Isolation Issues (SL 1200)

[steamshooter]

I made a wall shelf to get rid of the footfall problem. I can now jump and dance.:D But, now I have a feedback problem. 15" woofers right in front of and below the shelf. These cannot be moved at this time. (It's not my fault):smilemad: Set stylus in the groove on stopped record and turn up the volume, I get a very low frequency noise that will continue to get louder as it cycles.
Question: Do I need high-mass? (sandbox, concrete pavers ect)
or
Do I need to experiment with cones or innertube or what?????????. :dunno:

What do heavy unsprung TTs respond the best to?
Brad

[Wardsweb]

You could always ditch the shelf and suspend your TT. It's fairly simple. You can use four eyelets in the ceiling, a board to hold the TT with four eyelets in it and some very heavy monofiliment fishing line.
It's just a thought. I had to do this in college while living in a trailer to keep the tone arm from jumping on the album like a Mexican jumping bean during serious parties. :rolleyes:

[car67]

Tough one. If shelf is still vibrating and transmittng feedback, then quick fix might be to try some cones. Or some light and rigid platform between the tt and shelf. Or even a combination of the two. I've tried good quality plywood (less than half inch) with good results.

Another stab in the dark - are you using the dustcover when playing records? Try removing it altogether.

Jack

[steamshooter]

Ditching the shelf is not an option.
Dust cover is up when playing, will try removing it to see if that helps.
I'm on the hunt to find a family of coneheads to put underneath and see how they do. :D
Thanks for the suggestions
Brad

[bully]

Get two tennis balls. Cut each in half. Presto! Put one half under each foot.
Really cheap, and has cured similar problems.

good luck

[steamshooter]

Thanks Bully,
That's the kind of solution I like. If it doesn't work, oh well, nothing lost!
I read an article about using tennis or raquet balls (a sandbox with balls, instead of sand). My problem is I don't quite understand how to go about matching up a particular isolation method to a particular isolatation problem. Or just start trying till one works?
New question:
The low filter on my Hitachi seems to help with the problem. Is this the same as a "subsonic" or "infrasonic" filter? What's the cutoff on this??
Without the low filter I can go approx. to 9:30-10:00 on the volume with the bass and loudness on full. Then it starts a very low grumble.
With the low filter and bass and loudness on full I stopped at 1:30-2:00 for obvious reasons. No feedback whatsoever.
If I use the low filter, am I missing too much of the low end material? The frequency thread started by GeniX over in general leads me to think I'm not.
Brad
Every answer brings more questions :confused:

[Don]

Originally posted by steamshooter

Dust cover is up when playing, will try removing it to see if that helps.


There's your problem! 100% garaunteed! While the music is playing tap on the dust cover and you'll hear the sound come right through the speakers. I just went through this same problem. The guys here mentioned about taking it right off. I did and low frequency hum GONE completely!

[bully]

That's great Don! Yes, the stylus & cartridge acts like a microphone.

IIRC, use of the "subsonic" filter is for use with playing turntables & records. Probably cuts off at 20 HZ or a little below that.

Pete

[steamshooter]

Dust cover off, low filter in, loudness in, and bass all the way. Volume at 3:00 and ABSOLUTELY NO LF HUM! :D
Thanks guys, I'm going to try music at the 3:00 position;)
Brad

[car67]

Way to go, steamshooter. I think you can take the low filter off too unless you are playing really warped records - which IIRC is what it's for.

Just as an aside, if my memory serves me correctly, the SL1200 was one of those that actually had a type of sprung sub chassis albeit a very stiff one. Not one of the real springy types like Thorens or Linn but suspended nonetheless. It was quite unusual for direct drives to have that design and I think it was one of the reasons for it's ability to perform in just about any situation. Anyway, appreciate it if you or anyone else can clear this up for me.:) Just like to know that the ole brain is not playing tricks on me!

cheers
Jack

[Walt]

Right, my dust cover is coming off too when I get home ...

[car67]

Mine just rests(off the hinges still) on the tt when not playing. Watch out though if you have a cat that likes to jump on your hifi. Could get messy!:)

Jack

[virak]

On my SL-120Mk2, I'm using Isonoe isolation feet. They are incredibly effective feedback-killers!
They use 6M threaded bolts, and was designed especially for the SL-1200Mk2.
So if your SL-1200 feet are mounted the same way, I'd look into it. they are a bit expensive, though, at $200.

www.isonoe.com