "470-47K" ... so a 1:10 SUT in front of a MM phono stage will deliver the minimum! But I - and several others who have the ability to play with loading - think the LP sounds best at several Kohms; I use 4K7 ohms. This cannot be achieved using a SUT.
So, my opinion is that tube lovers who refuse to countenance a ss head amp are leaving themselves short. Sure, if they have a cart whose optimal load is 470 ohms or less, they can end up with the right load ... but - given the thread on loading which, as I said, I strayed into - this is not a simple matter. (Spoiler alert - you need to take the resistance of the transformer windings into account!
)Whereas with the right headamp they:
* will introduce no noise into their system, and
* can get a simple method of arriving at the optimal cart load ... by using parallel RCA load plugs (plugs loaded with load resistors).
Andy
Regardless of head amp, being able to do 25 to 100 uS EQ is worth trying. My head amp is passive 75uS ( 7K5 10 nF COG-NPO ) then active 3180/318. I have an additional passive 2uS at the output using 200R ( 200 R is a good idea anyway, the capacitor could be switchable ). Often a gain of 17 ( @ 1kHz ) is about right for the 3180/318 and the rest in the first stage. Many records are not exactly 75 uS and it is an allowable tone control with no negative qualities if a minimalist as myself. I don't use anything at the lower bass end and suggest if needed the speakers should be thought about.
If wanting something slightly different than NE5532 try MC33078, after that it's a subject in itself as to what's better.
I like the RCA plug for loading. I like Rean by Neutrik. Very cheap and exactly the right way of making a plug. You should find if the phono stage a good design loading isn't very important when MC. I have used a Lyra between 22R and 47K and mostly feel it was perfectly OK used with either. Lyra said 47K at the time. Shure MM like > 47K and even 1M. The treble EQ will help if so. Generally the Shure will sound more dynamic if lightly loaded. The frequency responce will be no worse than most listening rooms as a compromise. Use treble EQ to suit the both. There is some small advantage in having all EQ's variable, most will never need it. If like like 78's and early mono LP's then maybe.
If wanting something slightly different than NE5532 try MC33078, after that it's a subject in itself as to what's better.
I like the RCA plug for loading. I like Rean by Neutrik. Very cheap and exactly the right way of making a plug. You should find if the phono stage a good design loading isn't very important when MC. I have used a Lyra between 22R and 47K and mostly feel it was perfectly OK used with either. Lyra said 47K at the time. Shure MM like > 47K and even 1M. The treble EQ will help if so. Generally the Shure will sound more dynamic if lightly loaded. The frequency responce will be no worse than most listening rooms as a compromise. Use treble EQ to suit the both. There is some small advantage in having all EQ's variable, most will never need it. If like like 78's and early mono LP's then maybe.
Sorry, Nigel, You have me confused? In my lexicon:
* a phono stage does the RIAA EQ - whether active or passive.
* a headamp - like a SUT - simply amplifies the signal voltage.
Are you talking about a headamp?
Thank you for that - I will go look for them. (I've been using Vampire 557.)
Andy
PS: I found some pics - they look very similar.
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I don't understand why this is not possible. I'm sure I could come up with transformer to reflect that load if I needed it. Worst case I could have one wound.
My experience is that the "best" load value when using a transformer is not necessarily the same as when using a straight resistor.
Well, sure you could. But it may not do a good job of being a SUT (ie. 'stepping up'!).
If you want to end up with 4K7 when you have a default 47K load on your MM phono stage, you use basically, a 1:3.2 SUT. Which would increase the signal from a 0.3mV LOMC to 1mV ... which is probably too low for the MM phono stage.
Andy
You are speaking of "a cart which has an optimal load of 4k7", and then "there isn't an absolute figure...."
You, and several others, may prefer several kOhms for your Benz LP, but others, and maybe quite a few others, may prefer 470 ohm.
Actually the difference in step up is less than 1 dB; with a 470 ohm load the cart is already pretty much "unloaded".
To gain some insight in what loading does, I'd advice to read this:
mc step-up transformers explained
You were told already that a 4k7 load can be done with a 1:10 SUT, but IMO it makes no sense at all.
You are speaking of "a cart which has an optimal load of 4k7", and then "there isn't an absolute figure...."
You, and several others, may prefer several kOhms for your Benz LP, but others, and maybe quite a few others, may prefer 470 ohm.
Absolutely correct - I keep saying it is up to the individual pair of ears. But the person using a 1:10 SUT with their Benz LP has no option but to choose 470 ohms ... they will never know what higher loads make their LP sound like.
Whereas someone who uses a headamp can try out several different loads to find the one which pleases his - or her - ears the best.
Perhaps you are not aware that Mr Lucaschek provides a load of 47K (only) on his phono stage. To me, 47K gives delightful air to the LP but makes the bass flabby. So I prefer a lower figure. I have tried 470 / 1K / 1K5 / 2K2 / 3K3 and 4K7; I used 3K3 for a long time but have recently moved to 4K7, to give me just a bit more 'air'.
The resulting signal level at the chosen load is not the point; the point is ... how the sound of the cart changes with load.
If so then why does "Mr Benz" only offer 47K with his phono stage?
Yes, I have read that white paper. It is biased, IMO - IOW, it does not cover the whole story. Now, you might say that my own view is also biased ... the other way!
My view is simply that choosing to use a SUT is a decision which is not based on logic - simply emotion (IOW: "if I have a tube phono stage, I won't 'pollute' my signal putting an ss device in the signal chain"). IMO, there is absolutely no good reason to do this (given the SUT's limitations on cart load). Please show me how you do provide a 4K7 load with a 1:10 SUT. (I have already told you that you can't arbitrarily change the 47K load to 470K on the phono stage, without a sonic impact.)
Regards,
Andy
Andy,
Several moons ago you preferred some 500 ohm loading for your Benz LP (https://www.audioasylum.com/cgi/t.mpl?f=vinyl&m=445162).
What happened in the meantime?
Maybe you compensate hearing loss with weird loading?
Or different loudspeakers?
This discussion on SUTs vs headamps is meaningless.
Moving coil carts can be loaded perfectly through the right SUT.
The Benz LP is a bit of a strange animal with it's highish internal impedance of 38 ohm, requiring some 1:15 step up ratio to get to normal preamp input level. Maybe that's why it reacts not like about any other high quality MC cart?
Several moons ago you preferred some 500 ohm loading for your Benz LP (https://www.audioasylum.com/cgi/t.mpl?f=vinyl&m=445162).
What happened in the meantime?
Maybe you compensate hearing loss with weird loading?
Or different loudspeakers?
This discussion on SUTs vs headamps is meaningless.
Moving coil carts can be loaded perfectly through the right SUT.
The Benz LP is a bit of a strange animal with it's highish internal impedance of 38 ohm, requiring some 1:15 step up ratio to get to normal preamp input level. Maybe that's why it reacts not like about any other high quality MC cart?
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More great detective work, Pieter!
Actually that was nearly 12 years ago and, as you can see from that thread, this was just after I got Hugh Dean's "Paris" headamp. Yes, to me ~500 ohms sounded goog - but that was better than the 100 ohms which Hugh's previous headamp provided (because he was following the old wives' tale that LOMCs like 100 ohms loading). But I hadn't yet done much experimenting with higher loadings.Haha very good. I guess you would call 47K as a "weird loading" ... how are you going to provide that with a SUT?
Same loudspeakers - true-ribbon Maggies (whose tweeters deliver up to 40K).
The 'step up ratio' is associated with the amount of output you want the SUT to deliver to the MM phono stage. At 0.3mV output for the LP, a 1:15 SUT would produce 4.5mV - which would be just about perfect! However, the load seen (with the standard 47K-loaded phono stage) would be 47K divided by 225 ... so 209 ohms. Which is completely useless.
Andy
Well, sure you could. But it may not do a good job of being a SUT (ie. 'stepping up'!).
Andy
I still get 10dB gain and although it may not work with every commercial pre on the planet I can find more than a few that will work. Pretty sure I could build one that works just fine. Either way, I would say this is an extreme case and not really the best scenario to base an argument on.
That's exactly why I call the Benz LP a strange animal!
The very large majority of MC carts with 0.35 mV output have rather lower internal impedance; think of 10 to 20 ohms.
Benz specifies 400 ohms or higher; a 1:10 SUT and a 47k input impedance will provide that load.
When a higher load is preferred you can raise the input impedance of the preamp; however I don't see (and very likely will not hear) the benefit.
The spec sheet on my LP says 470 ohms, minimum. But, yes, a 1:10 SUT will deliver that load with the standard 47K input loading.
You cannot willy-nilly radically increase the input load of a phono stage without having a sonic impact (degradation). So, yes, the phono stage might still sound the same if 47K was upped to 100K (delivering 1K to the cart, with a 1:10 SUT) ... but I strongly suspect if you upped it to 470K (to provide a load of 4K7), the phono stage would sound worse.
Note, I myself am not interested in trying this experiment because I don't use a SUT.
I can get the right load by using a headamp instead.Andy
Aah, OK. Thanks.
So, a 0.3mV LOMC becomes 1mV ... and the cart sees 4K7 ohms.
Will you find a tube phono stage having 47K input impedance that will work with that low an input? (Because the only reason to be using a SUT is that you have a tube phono stage!
) I strongly suspect not.Andy
Any others - for those that
a) don't want a 70s/80s preamp, and
b) only want a tube phono stage, as they already have a good preamp?
Andy
Hi,
I think I start to understand the mod´s doubts.
Are You really interested in a fruitful discussion or just up to causing traffic?
Sorry, but if You wanna discuss a theme that has been discussed many times before You still could concentrate on typical applications first.
Most SUTs and soildstate prepres feature gains around 10x, i.e. +20dB.
Stretching the limits will always sooner or later ´proof´ the inferiority or even non-useability of a device .... regardless if its a piece of iron or a piece of sand.
But it doesn´t proof the qualities when used sensitively.
There´s no doubt that a active prepre offers potentially higher flexibility with regard to gain and load impedance and is typically less costly.
More care is required to find the right specs for a SUT.
If chosen wisely there´s no reason why a SUT should not perform perfectly sufficient.
The main advantages of SUTs over solid state - noiseless gain and galvanic isolation/dc-blocking- have been eaten up over time or don´t apply in this application.
So basically I agree, that nowadays SUTs are devices chosen rather by emphatics than technical reasoning (I won´t discuss sonic reasons here).
Imho the only technical reason left speaking in pro of a SUT is safety.
It can´t pass Bias currents or even lethal currents in case of a defect of the prepre through the precious pickup system.
jauu
Calvin
I think I start to understand the mod´s doubts.
Are You really interested in a fruitful discussion or just up to causing traffic?
Sorry, but if You wanna discuss a theme that has been discussed many times before You still could concentrate on typical applications first.
Most SUTs and soildstate prepres feature gains around 10x, i.e. +20dB.
Stretching the limits will always sooner or later ´proof´ the inferiority or even non-useability of a device .... regardless if its a piece of iron or a piece of sand.
But it doesn´t proof the qualities when used sensitively.
There´s no doubt that a active prepre offers potentially higher flexibility with regard to gain and load impedance and is typically less costly.
More care is required to find the right specs for a SUT.
If chosen wisely there´s no reason why a SUT should not perform perfectly sufficient.
The main advantages of SUTs over solid state - noiseless gain and galvanic isolation/dc-blocking- have been eaten up over time or don´t apply in this application.
So basically I agree, that nowadays SUTs are devices chosen rather by emphatics than technical reasoning (I won´t discuss sonic reasons here).
Imho the only technical reason left speaking in pro of a SUT is safety.
It can´t pass Bias currents or even lethal currents in case of a defect of the prepre through the precious pickup system.
jauu
Calvin
I think you are the first to say that or say it recently. When looking at common base or whatever it is worth asking what is the minimum resistance we might try. If it's 10 ohms and sounds good to you, so be it. For example if wanting a gain of 60 one might say 27R was the value to go for if using an inverting stage. That gets a bit more complex because the inductance and resistance of the MC coil + arm is part of the gain. It isn't just the 27R itself we will hear. I suspect when a transformer we would always use a non inverting input, makes life easier. The reason to mention inverting is that a double inverting stage will have small advantages for low coil resistance MC's.
Doubtless many will not go the old fashioned way on this. To me it's worth keeping things simple so as to be able to guess the problems. That is if it sounds wrong despite one's best assumptions, why? The best MM phono stage I heard was just two transistor and a fancy power supply. The guy had spent years getting to know his design. It sounded nothing like the nice sound of a Lenco head amp. It sounded like the better valve designs, proof if ever required that transistors given a chance can do that.
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