C2200 Humming.....Tubes?

[Stereofro]

I noticed while investigating issues I was having with my 275 that I have a low hum coming from my C2200 pre. The hum is there when the unit is in standby. When the tubes warm up and the unit comes out of start up the hum seems to ubruptly stop. I have tried my power conditioner, a different power conditioner and the wall outlet itself. I changed the power cord.I tried many things first eliminating one at a time until I noticed it for the most part went away once the unit comes out of warm up. Another thing I noticed is the tubes glow bright when first turned on and then tone down when they go into to warm up. This seems very unsual to me. My 275 is going away for service and I want to make sure that this is taken care of before I hook it back up to the 275. Any advice would be greatly appreciated.

 

[Pio1980]

Is the hum from the unit or the speakers?

 

[Stereofro]

Is the hum from the unit or the speakers?

Speakers

 

[Pio1980]

Speakers

OK, so only with the power amp lit.
In the olden days with nonpolar plugs, we coped by reversing the power plugs orientation until the background hum was lowest. In this case, I'm otherwise suspecting your ic cables from the pre to the power amp, but, if there is a way to switch ac power polarity to the pre and/or the power amp, I'd go there first.

 

[Stereofro]

OK, so only with the power amp lit.
In the olden days with nonpolar plugs, we coped by reversing the power plugs orientation until the background hum was lowest. In this case, I'm otherwise suspecting your ic cables from the pre to the power amp, but, if there is a way to switch ac power polarity to the pre and/or the power amp, I'd go there first.

 

[Stereofro]

I am not sure how to change polarity. I have tried a few interconncets and even suspended them as to avoid ground loop. Is it normal for the tubes to really light up for a second before going into warm up?

 

[Stereofro]

I am not sure how to change polarity. I have tried a few interconncets and even suspended them as to avoid ground loop. Is it normal for the tubes to really light up for a second before going into warm up?

 

[Pio1980]

Some tubes heaters will initially flash bright, then settle as normal for those examples.
To swap power polarity on the old ones, you'd just flip the power plug(s).
Modern polarized plugs don't permit that, you get what you get. If it's not loud, and not audible with the preamp lit and ready, I wouldn't worry.

 

[Stereofro]

Some tubes heaters will initially flash bright, then settle as normal for those examples.
To swap power polarity on the old ones, you'd just flip the power plug(s).
Modern polarized plugs don't permit that, you get what you get. If it's not loud, and not audible with the preamp lit and ready, I wouldn't worry.

Maybe it is in the actual amp inputs? There is obviously no noise with no IC's but then there is the fact that it goes away when the tubes warm up. 2 months ago I had none of these problems and the only difference is the speakers.

 

[Pio1980]

Are the new speakers significantly more efficient/sensitive than the previous set?

 

[Stereofro]

Are the new speakers significantly more efficient/sensitive than the previous set?

Yes. 90 and 91 vs 87 and 89. One other thing I noticed. If I touch the main outs(balanced) they seem to be live in standby and not once the unit is in full power. I say that because when I touch them and them only, I get a loud hum through the speakers.

 

[Pio1980]

Interesting, have you rerouted them away from other wires, ect?

 

[Stereofro]

Interesting, have you rerouted them away from other wires, ect?

Thats the thing. I am not even using the balanced inputs and the only set that is live is the mains and only when in standby. I have moved everything and nothing seems to effect the hum except turning it on and letting the tubes warm up.

 

[twiiii]

You may have a faulty ground in your electrical system of your residence. You might want to try grounding the system to a copper water pipe if it penetrates the ground, or by installing a ground rod. In my house they were using the flexible conduit as a ground, and I had to have new ground wires installed from the service panel. $$$$$$$

 

[Stereofro]

You may have a faulty ground in your electrical system of your residence. You might want to try grounding the system to a copper water pipe if it penetrates the ground, or by installing a ground rod. In my house they were using the flexible conduit as a ground, and I had to have new ground wires installed from the service panel. $$$$$$$

Thanks! Well I know there is a ground rod out by the main box and one outside my house close to the panel area. I have no idea at this point if it is still connected. Would the noise go away once the tubes warmed up if that were the case?

 

[twiiii]

There are mute relays in the pre-amp, but rather than terminating the output buffer inputs to ground it breaks open the circuit making it susceptible to noise, so if you don't have a good ground, noise can enter the pre-amp and radiate into the output section. When the relays connect the output buffers to the previous circuits of the amp they properly terminate the the two sections and the small amounts of interference can no longer enter the amplification chain of the pre-amp, is my theory.
But then again you could have a noisy component that is radiating trash in the unit gaining access through those same circuits and the ground be perfectly OK.

 

[rebellovw]

Are you talking about when you first turn the c2200 on? You hear slight hum while the "tubes warming up" message is displayed - then as soon as that goes away the hum is gone? That is likely completely normal - as I have the same thing with my c220. As the tubes are warming up message is on - the amps are humming slightly then once the warmup completes - the circuit switches and I then have dead beautiful silence.

If this is the case - then there is no problem at all.

 

[Stereofro]

Are you talking about when you first turn the c2200 on? You hear slight hum while the "tubes warming up" message is displayed - then as soon as that goes away the hum is gone? That is likely completely normal - as I have the same thing with my c220. As the tubes are warming up message is on - the amps are humming slightly then once the warmup completes - the circuit switches and I then have dead beautiful silence.

If this is the case - then there is no problem at all.

The noise can be heard through the speakers while the unit is not on(in standby). When it is turned on the noise goes away once the tube warm up display goes off.

 

[Stereofro]

There are mute relays in the pre-amp, but rather than terminating the output buffer inputs to ground it breaks open the circuit making it susceptible to noise, so if you don't have a good ground, noise can enter the pre-amp and radiate into the output section. When the relays connect the output buffers to the previous circuits of the amp they properly terminate the the two sections and the small amounts of interference can no longer enter the amplification chain of the pre-amp, is my theory.
But then again you could have a noisy component that is radiating trash in the unit gaining access through those same circuits and the ground be perfectly OK.

Makes sense. It sounds like a ground problem. Pretty much like the noise you will hear if not grounding a turntable. Is there a sure fire way to detect a ground problem with regular AC outlets? Would a unit like a RGPC 1200c help to clean it up?

 

[rebellovw]

The noise can be heard through the speakers while the unit is not on(in standby). When it is turned on the noise goes away once the tube warm up display goes off.

This is a non issue as you do not run the amps with the preamp off. Preamp on first then the amps. Reverse order for shutoff.

Just to be clear as perhaps you are having a different issue - but what it sounds like to me is normal.

When I turn on my system - I'll turn the preamp on first - then go to each individual tube amp - and turn them on - while the Mc is in "tube warming up mode.." - I can hear a slight hum from the amps - once the preamp switches and completes the circuit - it becomes dead silent and stays that way. If I then hit the standby/off switch on the preamp with the amps still on - the noise will immediately come back because the preamp is taken out of the circuit - load removed.

I typically always turn the amps off first - then the preamp - I'll sometimes turn one amp on - the middle preamp on and then the other amp on. The noise doesn't bother me since it is slight and really only temporary. Now if the noise was there once the preamp exited the warmup phase - that would be a huge issue that I would absolutely not tolarate.

Good luck.