I have used Urushi for almost 20 years and had used it with a pair of KPA as phono pre-amp. Now I have Ensemble Ponobrio and set loading at 132 ohmn. Over the years I set at around 100 ohmn. I have friend whose loading set at 47K. Since you don't get the air and space with it, it sounds more like your loading isn't correct. It will improves when the transformer fully break in. |
I don't like SUT with fine MC cartridges because they defeat the great transient response for which MC cartridges are known. The reason they even exist is that back in the day, most if not all MC cartridges were really low output (around 0.25mV) and hi-gain lo-noise phono preamps not available yet. (BTW, the Urushi has a fairly healthy output for a MC cartridge at 0.6mV)
I would suggest that if your CJ is almost enough to amplify the Urushi all by itself, then before you do anything else, get it loaded properly for the Urushi. The Urushi has an output impedance of 5 ohms. So using the 'ballpark' 25x rule, the correct loading for it should be 125ohms (probably a bit lower as Sam indicated) but not 47K! Correct loading will not only increase the perceived volume, but you will get detail and bass you haven't heard yet. If the 40dB gain of the built-in CJ phonostage really isn't enough, then I would recommend one of the many fine headamps (Creek makes a nice one) which these days are a better alternative to a SUT IMO. |
I agree with Nsgarch, but meantime you do have those Lundahls and maybe fooling around with the load resistors will help make them sound better. You say you "tried some different" values, but you don't say what values exactly. As others have said, the Urushi likes to see ~100 ohms load optimally but will probably work as well into slightly higher load Rs. Do you know the turns ratio of your Lundahl trafos? A trafo reflects an impedance that is related to the square of its turns ratio. If the turns ratio is 10:1, the square of that is 100 and therefore you want to place a 10K ohm resistor (100 X 100R, the preferred load for the Urushi) on the secondary side of the trafo that is driven by the Urushi on its primary. You don't say what values you've tried or whether you had professional help in selecting the values, but maybe this bit of info will help. If the CJ has fixed 47k ohm Rs in its phono input, you will need to calculate the value of R that will give you a net of 10K ohms, when placed in parallel with 47K ohms. Then solder those resistors in parallel with the 47K ones and you are done (or just remove the 47K resistors and substitute 10K ones). In addition to this simplistic approach, performance of the trafo can also be improved by a Zobel network, the design of which is much more complex. See the Jensen transformer company website for ideas on that or ask K&K. |
spider, the values one uses to match a MC cart to a SUT have nothing to do with the load resistance you would use if connecting the cartridge to a phono preamp or headamp. You need to do a search on vinyl asylum or here on Agon to get pointed in the right direction. BTW, the SUT's themselves can come in two or three ranges which work best with certain cartridges. Wish I could be more help ;-) |
OK here's the specifics of the set up so far:
Lundahl LL1681 MC transformers using the 13:1 tap.
With a primary resistance of 9.6 ohms and a secondary resistance of 1640 ohms, courtesy of K & K I get:
Req Load......Resistance
50..................15600
75..................24114
100................35310
125................50689
150................73135
175................108974
I've only got a couple of resistors to hand so I've only played around with parallel resistances of 18K, 47K (and 13K and 65K if you do the maths). None of them sound good.
Given the relationship of input:output load being the square of the step up ratio I can't see how I can get my Urushi to "see" the sweet 47K it used to?
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Nsgarch, You wrote, "spider, the values one uses to match a MC cart to a SUT have nothing to do with the load resistance you would use if connecting the cartridge to a phono preamp or headamp." Are you suggesting that my advice in my previous post was completely incorrect? If so, I'd like to know, because I hate to think I've misinformed spider (or anyone else). When he bought the Lundahls (presumably from K&K), I presume that they knew how he was going to use them and that therefore the ones he's got are already a reasonable match gain-wise for the Urushi playing into the CJ. |
Re your last post, the consensus among us other users of the Urushi is that you would be best off with a load of ~100ohms. If you really want 47K ohms, then just off the top of my pointy head you will need to replace the 47K resistor at the input of the CJ with a very much larger one; the value would be 169 X 47K (given your reported 13:1 turns ratio), nearly 10 Megohms! You may as well try 10M. I don't recommend it but try it if you are convinced that the cartridge performed best into 47K ohms load. You are not alone in this belief; Allen Wright, a well-respected designer and manufacturer runs all his LOMCs into 47K. You need either to remove the stock 47K load resistor entirely and replace it with 10M or to place 10M in series with the 47K one. |
Lew, probably what I should have said was that it takes different value resistors (across the transformer taps) to achieve the same load conditions for the cartridge as if it was simply driving a phono preamp. So your explanation of how to load the SUT seems perfectly logical to me, but then I've never tried to do it, so I have no credibility whatsoever ;-)
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I just did not want to be the dispenser of incorrect information. I've never used a SUT either, but I came close at one point and read some of the excellent white papers on the Jensen website at that time, to gain what little knowledge I have on the subject.
Spider, I hope it's clear in all this that the circuit should be as follows: cartridge to transformer to load resistor, so that the load resistance is on the other side of the transformer with respect to the cartridge and replaces the built-in load resistor in the preamp. To really make it simple, you could just leave the 47K resistor in place. With your transformers, that would result in a very acceptable load on the Urushi of about 200 ohms. (I'm too lazy to do the math.) |
The maths works out as 47000/(13*13) = 278 ohms and I'll give that a try tonight.
Trying to replicate a 47K load through the transformer works out as 8M (47K*13*13) ohms as Lew points out. That will require modifying the pre-amp and seems quite a big change that is surely going to have an effect on the phono stage as a whole.
My thinking is that I probably don't need 47K load to get the sound I am used to and that I should take the SUT out of the equation and change the loading of the MM stage down until I find the lower bound. If that turned out to be only 3K for instance then that means I would only have to change the pre-amp to be 500K which seems more reasonable. Does that sound right?
I actually got the Lundahls from diyparadiso but Benny has been on holiday so I haven't been able to go through this with him. I'll also checkout the Jensen website and lookup Zobel networks.
Thanks for all the help so far. |
Subbing the 47K load resistor with an 8M load resistor would only negatively affect the phono stage if the input tube or transistor cannot tolerate it. I'm not sure how it would work with a transistor input, but with a single-ended (as opposed to "balanced") tube preamp, the "load resistor" is actually the grid resistor as far as the input tube is concerned. (Actually, this is true for full balanced input as well, but it's a bit more of a complex topology.) The question would be whether that tube can tolerate such a high grid resistor. The typical tubes used for input in a tube phono stage (12AX7, 6922, etc) can tolerate a 1M resistor with no problem, depending upon the bias voltage. To determine whether an 8M resistor is problematic, one would have to consult a manual for the specs of the tube in question, and it would be prudent to know the bias voltge. But most likely - no problemo. As for the rest of the circuit, the value of that grid or load resistor would have no effect on RIAA equalization and should not effect the sonics except in that it affects the cartridge output, which is what we've been talking about. The only other thing that occurred to me was whether the behavior of the transformer will be unaffected when there's an 8M resistor (i.e., a very tiny load, almost no load) in it's secondary. But I think you're doing the right thing by leaving the 47K R in place, so the Urushi sees 278 ohms. You may be quite happy with that.
You're rationale for selecting the next highest load R below 47K sounds reasonable but tedious.
On the Jensen website you will find a white paper on use of Zobel networks with their transformers (which are excellent by the way). I don't see why the info is not also applicable to any other SUT, but it may be so if the design of the Zobel is based on the frequency response of their trafos in particular. |
It is a transistor pre-amp, I don't have a schematic of the PF1, the instruction manual only states that it is the industry standard 47,000 ohms shunted by 100 pF. It describes how to lower the impedance with a parallel resistance but not how to increase it.
I cannot find a Zobel network diagram on the Jensen website but their MC transformer diagram adds a capacitor in series with the modifying resistor - that may be worth trying.
At the moment I'd rather not dig inside the pre-amp without some guidance, perhaps I should try contacting CJ for a schematic. Otherwise I'll wait and see if it burns with more use. |
Have you yet tried connecting the trafo to the input with the standard 47K-ohm resistor in place, in other words with no other changes? Should at least work well. The networks etc are for touching up the response to make it as flat as possible; a Zobel or added capacitance is certainly not a requirement. |
Yes, I've tried pretty much every combination of set up including directly connected with no other loading - which would be a 278 ohm load on the cartridge - it all sucks. And pretty much to the same effect, there doesn't seem to be much variation whatever I try.
Have I set up the rest of my system to over compensate for connecting the Urushi into a MM load, such that doing the "correct" thing into a MC load is now throwing the setup so far out of whack? |
Can you be a little more descriptive? In what way does it "suck"? Do you lack gain even with the SUT? Is it bass heavy or exaggerated in the treble? Is it grossly distorted? Are both channels behaving in identical fashion? Etc...
Since I believe K&K are the importers of Lundahl, you may be able to get good advice from Kevin. He is very knowledgable. |
The "sucky sound" is a lot of harshness in the upper treble - quite unpleasant. Also, the sound stage has gone completely flat, all the air and space around the instruments has disappeared. Bass seems OK. There is no problem with the gain, the 13:1 ratio is just right.
I'm in the UK and didn't get the Lundahls from Kevin, although he did send me his spreadsheet for calculating the load resistance.
Both Sowter and Jensen recommend a Zobel network to reduce ringing in the transformer. It is just a resistor in series with a capacitor across the secondary windings. I have added such a network to the Lundahls and, on initial listening, this sounds very promising.
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I have used the exact Lundahl transformers that you are using. In the past, I've not been a big fan of "burning in". However, with the Lundahl's, you will notice a MARKED improvement at about 100 hours. If you want to speed the process - hook the outputs of a cd player with the inputs of the transformer. Hope this helps. |
Of course, I don't actually have a CD player but I guess a tuner would do. I did try a few days with it connected to the output of the transformer (cartridge disconnected) but you think connected to the input would be better? |
