It's not likely to be the turntable. Has the setup sounded OK in the past? If so, your arm and cart may have drifted out of alignment or the stylus is worn. OTOH if the rig has always done this, check arm and cart setup anyway, but check the phono stage first. Swap in another (maybe less cheap) phono stage and see if the nasties are still there.
The problem is overload of the signal strength.
My first guess is that your cart is too high an output for the phono pre..
(the RadioShack phono pre should be going into a line level input in your preamp, not a "phono" input!!!!)
Get a cheap used 'audiophile pre' here for $100.
Your amp may be the problem (unless it never happens with CDs)
Aaahhhh....the old '' distortion interruptus '' I hate when that happens.
Another thought is that your amp has reached its limit (power wise), and is sending audible distortion to the speakers (i.e. clipping).
A friend of mine did this (by accident of course), when we were auditioning amplifiers for his Avalon Eidolons. He likes to listen to his classical music at realistic sound levels (in the front row of course!), and while comparing the Manley Neoclassic 250 to the VTl MB-450, he actually managed to get the Manley to clip. (Yeah, Yeah, I know, we were listening way too loud).
Just a thought.
Good Luck in finding the cause (and more importantly, the cure!) to your problem.
Yeah first response, Radio Shack goes to the wooden shack in back, or your garage! I really don't know your model or the sound so just kidding, but realistically I would start there.
As pointed out above, the two most likely candidates are mistracking (either cartridge/stylus or arm...or both) and overloading your phono pre. If a friend has a different phono pre they could loan you...try it...that should give you the answer.
You left speakers off the list - they may not be able to handle the power or the drivers have reached their excursion limits.
You also do not make it clear if it's limited to vinyl only.
I think that the first thing to check is tracking force. You probably should start at the upper end of the manufacturer's range and then work down until you hear distortion (=mistracking) on heavily modulated areas of the LP, then go back up a little bit.
Before doing any of the above suggestions (which are all good ones that I completely agree with) you need to make sure your stylus is clean. A gummed up stylus will mistrack on dynamic passages that it could handle if it were clean.
Search for "Magic Eraser" if you don't know how to clean a stylus cheaply and effectively. Even if this isn't the cause of your mistracking problem, you may be surprised by how much better the music sounds after a good stylus cleaning.
After that, as others have said:
- try increasing VTF to near the maximum for your cartridge; use a reliable stylus force gauge, not the dial on your tonearm
- get a better phono stage; it's a highly likely contributor to your problem
- check the gain structure of your entire system; make sure no component is being overloaded
All the above is assuming these bursts of distortion are audible on both channels. If they're happening on just one channel you probably need to adjust anti-skating.
Thanks for all the great responses!
Tracking force could be an issue, since I've maxed out the adjustment on my tone arm and I can only get 1.5 grams. The Ortofon recommends 1.5-2g for that cartridge. What's the best way to add 0.5g to the cartridge end of the tonearm?
I'll be borrowing a friend's tube preamp, so we'll see soon whether the Radio Shack box is part of the problem.
I'm confident that that the amplifier and speakers are not a problem - CDs sound just fine, and the amp doesn't have a phono input.
I just got a Music Hall MMF-5.1 with the Goldring 1012GX MM cart. It recommends 1.5-2.5 grams I believe, but the Music Hall manual suggests that you set it at 1.7. I also am getting distortion at some points, especially when getting near the end of a side towards the middle of the disc. Could this be corrected by increasing the tracking force? I might play around with it once my cart is fully run in.
With the phenomenon you describe, worn used records seem to be the biggest culprit for me--some of my favorites among them. My assumption has been that years of mistracking in somebody else's hands wore the distortion into the groove. If I'm wrong about that, I'd love to know more...
Really, I just want to give a _tiny_ shout out to the Radio Shack pre: if it's the silver box powered by a 9v, Ultra High Fidelity magazine picked it as a budget favorite a few years back. It's discontinued now, but it's what I picked up when I decided to dip a toe into vinyl, and it did little wrong--especially at $20. I'd look elsewhere before blaming it.
I actually think that worn records may be the culprit here as Ablang described. I have a very old Living Stereo LP of Rachmaninoff's Piano Concerto No.2 that I picked up used for $1. It's a shame because it's a beautiful performance, and the quality of the recording is astounding for the time in which it was made. Unfortunately, it's just plain old worn out. Only 1 or 2 of my other LPs give me this problem of distortion, so to me it wouldn't make sense that the cause is anything else. The distortion only occurs during the loud passages as well.