A question of loading...


I have just replaced my aging tube preamp with a new model. When I was using my older model with tube phono stage, I would run my Lyra Kleos and other MC cartridges with a load of 750 ohms. So, I assumed that with my new tube phono stage, which also utilizes a transformer in the phono stage and is also built into my new preamp, that the same cartridge loading would apply. I listened to the Kleos for about a week with this loading, and frankly, while it was fine, I wasn’t bowled over. Tonight I decided to experiment, so the first thing I did was to run the cartridge straight in, with no loading plugs. WOW, the increase in overall musicality and soundstage width was eye opening! Lesson learned is that not all gear is going to react the same when it comes to cartridge loading, particularly if there is a transformer involved and even if you are using the same cartridge from one phono stage to the next! An eye opener, anyone else experience something like this?
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Showing 12 responses by daveyf

+ 1 Atmasphere.

OTOH, do tubes have a distinct advantage?? I would say that they do when it comes to overall SQ, plus the decreased likelihood of overload, BUT they are never 100% quiet...at least IME. There is always some minimal hiss..and this leads me to believe that their noise floor has to be higher than ss. 
Indeed, the CAT has plenty of gain available, almost too much. With Ken's new 47 step volume control, luckily there is plenty of control and there should be no issue running up a few steps.
@dover  At the moment, i am presuming that since I am not loading the cartridge at all, it is seeing 47K. This is what surprises me a little, as previously with the older tube phono stage sans the SUT, a straight in with no load was definitely inferior to the custom 750 ohm plug that i was using. Now, with the SUT and at 47K ( presumably) that is certainly no longer the case as the SQ is as described in my OP.
Loading is at the phono stage, but it absolutely has an effect on the sound of the cartridge. There is some belief that loading effects a MM cartridge more than a MC, but I am not totally sure this is the case.
The loading would seem to be dependent on the combination of what sounds best depending on the phono stage and the cartridge, wherein I was previously under the impression that it was somewhat cartridge dependent and NOT to do with the particular phono stage as much. Seems like it is both at this point.
@dover   Thanks. I was certainly quite surprised at the nice increase in SQ due to 'unloading' the cartridge ( even if maybe the load is as you say, at around 3500 ohms!) . Oddly, when I was using the older style CAT phono stage without the low gain transformers and the same cartridge, the SQ was definitely better at the 750 ohm level. Just goes to show that one cannot assume similarities in this area with different gear upstream.

@rauliruegas   Thanks for your post and the link. I did read the link. Seems like FM believes that 20-500 ohms works best for MC cartridges. While this may be true with their preamp, it was not true with my older CAT as it sounded best loaded to 750 Ohms and NOT lower and as stated in my OP, my new model CAT sounds way better unloaded! 
@atmasphere Ralph, thank you for contributing to this topic. What you posted was extremely informative and interesting. I certainly think that a lot of fellow a’philes can learn a lot from you.

In my case, i am still a little surprised as to why the new preamp which features a phono overload spec of 70mv rms for MC’s is so very different to my old model, I am guessing that this is high enough to not risk ringing with my particular cartridge, a Lyra Kleos that puts out 0.5mv. What is odd, and I am not quite understanding this part, is why with my older CAT phono stage, which did not use a SUT at all, that a load of 750 ohms was better sounding than straight in at 47Kohms, yet with my new model, this is definitely not the case. Presumably due to the SUT in my new CAT?? One thing, the CAT has a healthy output voltage at about 50 volts..
@dover   Good point about the overall gain in the system. However, my ancillary gear is exactly the same, with the exception of the old preamp vs the new preamp. So. I would have to believe the overall gain should be the same. My amps ( i use both a ss stereo amp and a tube mono block..(not at the same time) do have similar gain structures ( the ss amp has a gain switch to switch between two settings- a very useful feature that I wish more amps featured)) .
@atmasphere  Once again, very interesting and informative..thank you.

Ken uses a SUT that doesn't really have a lot of boost because I think he believes that as the step up increases, the loss is SQ is too great. What i am still guessing at is that the SUT allows for a better synergy with my Lyra as to what it wants to see as a load than the prior 750ohm resistor that I was using. The Lyra has a fairly healthy output for a MC at 0.5 mv and I am sure this is not putting much stress on the SUT. It was not putting too much stress on the phono stage before on my old non-SUT unit. Now the advantage of using an SUT has aways been to me that I could entertain ultra low output cartridges without too much tube noise, by ultra low, I am saying below 0.3mv...which there are quite a few very good ones out there.I wonder if that would be an option with this new CAT model, somehow, I doubt it???
@rauliruegas  I have played around with the loading on several different MC's in the past..the results were not anything that could really be anticipated. BUT one thing that was never in question, was that the cartridge was mis-tracking in any way...which IME is very easy to hear! 
With my current Lyra, the tracking is spot on and is certainly not effected by the load applied at the phono stage, YMMV.
@fsonicsmith Let’s give Raul some credit here. He is posting in a foreign language about technical issues that are somewhat difficult to extrapolate on even if you are fluent in the language. I appreciate the fact that Raul clearly is one of the more dedicated audiophiles here- and while i may not agree with some of his posts, I do think he contributes points of interest. I know that if we ( natural english speakers) were attempting to do the same thing in Raul’s native language on a foreign web page, I seriously doubt we could make ourselves understood as well as he does. ( even if we have to translate a little in our minds as to what he is trying to put across..:0) ).
Last night i decided to do a little more experimenting with loading. I had felt that the change from the 750ohm load to wide open ( presumably 47Kohms) was beneficial. The sound was like I described in my OP. However, over more time, I was hearing a very slight increase in brightness on wind instruments, particularly trumpet. Since it was suggested in my preamp manual that a load would be beneficial to reducing any kind of brightness in the cartridge, and that a load of 300ohms was a great place to start, that is what I did. Sure enough the minimal brightness was no longer a factor...and the soundstage benefits i had previously heard were still there! So, for now, 300ohms is where I am at.