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Fired up the Gates project today and it sounds awesome. The biggest change from my last table is now I'm using a Schick 12" arm. After listening to 3 albums I decided to crank up the volume. This brought on a loud hum or harmonic sound that remains until I lower the volume. It's not really like a electrical hum it's more like a mechanical roar. Wish I could describe it better. Any ideas?
Follow Ups:
It's very easy to test whether it's motor noise.
Do NOT turn on the turntable and place the cartridge on the vinyl and begin turning up the sound. If the problem is structural feedback.....there will come a point where the 'roar' will begin. You can actually stop at this point and you will hear the 'roar' actually increase on its own.
If you cannot indiuce this feedback......then it's likely to be turntable/motor related?
That's exactly what's happening. Without the idler wheel even turning the roar happened. Now it's on to a cure. Perhaps my TT is too close to a speaker. Maybe the spikes the TT rests on are inadequate. I'll do some playing. Thanks for the tip.
Structural feedback has nothing to do with your speakers......that's air-borne feedback.
A suspended concrete slab can be like a stretched membrane (especially pre-stressed suspended slabs which are often used in new construction) and will bounce and flex especially away from supporting walls.
That movement in itself will induce low frequency noise throughout the slab which.....as it's actually moving.....will change in frequency.
This low frequency energy will be transmitted to everything which is in contact with the floor and will vibrate at the resonant frequency of each particular object. Your timber stand is vibrating as we speak....and transmitting this energy into your plinth and platter which you hear picked up via the cartridge under amplification.
Changing your support to a wall-hung shelf may solve the problem if the wall is a supporting wall and not just sitting on the suspended slab.
Otherwise....an isolation base for your turntable (like the Minus K ones) can often do a good job.
Good luck.
I have felt like I live in a brick Sh** house but what you offer makes alot of sense.
OK.....glad you isolated that.
When you say your concrete floor is 'stable'......is it on the ground or is it suspended?
I'm guessing the latter?
Correct, it's the later (suspended). I'm thinking I need to move the TT as it's only 2' away from a speaker. That brings up the next question. If I have to run 8' of cable will that work from tonearm to phono stage or do I run 8' from phono stage to amp? Thanks again for your assistance.
Best to run long cable runs from phono stage to amp/preamp. Long cable runs from the tonearm to the phono stage with a moving magnet cartridge may not work, high frequencies may be dramatically reduced. Moving coil cartridges don't have this problem, though.
I'm sure someone will chime in if I'm incorrect, but I have found in my own system that long cable runs with MM cartridges don't work.
TR
Use a cable with a capacitance less than 50pf,better if it is less than 20pf short not longer than 40-50cm,between turntable and RIAA!
(low impedance would not help its the inductance and the capacitance that is problematic)
The most important cable in a system is the cable who distributes the weakest/smallest signal,the cabel from tt to RIAA is not a "cable" in a usual content,its an integral part of a resonance circuit.
The cartridges inductance creates together with the cables inductance and capacitance a resonance circuit that is damped to a suitable Q by the the RIAA circuits input resistance.
This brings together two problems:
1 : to get a cable where the resonance frequency is out of the hearing region.
2 to choose the input resistance of the RIAA so the systems resonance is damped and no resonance peak in the RIAA frequency is present
Thanks.
Thanks for all of the input and ideas. I'll try some different things today and post the results. When I went through all of the mechanicals on this I replaced the idler with a new "aftermarket" one. I'll put the stock one back on and test. I'll also try headphones to verify that it's acoustic feedback. BTW when I removed the copper mat and replaced it with felt I noticed that the music sounded much thinner and putting the copper mat back on returned the full bodied authority to the music. Again thanks to all.
The idler wheel turntables invented the word "rumble"!
The famous Lenco roooooaming is well known around the world!
/m
Yep, you got it.
Never attribute to malice that which can be adequately explained by stupidity.
A common problem for all kinds of turnables. To find out for sure, listen with headphones. If you no longer hear the roar though phones, it's acoustic feedback. If you don't have phones handy, you can also try reducing the bass control on your preamp/receiver to see if it goes away.A couple of fixes are to put your turntable on a wall-mounted shelf, or put a subsonic filter in the signal path.
I have a switchable subsonic filter on my preamp & it totally fixes the problem with no audible degradation to the sound. That's probably the easiest fix.
Great looking turntable, by the way!
Cheers & good luck!
Bobbo :-)
Edits: 06/01/12
Another easy way to tell if it's airbourne acoustic feedback is to set the stylus down on a stationary record & crank up the volume. If you hear the roar when the motor is off, that's acoustic feedback & can be fixed with either a better support for your turntable or a rumble filter.
Cheers & good luck,
Bobbo :-)
Thanks for the suggestion. The roar is there even when the TT is not spinning. I think I should relocate is as it's pretty close to one of the speakers. Thanks for your help.
I'll bet when you get it sorted out, that'll be a sweet sounding turntable! Should be a pretty easy fix.
If relocating the turntable doesn't work for you and you decide to go the subsonic filter route, here are a couple of options:
$55 with shipping:
http://www.ebay.com/itm/SUB-SONIC-FILTER-Harrison-Labs-PFMOD-SUB-tm-NEW-/190367536675?pt=LH_DefaultDomain_0&hash=item2c52ca1623#ht_500wt_969
$180:
http://www.kabusa.com/rf1.htm
I don't know what phono preamp or integrated amp/receiver you have, but some of those are equipped with built-in subsonic filters. Some equalizers have them, too.
Good luck & let us know how it works out for ya!
Bobbo :-)
Hi Scott,
Is the arm board supporting the Schick a relatively thin piece of wood? Sitting on a hollow space? Have you taken a stethoscope and listened to the Gates top plate and then to the plinth, arm board, etc?
In your new setup, looks like the Schick is picking up noise transmitted from the motor/idler.
Yours,
Jonathan
By the way the Schick is mounted to a 2 1/2" thick block of solid mahogany. A stethoscope indicates fairly equal reading from arm board to plinth to TT.
Interesting, I started with the heavier counter weight assuming I needed it with the weight of the ZU. When I changed to the lighter weight the issue is still there but much less noticeable. Thanks for your input.
Try listening with headphones, no speakers. Good luck getting this squared away. I'm really looking forward to hearing this project being proclaimed a resounding success.
Try it again without the copper mat (substitute any other kind of mat you have available). A good friend of mine had no end of problems he traced to the same kind of mat and ultimately gave up on it. I remember reading someone posting here on AA who had similar problems.
Edits: 05/31/12
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FEEDBACK ?
OK the copper mat has been replaced by a felt mat, no difference. Also I'll point out that this is replacing another Gates CB-77. I made a new heavier plinth to accommodate the 12 " arm and it is a different CB-77. All else is the same. Cart is a Zu-103. It actually does sound like low frequency feedback.
What is the construction of the shelf supporting the turntable and how is IT supported?
The table is supported on a Mapleshade "Samson" rack same as my old one and is very sturdy. The floor is concrete and very stable.
Hello,
Did you check out Art Dudly's Stereophile review of the Schick tonearm. He apparantly had problems with noise from it too. May not be the same problem you have but could be worth a look. I believe that he was able to solve the issue and then went on to rave about this tonearm. BTW, if you ever decide to let the Schick go, I'd be glad to take it off your hands. I plan on using one for my Lenco project.
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