Turntable help

[John M]

Hi,

On the spur of the moment I bought an Akai AP-B20C turntable from a car boot for £20 at the weekend. Got it home cleaned it up and it works a treat! However I noticed that the speaker drivers sort of bounce around quite a bit, in and out as the volume is eased up but not to loud, so I don't think it's feedback from the deck. Obviously feedback does kick in at louder levels of volume. The speaker problem doesn't happen when say the same music is played from Spotify.

It had a Technics 270C cartridge fitted which seemed to have quite an acute needle rake angle which I thought may be the problem, so I ordered an Audio Technica AT95E (recommended) which came today. After fitting the new cartridge it's still the same though the needle angle now seems correct.

The speakers are B&W 602's with a Yamaha RN500 to which the deck is plugged into the phono stage.

Any help much appreciated.

 

[expat_mike]

You may enjoy this.

http://revintages.com/akai-ap-b20-auto-return-turntable/

 

[John M]

Yes it's just the same. I came across that he other day when I was researching it thanks.

 

[John M]

Well after googling the problem I tried taking the deck off the top of the amp on the cabinet and putting it on the marble hearth around 3 feet away from the nearest speaker and it's much improved. So then sonic feedback after all.

Also I tried just tapping the cabinet very lightly when the deck was on the unit and the drivers jumped around like crazy! Just getting used to owning a new (old) deck *biggrin*

 

[BigH]

Well after googling the problem I tried taking the deck off the top of the amp on the cabinet and putting it on the marble hearth around 3 feet away from the nearest speaker and it's much improved. So then sonic feedback after all.

Also I tried just tapping the cabinet very lightly when the deck was on the unit and the drivers jumped around like crazy! Just getting used to owning a new (old) deck *biggrin*

You need some isolation then, its not because its old. A wallshelf is best if you have solid walls, if not there are plenty of other solutions, even diy ones you can do.

 

[ColinLovesMusic]

Or flapping drivers are caused by subsonic frequencies like turntable motor rumble being produced and fed to the amplifier and then to the speakers. Subsonics are the very lowest bass frequencies below the range of human hearing which is 20Hz. Rumble is in the subsonic frequency range. An old second hand Akai is not likely to be a well engineered piece of kit but if the problem of rumble can be identified and cured within the turntable that would be ideal. Also attempt to isolate the turntable from vibration that may be in the vacinity. Wall shelves are preferable to tables. But if using a table this is my isolation method that I use for my turntable and it costs £2 - Take one plump cushion from settee or wherever and lay it flat on the turntables table. Onto cushion place flat piece of wood or particle board of appropriate size. Then place turntable onto that. Acquire a turntable spirit level for about £2 and place onto turntable plinth. Now wiggle turntable about until spirit level bubble is dead centre. Next play a record and enjoy. Then even better still after turnatable is sorted out stop any remaining subsonics being reproduced by the amp. Amps used to come with a subsonic filter but few do now. If your amp has one use it and it might cure the problem. Another option is to add a graphic equalizer or other sound processor that has a switch or control to cut output below the audible frequency of 20Hz. Usually called a 'Bass Shelf' and known as Bass shelving. Also sometimes labelled 'Low Band Cut' It is like the frequency at 20Hz drops off a cliff and nothing below is amplified. Best company for producing these products at low prices but with good audio qualities is 'Behringer' much loved by sound engineering students and bedroom recordists. Other companies like Alesis and Roland produce same products although pricer. None are home hifi companies but pro/semi pro audio companies but perfectly compatable with domestic hifi although usually coming in 19inch width.

 

[BigH]

There is a similar isolation method that involves 2 pieces of plyboard with an 18" cycle inner tube in between, slightly inflated. It does not cost much but is said by a well known sound engineer to be about the best way to isolate a turntable. If there is vibration through the plinth then you can stick SORBOTHANE SHEETS to the inside to reduce those, as its worse when you turn up the volume I think those could help.