Helikon LOADING

Thanks for lot of inputs and data points for me to work on. 47K for set up I am trying is definitely way too thin sounding. 40 ohm is a tad fat. 400 ohms leans towards lower side of lean, closer to flater, very tight bass but little hot on high freq still. Which means 100, 150, 200 ohm might work for the set up. Although I will try out 1000 ohm just for another data point.

Thanks.

Hi Jeff, re: impedance matching of cartridges:

A device which is generating a voltage into a load (could be a source like a tuner or CDP into a preamp, or a preamp into an amp, or a cartridge into a phono preamp) has to "see", or work into, enough of a load (resistance or "impedance") so there will be voltage registered at the other end. Or to flip it over, if the other end were just a short circuit (no load) no voltage would register and there would be nothing to amplify.

Depending on the difference between the ouput device's inherent impedance and the input (load) impedance of the driven device, there is an optimum combination that will deliver the best signal transfer, i.e. the most voltage and the most faithful (to the source) frequency response.

You hear more about "impedance matching" between preamps and amps, when someone experiences problems like not enough gain out of their amp, or poor frequency response (usually loss of highs) when their impedances are not optimally matched. Another instance where you often run into this issue is amp-to-speaker impedance matching, which is the reason for the use of auto-formers like the ones Paul Speltz markets.

The cartridge-to-phono preamp interface is no exception. Although to be absolutely fair, I should point out that cartridges are really current producing devices, but there are very few current amplifying phono preamps, so we always speak of a cartridge's output in terms of (micro) volts.

If one takes the time (and it is a bit tedious I admit) to experiment with a variety of load values, it's actually quite easy after awhile to hear when you're getting the flattest response and strongest output from a given cartridge.

The "25-times cartridge impedance (or coil resistance)" convention is a bit like setting an initial 1.5 degree Stylus Rake Angle. It's just a quick way of getting yourself firmly "in the ballpark" so that you don't have to go too far one way or the other in order to find just the right spot.

Jeff: Well, yes, you are endeavoring to impedance-match the cartridge to the phono preamp. The 25x value may turn out to be right on the nose (after experimenting a little up or down and making listening comparisons, taking notes -- always take notes!)

But if it isn't right on the nose, the 25x value will still be pretty close, thus saving you a lot of time.

If you're using a MC cartridge with a typical output and coil resistance of +/_ 10 ohms (optimum loading around +/_ 250 ohms) you could also follow another approach which would take about the same amount of time. And that would be to start at the low end of value range (i.e. optimum less 50%) and work your way up in increments of say 25 ohms. In this example, 125, 150, 175, 200, etc.

I've done it this way too, and it may actually work better (in terms of training one's hearing) for someone who has never done it. You are guaranteed to start with sloppy bass which slowly tightens up and (if you keep going) eventually gets very thin, or disappears. That's when you back down 25 or 50 ohms and can be confident you've found the best match.

Years ago, all Lyra's were made for 47k, but only a few Phono Stages made that, so the manual changed the loading recommendations. I think, it is System dependent, too. When you have an adjustable one, you can check it out, from from setting you will loose high frequency information. I use most of the time 47k with a Klyne Phono Stage and it's own Filter settings, but there is not only 1 right value I guess.