Hum

[heeman]

I had a friend over the other day to enjoy sometime in the HT. He has been over once since the new PSA Speakers were added. After firing up the system, he said "where did that hum come from" I said, "What Hum" He said, don't tell me you can't hear that? I said No and moved closer to the speakers and heard the slight hum.

I think I have tried just about everything (as listed below) and nothing fixed it. It is a very low hum and does not very at all with the volume of the system.

1. Disconnected the cables from the pre/pro to the amps. This is the only thing that worked!
2. Disconnected all inputs to the Pre/Pro. Still Hum.
3. Swapped cables from Pre/Pro to the Amps. Still Hum.
4. Only the amps are grounded, put ground busters in. Still Hum.
5. Plugged the Pre/Pro into the same outlets as the AMPS. Still Hum.

The one thing that I haven't tried yet is to connect the chassis of the Pre/Pro to the Chassis of the Amps. Not sure if this will work??

Could this be a problem with the Pre/Pro, it seems that this is the only component causing the Hum?

Could this always have been there, but now with the High Efficiency Speakers it is now apparent?

Any help is appreciated.

 

[PaulyT]

So you get no hum when the speakers are connected to the amps, and the amps on, but no connection from amp to pre/pro? That is, it's not the amps themselves, right?

Is it coming from all channels?

 

[Flint]

Do the amps and prepro have an option for balanced interfaces? XLR?

 

[heeman]

So you get no hum when the speakers are connected to the amps, and the amps on, but no connection from amp to pre/pro? That is, it's not the amps themselves, right?

Is it coming from all channels?

Yes

Right

Yes all channels and the LF and RF are powered by a (2) channel amp and the C, LR and RR are powered from a (3) channel amp.

 

[heeman]

Do the amps and prepro have an option for balanced interfaces? XLR?

The Pre/Pro - No Balanced Interfaces

The (2) Channel Amp - has this option

The (3) Channel Amp - I will have to check when I get home.

 

[Batman]

I can't believe you just posted this, I'm gonna start my own thread but I have been experiencing a similar issue. I was messaging Zing and Cmonster about it this AM.

 

[heeman]

^ Chris, I wanted to post a while back, however I wanted to eliminate all possible variables that I could think of prior to posting.

I hope that someone here can recommend a few more things to try and hopefully fix it.

Good luck with your problem.

Keith

 

[Deleted member 133]

1. Stand in the room with everything powered off. All room lighting off. Hum?

2. Turn system off and room lighting on. Hum?

3. Power on the system but keep all the lighting off. Hum?

4. With system on, turn on the lighting. Hum?

I know it sounds stupid but in my main system bullet 2 above produces hum (as does 4.) Basically I get some EMI from the room's lighting that induces a current somewhere in the system (possibly speaker voicecoils?) that produces the hum. I've never tried to fix it since I don't use the room lighting while watching or listening.

It's a one minute test to try before you start ripping shit apart.

Jeff

 

[Towen7]

If you don't have the option of balanced interconnects between the processor and the amp than the only options you have is to try connecting the two chassis together. I was going to suggest cables with better shielding but since the volume of the hum doesn't change than it's unlikely to be induced signal onto the audio input to the amp.

 

[heeman]

1. Stand in the room with everything powered off. All room lighting off. Hum? No

2. Turn system off and room lighting on. Hum? No

3. Power on the system but keep all the lighting off. Hum? Will Try.

4. With system on, turn on the lighting. Hum? Yes, the hum is coming directly from the drivers.

I know it sounds stupid but in my main system bullet 2 above produces hum (as does 4.) Basically I get some EMI from the room's lighting that induces a current somewhere in the system (possibly speaker voicecoils?) that produces the hum. I've never tried to fix it since I don't use the room lighting while watching or listening.

It's a one minute test to try before you start ripping shit apart. I will try the suggestions when I get home.

Thanks Jeff.......

Jeff

 

[heeman]

If you don't have the option of balanced interconnects between the processor and the amp than the only options you have is to try connecting the two chassis together. I was going to suggest cables with better shielding but since the volume of the hum doesn't change than it's unlikely to be induced signal onto the audio input to the amp.

I forgot to add that to the things that I tried.

I tried different cable routing, and better cables from the Pre/Pro to the amps. It appears that this is conductive, not a radiated noise issue.

 

[heeman]

3. Power on the system but keep all the lighting off. Hum? Hum!

 

[Flint]

There is a tricky wiring technique where you can use an unbalanced output to a balanced input which can sometimes eliminate ground loop hum (which it sounds like you have.

1) get an XLR cable and cut off the female end.
2) get an RCA plug and solder the "positive" signal lead in the wire to the RCA center pin and the "negative" signal lead to the RCA shield
3) Be sure the cable's shield never comes in contact with any part of the RCA plug in any way shape or form. That might remove the hum.

That said, check each amp individually. Does each amp hum separately when the other amp not connected to the preamp? Or, does only one amp hum? If only one amp hums, then maybe just ground the amp chassis together.

you could also try using a good AC power device, like the Tripplite ISObar products or HUM-X. Though not always effective, in 1 out of 10000 systems with hum one of them will work.

It will affect the sound in a very minor way, but a good RCA isolation transformer (like one from Jensen Transformers) will almost always remove all audile hum. The side effect can sometime be a very slight increase in bass distortion.

If the amps have Gain controls on them, try turning them down significantly until the hum is completely inaudible in the room, then turn up the preamp appropriately to hear the music at the levels you like.

finally, and this is expensive, a proper AC isolation transformer to get balanced AC power for the entire system will significantly reduce noise and hum. Furman and Tripplite make these.

 

[Zing]

I had a friend over the other day to enjoy sometime in the HT. He has been over once since the new PSA Speakers were added.

Just to clarify, this friend had been to your house previously and heard your system with the new PSA speakers and did not notice or comment on the hum at that time, correct? But now this second visit, he heard it and made the statement, correct?

What has changed - anywhere in your house with anything at all - since his last visit? Did you buy a new lamp for another room? Did a repairman come by to fix your A/C unit? Did you move a computer from one location to another? Any changes at all? Anything??

 

[heeman]

^ Thanks Flint (From Spain)!

I will see what I can do with obtaining the XLR Connector/Cables and see what that does.

The other suggestions maybe an option in the future if the XLR doesn't work.

 

[heeman]

I had a friend over the other day to enjoy sometime in the HT. He has been over once since the new PSA Speakers were added.

Just to clarify, this friend had been to your house previously and heard your system with the new PSA speakers and did not notice or comment on the hum at that time, correct? But now this second visit, he heard it and made the statement, correct?

What has changed - anywhere in your house with anything at all - since his last visit? Did you buy a new lamp for another room? Did a repairman come by to fix your A/C unit? Did you move a computer from one location to another? Any changes at all? Anything??

Thanks Zing,

I wish I could put my finger on it!

heeman

 

[Towen7]

Regarding Isobars ...

It's possible that there is some noise being generated by some other device in the home that is being transmitted through the power lines. You can try Jeff's plan and, with the HT system on, start unplugging/turning off stuff in the home... especially anything with a motor; refrigerator, air conditioner ... but also TVs and computers. If you get lucky and find a culprit, plug IT into the isobar.

 

[heeman]

There is a tricky wiring technique where you can use an unbalanced output to a balanced input which can sometimes eliminate ground loop hum (which it sounds like you have.

1) get an XLR cable and cut off the female end.
2) get an RCA plug and solder the "positive" signal lead in the wire to the RCA center pin and the "negative" signal lead to the RCA shield
3) Be sure the cable's shield never comes in contact with any part of the RCA plug in any way shape or form. That might remove the hum.

That said, check each amp individually. Does each amp hum separately when the other amp not connected to the preamp? Or, does only one amp hum? If only one amp hums, then maybe just ground the amp chassis together.

you could also try using a good AC power device, like the Tripplite ISObar products or HUM-X. Though not always effective, in 1 out of 10000 systems with hum one of them will work.

It will affect the sound in a very minor way, but a good RCA isolation transformer (like one from Jensen Transformers) will almost always remove all audile hum. The side effect can sometime be a very slight increase in bass distortion.

If the amps have Gain controls on them, try turning them down significantly until the hum is completely inaudible in the room, then turn up the preamp appropriately to hear the music at the levels you like.

finally, and this is expensive, a proper AC isolation transformer to get balanced AC power for the entire system will significantly reduce noise and hum. Furman and Tripplite make these.

Bad News! The 3 channel amp does not have the XLR inputs.

Just to clarify...................

The 60Hz signal from the power source is somehow coupling with the signal source.

This may not have anything to do with it, but I must ask........

Many years ago I was making signal cables and you made it a point Flint to float the shield on one side of the cable. I can't remember if it was the Amp side or the Signal side? I am not using these cables, however if it would help, I could...........but shielding does not appear to be the issue!

So how do we de-couple this ground hum from the signal path?????

 

[heeman]

Regarding Isobars ...

It's possible that there is some noise being generated by some other device in the home that is being transmitted through the power lines. You can try Jeff's plan and, with the HT system on, start unplugging/turning off stuff in the home... especially anything with a motor; refrigerator, air conditioner ... but also TVs and computers. If you get lucky and find a culprit, plug IT into the isobar.

What is confusing to me, and I have experience with FCC EMI Testing in the past with switchmode power supplies for radiated and conductive emissions........is that the only grounded components in my system is the 2 power amps. Understood that all signal paths are typed to the chassis's however this is not ground, even though all neutrals are eventually tied to ground back at the service panel.

Yes, this is a stumper for a lot of experts, however I was hoping this could be easily solved................it could have been here all along, however with the high efficiency speakers it is now audible!

I may swap out the pre/pro, this weekend with the Onkyo AVR and see if the HUM goes away...............

BTW - Both Amps are on dedicated 20 AMP circuits, i did connect the 2 amps and Pre/Pro to the same circuit and the problem is still there.............

:angry-banghead: :angry-tappingfoot: :angry-banghead:

 

[Zing]

...it could have been here all along, however with the high efficiency speakers it is now audible!

I'm thinking ^ this. All amps emit some amount of buzzing. But what threw me was the fact that you said your friend didn't notice it (or at least say anything about it) the first time he was there. So that made me think it was something new that transpired since that first visit of his.

Connect your Quarts and see if the hum diminishes or disappears.