Hum from Sherwood PM9805 Turntable

[A K Bhattacharjee]

For the last few days I am watching that whenever I play a record, hum is heard by touching the body of the turntable. Also I feel that extra bass or hum is generated at the end of records.Hum is only heard when the cartridge is on the record & record is moving. I have tried many options like change of ground wire. Connecting cables & two cartridges, like Shure m447 & AT95e but no result. Any help?

 

[Hari Iyer]

Turntable hum could be because of the following reasons,
- Turntable ground wire not connected to the amplifier ground. Connect the TT ground to the amplifier ground if this the reason.
- Ground loop formed between turntable earth and amplifier earth. If both the TT & amplifier is connected to the wall outlet earth a ground loop can be formed. Remove the TT earth from the wall outlet pin and see if the hum is reduced.

The hum is mostly RF & EMI noise picked up from the air and can be reduced if the Phono pre-amp is shielded by an aluminium mesh and then grounded. It will be tricky to check grounding issues without a continuity tester or a multi-meter.

 

[frend2001]

I have faced the issue with my Technics SL - 220.

I found the headshell was not making proper contact with the tonearm.

Cleaned the contacts with IPA and rubbed with soft cloth.

Hum is gone.

Hope this helps.

 

[A K Bhattacharjee]

I also feel that. Let me try. IPA 90% or to be diluted?

 

[reubensm]

Hearing hum with the tonearm is near the end of the record signifies wiring issues. You may want to check the wiring inside the tonearm and were it exits (either a tag board in some case or mostly the socket where your turntable interconnect plugs in. Breaks in wiring, especially the earth / ground wiring can cause this. I suggest you check the entire circuit from the cartridge pins to the interconnect plugs. Turn off the turntable, and run these checks with the tonearm positioned as though it would be nearing the end of a record. Don't forget to cap the stylus with its protection guard to safeguard against damage.

 

[A K Bhattacharjee]

Hearing hum with the tonearm is near the end of the record signifies wiring issues. You may want to check the wiring inside the tonearm and were it exits (either a tag board in some case or mostly the socket where your turntable interconnect plugs in. Breaks in wiring, especially the earth / ground wiring can cause this. I suggest you check the entire circuit from the cartridge pins to the interconnect plugs. Turn off the turntable, and run these checks with the tonearm positioned as though it would be nearing the end of a record. Don't forget to cap the stylus with its protection guard to safeguard against damage.

Recent development is when bass is kept at minimum lebel, hum is very much reduced.Except opening the turntable I have tried all options but problem remains the same.

 

[greenhorn]

Have you moved your speakers around recently? may be acoustic feedback

 

[frend2001]

Recent development is when bass is kept at minimum lebel, hum is very much reduced.Except opening the turntable I have tried all options but problem remains the same.

Hum could be very annoying and frustrating.

Your problem seems to be ground loop. A few things to check are :

1. TT ground wire is properly connected.
2. The interconnects from TT to Amp are not near any EMT (electromagnetic turbulence) inducing device like adapter / charger . WiFi router.
3. The condition of interconnects itself.
4. Also check if the Amp still gives hum after disconnecting all input interconnects.

Above are the usual suspects. Round em up and you may have your culprit.

Hope this helps.

 

[jls001]

Have you moved your speakers around recently? may be acoustic feedback

If the TT has a cover, remove it temporarily. By removing, I mean removing it entirely and placing it away from the TT. The large surface area of a cover can get excited by the sound energy from the speakers, especially when the cover is stood up. The vibration induced on the cover will get transmitted to the TT which will in turn produce spurious vibration on the tonearm + cartridge which can be heard as a bassy sound. If removing the cover doesn't make a difference, the problem should be something else.

 

[Hari Iyer]

Have you checked your phono preamp? Do you get the hum after disconnecting the RCA from the TT? Iis this a 50 Hz hum or 100 Hz buzz? Try shorting the TT input wires and check if hum still exist. Based on your diagnosis the following could be solution.
1. If 50 Hz hum, then PSU of phono preamp is having AC ripple and needs additional capacitors or a choke filter to reduce ripple.
2. If it's a 100 Hz buzz, perhaps an RC filter in the PSU to remove the buzz.
3. If shorting the RCA input removes the hum, it could be poor interconnects wires or shielding. Try to put an external shield on the RCA interconnects wiresand ground it to the amplifier chassis. Also check if your TT Chassis, tonearm and head shell are properly grounded. Check the resistance of each ground point individual. Anything more than 1 okm can behave like an antenna and cause RF/ EMI interference.
Hope this helps.