Cornet Hum :(

theclipper · « **on:** 9 Apr 2009, 10:57 pm »

Hi,

I posted here about a month ago as I was contemplating buying a used unit on Audiogon. I ended up buying the unit and hooking it up today.

I was hoping someone out there might be kind enough to try and help me out. I will try to explain my situation as best as possible.

There is a definite hum present when I get the volume control up to about half

. My system consists of; Fisher 400, Cornet, Rega P5 w/Ortofon 2M Black cart, Klipsch Forte II speakers. I made sure to crank the volume on the other inputs and sure enough its just coming from the AUX input that I have the Cornet hooked up to. I then hooked up my computer to that input to make sure it wasn't the input and there was no hum present. The hum continues even of the Cornet is unplugged. The only time it stops is if the RCA cord is disconnected. I swapped RCA cords to make sure it wasn't a faulty cord. The guy I bought it from upgraded it to a CCS so I was thinking this would help with potential hum. I also ran a wire from the Cornet to the TT and the Cornet to the Fisher and neither removed the hum.

I am willing to try anything to deal with this. I'd greatly appreciate any response!

Thanks so much

Chris

Bill Epstein · « **Reply #1 on:** 9 Apr 2009, 11:59 pm »

Here's a link to a certain 'Doctors' troubleshooting riff that really breaks it down and helps out

http://www.bottlehead.com/loosep/troubleshooting.htm

theclipper · « **Reply #2 on:** 10 Apr 2009, 01:21 am »

Hi Bill,

I appreciate the link, I went through it but it didn't really seem to remedy the problem at all unfortunately

Thanks,
Chris

theclipper · « **Reply #3 on:** 10 Apr 2009, 01:32 am »

I just realized that if I get a good buzz going at a high enough volume than a second high pitched sound will come in. This second sound goes away if I move the Cornet off the rack and away as far as possible.

hagtech · « **Reply #4 on:** 10 Apr 2009, 04:39 am »

The problem is through the power cords. Ground loop with the interconnects. You're picking up magnetic fields from transformer somewhere. Try moving cables or equipment around. Or disconnect something else. The noise will disappear when you remove the right piece. Just a system issue. I doubt anything is wrong with the Cornet.

jh

theclipper · « **Reply #5 on:** 10 Apr 2009, 10:29 pm »

Hi Jim,

I really appreciate your response. I have been trying to unplug my other gear and when I uplugged my HD-DVD player the hum was reduced. The problem is that the hum is definitely still there though. I tried moving around all the innerconnects to keep them away from the power cord and transformer but that didn't seem to help. Is there anything else I could try? Do I need some really expensive power cord?

Thanks,
Chris

stereohifi · « **Reply #6 on:** 11 Apr 2009, 03:32 am »

Hello, at first when i first turned on my cornet 2, i notice a little hum.
Make sure the power transformer is properly grounded. The hammond as a static shield and it is on one of the attachements (4 screws)
Make an ohmmeter mesurement bethween the groung tip of your AC plug ( please unplug it first!) and the chasis ground. The transfomer as to be prerly grounded...make contact.
Them make sure that all ground or returns are all on a single point (star ground).
There also poor quality female chassis RCA connectors on the input is very important. Don't use cheap stuff there.
I had the Eichman RCA's male on my TT, i had to replace them, for better integrity contacts on shield with locking type WBT.
Good Luck!

tubesforever · « **Reply #7 on:** 11 Apr 2009, 02:19 pm »

Jim, I had a nasty hum from my Cornet 2 due to two reasons:

First I had not gotten my RCA chassis insulators correct. They have a tab that sets into the 3/8 inch hole to float the ground on the RCA body to the case work.

I just had to flip that tab around so it properly floated and things were good.

The second issue was when I tried to jumper the right and left rca grounds and take them back as a single wire to my PCB.

I got my C2 completely quiet when I ran independent wires from the right and left rca chassis grounds back to the PCB.
Basically the jumpered ground wires at right and left chassis grounds were creating a loop before that ground could see the earth ground pathway at the board.

Those two changes got my C2 silent.

There is nothing like success!

Chris, I would like you to pull the cover and check with an ohm meter to see if your ground rca is toning to the earth ground. Second check the incoming ground wires from the RCA pieces and see if these are independent or jumpered. These are the easy things to look for.

Chris, all IC's are not created equally. Some are shielded IC's and some are not. If they are not shielded you run the risk of any transformer becoming a 60 hz radio beacon. The EMI can easily overwhelm a low signal source like a phono IC. The phono IC becomes the antenna.

Some shielded IC's have the shielding soldered to the neutral wire of both sides of the IC. On mine I make sure one shield goes to one neutral rca and the other side of the shield floats. That way the ground cannot loop inside the shielding. When in doubt get some Audioquest wire and check out to see if they quiet down the hum. These are always properly shielded.

So here is my recommendation. This is a three step process.

Step one: We need to make sure the grounds on the rca pieces are not connecting in any way to case. Chris this includes the ground body of the RCA jack you are inserting to your female chassis piece. It cannot touch the case or you get the same ground loop issue.

Step two: We need to make sure there are independent wires going from the right and left rca's back to your PCB.

Step three: We need to make sure you are running properly shielded tonearm cables that are adequately positioned to reduce EMI.

Get these three things right and I bet your Cornet will be as quiet as mine. If all this works out to be done right as your Cornet sits now, then we need to look for a cold solder joint on your PCB.

theclipper · « **Reply #8 on:** 11 Apr 2009, 06:52 pm »

Hey Tubesforever and all,

Thanks for the very detailed and thoughtful response, you have been a huge help to me thus far.

As you know, I am fairly new to this so you lost me at a few spots, I will try to best explain what I got from your post.

I have added a link to some pictures so you can try to see if there are any obvious problems. Please let me know if any other close ups would help

http://picasaweb.google.com/wolford.chris/Cornet#

First off, none of the RCA jacks are touching the case, there is a little white disc between the female part and the case and the male parts only touch the female parts.

Secondly, it looks as though every RCA spot has a ground wire running to the PCB. I see that the ground wire for these jacks comes from a metal protrusion off the jacks, I was wondering if this metal should be bent to touch the chassis or not.

Third, I am using the tonearm cables that are connected to the Rega as they are nonremovable. They would seem to be fine as they did not produce this symptom into the Fisher phono input. Actually though, there was a slight hum but this was totally eliminated as soon as I ran a groundwire from the external power supply of the Rega P5 to the chassis of the Fisher.

I am unsure of how to check "to see if your ground rca is toning to the earth ground", if you could elaborate on that more it would really help. Sorry I'm a little slow with these things.

Again, I really appreciate all the help I am getting.

Thanks much,
Chris

theclipper · « **Reply #9 on:** 11 Apr 2009, 10:05 pm »

As an update, I got some shielded cables from radio shack to see if they would help, but they did not help in the least.

jameshuls · « **Reply #10 on:** 12 Apr 2009, 04:00 am »

Hi Chris;

Having looked at your pictures, it seems that some of your ground wires may be touching the case. Might be worth a try to make sure that there is some space between them.

Good luck!

James

theclipper · « **Reply #11 on:** 12 Apr 2009, 05:33 am »

Hey James,

Thanks for pointing that out, I will look again once I get back home. I believe I was able to get at least a finger nail between each of them and the case but I may be wrong.

Thanks,
Chris

nimrod · « **Reply #12 on:** 19 Apr 2009, 05:14 pm »

Quote from: tubesforever on 11 Apr 2009, 02:19 pm

Jim, I had a nasty hum from my Cornet 2 due to two reasons:

The second issue was when I tried to jumper the right and left rca grounds and take them back as a single wire to my PCB.

I got my C2 completely quiet when I ran independent wires from the right and left rca chassis grounds back to the PCB.
Basically the jumpered ground wires at right and left chassis grounds were creating a loop before that ground could see the earth ground pathway at the board.

Those two changes got my C2 silent. There is nothing like success!

I tried this on mine, and it did reduce the hum noticeably. Thanks for the tip.

It got me wondering that maybe the wiring from chassis mount RCA jacks to the board is causing part of the hum problem, and that using the board mount RCA's
in the parts list would be better in that regard?

hagtech · « **Reply #13 on:** 19 Apr 2009, 07:07 pm »

Are you using metal standoffs? Does it hum with no input connected? I'm pretty sure the problem is not the Rega.

jh

theclipper · « **Reply #14 on:** 22 Apr 2009, 08:58 pm »

Hi Jim,

What are metal standoffs?

It does in fact hum with no input connected.

I took it to a guy who really knows tube gear and he was able to reduce the hum a bit when running a jumper wire from a trannie screw to a metal plate seated below the Cornet. He let me keep the metal plate to seat the Cornet on and I did this same thing at my house but didn't seem to get as much of an effect.

Funny thing is that the hum seems to be reduced a bit when the unit is flipped upside down.

Any ideas on what might be causing the problem?

Thanks Jim and all,

-Clipper

galyons · « **Reply #15 on:** 22 Apr 2009, 11:54 pm »

Quote from: theclipper on 22 Apr 2009, 08:58 pm

Hi Jim,

What are metal standoffs?

Metal standoffs are standoffs made of metal as oposed to plastic standoffs, (made of plastic!

). These are the threaded plastic "towers" that lift the board off of the chassis. Metal standoff's will likely ground the board to the chassis and if that is not the primary grounding scheme create a ground loop, which, mostly will hum!

Quote from: theclipper on 22 Apr 2009, 08:58 pm

It does in fact hum with no input connected.

Then most likely the hum is coming from garbage emitted by a close-by component or cold solder joint(s) in the Cornet. Digital is always a likely suspect. Then large transformers in amps or preamps. Also check for unshielded AC cords close by. You mentioned a computer earlier, get it out of there, if not already done.

Quote from: theclipper on 22 Apr 2009, 08:58 pm

I took it to a guy who really knows tube gear and he was able to reduce the hum a bit when running a jumper wire from a trannie screw to a metal plate seated below the Cornet. He let me keep the metal plate to seat the Cornet on and I did this same thing at my house but didn't seem to get as much of an effect.

Funny thing is that the hum seems to be reduced a bit when the unit is flipped upside down.

Check by unplugging and moving the components immediately above and below away from the Cornet. Again may be a bad solder joint that makes better connection when the unit is inverted.

Quote from: theclipper on 22 Apr 2009, 08:58 pm

Any ideas on what might be causing the problem?

Seems that you are always using the Aux input. Did you try a different input "Tuner" "Tape"? "Any ideas....???!!! You have been given a bunch!!

Cheers,
Geary

theclipper · « **Reply #16 on:** 25 Apr 2009, 08:53 pm »

Hey Geary,

It looks like my unit is using metal standoffs. I tried it in a room with no computer and it still hummed. Also, the computer in my room isn't that close to the cornet and does not share the same outlet. I moved all my gear around and nothing seemed to help. Also, I tried all the inputs on the Fisher with no real change either.

I was wondering if anyone had the instructions and schematic for the Cornet? My local guy wants to take a look at them to make sure my unit is still assembled properly. Also, what mods would be done to the Schematic to incorporate the CCS? Mine has that mod so I'm wondering what will be different.

Thanks Much,
-Clipper

WGH · « **Reply #17 on:** 25 Apr 2009, 09:49 pm »

Quote from: theclipper on 25 Apr 2009, 08:53 pm

I was wondering if anyone had the instructions and schematic for the Cornet?

Here it is:
http://www.hagtech.com/cornet.html

The manual has the signal coupling cap upgrade info.
The standoffs are supposed to be nylon, that would be the first item to change back to spec.

theclipper · « **Reply #18 on:** 26 Apr 2009, 05:19 am »

Thanks WGH!

I will let my guy know that the standoffs should be nylon. Hopefully he can figure this thing out for me so I can be humless soon!

Quote from: WGH on 25 Apr 2009, 09:49 pm

Quote from: theclipper on 25 Apr 2009, 08:53 pm

I was wondering if anyone had the instructions and schematic for the Cornet?

Here it is:
http://www.hagtech.com/cornet.html

The manual has the signal coupling cap upgrade info.
The standoffs are supposed to be nylon, that would be the first item to change back to spec.

jameshuls · « **Reply #19 on:** 26 Apr 2009, 06:01 am »

I just painted the parts of my metal standoffs that could be a problem. No hum.