Cornet2 Input Hum

0 Members and 1 Guest are viewing this topic. Read 5246 times.

el34

Re: Cornet2 Input Hum
« Reply #20 on: 11 Apr 2012, 09:09 pm »
In that case, the wire from the turn table ground to the PCB should suffice.  I can't trace a line so I drew arrows to show the line from the turntable plug from the chassis that goes into the PCB.  It's hard to see it because it's black.  I didn't have any green wire at the time.  The Saftey ground is also soldered onto that connection as well.  So as it stands now there are 3 things connected to that turnable ground: the PCB, the saftey ground, and the transformer ground. 



Yes, that's how I traced it out, and was concerned for two reasons, the possible mixing of "noisy" and "clean" grounds, and having too many things on that ground post, which might make the connection less secure, which, with the safety ground in particular, is bad news.  A loose signal ground would cause noise.

Note the hole pattern for the RCA input and output modules (if you were using that part)... There are 5 holes per module, so one each for:
  • left shield
  • left signal
  • ground post
  • right signal
  • right shield


poty

  • Full Member
  • Posts: 616
Re: Cornet2 Input Hum
« Reply #21 on: 11 Apr 2012, 09:52 pm »
Yes, that's how I traced it out, and was concerned for two reasons, the possible mixing of "noisy" and "clean" grounds, and having too many things on that ground post, which might make the connection less secure, which, with the safety ground in particular, is bad news.  A loose signal ground would cause noise.
I think you mixed up things here. As I already wrote the signal ground is completely on board (as the connection to "noisy" power supply), so it can't be loose and noisy.
According the rules for safety ground it should be connected near the mains earth input either by it's own nondetachable connection or with other connections, but the wire should be nearest to the metal part of case and be connected by different means than other wires (that means you should be able to disconnect other wires while the earth wire stays safely connected).
I'm agree that the electrical contact with th case should be good, that means you should remove paints, anodising layers and other obstacles which prevents the good connection.
Note the hole pattern for the RCA input and output modules (if you were using that part)... There are 5 holes per module, so one each for:
  • left shield
  • left signal
  • ground post
  • right signal
  • right shield
No, if you look through the datasheet for the part you find, that leftmost and rightmost hole is for mechanical purpose only. The central pin is common ground, left and right - corresponds to respectable signals.

I think you should begin with changing wiring for inputs and outputs, then measurements, then anything else.

el34

Re: Cornet2 Input Hum
« Reply #22 on: 11 Apr 2012, 10:54 pm »
Yeah, I mis-wrote that, I meant the turntable ground, signal ground comes in on the RCA jack outer shell.

Didn't look at the datasheet, just a guess looking at the board, my bad.

I still think putting all that stuff on the post with the safety ground is asking for trouble, it increases the chance for it to come loose.

That transformer "ground" wire is for-sure a shield and not a center tap for something?  It looks black in the picture, same color for primary neutral, if I remember correctly.

tubesorbust

Re: Cornet2 Input Hum
« Reply #23 on: 12 Apr 2012, 01:23 am »
Well guys I had my celebratory beer that tonight!  Thanks guys for all your help.  I ended up just cleaning up the RCA connections to the board and twisting the lead from the tranny to the ground post.  I figured after I cleaned it up I might as well give it a try.  It sounded great!  There is a slight hum from the right speaker still but as soon as the music starts playing it disappears.  In fact I tried looking for it during a song and I just couldn't find the hum.  In any case I'm sure I'll clean the rest of the Cornet eventually to see if i can get rid of it all together.  BTW
Quote
It looks black in the picture, same color for primary neutral, if I remember correctly.

It's black because I had to extend the wire from the tranny to make it reach, and black wire is all i had.  It originally is grey.  I'll probably end up shortening that eventually.   

In any case thanks both you guys for all your help!!  This is what it ended up looking like.






DeadFish

Re: Cornet2 Input Hum
« Reply #24 on: 12 Apr 2012, 02:14 am »
Good for you!  Perseverance furthers.  I put up with hum on the Cornet 2 I built, but eventually ran it off, with a lot of help on the way.  I just didn't know enough to help you. It is a nice phono stage, enjoy!

el34

Re: Cornet2 Input Hum
« Reply #25 on: 12 Apr 2012, 02:53 pm »
I'm glad you got it worked out!