Learning about SUT's

[AvFan]

Let me echo @mkane and add my appreciation for everyone's participation in this thread. SUTs have been this "black box" sort of device to me but I think I better understand what they do. @rothwellaudio, I finally got the math and now can determine the final cartridge loading and output knowing the SUT turn ratio and the cartridge's (source) impedance. So now that we know the output and load what do I do with that information?

I've often heard that a cartridge's target loading is 10 times its internal impedance. Thoughtful cartridge and SUT selection may yield near that loading but not always. So I'm on the learning curve again: When the loading doesn't match up the MM preamp's load (typically 47kohm) needs to be changed by adding resistors in parallel. After this discussion I think I could add resistors after the SUT to change the load. One caveat: You can only lower the load below the fixed load in the MM preamp. I've done this with load plugs between my Grado cartridge and 47k MM preamp to get to 10k but never with a SUT in the path. My simple equation looks like:

1/47k+ 1/added resistor = 1/target load
​

So what does this equation look like with a SUT in the path? Is there one more variable?

This may be a topic for another thread but...

....
Is the load impedance critical to getting a good sound? I think it's a lot less important than many people assume it is....

My experience is, yes, load impedance is very important but only below 10x cartridge internal impedance. Above that number has much less impact on the sound but if the cartridge is loaded too far below the 10x load the sound becomes dull and soundstage gets squeezed. So if I have to err it will be on the high side of the 10x number.

 

[wyn palmer]

Let me echo @mkane and add my appreciation for everyone's participation in this thread. SUTs have been this "black box" sort of device to me but I think I better understand what they do. @rothwellaudio, I finally got the math and now can determine the final cartridge loading and output knowing the SUT turn ratio and the cartridge's (source) impedance. So now that we know the output and load what do I do with that information?

I've often heard that a cartridge's target loading is 10 times its internal impedance. Thoughtful cartridge and SUT selection may yield near that loading but not always. So I'm on the learning curve again: When the loading doesn't match up the MM preamp's load (typically 47kohm) needs to be changed by adding resistors in parallel. After this discussion I think I could add resistors after the SUT to change the load. One caveat: You can only lower the load below the fixed load in the MM preamp. I've done this with load plugs between my Grado cartridge and 47k MM preamp to get to 10k but never with a SUT in the path. My simple equation looks like:

1/47k+ 1/added resistor = 1/target load
​

So what does this equation look like with a SUT in the path? Is there one more variable?

This may be a topic for another thread but...


My experience is, yes, load impedance is very important but only below 10x cartridge internal impedance. Above that number has much less impact on the sound but if the cartridge is loaded too far below the 10x load the sound becomes dull and soundstage gets squeezed. So if I have to err it will be on the high side of the 10x number.

I use a Miyajima Madake. I generally load it with 60 ohms approx., as do many other users. The internal resistance is c. 15 ohms. It absolutely does not sound dull nor is the soundstage in any way diminished. Rely on your ears to judge.
Having too large a load R can create problems due to the electrical resonance produced by the LRC of the cartridge and load. This can cause ultrasonic peaks of 30dB or so and can overload some RIAA stages.

 

[AvFan]

I use a Miyajima Madake. I generally load it with 60 ohms approx., as do many other users. The internal resistance is c. 15 ohms. It absolutely does not sound dull nor is the soundstage in any way diminished. Rely on your ears to judge.
Having too large a load R can create problems due to the electrical resonance produced by the LRC of the cartridge and load. This can cause ultrasonic peaks of 30dB or so and can overload some RIAA stages.

I certainly agree that folks should experiment with loading and find what sounds best to them but you need a point to pivot around. In addition to the 10x guideline I also do searches to see if owners are reporting success within a range of loads. It can be time consuming to find what sounds the best so I'll take any help I can get! Thanks for adding your thoughts on the Madake. If someone does a search on that cartridge they will likely find your post on your experience with it.

 

[wyn palmer]

I certainly agree that folks should experiment with loading and find what sounds best to them but you need a point to pivot around. In addition to the 10x guideline I also do searches to see if owners are reporting success within a range of loads. It can be time consuming to find what sounds the best so I'll take any help I can get! Thanks for adding your thoughts on the Madake. If someone does a search on that cartridge they will likely find your post on your experience with it.

I've posted many observations concerning the Madake and Miyajima cartridges in general. I've extensively modelled them and even retipped them with alternative cantilever materials. They are interesting- very 1970-ish in their frequency response.

 

[heavyrock]

Excellent thread. I'm going to get my thinking cap on in reference to what sort of SUT would work best with my Koetsu Black when I return to it and some other improvements I discovered I need to make in my setup with htis cart.

Reading through this thread begs me to ask a question concerning the Goldring Eroica H. Of course this cart is intended to work fine into a MM input. With this relatively low level 2.5mv sensitivity, would this cart benefit being used with any sort of SUT? One would have to crank the volume with this cart into a MM input versus a standard MM cartridge, depending on your phono stage.

 

[robnec]

Hello. I always read threads about SUT with some amusement. I have and used many of them in the past. Now I am using only head amplifiers. It makes loading issue very simple and sounds great. Most of the posters claim exellent sound when sut are used. I have never seen them showing anything to support flat response of cartridge, sut and mm phono pre together. Simple voltage measurments of output at 100, 1000 and 10kHz would prove it. Years back cartridge manufacturers were providing loading sugestions with added note "when used with head preamplifier". Ussually three times cartridge resistance. Robert.

 

[rothwellaudio]

I finally got the math and now can determine the final cartridge loading and output knowing the SUT turn ratio and the cartridge's (source) impedance. So now that we know the output and load what do I do with that information?

Good question. My advice is to aim for a signal voltage of about 5mV into the following phonostage and not worry about the load impedance.

I've often heard that a cartridge's target loading is 10 times its internal impedance.

Yes, that's about right, but really it's general advice relating to the source/load impedance of audio equipment in general, not specifically lomc cartridges. We're aiming to transfer voltage from the source to the following piece of equipment, and the bigger the ratio of the load-to-source impedance is, the greater the voltage transfer. The absolute maximum voltage transfer would occur if the load impedance was infinitely high and the source impedance was zero. Anything less than that results in some of the voltage being dropped across the source's own internal impedance instead of being transferred to the next bit of equipment. Do we need to go to the extreme of infinitely high load impedance and zero source impedance? No, not at all. If we say that dropping a bit of voltage is ok as long as it is less than 1dB we arrive at the rule of "load impedance should be ten times greater than source impedance". These are nice, convenient numbers that make sense, that's all. "Load ten times source means less than 1dB lost." It's a sensible guideline, not a hard-and-fast rule.
There is a caveat to the above - it all makes perfect sense as long as the source and load impedances are pure resistances. When you introduce capacitance and inductance - ie enter the real world - there are complications with regards to frequency response.

When the loading doesn't match up, the MM preamp's load (typically 47kohm) needs to be changed by adding resistors in parallel. After this discussion I think I could add resistors after the SUT to change the load.

This is the conclusion that many people jump to, but why? Why do you want to alter the load seen by the cartridge? If you want to alter it, why alter the reflected load via the transformer instead of altering the direct load on the primary side of the transformer? What's happening to the frequency response? Does the SUT have the same frequency response with a lower impedance on its secondary side?
These questions are usually not addressed at all - they're simply overlooked in the rush to achieve "the optimum load".
My advice is to do one of the following:
1) forget about adding resistors to get an optimum load impedance
2) add resistors chosen because they sound right to you rather than chosen by an arbitrary formula which promises perfection
3) add resistors and/or a Zobel network based on measurements taken with your particular transformer and cartridge source impedance.

Option 3) is best, but requires some knowledge and test gear.

Reading through this thread begs me to ask a question concerning the Goldring Eroica H. Of course this cart is intended to work fine into a MM input. With this relatively low level 2.5mv sensitivity, would this cart benefit being used with any sort of SUT? One would have to crank the volume with this cart into a MM input versus a standard MM cartridge, depending on your phono stage.

The Goldring's output is 2.5mV, which is not far off a typical mm cartridge. I usually aim for about 5mV into an mm phonostage but some mm phonostages are more sensitive than others and are quite happy with 2.5mV at their inputs, some are less sensitive and would benefit from more than 2.5mV.
If you think the cartridge could do with a bit of lift you have two options:

1) Use a step-up transformer, but it has to be one designed for the job. A low turns ratio is required (about 1:3) and it has to cope with higher source impedance of a HOMC compared to a LOMC. I know of only one on the market I make it
http://www.rothwellaudioproducts.co.uk/html/sut_for_homc.html

2) Use a headamp. Again it has to have low gain (about 10dB) and be designed to handle HOMCs rather than LOMCs. I know of only one suitable headamp on the market and I make it
http://www.rothwellaudioproducts.co.uk/html/headspace_mc_headamp.html

Hello. I always read threads about SUT with some amusement. I have and used many of them in the past. Now I am using only head amplifiers. It makes loading issue very simple and sounds great. Most of the posters claim exellent sound when sut are used. I have never seen them showing anything to support flat response of cartridge, sut and mm phono pre together. Simple voltage measurments of output at 100, 1000 and 10kHz would prove it. Years back cartridge manufacturers were providing loading sugestions with added note "when used with head preamplifier". Ussually three times cartridge resistance. Robert.

Glad to provide you with some amusement
With a headamp you can alter the load impedance without altering the gain, and vice versa. With a SUT the load impedance and voltage gain are interdependent which clearly complicates things.
Yes, a flat frequency response is the aim, but I think you're right - aiming for a particular load impedance does not guarantee you're going to get it.

 

[AvFan]

@rothwellaudio, thank you again for your insights and participation in this thread. Are you saying it is best to just change the 47k resistor in the MM preamp versus adding resistors elsewhere in the chain? That is the way my Parks Audio Budgie works to set cartridge loading. I currently use a 1:20/1:40 Budgie SUT that uses Cinemag 1254 transformers.

My use of the word "target" when describing the cartridge load that is 10x the cart's internal impedance may have caused some confusion. I use that number as a starting point to then determine, up or down from that number, what sounds good to me in my system. 5mv is a good output value and as I was doing the calculations for various SUT turn ratios with my MC carts it became obvious which ones would achieve at or near that output level.

Of the options you listed #2 is my likely path. #1 doesn't seem to optimize a cartridge's performance or requires that the SUT and cartridge to be selected with each in mind. I already have several MC carts I'd like to figure out how to make them sound the best to me in my system when using a SUT. Honestly #3, is beyond my skill level.

 

[robnec]

Hello. I had an hour of free time so decided to play with sut. I had on hand Otari 17 to1,7kOhm input transformer. I added some parts and in no time I had it connected to MM phono pre. Cartridge used was AT F5 impedance 12 ohm. It sounded exellent. It was a little lower in loudness than Mm cartridge but nothing to talk about. I plugged it into reel to reel recorder and played 1khz signal from test record. Level was set to 5db. As seen it is almost flat besides roll off below 500hz /I think value of resistor or cap has drifted/. It was really very simple and fast and should be always done to set some kind of reference. Later we can play with it as our hearts desire. I do it as well. Robert.

 

[rothwellaudio]

Are you saying it is best to just change the 47k resistor in the MM preamp versus adding resistors elsewhere in the chain? That is the way my Parks Audio Budgie works to set cartridge loading.

It doesn't matter if you change the 47k resistor in the preamp or add loading resistors - it amounts to the same thing. Yes, the Parks Audio Budgie adds loading resistors and you will see the technique advocated all over the internet, but it isn't a technique that impresses me much. People do it because other people do it. Doesn't mean it's the right thing to do. It can have benefits, but not always.

Of the options you listed #2 is my likely path. #1 doesn't seem to optimize a cartridge's performance or requires that the SUT and cartridge to be selected with each in mind.

Option #2 is what many people do, but it isn't really based on anything sensible. I ask again, why not put loading resistors on the primary side of the transformer to load the cartridge directly? Why does the load have to be on the secondary side of the transformer?

I already have several MC carts I'd like to figure out how to make them sound the best to me in my system when using a SUT.

If you add a resistive load to the secondary of a transformer you might get lucky and improve the sound - or you might not. There's no reliable theory or formula to predict it unless you know all the parameters of the transformer such as leakage inductance and interwinding capacitance. Measurement is the only reliable way to proceed.
As Wyn Palmer has pointed out in another thread http://audiokarma.org/forums/index.php?threads/lomc-treble-peak-capacitor-cure.838117/ if the cartridge has a treble peak which needs to be tamed you can add a capacitive load, either on the primary side of the SUT (working the cartridge directly) or a much smaller capacitive load on the secondary side of the SUT (working on the cartridge via the transformer). However, without any measurements you would be relying on your ears to guide you - not that there's anything wrong with that. Anyway, the point is that if you want to alter the tonal balance it's more effective to work with some capacitance (or inductance) rather than just resistors.

 

[SB12345]

Hello. I always read threads about SUT with some amusement. I have and used many of them in the past. Now I am using only head amplifiers. It makes loading issue very simple and sounds great. Most of the posters claim exellent sound when sut are used. I have never seen them showing anything to support flat response of cartridge, sut and mm phono pre together. Simple voltage measurments of output at 100, 1000 and 10kHz would prove it. Years back cartridge manufacturers were providing loading sugestions with added note "when used with head preamplifier". Ussually three times cartridge resistance. Robert.

Nothing wrong with using a head amp and figuring out your own preferred settings if that's how you wish to tailor the sound. Personally, I prefer the sound of SUT's that have already been calibrated for use with my favorite cartridges. Keith Aschenbrenner (sp?) designed and manufactures his Auditorium23 SUT for my DL-103 type cartridges, while Bob Sattin (Bob's Devices) does the same with his Sky 40 for my SPU pickup heads.

"Horses for courses"

 

[AvFan]

@rothwellaudio: Thank you for the link to the discussion about adding capacitance on either side of the SUT to tame a LOMC high frequency bump. I was unaware there was an easy to implement alternative to adding resistors on the secondary side of the SUT. As I noted above I can calculate the output and load from a LOMC cartridge and various SUT ratios. Cartridge manufacturers often recommend a range of resistance load or absent a recommendation10x the internal impedance can be used as a starting point. Assuming the post SUT cartridge output is in the vicinity of 5mv does it matter that the load is different than either the load recommendation from the manufacturer or the 10x guideline? If so, how much of a difference gives you concern? Thanks.

 

[rothwellaudio]

Assuming the post SUT cartridge output is in the vicinity of 5mv does it matter that the load is different than either the load recommendation from the manufacturer or the 10x guideline? If so, how much of a difference gives you concern? Thanks.

I don't think it matters much. Many manufacturers don't specify a recommended load anyway, just a minimum load. I'd say 10 times the cartridge impedance is a good guideline. When you get as low as 3 times the cartridge impedance you will definitely notice a difference - certainly in output level if not in anything else. I wouldn't want to go less than 3 times the cartridge impedance.
The headamp I make lets you try a range of load impedances from 55 ohms to 1500 ohms without affecting the gain.
http://www.rothwellaudioproducts.co.uk/html/headspace_mc_headamp.html
Personally, I don't notice a huge difference in sound at the different load settings other than a slight drop in volume at the lowest settings but customers have reported a significant difference. I wonder if they're mistaking "a bit louder" for "more dynamic" Either that or I'm just deaf

 

[robnec]

Nothing wrong with using a head amp and figuring out your own preferred settings if that's how you wish to tailor the sound. Personally, I prefer the sound of SUT's that have already been calibrated for use with my favorite cartridges. Keith Aschenbrenner (sp?) designed and manufactures his Auditorium23 SUT for my DL-103 type cartridges, while Bob Sattin (Bob's Devices) does the same with his Sky 40 for my SPU pickup heads.

Hello. I am in no position to tell anybody how to achieve music nirvana. My intention was to introduce some sanity into subject of SUT. Yours transformers were designed for cartridges in use by someone with knowledge and tools to do it. Transformers are a complecated beasts. Our frequent adisor here, Rothwellaudio, is trying to make us realize it. I am grateful for his work. Most of the time we concentrate on gain and forget about our goal of flat response of cartridge. Sounding good is not enough as our hearing is misleading. I had a proof of that fact last night. Test record and any recorder or voltage meter is all that is needed. When we are sure that we hear what we should be hearing then our fun starts. Robert.

 

[AvFan]

I don't think it matters much. Many manufacturers don't specify a recommended load anyway, just a minimum load. I'd say 10 times the cartridge impedance is a good guideline. When you get as low as 3 times the cartridge impedance you will definitely notice a difference - certainly in output level if not in anything else. I wouldn't want to go less than 3 times the cartridge impedance.
The headamp I make lets you try a range of load impedances from 55 ohms to 1500 ohms without affecting the gain.
http://www.rothwellaudioproducts.co.uk/html/headspace_mc_headamp.html
Personally, I don't notice a huge difference in sound at the different load settings other than a slight drop in volume at the lowest settings but customers have reported a significant difference. I wonder if they're mistaking "a bit louder" for "more dynamic" Either that or I'm just deaf

Thank you for the guidance. Am I correct to infer that if the load is above the 10x guideline or the manufacturer's recommendation that it is not a big concern? My limited experience is that higher loads have minimal impact. For example I used my Denon DL-103 at 10kohms then 430ohms (via plugs) into a standalone MC preamp and didn't hear all that much difference.

Hello. I am in no position to tell anybody how to achieve music nirvana. My intention was to introduce some sanity into subject of SUT. Yours transformers were designed for cartridges in use by someone with knowledge and tools to do it. Transformers are a complecated beasts. Our frequent adisor here, Rothwellaudio, is trying to make us realize it. I am grateful for his work. Most of the time we concentrate on gain and forget about our goal of flat response of cartridge. Sounding good is not enough as our hearing is misleading. I had a proof of that fact last night. Test record and any recorder or voltage meter is all that is needed. When we are sure that we hear what we should be hearing then our fun starts. Robert.

Yes, @rothwellaudio and @wyn palmer in the thread started by @bimasta (and his Hi-Fi News find) linked in post #50 have provided valuable information on how to SUT's can fit into our TT setups. That I can adjust the sound by using some capacitors in a RCA Y connector following the SUT is simple, inexpensive and we've learned is a better way of tailoring the sound to our individual preferences. This AK at its best!

 

[Nashou66]

Now I can't decide if I should get a headspace amp or the MCL. I do have a few MC carts three are HOMC and the lone Entre' EC-20 is the LOMC.

So It might be best to get the headspace, am I correct to assume this?

Athanasios

 

[chink8ball]

I started using SUTs as my tube phono pre, ARC PH 3SE (54db gain) did not have enough gain for a LOMC straight in and was marginal at best with carts having .4mV. I had a LOMC, .27mV output, impedance of 6 ohms and asked Bob Sattin of Bob's devices for a recommendation after giving him details on the rest of my system. I ended up with a Bob's SUT Cinemag 3440AH trannies, user switchable between 16:1 and 30:1. I actually ripped 1500 lps to digital format using this setup which included a SOTA Star and SME V. The sonic reproduction of this setup was excellent for frequency response, soundstaging and dynamics. State of the art? No but good enough for my system. I play these rips a lot and knowing what I know today about SUTs, phono pre's, gain and loading, I thank the stars that Bob picked that SUT for my setup.



The cantilever eventually failed in the cart and it was replaced with a NOS Benz Glider L2, .4mV and impedance of 12 ohms and a Shelter 501Mk II, same output and impedance. With either cart, too much gain with the ARC phono pre and Bob's SUT, even at the 16:1 setting. I ended up reducing the ARC gain by 7db via a voltage divider using factory provided instructions, a simple mod and one which by adding switches I could switch the phono pre gain between stock, 54db and reduced, 47db. This got me thinking about the relationship between SUT turns, LOMC output and phone pre gain.



I then purchased a Cary Audio PH301MM, a classic 2x12ax7 and 1x12au7 tube circuit with an outboard SS regulated power supply and 42db gain. I have two separate TT setups and hooked the Shelter cart>Bob's SUT>Cary phone pre and this was the first time I was really happy with the sound of the Shelter. Interestingly, it sounded better using the 30:1 vs 16:1 setting. The former showing the cart a load of 50 ohm vs 180 ohm for the latter. No long discussion on the merits of loading but I do believe in trying different load settings.

Simultaneously I purchased a couple Jensen JT44dx transformers and made a DIY 10:1 SUT. I then set the ARC phono pre back to stock gain, 54db and used the 10:1 SUT with the Benz Glider. Excellent sound. Using the Glider, I compared the DIY SUT>ARC to the Bob's SUT>Cary Audio and the former setup was just slightly better for my ears and system. Also, I preferred the Glider to the Shelter in my system so I ended up selling the Shelter. BTW is set up the DIY 10:1 SUT so that the load was about 115ohm.



Next step was buying a Benz Ebony L, a bit of an odd ball in the Benz line up with .27mV output and 3.5ohm impedance. This cart predates their current LPS and predates their Ruby generator. I used this with the 10:1 DIY SUT and ARC phono pre at 54db gain but after a few months decided that the stylus needed replacement. Off it went to Soundsmith for a line contact retip, retaining the OEM boron cantilever. I also purchased a couple of Jensen JT 347dx transformers and built another SUT. These transformers can be wired for 8:1, 12:1 and 24:1, single ended or balanced, and are much more substantial than the JT44's.



The Ebony L came back and I wired the JT347 for 8:1 into the ARC phono pre, it was good but not great. I called Jensen and they suggested 12:1 and then asked what dampening/loading was I using and I told him the one in their schematics. He explained that those schematics were for testing and then sent me values for capacitor/resistor networks (Zobel) based on balanced or single ended, each of the 3 gain settings with a table of cartridge impedances. Bingo! The system sounded great.



I moved the first DIY SUT over to the Cary phono pre using it with the Benz Glider and sold the Bob's SUT. I was pretty happy with either TT setup and loved to spin records alternating between the two phono setups.



This summer I was able to acquire a Zesto Andros 1.2 for cheap and it can take two phonos, one on the MC input and the other on the MM input. One switch for each channel to switch between the two inputs. This allowed me replace the ARC PH3SE and the Cary Audio PH301mm with one box. The Andros is super quiet and the level of distortion compared to previous setups is very low.



The Andros uses Jensen 44s on the MC inputs with two gain options and numerous loading choices and claims 47db on the MM inputs. I run the Benz SL setup into the MC inputs and have the load at 100ohms. I run the JT347 SUT, now at 24:1, into the MM inputs. I've used the Jensen recommended values resulting in a loading of about 9ohms and 3x the cartridge impedance. Interestingly the designer George Counnas uses the JT347s in the Tessera, Andros Deluxe and Allasso and he's been very kind in sharing his knowledge and setup. He finds the biggest difference between the Jensen 44 and 347 is the imaging. Obviously the 347 has greater flexibiliy and frequency extension. I'm done for now although I have enough parts to make another SUT, just need to pick the trannies. That will not happen unless I find a super deal on another LOMC.

FWIW I use Takman 1/2 watt carbon film resistors and Vishay film capacitors for the Zobel networks.

Note that this journey took place over 5+ years. My takeaways were as follows: 1) Learn about the relationship between cart output, SUT turns ratio, phono pre sensitivity and then system sensitivity. 2) Understand the relationship between the cartridge impedance and inherent load of the SUT (all assuming 47k phono load) and if you do load by adding resistance on the secondary side of the SUT, how many times the cart impedance is the correct range of possibilities? 3) I had great experiences talking with Bob Sattin, the people at Jensen transfomer, George Counnas at Zesto and reading on this forum what the gentleman from Rothwell has to say.

KAB calculator for gain

https://www.kabusa.com/pregain.htm

Alternative method for calculating gain

http://forums.stevehoffman.tv/threads/rethinking-phono-preamp-gain-settings.682880/

Hagerman calculator for loading

http://www.hagtech.com/loading.html

 

[rothwellaudio]

Am I correct to infer that if the load is above the 10x guideline or the manufacturer's recommendation that it is not a big concern? My limited experience is that higher loads have minimal impact. For example I used my Denon DL-103 at 10kohms then 430ohms (via plugs) into a standalone MC preamp and didn't hear all that much difference.

I agree that when the load impedance gets to a certain point (roughly 10x cart impedance?) going any higher makes very little difference.

Now I can't decide if I should get a headspace amp or the MCL. I do have a few MC carts three are HOMC and the lone Entre' EC-20 is the LOMC.
So It might be best to get the headspace, am I correct to assume this?

The Headspace certainly has more flexibility than a SUT and gain and load can be altered independently of each other. I would use the Headspace if I wanted something that would handle a range of very different cartridges.

I started using SUTs as my tube phono pre, ARC PH 3SE (54db gain) did not have enough gain for a LOMC straight in...

Yes, some of the Audio Research phonostages are a bit of an oddball with 54dB gain - it's too much gain for an MM cartridge and not enough for a LOMC cartridge. It's more normal to have round about 40dB for an MM phonostage and 60dB for an MC phonostage. If the MM phonostage you intend to use has higher or lower sensitivity than normal it makes sense to take that into consideration when choosing a SUT.

 

[Nashou66]

I agree that when the load impedance gets to a certain point (roughly 10x cart impedance?) going any higher makes very little difference.

The Headspace certainly has more flexibility than a SUT and gain and load can be altered independently of each other. I would use the Headspace if I wanted something that would handle a range of very different cartridges.

Yes, some of the Audio Research phonostages are a bit of an oddball with 54dB gain - it's too much gain for an MM cartridge and not enough for a LOMC cartridge. It's more normal to have round about 40dB for an MM phonostage and 60dB for an MC phonostage. If the MM phonostage you intend to use has higher or lower sensitivity than normal it makes sense to take that into consideration when choosing a SUT.

Now which will have a lower noise floor? I assume the SUT, but would this be substantially noticeable at normal listening levels?

Nashou

 

[wyn palmer]

Now which will have a lower noise floor? I assume the SUT, but would this be substantially noticeable at normal listening levels?

Nashou

I like to design my phono stages to provide a 1vrms output- so for a 0.25mv @1kHz, 5cm/sec standard input I need a gain of 72dB. The unweighted thermal noise limit of MC cartridges over the audio band is c.70-75dB depending on various factors so for a 1v RMS output with a perfect amplification system you could get c.1/4000 vrms of noise or about 250uv at the output. A MC preamp that I recently built/simulated with 72dB of gain had an RMS noise output of 500uv with a 16 ohm DC resistance cartridge- or a S/N ratio of 66dB. A similar MM preamp with a 20:1 transformer added before, 46dB of gain and using the same cartridge had an output noise of 520uv- basically the same.
In practice the SUT based channel had a tad more hum, but at normal listening volumes the background noise- including the hum- was inaudible for both implementations and better than my MX50 tape deck using 1/4" 15IPS 250nW/m tape.