Friday, April 6, 2012

Experiments on Linn Valhalla with Panasonic SG

I'm pretty sure now my stylus is OK.  I've played the pipe organ record over several times and it sounds the same (slightly distorted) at the very end.  It doesn't sound like mistracking, it sounds like the distortion is in the recording itself.  It always seems like organ creshendos occur right at the end of the LP.

I tried running the strain gauge cartridge straight into my ADC.  It works if I crank up the digital gain on the ADC to +15dB, and then also crank up my main Tact to +6dB, I get reasonable volume.  It sounds very clean, but it's noisier than through the tube preamp, and the noise has a distinctly edgy sound like digital aliasing.

So it appears this cartridge does need to have about 30dB of gain for comfortable use, or about 24dB minimum, and the preamp does have to be fairly low noise.  Just judging from these facts (I didn't do any measurements or web searching yet) the Panasonic cartridge requires about as much gain as a moving magnet phono cartridge, and it must be very low noise amplification.  The equalization is very different, the bass rather than treble is attenuated.

I tried using a nice transistor preamp, an Aragon 28k, but it wouldn't work as the 28k is direct coupled and the strain gauge runs on 7.5V bias supply.  I could add two caps in line, but for now just brought back the tube preamp.

I also tried using my Michelle clamp.  It made the sound duller.  I think that is because it is reducing resonances, so the dull sound is really more accurate, in fact it made me think immediately of the sound of my Sony turntable where I use the same clamp.  But it also added a mechanical quality to the sound.  I think that is because the resonant platter and bearing then become better coupled to the record surface.  The felt used by Linn is very thin, about 1/4 the thickness of typical felt cloth, so there's not much there for damping.  I think the Linn strategy is to keep the record from being perfectly coupled to the platter to reduce noise.  The felt damps the record very slightly, and protects it, but that's about all.

Overall, I think the clamp made for slightly better sound, though it's a mixture of plusses and minuses.  A lighter clamp combined with a different mat might would probably be a better solution.  With the existing mat, the improvement gained with a clamp isn't worth the effort.  The super soft suspension makes it a pain to put the clamp on and off.

Not messing with clamp makes playing records much easier.  The Linn is designed in such a way as to make clamp pointless.  It's really not a high fidelity product, seeking the highest fidelity.  It's a lifestyle product, whose point is to encourage you to play lots of records, by making the record playing process very simple, and tuneful, but not necessarily accurate sound.

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