[Bill Epstein]

Finally, a year after the explosion, I've got my Cornet back together in the original case which was quiet when it had the Cinemag inputs. W/O the Cinemags, with IEC ground and board Earth to the chassis, it hums like mad. How can that be

[tubesforever]

More often than not, when this stuff happens your RCA ground/s are touching the case work.  You have to float the chassis RCA ground or you get a serious hum.  Recheck the input and output chassis RCA grounds.  Make sure they do not establish continuity to the case or the earth ground. 

I hope this helps Bill!  Happy New Year!  Its fun to see you posting around these parts.  Bill can you call me?  I have a question about your copper foil (like where can I get this stuff).

[Bill Epstein]

Hey Tuibes, Happy New Year backatya, and to all!

Not the RCAs, already checked that. Gonna try a jumper wire from the input RCA grounds to the star ground. Where's the board EARTH on the schematic? The only pitchforks I see are at the AC in.

Copper foil comes from Michaels or any craft store where you will also meet chicks aa

[tubesforever]

Bill, I assume you are using chassis ground RCA's, so make sure that the wires going from the rca's to the board are well soldered.  A cold solder joint at that point would make this kind of noise. 

Also recheck the output RCA solder connections.

You have a gremlin!  This is not fun.....I bet it is something silly stupid.  Did you check all the tube wipers to make sure you are getting good connection at that juncture?

Keep us in the loop....(ok, that was a really lame attempt at hum/ground loop diy humor).   Its time to get back to my 12 step diy program.

Cheers!

[ScottRT]

Try grounding the tranny housing directly to the ground lug. You can simply experiment by touching a bare wire from the right bottom tranny bell bolt (where the internal ground wire is attached) to the ground lug and see if anything improved.

It made an overall improvement on the unit I was just troubleshooting.

Scott T.

[hagtech]

Hum or buzz?  Could just be an ungrounded tonearm?  Does it hum with nothing plugged into the inputs?

jh

[Bill Epstein]

Had a chance to check today, the hum is the same without an input.

Will re-visit the RCA-touching-the-case thing.

[tubesforever]

Bill do not allow the RCA chassis grounds to go to the earth ground.  The earth ground should be the shortest pathway to ground for the board.  If you go RCA ground to earth, then the ground will loop at that connection and ruin your sound.

I go so far as to run the ground wire of right and left individually back to the boards signal ground input.  So they only see the common ground at the board. 

I have no idea at all if this is better or not.  From a straight engineering standpoint, the ground could be connected at the rca and then brought to the board.

So here are my grounds going to star.  1. the IEC earth ground, 2. the board earth ground, 3. the hammond ground wire, 4. other miscellaneous grounds going to my source selector switches. (Jim recommended I ground those long brass tubes that actuate my switches.  I do plan to replace these with styrene tubes in the future.  The ground post near the RCA inputs is my star ground point and it grounds to the aluminum case by default.  I make sure the shortest wire is the one to the IEC. 

For some SUT's you see them using a series resistor to change the ground plane between the earth ground and the transformer ground.   I think a 10 ohm, 20 watt Mills wire wound resistor would be all it would take to establish a different grounding plane for the board. 

Jim any comments on this from your experience?  I know the CineMags seem to benefit from the added resistor.   

[Bill Epstein]

So here are my grounds going to star.  1. the IEC earth ground, 2. the board earth ground, 3. the hammond ground wire, 4. other miscellaneous grounds going to my source selector switches.

That is perzactly how I have my grounds now and still have loud hum. I just put the Cornet back on the bench to dis-wire the RCAs and re-seat them.

Played it last night hum and all with Cinemag 150 ohm setting. My memory of the Auri-output caps is hazy but I think maybe the Jantzen Super Zs image better with a slight loss in bass clarity. 'course that's just the first hour.

Wishful thinking dep't.: wish Vampire or somebody would make RCAs with the loose nut on the outside; would make installs and changes so much easier. I do like the CM Hex, tho' and the price is right.

[ecir38]

Hey Bill, see CM2F

http://www.vampirewire.com/c-17-chassis-mount-rca-female.aspx

I like the PCB2F because it looks to be plastic that would penetrate the rear of the chassis. This way you know the rca will never ground to the chassis. The problem is I think the pinout doesn't look to be the same.

The PCB2F/S could be used if you just hard wire it.

http://www.vampirewire.com/c-19-pcb-mount-connector.aspx

BR