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Thread: Active MC Phonostage, or MM+Steup?

  1. #21
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    Thanks Andrew, how do i know what the resistance i need is, eg if the output of the trannie is 20ohms, how do i make it say 30ohm. what value resistors would i need.

    RE AN, yes the Io is 1ohm, but it's also about 1/3rd the output of my cart, the AN-S2 i'm using at the moment is for an io, and it's too loud, i'll need to check what my pre's gain is, and work from that, with the Rhea i used 56-62db into the line stage.

    RE PQ, quite but then again I'm sure i can get a little discount, being a dealer and all, (tough life innit)

  2. #22
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    mmm, stuck the rhea back on. some things it does better than the trannie/mm, need to more experiments, with the trannie it has more slam, and more bass, but the soundstage isn't as deep, and the midrange is a little bit less prminent, the top end also sounds more spalshy, but that could be because i have too much gain, will need to do some more experimenting, got a new cart to try as well, so may revert back to the stage i know for the time being, mmmmmm

  3. #23
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    Prof,

    Too much to drink this evening to do any maths and what you really need to know is not the impedance number on the transformer, but the turns ratio or the impedance ratio. Can you get that from PQ? You can't make that 20ohm any larger, only smaller, so start with the 80 ohm tap. Here is a much better explanation than I could ever hope to write courtesy of Dave Slagle. WARNING, it's long and possibly boring.

    There seems to be a lot of confusion on how to select a transformer for a particular MC cartridge. Many people consider this black art and I have to admit I have been shocked by the sonic differences from devices with similar electrical characteristics. I'll try to be brief and cover some of the relationships in a few short paragraphs.

    It's about the turns ratio.

    The first thing you need to know about the SUT in question is the turns ratio. This is an easy number to find out and is the most important. The idea here is the turns ratio tells you the gain but it also plays a major part in the load the cartridge sees. The rule is impedance is the square of the turns ratio. If you have a 1:10 turns ratio, you get a 1:100 impedance ratio. If you assume that the 1:10 will feed a phono stage with a 47K input resistor the 47K will reflect back 47K divided by the impedance ratio (100) or 470 ohms. It is really that simple. Many transformers (particularly the vintage ones) are speced with impedance numbers like 150:50K which simply translates to a 1:18 step up ratio. (sqrt(50000/150)). The impedance numbers are somewhat important since they suggest the ballpark of where the unit was designed to operate, but it is easy enough to toss that info out the door and measure things for yourself. One other important thing to realize about the turns ratio is that "More" isn't always better. It is surprisingly easy to have too much of a step up resulting in a situation where you overdrive (clip) your phono stage.

    Relating the turns ratio to load.

    Sticking with the above example of a 1:10 driving the 47K input, our cartridge in a perfect world sees a load of 470 ohms. Now what if we have a 103R with a 15 ohm internal impedance and we want to play with larger loads. (A larger load is one that is smaller in value) The traditional way to do this is to add additional resistance in parallel with the 47K to get the desired value. Again this is a simple application of the turns ratio. If we desire a 150 ohm load we would need to parallel a 22K resistor with the existing 47K, which nets us 15K across the secondary. (47000||22000=15000) Dividing the 15K by our impedance ratio of 100 nets us our desired 150 ohm load.

    Houston, We have a problem

    Everything here is nice and clean upon firs glace, but we have actually hit our first speed bump. When we terminate the transformer with a different value, we not only change the load seen by the cartridge we change the behavior of the transformer itself! This means we are changing two parameters which creates a very unpredictable situation which goes a long way to explain why results of playing with secondary loading on SUT's has lead to such varied results since you cannot be sure what you are fixing.

    Why the need for a load anyways.

    The simple answer is all cartridges have a peak (resonance) at some high frequency and by increasing the load the peak is damped smoothing out the measured response. The general effect is when the load it too low (say unloaded) the cartridge sounds bright and when you take it to the other extreme and increase the load the highs start to sound rolled of. At some point in the middle the "sweet spot" is found and the only way I know how to this is in system by ear. The 800 pound gorilla sitting in the corner is the fact that the SUT will show the exact same behavior as the cartridge and loading will have a similar effect. Typically the resonance in the SUT will be an octave to a decade higher than that of the cartridge. Unfortunately there is no way to know if your choice of secondary load has damped the resonance of the cartridge taming the highs or simply rolled of the SUT masking the brightness of the cartridge resonance.

    Gorilla Wrangling

    How do we tame that gorilla in the corner? Menno van der Veen presented the best approach I have seen in his white paper on his SUT’s. Essentially his approach is to determine the load needed to make the transformer behave as desired and then add any additional load required by the cartridge to the primary of the transformer. He even goes as far as to measure his SUT’s under a number of conditions and provides the needed loading info for various impedance cartridges. This is the little brother of the 800 pound gorilla, lets call him the 400 pound gorilla on the couch. Just as increasing the load on the secondary damps transformer resonances (ringing) decreasing the source (cartridge) impedance tends to increase ringing. This makes the once simple loading of a transformer become a far more complex relationship. A few other gorillas strolling about the room involve the belief by some that the loading of transformers can cause more sonic harm than the problem it fixes and the idea that loading a transformer secondary causes phase shift at high frequencies.

    Jane Goodall to the rescue.

    Rather than ignore all of these primates strolling around our listening rooms the best approach is to attempt to understand them and learn how to live with them. The best way I know how to do this is to converse about experiences and understand that ultimately it comes down to first understanding ones musical preferences so their experiences can be related to the info available to us.

    A final anecdote.

    For some time now I have been a fan of primary loading of the SUT. Over the past few years I have encourages a number of people to play with primary vs. secondary loading and the results have been mixed. The one interesting thing was that consistently the people who preferred secondary loading said primary loading was “harsh” sounding and the people who preferred primary loading stated it brought more of the music out of their system. In looking at the measured response of the transformers in question with the known source and load impedances it quickly became apparent that the people needing the secondary loads were not only damping the ringing in their cartridges, but also taming a peak in response in the transformer. By loading the primary they actually made the transformer ringing worse, which is a very plausible explanation of what they heard. When looking at the measured response of the transformers used by those who preferred primary loading, the resonant peak was reasonably controlled and substantially beyond the audio band.
    _____________________
    There are a few online calculators for figuring out the resistors to use, but you will need either turns or impedance ratio. Here's 2

    http://www.intactaudio.com/forum/viewtopic.php?t=1073
    http://www.edsstuff.org/tools.htm#StepUpLoading2

    Andrew

  4. #24
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    Thanks Andrew, i don;t really understand it all at this time of night, but i'll do some digging, appreciate your help.

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    Prof,

    Well I'm sober, but not an expert, so the following may wrong. I'll lay out my assumptions so that smarter folk can laugh/correct me.

    Assumptions
    preamp is 47K ohm phono
    transformer reflected impedance is 20 ohm and 80 ohm

    Using the example given above where 47k Ohm phono input with 1:100 impedance ratio transformer gives a reflected impedance of 470 ohm, then I calculated
    47000 ohm/20 ohm = 2350 impedance ratio or the sqrt is 1:48.5 turns ratio
    47000 ohm/80 ohm = 587.5 impedance ratio or sqrt is 1:24.2 turns ratio

    using this loading calculator http://www.edsstuff.org/tools.htm#StepUpLoading2

    I got 28.1Kohm loading resistance on the 80 ohm tap to give 30 ohm reflected impedance. One of the US Audio Note techs told me many years ago that a place to start your loading experiments was ~ 10X the cartridge impedance. So for the Orpheus at 3 ohm, 30 ohm would be the place to start. As the reflected impedance number increases (meaning less loading) then you should get more highs since the mc cartridge resonance is less damped. Some folks like to run mc cartridges at 47K. Do you have enough gain in your Rhea and your other preamp to try that?

    Happy hunting,
    Andrew

  6. #26
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    Wow thanks again Andrew, btw mine is an Orpheus L and is 1 ohm not 3

    I have an audiophile products mct-1 which became the Kiseki MCT-1, it's 3-5 ohm silver wired, not sure on it's gain, but my mm stage has 41dB so I need a tranny around 20dB. Will be trying it shortly over the weekend, perhaps if it's still not right I will get me solder iron out.

    My thoughts are if I decide to go this route, then I fancy an audio note S5 or S8 normally these are 1 ohm and 33 db or 64 ohm and 22db, I'm thinking on perhaps getting one with 1 ohm, or maybe 10 as your suggestion, but with low twenties gain.

    Perhaps I should just get a Nagra VPS and be done with it

  7. #27
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    I can run the rhea with enough gain at 47k, but, and here's the rub, the reason I like the Orpheus is because it doesn't have the top end lift, I prefer the highs to be natural, most mcs to me are too bright, the rhea only goes as low as 75 ohm, and the other pre only has 41db gain, so a bit too low. I need between 55-65 db to get the volume I like. Currently have a brand new Allnic Puritas in, but it's still a tad bright even with the Kiseki, of course it's still to run in, I'll be swapping the Orpheus back in shortly and will report back.

    Re ideal loadings, I've heard anything from 10-25 times the cart imp, but Peter reckons 3-4 times your cart, so the Kiseki is in that range, but I still think the gain is a little too much, one thing though, PQ suggests 3-4 times internal imp, yet he recommends 1 ohm for his carts, transfig only suggest >3ohms

    Bit of a headscratcher this innit, as I said perhaps I need to stick to what I'm used to , after saying ghat though, I'm loving the bass from the stepups, but the soundstage seems a but lacking in depth compared to the rhea, mmmmm decisions, decisions.

  8. #28
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    update: So far i'm liking what this Kiseki is doing, all silver wired with silver wired trannies, so perhaps 3-5 ohms is my target, less gain perhaps, but i don't know what the gain is on this, it doesn't have the bass weight or slam of the AN, so i might talk to Peter about that, getting something similar, in s5 or s8 form (depending on price, would rather have the 8 as it has no adjustability, and should sound better than the s5 as a result.)

    http://www.audionote.co.uk/products/...an-s8_01.shtml

    will see if one of these with 3-5 ohms and 20db, should be about perfect, whats your thoughts Andrew?
    Last edited by The Professor; 19th November 2010 at 13:48. Reason: spelling

  9. #29
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    Why not just stick with the Rhea and enjoy the music? I've heard it a few times and it's a great phono stage with imo unbeaten versatility. You once told me that suts were not a universal panacea etc so what's changed?
    Si.

  10. #30
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    Yes Si you have a point, what's changed, well my preamplifier has a great mm stage that I'd like to use, and my new record deck is allowing me to hear even more. Yes I said they weren't a universal panacea, I'll still stand by that statement, they aren't for everyone, and they aren't always better, but with my new pre and with that cart/arm/deck combo it's sounding better, or should I say I think I prefer it.

    I haven't fully decided yet, I may still go the phonostage route, but I want to get away from a hot ten tube phono, also the rhea has 3 inputs that I'm unlikely to use, so the rhea would be ideal for someone with more than 1 deck/arm.

    I'm playing just now, I can see me living with these amps and deck for a long time, and the phonostage is the final link in the chain.

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    Fair comment Paul. Your new pre must be something special if its MM stage plus txs are good enough to give the Rhea the elbow. I'm a transformer fan as you know ( I like the quietness of txs ) but if I had the money and I could justify it, your Rhea would be sitting next to my pre amp I do think it's that good.
    Si.

  12. #32
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    Yes Si the rhea is a bit special, I'll live with the tranny for a wee while then stick the rhea back in, the tranny may not be better, just different, only time will tell, I also have my eye on another phonostage so I'm not done yet, bug I'm close.

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    Quote Originally Posted by The Professor View Post
    I'm playing just now, I can see me living with these amps and deck for a long time.
    Seem to have heard thay someplace before,,,Paul.
    Coincidences - Gods way of reminding you that he's here.

  14. #34
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    Decisions Decisions.

    Ok for some
    Do to others as you would have them do to you. (Luke 6:31)

    From that time on Jesus began to preach, “Repent, for the kingdom of heaven has come near.” (Matthew 4:17)

  15. #35
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    Quote Originally Posted by The Professor View Post
    will see if one of these with 3-5 ohms and 20db, should be about perfect, whats your thoughts Andrew?
    I still reckon you should play with loading resistors to get the best compromise before ordering your unit if you are getting a fixed value. Will you order a transformer with fixed interconnects just to get rid of a few solder junctions?

  16. #36
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    You are right Andrew, but I think it may be beyond my patience levels, tried my Rhea again and another Active phono stage, and I think I prefer the Rhea, got another phono to try, if that is better than the Rhea I'll have it, or I'll maybe do a bit of saving a get the rhea reference.

    Thanks for the help and advice though, it is appreciated and the info is useful for others looking to try the same thing.

  17. #37

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    If you can open up the phono stage and replace the 47K with a big resistor (say1 Meg, just to ensure the grid of the valve is properly tied to ground), then next place the cartridge's load resistor (at the exact value you require, eg 100R) on the primary of the step up, rather than, as usual, on the secondary, you will hear a very different sound, it will have much more pace and timing without sacrificing detail.

    Andrew

  18. #38
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    Quote Originally Posted by Andrew View Post
    If you can open up the phono stage and replace the 47K with a big resistor (say1 Meg, just to ensure the grid of the valve is properly tied to ground), then next place the cartridge's load resistor (at the exact value you require, eg 100R) on the primary of the step up, rather than, as usual, on the secondary, you will hear a very different sound, it will have much more pace and timing without sacrificing detail.

    Andrew
    That's way beyond my limited skil Andrew I could probably kill myself doing that

  19. #39
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    OK update chaps, first of all many thanks for your help guys, especially AKY and Andrew, after trying a few things, and got a friend to confirm, I liked the way the step up did some things, but in my system it was a little 'toppy' even at 3-5 ohms, my reasoning for not going any further with impedance changes i figured that if it was still too bright at the top with 3 ohms then brighter still at 20 ohms, and even brighter at 80 ohms i figured that it was probably just too raw for me, i put my Rhea back on and although perhaps not as direct sounding overall i preffered it's presentation, who knows perhaps in the future i'll experiment again.

    I'm still selling my Rhea, I want to try something else, and at high gain, I use 62-65dB, and also when playing at silly volumes a little tube rush can creep in, I have decided on what i want to replace it with, just need to sell the rhea first to fund it, so watch this space.

    In the meantime i'm gonna make this a sticky thread as there is a huge amount of info in it for others, thanks to the guys mentioned, so watch this space ffor changes if you're interested, if i don;t get on with the new phonostage i'll egt a Rhea signature or look more into step ups. Thanks for looking in

  20. #40
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    Is it a Sunilda?????? C'mon spill........
    You can only be young once, but you can be immature for ever.....

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