The No.1 Website for Pro Audio
 Search This Thread  Search This Forum  Search Reviews  Search Gear Database  Search Gear for sale  Search Gearslutz Go Advanced
Noise / Hum when Reamping (with reamp box)
Old 4th September 2011
  #1
Gear Nut
 

Noise / Hum when Reamping (with reamp box)

The noise is not 50/60hz, although upon analysis, some of it appears to be 150Hz hum..

With one of my computers, reamping via a balanced output to the reamp box, then a short balanced lead to the amp is fine, but with my main rig, It's really bad, and turning on one of my dual screen monitors introduces another hum. Ground lift makes no difference to this situation.

When the computer is opening / shutting windows, a temporary noise occurs, and when the machine is processing a higher load (ie when I'm running my DAW software, it introduces a more intense buzz)

I tried running everything off one socket with the same result. Everything in my building is on the same circuit anyway.

Here is a sample of the result through the crunch channel of the amp
http://dl.dropbox.com/u/6058261/Hum1.mp3

0:00 to 0:12 is me running my DAW
0:12 to 0:21 is the second monitor (display) switched on
0:21 - monitor switched off
0:24 to 0:45 - me creating / switching windows on the computer
0:45 to end - monitor switched on again

If anyone's got any sensible suggestions, I'd be very grateful
Old 4th September 2011
  #2
Registered User
Is this a real Reamp box, or a generic reamp box?

The real (patented) Reamp box is a passive transformer box, which gives real isolation and I find it tends to solve hum problems.

If you have an active reamp box, then there may not be any transformer isolation, and you are prone to get ground loop hum. In that case you may have to ensure that all AC power equipment comes from the same source, and ideally is star grounded. You might need to disconnect the earth connection of your audio cables at one end, to avoid AC current flowing in the audio shields.

What is your audio interface and/or convertors? Computers are a very dodgy electrical environment, and you really want standalone external converters. There may be grounding issues inside the computer - but they are noisy suckers at best.

A good idea for serious studios is to have clean power and dirty power circuits. Stuff like computers and switching PSU etc can go on the dirty power circuit, because they tend to dump this sort of crap into the ground.

I bashed my head against a wall with recording guitars without hum. I love battery powered stuff for avoiding AC issues ... and I love passive transformers, such as the Reamp V2.0 boxes. Keep unbalanced cables as short as possible - the Reamp box should sit on top of your amp with just a patch cable.
Old 4th September 2011
  #3
Gear Nut
 

Hey, thanks

It's one of these passive dacappo reamp boxes

I'm using an Echo Audiofire Pre8, a pretty decent interface I'd say.

I'm glad too you said about the patch lead and sitting the unit on top of the amp, as that's also what I'm doing to try to avoid problems.
Old 4th September 2011
  #4
Registered User
Hmmm ... you seem to be doing all the right things ...

Is the noise directional? Trying moving things around ... i've somethimes found these strange EMI problems can be very directional. The reamp box is basically functioning like a guitar, and can still be prone to airborne EMI.

Laptop? I've found lap top switching PSU can be very noisy. Especially if overloaded - getting a higher wattage one can help. Can you run on batteries?

Is the DI'd guitar track clean? Is this noise only being introduced at the time of reamping?

Does the noise change during the day/night? (I have some AC noise problems that go away at night when the load on the grid is less).

A lot of computer monitors have fluroscent lights in them, and the dimmer wreaks havoc with audio. I have one monitor where I have to set it on full brightness (to cut the dimmer out of the circuit), and then adjust the brightness via software instead ...

How I hate AC ...
Old 4th September 2011
  #5
Gear Nut
 

One of the monitors definitely introduces an unpleasant noise..

I tried moving it about a bit too / shaking the lead, but it doesn't do a great deal

The noise is actually not related to the DI tracks (which are nice and clean)

The noise is just related to the amp being on and the reamp box being connected sadly. :(

The noise SEEMS so far to be the same in the evening and during the day, and same in the early hours of the morning.

How might I set myself up a clean / dirty power circuit? That sounded quite interesting

Thanks again btw
Old 4th September 2011
  #6
Registered User
My solution for clean power is a pure sinewave inverter and a lead acid battery. Drive a stainless steel rod into the dirt outside your studio and run a clean earth. This is the cleanest AC power possible, as it has no connection with the grid at all. (Keep it topped up with a battery charger and/or a laboratory grade high amp PSU).

IMO, commercial UPS and power conditioners etc are a total waste. And all of them, legal and safety reasons, connect up to your electrical ground - which often is the biggest culprit!

Safety is essential - but you won't go wrong with a standalone pure sine inverter and a good solid earth.

If your AC is less that ideal, it can be amazing what a difference clean power like this can make. Very noticable with tube amps.

For diagnostic stuff, I recommend you get a battery amp. A Pignose is ideal. I have a crap single coil pup on a short cable, and connected to a Pignose this allows me to detect airborne EMI. Find out what is emitting crap and deal with it.

Simply having an excellent ground/earth connection can solve a lot of these problems: an audio shield on works if properly grounded.
Old 4th September 2011
  #7
Gear Guru
 
Muser's Avatar
sometimes if you pull out a mains plug and the noise goes, it indicates that that plug might be good to have it's earth removed.

keeping things switched off doesn't make any difference in that case, because the earth loop is still finding ground through the earth pin.

so for example, if you pull the power cable out of a monitor and it goes, thats a good candidate for an earth pin lift.
Old 5th September 2011
  #8
Gear Nut
 

Quote:
Originally Posted by Kiwi View Post
My solution for clean power is a pure sinewave inverter and a lead acid battery. Drive a stainless steel rod into the dirt outside your studio and run a clean earth. This is the cleanest AC power possible, as it has no connection with the grid at all. (Keep it topped up with a battery charger and/or a laboratory grade high amp PSU).

IMO, commercial UPS and power conditioners etc are a total waste. And all of them, legal and safety reasons, connect up to your electrical ground - which often is the biggest culprit!

Safety is essential - but you won't go wrong with a standalone pure sine inverter and a good solid earth.

If your AC is less that ideal, it can be amazing what a difference clean power like this can make. Very noticable with tube amps.

For diagnostic stuff, I recommend you get a battery amp. A Pignose is ideal. I have a crap single coil pup on a short cable, and connected to a Pignose this allows me to detect airborne EMI. Find out what is emitting crap and deal with it.

Simply having an excellent ground/earth connection can solve a lot of these problems: an audio shield on works if properly grounded.
Thanks, I might have to look into these.

Am I being silly in assuming that my balanced audio signals should not be affected by much really? It only seems that noise is produced in the impedance change (lo to hi) in the reamping process..

I tested my theory out by running a balanced lead into an active PA speaker I have and turning it right up to discover no hum... more just the hiss of a loud speaker, which was present without a lead plugged in..

Is this normal?
Old 5th September 2011
  #9
Gear Nut
 

Quote:
Originally Posted by Muser View Post
sometimes if you pull out a mains plug and the noise goes, it indicates that that plug might be good to have it's earth removed.

keeping things switched off doesn't make any difference in that case, because the earth loop is still finding ground through the earth pin.

so for example, if you pull the power cable out of a monitor and it goes, thats a good candidate for an earth pin lift.
Is this legal in the UK? not that this concerns me too much, as long as it's not going to kill me is all. Also.. sadly my computer itself is one of the major noise producers in this, and I'm not sure I should remove its earth..

Thanks
Old 5th September 2011
  #10
Registered User
The earth is there for your safety. So many things can happen outside of your control: a tree could fall on a power line, connecting the hot cable to your neutral and making your cases live ... wearing an electric guitar you are very vulnerable, since your body is typically connected to your electrical cases (via the audio shield) ...

I recommend using Residual Current Detectors, especially playing guitar. They are cheap enough, and I use then as inline switches to turn the amps on/off.

Sometimes you gotta do what you gotta do ... but if hum goes away by lifting ground, I would seek a safer permanent solution.

I'm a big fan of transformer based hum isolation. Check out the Ebtech and Radial websites for good solutions. But not all hum problems are ground loops.

Should balanced cables cause noise? In practice - a lot of cheap audio gear uses fake electronic balancing which offers little or no noise rejection. It's a big issue, and we should be rubbing their noses in it far more than we do. Consumer fraud I call ...

The Jensen website gives some good white papers on this stuff. Obviously they want to sell transformers, but there are good reasons to use real transformer balancing. In a digital world, it's not a bad thing anyway ...
Old 5th September 2011
  #11
Registered User
Hiss is normal for any active component. It can be lowered with high quality components such as resistors, and with correct impedance matching and proper gain staging. Welcome to analog.
Old 5th September 2011
  #12
Gear Nut
 

so.. I feel a bit silly now for not having checked this...

Pin 1 on the XLR lead was soldered to the chassis of the XLR plugs... And there was me wondering why ground lift wasn't working! These are cables I purchased rather than made myself. I worked it out by using one of my own leads and establishing the difference.

There's still a bit of noise, but it's noise I can probably live with now

Thanks very much guys!
Old 6th September 2011
  #13
Gear Guru
 
Muser's Avatar
Glad to see you got it worked out. The exact safety of earth schemes is hard to properly work out because different things ground in different ways sometimes. so they ground parts of circuits that work in different ways. the lead is a good example.

usually I have a a cable tester and a small meter lying around. I use a Pyle PCT40 because it has a beeping continuity tester as well. so you can test what kit grounds where. I guess it's best to lift the earth only on things which have the least high voltage elements if you can. a monitor I suppose has a high voltage section to drive the screen light. so it would be better to find something other in that case. the reason why switching off a piece of kit doesn't disconnect ground is because usually only the live wire is lifted by the mains switch on gear.. so the earth and neutral are often still connecting. so pulling a mains connection completely takes out everything. I had to do it on a unit recently.


Quote:
Originally Posted by alasdair View Post
so.. I feel a bit silly now for not having checked this...

Pin 1 on the XLR lead was soldered to the chassis of the XLR plugs... And there was me wondering why ground lift wasn't working! These are cables I purchased rather than made myself. I worked it out by using one of my own leads and establishing the difference.

There's still a bit of noise, but it's noise I can probably live with now

Thanks very much guys!
Post Reply

Welcome to the Gearslutz Pro Audio Community!

Registration benefits include:
  • The ability to reply to and create new discussions
  • Access to members-only giveaways & competitions
  • Interact with VIP industry experts in our guest Q&As
  • Access to members-only sub forum discussions
  • Access to members-only Chat Room
  • Get INSTANT ACCESS to the world's best private pro audio Classifieds for only USD $20/year
  • Promote your eBay auctions and Reverb.com listings for free
  • Remove this message!
You need an account to post a reply. Create a username and password below and an account will be created and your post entered.


 
 
Slide to join now Processing…
Thread Tools
Search this Thread
Search this Thread:

Advanced Search
Forum Jump
Forum Jump