A Phonostage Buzz Hum but the other don't..Why?

[Spider27]

I am aware of that phono input usually has more noise or hum than any other input because of the higher gain, they do have higher noise levels but not necessarily hum or buzz. I recently got DIY phonostage and it sounds good but it has higher level of buzz/hum than other phono-stages that I have tried before.

 

I am trying to reduce the hum/buzz so enjoy listening records with the phonostage. Here are a few findings after trying various troubleshooting.

 

• Buzzing noise goes up and down with volume. At normal listening volume level, it can be heard when there is a pause or lower background music.
• When tonearm cable unplugged from phonostage, then not buzzing but lower level hum gets very loud so it is not tonearm wire that causes.
• When RCA plug either input or output from phonostage at the back are touched, it changes the tone of buzzing. Not necessarily lower buzzing, but touching RCA plugs makes difference in buzzing.
• Trying several different RCA interconnect cables for input and output from phonostage, does not make difference. I do not have very high quality but decent enough to test but did not make noticeable difference.
• I also tried plug phonostage into different power outlet and it does not make noticeable difference either.

 

In my opinion, these findings indicate either power supply noise leakage or a ground issue with the electronics. However, not 100% sure and how to tackle further.

 

If anyone have any suggestions to check or possible solutions that could shed light on the cause of buzz, please do share and be my saviour...... 

[Spider27]

I think that I found the solution. It seems that it is caused by some kind of electric field. I thought that it might be crazy but just put aluminium foil wrapped on the phonostage and put power cable and input and output RCA interconnect at the back and buzz/hum disappeared.

 

It looks stupid at the moment covered by foil. One thing that I am not 100% sure is if it is because covered interconnect RCA plug or phonostage itself but I strongly believe that it is phonostage. 

 

Does anyone know how to shield case internally instead of externally to avoid this stupid look?

 

[Full Range]

You can use a product called mu metal in specific areas 

 

Have a look at a few YouTube videos on how mu metal is used in electronic components to get an idea 

[H.E. Pennypacker]

I used this on the internal cavities of electric guitars - amazing results:

 

https://www.3m.com/3M/en_US/company-us/all-3m-products/~/3M-EMI-Copper-Foil-Shielding-Tape-1181/?N=5002385+3293719476&rt=rud

[Spider27]

I tested a few more ideas and solved the issue. Here is my dummy trial and errors and hope this helps with anyone who has similar issue and save their time and effort.

 

Test #1) Completely seal the box with aluminium foil but looks very ugly.

It worked with a condition which I found later.

 

Test #2) Shield inside box with aluminium foil completely instead of externally.

It did not work somehow.   

 

Test #3) Put small cardboard box to cover preamp section only and covered the box with aluminium foil.

The reason that I did put cardboard box first is to prevent shorts in circuit and covered the cardboard box with aluminium foil. However, this also did not help. 

 

Test #4) I replicated Test #1 but this time, I could not solve the hum issue.

I dig deeper and found that it only works when aluminium foil touches one of RCA plugs. 

 

Test #5) this time I soldered a small wire between one of ground socket of RCA female plug and ground wire socket.

I google searched and it is actually poor shielding on signal wires inside phonostage and this method completely eliminated the hum and dead silent now.

 

Thank you for those who shared ideas in this thread.

[Batty]

Try to make that wire as short as possible and keep the insulation as close to the soldered joint as possible.

 

Another question, are all the RCA on a common ground? i.e. soldered to each other.

[Spider27]

6 hours ago, Batty said:

Try to make that wire as short as possible and keep the insulation as close to the soldered joint as possible.

 

Another question, are all the RCA on a common ground? i.e. soldered to each other.

Noted well and thanks for the suggestion. I will try that in the future. At present, it is dead silent so no urgent need to make any change. 

 

I am not sure what the common ground is. Sorry mate. I am not tech savvy. What I know is that each RCA has separate ground and not connected together.