[theclipper]

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

Nice, I'll mention this to my guy, I'm hoping that these standoffs are what is causing the problem.  Just so I have the straight, they are just the 4 screw type things that hold the PCB board to the chassis?

[jameshuls]

You got it!

[harryf]

I have this exact hum problem as the original poster.I also seem to have not installed the chassis mounted rca's like i should of.So the proper procedure is make a hole big enough for the nylon round rca spacer to fit into.Mount the rca with nylon spacer's on each side.One on the inside is male fit's into the larger hole.Then last on the inside add the tab that goes to the ground?
I put mine on the chassis thinking it would ground it.
Then add two separate ground's from the rca tab's to the chassis?
Would running a ground wire from the tab to the ground bus be of any use?
Scrapeing some of the anodizing off under the transformer leg's will solve that ground issue?
Any help thank's!

[harryf]

Well i tried remounting the rca's no luck.I didn't run two ground's from the board though.I joined the rca's then the ground in the middle.I don't see how that could make a difference.I did this in my clarinet and it's dead quiet.
I tried moveing it around and did find one of my cable's really picked up alot of hum.I swaped that out for another which helped a bit but when i brought it near the power transformer i found that this indeed is the source of the hum.
What to do?I used brass standoff's.This might be it?
Or maybe it's the transformer grounding?I will try that tommorow.
The hum/buzz is from the transformer i'm sure of that.

[harryf]

Ok i tried a few thing's today.
I scraped under each leg of the transformer.
I added two separate ground's for the rca's.
Neither really did much.
I seem to have a low squeel,a low buzz,a low hum 60 hz.
So i unplugged my laptop.High squeel gone.Low buzz and hum still present but if i bring my inter connrct's near my transformer it make much less difference now so i did something right.
I still need to replace my brass standoff's.
I doubt that will do it but maybe?
I think it's the power cords.I'm useing a powerbar for my clarinet,cornet2,dvd player,chime and laptop.
Another for my cymbal's.
I moved the powerbar's around and i get a loud buzz.But if i route it right i get a dead silent cymbal,clarinet,chime system.I mean no hum no buzz no hiss,perfect.
Go to the cornet 2 and at half volume i get hum and buzz.
I use my piccolo right now at it's highest setting to listen and it sound's good but go to 12 o'clock and hummmmm.
I'm wondering how to stack this system for lowest hum and how to route the cord's.I have a target like rack.

[harryf]

Ok i made some nylon standoffs with nylon screws and nuts.
Well it made a little difference.
I would say 10 % of my hum was fixed going to the nylon spacer's and running seperate wire's to my rca's.Almost none was from fixing the jack so the nylon spacer fit the hole better.
I found a bit of squeel reduction by getting rid of my laptop ps.
So i got about 15% reduction and can turn the volume knob on my clarinet to 65% now then i get a hum.
The great thing is i fixed my buzz and squeel entirely.
What i also noticed was that my cable's are picking up the transformer.As i move them to the tranni the hum increases.So that's where i go next two pair's of sheilded rca's.
They make those i assume.
I have my piccolo installed and i go full volume at 50% so i can listen and hear very little hum.
I do notice it sound's better on a lower setting though.

[harryf]

oK UP TO DATE this is what i have done.Scraped the anodizing under the transformer to provide a better ground.
Resoldered every joint.
Bought new tubes.
Swaped tubes.
Added separate ground's.
Moved all the componant's so none are near to cause a hum.
So this is what i have.A cornet 2 that goes to 45% volume before it hum's to much.
I compensate by useing my piccolo to boost the gain so i can listen but i still feel someting is really wrong.
I have chassis mounted rca's.The are insulated from the chassis.
What i think is wrong is hum being picked up from the wire's i have running in the unit from the board to the rca's.
They are not insulated wire's but i used them in my clarinet and got no hum.It's dead quiet!!!

So i am aiming for the same noise floor in my cornet 2.
So do i add insulated wires for the rca's?
I have been advised to use coaxial cable like for a tv in this unit.What do you think?
I also am building rca's out of the same wire.
i think the hum is from the transformer to either the rca cable's or both them and the internal wire's.
What do you think?
i do know the hum is from the ps transformer as i can get the hum to go up in volume if i bring the rca's close to it.
Both are now routed as far away as possibe.Hummmmm!

[hagtech]

Have you posted photos?  Usually it is easier to see what is wrong than trying to put everything into words.

jh

[ronpod]

Harry,

Stay with it, your persistence will be rewarded. Here is a quote from my earlier experience; hope it helps

"I have been working on, and continue to work on reducing the hum. Whether it is a hum or a buzz may be an important distinction that I am not sure I can entirely distinguish. But this quest of noise reduction has been fruitful in moving down the noise floor.

A large reduction in noise occurred when I replaced my "economic" used tubes with NOS Telefunkens. The 12AU7 Telefunkens in the Clarinet were very quiet except for an intermittent ring. The ring was not volume dependent or input dependent. So it was evident that the ring came from the Clarinet. Tubesforever wrote that he experienced similar ringing that was solved by tube selection. So I tried swapping the tube positions and the ringing went away.

The Cornet2 is now the major focus of noise reduction. I have noticed that when I place my hand on the transformer, the Cornet TX is hotter then the Clarinet's. There is one more tube in the Cornet than the Clarinet so this may be the reason. But, I have a notion that heat is equated with noise (entropy). The first stage tube in the Cornet may be the most critical position for a low noise tube. Isn't this a reoccurring theme throughout the archives of this chat site? I've tried a GE, Mullard, Amperex Bugle Boy, and Telefunken 12AX7 tube in this critical spot and the the Telefunken is clearly the lowest noise winner in my system. Unfortunately, the Telefunken is also the most expensive. However, apart from the noise, each tube has interesting sound characteristics that could appeal to different tastes. The GE was used, noisy and used for component burn-in so its sound was not expected, nor performed to the standard of the others. The Bugle Boy added a liveliness to the music that is fun and beyond the laid back sound of the Mullard and Telefunken. I would likely be happy with the Bugle Boy if I could find one (they seem to be harder to find) with lower noise. The Mullard has a full, well behaved, maybe even lush sound that is pleasant that I would also be happy with if the Telefunken was not so quiet. But because the Telefunken is so quiet with a reputation of having a long life with little drift, this is my choice (today).

The laying of hands was an interesting experience. When I placed one hand on the Clarinet transformer, I could move my other hand over various components and places around my system to induce noise. I took this as a way to identify what items may benefit from further modification. I did a similar test with the non-shielded interconnects as written previously. When the noise increased when my hand or the cable was in close proximity to any item, that item was suspect. The shielding of the interconnects was very important in my system. These shields are connected only to the source ground lug. When I lift these connections a definite rise in hum occurs, so I am encouraged that something good is accomplished. In terms of the most critical interconnect, it seems to be the IC between the SUT and the Cornet2. The SUT can be quite noisy if not properly grounded. I have tried to examine my grounding system to determine where the center of the star grounding is. It appears to be the shield of the Cardas tone arm cable from the turntable at the SUT input. This arrangement provides my system the lowest noise floor so far (but is subject to further testing) and creates the largest hum when disconnected."

ronpod

[poty]

Scraped the anodizing under the transformer to provide a better ground.

Better to connect ground wire from the transformer to the ground star. ONE WIRE, not 4 legs.

Resoldered every joint. Bought new tubes. Swaped tubes.

Good.

Added separate ground (wires).

You mean to RCA? Good.

Moved all the (other) components so none is near to cause a hum. ...
I have chassis mounted rca's.The are insulated from the chassis.

Good.
And still:

A Cornet 2 till the 45% - no hum.

Hmmm...

What I think is wrong is hum being picked up from the wires ... running inside the unit from the board to the RCAs.
...
So should I add insulated (shielded you mean?) wires for the RCAs?

Very easy check - shorten the inputs on the board just in the place where they soldered. It effectively shortens ANY signal from the wires and earlier (including noise). If it'll led to huge improvements - go to that way.

I used them in my Clarinet and got no hum.

Incorrect comparison. In the Clarinet input you have the hundreds times more stronger signal than in the Cornet 2.

I also am building RCAs (cables) out of the same wire.

If you mean you have unshielded cables - you should immediately obtain shielded one.

I think the hum is from ...

1. Check ground wire (the third one, which is not phase and zero) in your power outlet (or something you use to AC power your components).
2. Check that the ground wire securely fastens to ground star of the Cornet 2 and the music source device.
3. Check (as described earlier) that Cornet 2 is not picked noise from outside (input cables, RCA connectors, to-board wires).
4. Check electrolytic capacitors in both heating and plate voltage.
5. Check if the Cornet 2 works with different preamp.
If nothing from above helps you can try to pull out tubes (beginning from the V1, one at a time) and understand, what stage add so much noise. Than check the stage closely, maybe swap tubes.

Good luck!

[harryf]

Well here's what i'm going to do even though i don't want too.I ordered the original rca's that jim recomended.
I have chassis rca's on all my unit's.The look great professional even.No hum in any but the cornet 2 2.But these rca that are chassis mounted give nothing but problem's in the end Just tightening them is a pita.
If you ever need to swap or fix anything you want the board mounted rca's.
If there was a way to secure the trace that the wire's are mounted to chassis mounted rca's might be ok but if you need to play around like i need to now it's a pita.
So i'm going back to the stock pcb rca's as i feel the longer unsheilded wire's are the problem.
We'll see.
Great post's all.i will check back.

[harryf]

oK I PUT HTE STOCK  rca jack's in my cornet 2.Exactly what i thought would happen did.I pulled a trace and had to lift the wire out of the pcb and solder it to the post.It look's bad but works.
So here's the deal i lost 15% of volume.It actualy hum's louder!Darn!.
I did notice this though that with all my other electronic's on if i turn off the cornet 2 i get about 5 second's of hum free music.
I'm thinking it's the transformer?I even unlosened it today and sanded the bottom of the trani leg's.
Still a hum?
I have read there is a wire that ground's the transformer internal to it.
I wonder if takeing it apart and inspecting it might help?
I wonder if i should add a ground strap from this leg to the star ground point?
I'm going to take it into another room and test it tonight away from any other electronic's.
I am building cables from sheilded coaxial cable.I'm going to test voltages tonight too.

[harryf]

Ok last night i tried something different.I tried tieing the  rca jack ground to the star ground point.
From that point on only my rectifier come's on but very slowely.No 12au7 or 12ax7 glow.
So i tried cutting the ground's i made still nothing.
So i took a look around inside and i have some sort of burning on the outside of the rectifier socket.
The funny thing is inside all look's fine.
I'm going to measure everything later to see if a resistor died.
The voltage's too.
While everything was apart i unscrewed the transformer.I scraped bare all the legs and the chassis so it's bare metal.
I also added a wire that lead's to the star point from the ground point on the transformer.
I do notice that the transformer turn's on because it will do sort of a vibrational hum.Not a normal hum because none of my other transformers ever acted like this.Nor did it act like this in the last few years.
So maybe the tranni went south as it takes very long for my 5a4d to light up.I tried two known good tubes.

[harryf]

oK I TESTED THE THING ON ANOTHER outlet and figured out why the small tube's didn't light up.
I pluged it into a powerbar that's connected to my tt speed controler!duh.
So i measured it on another outlet and everything lit up.
All voltage's are spot on except the 155 on the 12au7 which is 136 v.Which is within spec.
I put it in my regular system.
I get a hum at 55%.The hum is different than before it's deeper.
I guess what i did earlier had some effect.
This is a 60 hz hum i expect.
I moved it all around and i get no difference in hum from it sitting right next to my clarinet.
I can and will finish my sheilded cables but i think it is not the problem.I think it's the transformer?I'm not sure how to check this other than just buying a new bx370?.

It does not hum at zero volume the 370 i mean.So other than swaping out a new ps tranni or sheilded cables i don't know?
I have a beefy power cord on it could this be a problem?I have another but much cheaper i'll swap that in.

[poty]

It seems you do anything but the requested. Why not post photos as asked by JH or try easy tests from my post?

[harryf]

Hi poty i have done everything requested..Except pic's because i'm not that computer savy.I have posted pic's on another site but it was hit or miss as to if they could be seen and i'm not even sure why?
To this point i have scraped under the star ground to get a better ground.
Resoldered everything.Inclueding the ground.Added a ground wire from the transformer bolt to the star point.
Rewired all the transformer wire's so their neat and tidy.
Add the original type rca to shorten the length instead of chassis mounted rca's and wire.
Fooled around with all the tubes.Swaped in several other known good tubes.Switched positions of them too.
Added nylon standoff's.
So at this point the only thing i have noticed is that is i turn the power off the thing stop's humming until the caps let off all their power.
I have also moved it to another system,moved it all around and messed with cables.
The cables are no longer the problem as i have two pair that are properly sheilded.
So i'm at the point i think it's the transformer.
I have the part's that i could remplace the caps in the power supply.
I have not measured all the resisitor's so that's next.
If you think i need to measure the plate cap's i will do that next.
I have several other bx 370's in my chime and in my clarinet but i really dont want to pull that good tranni to cheak as both unit's are working great.

[harryf]

Ok i'm hopeing i found the problem.Ro1 specs out at 300 ohm when it should be 220 ohm.
Is also lead's or come's from the red wire that connect's to the transformer.
Also on the outside of the pin ro1 lead's to is the burning.So i'm guessing this might be the problem!
I hope.I guess something let lose inside that resisitor.

[poty]

"Better to connect ground wire from the transformer to the ground star. ONE WIRE, not 4 legs."

Added a ground wire from the transformer bolt to the star point.

Half a measure, because you now have four legs effectively touching chassis. But at this point I don't think it is the source of problem. Just for the future job...
"... shorten the inputs on the board just in the place where they soldered." - Was there any effect about it?
"1. Check ground wire ... in your power outlet."
Maybe you do not have the ground wire connected to your power outlet?
"2. Check that the ground wire securely fastens to ground star of the Cornet 2 and the music source device.

...scraped under the star ground to get a better ground.

Done.

...if I turn the power off the thing stops humming until the caps discharged.

I think (if it is possible, because if you do it wrong it is dangerous!) you can try to disconnect B+ voltage instead of full power off and hear again. Maybe there is problems in one of the rectifiers. (For example - bad diodes or capacitors which brings more AC to the DC lines.)

I have the part's that i could remplace the caps in the power supply.

Better to know what to change first!

[harryf]

Well i replaced r01 and the resistor both read low and and burned up.This was a 2 watt kiwami.
So i remeasureed a new one the put a 1 watt takman in it and it burned too,So i pulled the .01 cap next to ro1 and sure enough it read's 6 nf when it should read 10 nf so i think i found my problem:0
The cap was going bad affecting the resistor.Would this make it hum?I'll try tommorow.

[harryf]

Well i replaced the .01 cap that was bad and the resistor too the 220 ohm one.The 220 resisitor literally burned up in a flash of fire!A 1 watt takman carbon resisitor.So i have come to the conclusion that the transformer must be bad of some parts in the power supply have gone bad.
When i built this i built it with a combination of stock resistor's and cap's with auricap's in the signal position's.My clarinet, chime and cymbal's are all auricap's and takman's and kiwami's.
I alway's ment to rebuild my cornet 2 to the other componant's standard's but never did because i felt it sounded good enough.So it seem's now is the time to rebuild the thing and check every cap.
It's just better in the long run than burning up resistor after resisitor until i find the problem.
It there a way to test the transformer?
All the other part's i either have or won't cost much.Except for the 370bx