Mono clipping/distorting

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It was my birthday last week and my sister got me a sundazed re-issue of one of my favorite LPs Otis Blue/Otis Redding Sings Soul (Awsome)

Original master tapes, 180g vinyl etc; I was expecting big things; but playing it through my rig

Grado Prestige Black - DIY JFET Le Pacific RIAA Phono Pre - Various Pre/Power combos

I get some serious breakup of the sound when Otis hits those powerfull high notes or the brass section blows really hard.

I also tried it through the Phono stage on my NAD 3130, same problem; not as pronounced but the sound is much flatter through the NAD anyway; that's why I built the Pacific.

I was going to blame the Pacific, but When I go back to my point of reference, a nice Stereo first-pressing of Bob Marley's Uprising; all is fine!

I'm wondering if it could be somthing to do with using a Stereo Stylus in a mono groove? Could this be the issue? I was also listening to a not so great mono copy of Lady sings the blues yeaterday and i noticed a similar problem.

your experience would be apriciated.
 
A mono groove has no vertical modulation. The groove should look the same width everywhere. That's not quite true, as the waveform moves through the cycle the width becomes apparently wider on the fastest changing parts of the waveform. The actual track width is identical, since it is the width of the cutter.

There is no harm in using a stereo stylus nor using a stereo cartridge. The difference is that a mono cartridge is very stiff in the vertical direction (near zero compliance) whereas a stereo cartridge is compliant in both the horizontal and vertical directions.

I wonder if the problem could be mistracking? Your cartridge maybe cannot follow the very high energy transients.
 
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I'll have a look at the biasing on my pacific when I get time, see if its the likely culpret; I cant remember exactly how the power was rigged I might be able to up the voltage. That said the Grado black is suposed to be a fairly low output mm cart and the Preamp does seem to play my Stereo albums fine. so I'm reluctant to blame it.

I really do struggle when I do listening tests comparrisons but when I play the TT back through the NADs Phono Pre with the amp in Mono mode it all sounds a lot more stable. could that be a clue?

How would I investigate the tracking issue?
 
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