advertisement


Turntable "Feedback" at volume

A

Alan McClymont

AMCC
I tend not to crank up the volume too much as a rule. However, when the neighbours are out and the mood takes me it's good to have a bit of a blast.
I have an issue when playing vinyl when above moderate listening where I get what I can best describe as feedback - a deep humming which, once it has begun, only disappears when then the volume is reduced. The hum is not present using digital source. Also, using analogue input the volume can be raised to near max when the cartridge is not in contact with the record. Of course this is of no use at all to play vinyl but it does lead me to suspect the issue is with vibration rather than earth loop type problems. Speakers are stand mounts (10 inch bass units) on a wooden carpeted floor.

So the question is do I attempt to isolate the turntable from the rack or isolate the speakers from the wooden floor. If the answer is both, can anyone suggest a cost effective isolation solution?

Thanks,
Alan
 
Any prospect of mounting the turntable on a proper turntable shelf bolted to a structural wall? Tall hi-fi racks, despite their popularity, are about the worst place one can possibly put a turntable.

PS Out of interest what is the turntable? My comment above applies to pretty much any turntable, but there may be more specific advice available depending on the model.
 
Ahh ! We are firmly in the land of compromise here where visual acceptance plays a significant part.

First off the hifi is in the third bedroom which doubles as a guest room. It is all (bar speakers) housed in what can be best described as an off the shelf cupboard (Ikea) - so hardly anchored to the floor. A proper turntable shelf is unlikely to get Board approval. The turntable itself is a modded Lenco GL75. Appreciate all of this must seem horrendous.

The sound though, with some Troels speakers I have put together (with some soldering guidance from yourself and others on this site) is not at all shabby- in fact I am very pleased with it. Just wished I could crank the analogue side a bit more on occasion.
 
The feedback (vibrations from the speakers) could be getting to your pickup through the floor and furniture, or through the air. In the first case, more likely since the Lenco has no suspension, you could try putting a thick sheet of neoprene or anything soft under the deck (I know, audiophiles will cringe in horror). In the second, try to avoid the speakers aiming towards, or being close to, the deck.
 
A small bicycle inner tube, as Townshend used to use, partly inflated might do the trick. Cheap and simple. I still use plinths made with them under my loft speakers.
 
Thanks all for your helpful replies. It certainly seems possible then my feedback issue may be caused because of vibrations. This is a relief. Earthing related problems could have been a bit of a nightmare. I built the plinth a couple of years back and know what a pain it would be to pull the thing apart, arm removal etc. The 3 feet of the turntable are hefty spike designs and the problem may at least be reduced by using neoprene feet as replacements. The speakers are fairly close to the Ikea unit and they too are on stands with spikes so I guess ultimately everything is kind of connected by the wooden flooring.
Like the idea of a concrete slab but have serious concerns over the strength of the Ikea unit. A very heavy Luxman integrated and a substantial weighty plinth already surely must have it creaking. Collapse would be expensive!
First action surely must be to find isolation feet for the turntable. There seem to be some fairly inexpensive options on ebay. Neoprene or some 4 spring 2 part feet arrangements. These could work although they look a bit too heavy duty and this type of anti vibration device is better suited to placement under heavy speakers?
 
Before undertaking major reconstruction work, you might just try putting a pillow under the TT, levelling it more or less, and trying it out. If At high volume you don't get the feedback at least you know the problem is through the floor and furniture.
 
Turntable feedback is conceptually very similar to microphone feedback. It is dependent on frequency, distance etc. It is very unlikely to be broadband, it will just be one note that starts to howl. As such when addressing it altering the resonant frequency is usually the best approach, e.g. the location of the turntable, the mass of the stand, the type of feet, suspension behaviour etc.

A good diagnosis approach is to lower the stylus onto a stationary record and gently tap the deck and support at your normal listening level. Be very cautious here as if you obtain a feedback-loop (howl) it may well kill the speakers pretty fast.
 
Tony L said:
A good diagnosis approach is to lower the stylus onto a stationary record and gently tap the deck and support at your normal listening level. Be very cautious here as if you obtain a feedback-loop (howl) it may well kill the speakers pretty fast.
Click to expand...
And if you have an accelerometer app on your phone, you might be able to find out the frequency.
 
Most chromatic instrument tuners, of which hundreds are available as smartphone apps, will display the frequency in Hz.
 
For the sake of completion, just to report a very cost effective solution to the feedback issue. A youtube video suggested a foam swimming pool tubular float aid would fix the problem. Didn't fancy bright green or yellow feet under the turntable so instead bought a length of copper pipe insulation sleeving from the local builders merchant and cut five 25mm sections - one for each corner and one for the middle. Checked for level and there you go, no more volume related feedback.

Thanks for the help.
 
Alan McClymont said:
For the sake of completion, just to report a very cost effective solution to the feedback issue. A youtube video suggested a foam swimming pool tubular float aid would fix the problem. Didn't fancy bright green or yellow feet under the turntable so instead bought a length of copper pipe insulation sleeving from the local builders merchant and cut five 25mm sections - one for each corner and one for the middle. Checked for level and there you go, no more volume related feedback.

Thanks for the help.
Click to expand...
A similar idea to this maybe.

IS139223-01-01-BIG.jpg

www.juno.co.uk

Freefloat Deck Turntable Stabilizers (orange) at Juno Records.

Buy Freefloat Deck Turntable Stabilizers (orange) at Juno Records. In stock now for same-day shipping.
www.juno.co.uk
 
You must log in or register to reply here.


advertisement


Back
Top