cornet "burn-in"-and hum problems

gehano · « **on:** 30 Mar 2010, 06:06 pm »

hi guys,
after a few weeks of work, my cornet2 is ready 2 play.
..and since a few days (all together about 15 hours )the amp is running. HOW many hours does it until the amp is "burned in" ?
also there is a little hum as a "background" sound during listening, ..when i switch from mono 2 stereo, the hum changes also, its louder on stereo...

i`ve read about the problem, and someone said, the transformer can be a problem, what can be done 2 slove this probelm.
drilling wires ? better isolation on the wires ?

my turntabe dont have a cable for the grounding (RB300-REGA), so i dont have a grounding on backside, is this a problem ?

thanx for your help

WGH · « **Reply #1 on:** 30 Mar 2010, 06:19 pm »

Can you post a photo of the innards so we can see your wiring and grounding connections? An ungrounded turntable can produce hum.

The burn-in time depends on who you believe and what capacitors you have used, it can vary from 15 minutes to 400 hours.

Wayne

SET Man · « **Reply #2 on:** 30 Mar 2010, 06:21 pm »

Hey!

Oooooh! That's pretty

Take care,
Buddy

harryf · « **Reply #3 on:** 31 Mar 2010, 04:39 am »

Very nice work!Is your cornet around any stray magnetic field's from other componant's?

harryf · « **Reply #4 on:** 31 Mar 2010, 04:43 am »

Did you leave any bare metal between the transformer and the chassis?I did and have very little hum but i have 96 db speakers.If i had to use my 89 db speaker's and crank it up i do get a small hum but what i would expect from a tube componant.

gehano · « **Reply #5 on:** 31 Mar 2010, 09:58 am »

thanx for your comment.
here are some more pic,
...the chassis is realy very tight..so i hade 2 make some little "modification

i also changed the line-up that the cornet is on top, its a bit better.
my Turntabe-tonearm RB300 from rega dont have his own grounding ... hopefully this is not the problem.

thanx

gerhard

kenm · « **Reply #6 on:** 31 Mar 2010, 07:06 pm »

I would try earthing the tonearm to the Cornet to see if it makes a difference. I've never owned a turntable without an earth lead before ! You should make up a piece of wire with alligator clips on both ends and then you can easily try different connections to earth. I've had a cornet for a while now but still have a bit of hum when running at half volume. I suspect it's the transformer that is the cause of the hum. I'd really like to try a better quality C-core or toroidal if I can get one made up. Has anyone tried a different transformer on the Cornet ?
Apart from a small amount of hum I love the sound. It's a big step up from a Bugle.
Very nice build by the way.

poty · « **Reply #7 on:** 31 Mar 2010, 08:10 pm »

I'm not sure about the green-yellow wires coming to one of the corner of the chassis - are they connected to the metal part of the chassis?
I'd try to short the input RCA-connectors (disconnect all cables first) and to listen to the differences. If the hum disappears, then it is from the cables (maybe you have to ground your turntable). If not - try to relocate ground wires and check all connections/soldering.

Yoda · « **Reply #8 on:** 31 Mar 2010, 09:16 pm »

One thing might be proximity to your turntable or cable routing. (Carefully) hold your cornet and move it about while the phono is selected on your amp and turn up the volume. Does the hum change? Do you have the same hum if you unplug your tonearm from the cornet? IIRC, the Rega is grounded through one channel. I have one and it is pretty quiet w/ the stock cable.

This is from a previous post 'Clarinet for Christmas' by another user. (look for the section about the grey wire in the transformer):

I previously has a rag tag bunch of interconnects so I ordered parts from Percy Audio to DIY some ICs. A representative pair are seen in the above photos. The ICs started as 28ga. solid silver wire in cotton sleeve that were gently twisted around a cotton rope and wrapped with Teflon plumbers tape. Eichmann Bullets were used for RCAs. In the unshielded version, I could assess the emissions emanating from the stereo components. The Hammond transformer on the Cornet2 was a major noise creator. I disassembled the Hammond TX and fished out the "grey" wire that was not really contacting the TX case. So I star grounded to the Cornet2 chassis ground lug. That reduced the radiated noise in the immediate environment dramatically. I did the same to the Hammond transformer on the Clarinet.
I also decided to wrap the interconnect cable with shielding braid with a single ended grounding wire. These modifications quieted the system to an amazing low noise floor.

gehano · « **Reply #9 on:** 31 Mar 2010, 09:33 pm »

..well i`ve tried an other preamp ..its a _graham slee- communicator_
and if i use the same cable,...there is nearly no hum,...

so i cant imagine that the turntabe or the cables, or the positon of the turntabe-phono pre is the problem.

I'm not sure about the green-yellow wires coming to one of the corner of the chassis - are they connected to the metal part of the chassis? (poty)

i just cut these cables they were for the grounding, ...inside because i dont have an outside grounding with Phono cable,but no improvement
Do you have the same hum if you unplug your tonearm from the cornet?(Yoda)
when i unplug the turntabe from the cornet, and let the output plugged, the hum is much more !

do YOUguys use any isolation between the transformer and the chasis ? i did you different screws

hotrod · « **Reply #10 on:** 31 Mar 2010, 09:39 pm »

Looking at the pics I do not see the grey tranny groung wire,Did you remove it from one of the lower bolts from inside the end cap?Lengthen the wire,run it down thru the top plate and attatch it to the chassis ground.
Make sure the body of the RCA connectors do not come in contact with the holes in the chassis.
I removed most of the hum by playing with the placement of my interconnects and keeping my SUT as far away as possible.
There are ALOT of posts about this very issue,go through and read,some very useful info to be had.It does take some time,but a silent Cornet/Clarinet can obtained.
Are you using plastic standoffs?It looks like no,that would be another thing to consider.
I'm not sure what you mean by you cut the ground wires,the board needs to be grounded to the chassis along with the plug ground and tranny ground.

gl

david62 · « **Reply #11 on:** 31 Mar 2010, 10:26 pm »

If the body of a RCA contacts the chassis of the Clarinet Line stage,can that cause noise or hum in that amp.as well?Thanks,
Dave

hotrod · « **Reply #12 on:** 31 Mar 2010, 10:39 pm »

I believe it will.You want to make sure the teflon washers are in place,these are what keep the RCA jacks isolated from the chassis.
Since the body of the jack is already grounded to the board,another ground path may create a ground loop issue,at least thats my take.

david62 · « **Reply #13 on:** 31 Mar 2010, 10:57 pm »

Thanks for the ground loop information.I need to check for contact between one of the RCA bodies on one channel of the output of my Clarinet.Can somebody tell me what kind of noise a ground loop causes?Thanks,
Dave

gehano · « **Reply #14 on:** 2 Apr 2010, 01:16 pm »

Quote from: hotrod on 31 Mar 2010, 09:39 pm

Looking at the pics I do not see the grey tranny groung wire,Did you remove it from one of the lower bolts from inside the end cap?Lengthen the wire,run it down thru the top plate and attatch it to the chassis ground.

so you mean there is comming a grey cable from inside the transformer ! for the grounding ?

hotrod · « **Reply #15 on:** 2 Apr 2010, 02:59 pm »

In theory the ground wire is attatched to the tranny housing in which the feet of the transformer are to come in contact with the metal top plate to ground the tranny.If the paint is not removed(bottom of tranny feet and anodize top plate)it will not be grounded.
Remove the bell caps and you will see the wire attatched to one of the lower bolts,this is the wire you want to run to the star ground on the chassis.
Read this link to prior post,pics included here.http://www.audiocircle.com/index.php?topic=68319.0

This alone may not solve the hum issue,but this along with other schemes will get you there.
Install a groung lug at the rear of the chassis and make sure the board ground,plug ground,and tranny ground are attactched to it.Then try grounding the TT/arm to the lug and see if the hum has decreased.
Placement of cables and the component itself are important,play around with these for further improvement.
You'll get there.

Yoda · « **Reply #16 on:** 2 Apr 2010, 06:39 pm »

i noticed you used brass hardware to connect the pcb to the chassis. The stand off's on the traditional build are nylon. Because the brass might connect the ground plane and the chassis don't know if it messes up the star ground system. Your cornet should be hum and noise free when there is nothing plugged into the inputs, so there must be a loop somewhere in your build. Did you check input and output polarities?

gehano · « **Reply #17 on:** 2 Apr 2010, 07:20 pm »

thanx, very much
...so i had some work to do....

..so i also need 2 remove the paint from the chassis, ..
do you use anything for a better contact between the chassis and the transformer ?

i use the standoffs inside, but i had 2 cut them because the chasis is very small

hopefully the brass is not the problem,

jomar · « **Reply #18 on:** 4 Apr 2010, 03:31 pm »

Quote from: gehano on 2 Apr 2010, 07:20 pm

thanx, very much

i use the standoffs inside, but i had 2 cut them because the chasis is very small hopefully the brass is not the problem,

Previously i also use metal standoffs and i have a slight hum ... changing them to a Nylon/plastic made the background dead quiet. Seems like the metal standoffs are making some ground loops. hope this helps

taskerc · « **Reply #19 on:** 4 Apr 2010, 09:42 pm »

Quote from: jomar on 4 Apr 2010, 03:31 pm

Seems like the metal standoffs are making some ground loops.

They are, or can do. There is a reason Jim Hagerman specifies the plastic version. As you will find, aside from potential component tweaks and upgrades, Jim has figured it all out to a very high degree.

From reading the various discussions on this topic, the biggest sources of hum have been metal standoffs, RCAs that are grounding on the chassis and interconnects with faulty shields. Transformers (and the grey wire as mentioned) are also frequent but personally I have no hum from mine and did not touch the grey wire.

Chris

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cornet "burn-in"-and hum problems