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R/E/P => R/E/P Archives => Bruno Putzeys (Designer) - Dave Hecht (Master Tech) => Topic started by: lucey on April 22, 2004, 11:14:41 AM

Title: buzzzzzz
Post by: lucey on April 22, 2004, 11:14:41 AM
a dumb question ... that's why i have been looking at it for months!

just can't track down a little buzz in the monitors (adam-powered)

it's not 60hz, more of a low sizzle.  and it's there at all times, at a very low level (workable yet present)

there are low voltage halogens in the room, and in other rooms nearby, yet turning them off does nothing

everything is on a furman bal. pwr. box

i'm thinking the overall ground, as in stake-to-earth, may be at issue???

what are the key ingredients to grounding at the mains?
Title: buzz... hmmmm
Post by: John Klett on April 23, 2004, 01:53:12 AM

well - (as usual) I am reading this as my leaden lids are loosing today's battle against gravity (read this as I just got home, it's late, and I have to be up again in... four hours).  I'll be fast asleep in about three minutes...

I'll come back but here are a couple questions...  

is this just in your monitors?

does it change with the monitor level pot/control?

what (briefly) is your setup...  workstation, analog/digital console...  what is feeding the ADAM's...  where and how is your power distributed...  what is the lay of the land?

you may be right about your main ground but I need to step through it a little more before I can advise...  then I can 'go off' on power and ground and such

oh!  when you say sizzle...  you mean sizzle that comes mostly out of tweeter or like a frying rumbly sort of noise...  mids and lows...  does it spit?  ...like it's going uniformly for a while then ftzzppt!   ?

I'll ask some more stuff when you come back with more info
Title: Re: buzz... hmmmm
Post by: barefoot on April 23, 2004, 05:24:23 PM
First thing is to do is unplug the input to the monitors.   If the noise goes away, then you know it's an issue in the signal path upstream, or with grounding.   If it remains, then it's an issue with the monitors themselves.  

Let us know what you find out.  

Title: Re: buzzzzzz
Post by: lucey on April 25, 2004, 02:44:37 AM
it's at a constant level, not effected by anything excpet removing the input.  the exact sound of it? ... i'll get back to you on that

i think it may be this new console (Tactile M4000) as that it the only new variable.  it was not there with the Series II previously

(i have an analog 16track-to-2track and a mastering set up both in one room)

everything is on the same power, the furman box, with breakered strip/boxes splitting out to all the outboard, etc
Title: Re: buzzzzzz
Post by: R. Foote on April 25, 2004, 10:49:32 AM
Here is a test you can try...

Assuming the connection between the console and monitors is a balanced one, make or modify a set of balanced cables so that the shield is not connected at the mixer end (on both cables).

If that fixes it, it means there was a ground loop between the console and monitors. I have built 6 or 7 project studios, and all had this issue. It seems to be more prevelant with powered monitors. Of course the last studio I put together that didn't use powered monitors used Hafler amps that had a ground lift switch, so I didn't have to make a ground lift cable set.

Here is a document that has loads of info on studio wiring:


Hope that helps

Title: Re: buzzzzzz
Post by: Fibes on April 27, 2004, 11:38:45 AM
I have the same issue and I use the Furman 1220? and have new Adams too. My old monitors don't do it so i'm assuming it's in between the pot and cone. Hmmm? It's a low hiss...
Title: Re: buzzzzzz
Post by: John Klett on April 27, 2004, 01:27:28 PM
The issue of low level broadband noise with no line related noise is probably related to gain structure more than anything else

One of the items that are an exception to the guideline we use for studio wiring and ground are monitor amplifiers, powered speakers and related.  In order to eliminate noise we will sometimes use high quality transformers to completely disassociate ground between the console or patch feeds and the monitors and speakers.  These can be inserted before balance line level monitor switchers or at inputs to amplifiers.  

Transformers are not always required because actively (transformerless) balanced outputs connected to actively balanced inputs will cancel common mode noises - which, in most cases, is where ground hum and noise will fall.  Common mode rejection is not the same thing as common mode range.  Since the power supplies that feed the active balanced electronics on both ends are referenced to whatever ground is present at each end.  Depending on how the receiving input amplifier is configured the common mode rejection can reduce when gain is raised...  and common mode range can interfere with clean headroom.  Transformer eliminates the CM Range problems and greatly improve common mode rejection ahead of the monitor system.

Ground Loops are another issue but those (as pointed out above) can be eliminated by dropping a shield at one end or the other...  there are various rationales for which end of a wire (source or destination) should be dropped that I will not roll out here but suffice it to say that some outputs work better with the shield attached at the source (i.e. Studer A800 - transformerless) and other equipment will want the shield connected at the inputs or destination end.  It does vary.  

Some monitor systems can have gains in them POST the console outputs that can run up to 30dB hotter that your average listening level.  My "loud" listening level (that I don't run for long time periods) is 95dB SPL while other clients that may walk in that want to run up to 115dB SPL and higher (I see this a LOT with Hip Hop for whatever reason). I've had to design and build custom systems to do that with over a KW of power on each side.  

High gain monitor systems produce a hiss or wide band noise and can bring up line noise significantly.   Transformers can help with common mode line noise but broadband noise is harder.

As far as powered speakers go you can see if broadband noise (hiss) is present with the inputs disconnected and then see if gain control on the speaker (if there are any controls) can be reduced and see if that reduces the hiss.  Line noise can be reduced or eliminated by dropping shields but you can change gain structure by turning down amplifiers and running the signal from the console monitor output hotter.

Hum and Buzz are far more annoying than hiss.  Your brain tends to hear around or ignore broadband noise - at least for "pink" noise (equal energy per octave).  White noise (energy is linear with frequency) is a whole other problem and is more objectionable.  Unfortunately a lot of noise in these situations is more white than pink and sometimes, if it really bothers you you have to look at what equipment you are using or possible modifying equipment to reduce noise at the source.

You also have to look at where the noise is coming from.  If your speakers and monitor systems are silent when all feeds are disconnected then look at the interconnection.  If the noise is changed by the control level pot it still could be after that pot - maybe an amplifier following the pot has a sensitivity to source impedance.  Otherwise look to what is feeding the pot.  If you control room pot "gets loud" before mid position you may want to reduce the amplifier gains - some consoles have jumpers to change output levels at the monitor feed outputs.

so...  those are some of the factors with monitor system noise - mostly it's gain structure and interface.

Title: Re: buzzzzzz
Post by: Fibes on April 27, 2004, 05:24:28 PM
I've been thinking it was gain structure since the passive speakers fall at a different level. If it isn't what kind of transformers are available for this type of application?
Title: Re: buzzzzzz
Post by: cymatics on May 13, 2004, 07:32:27 AM
Fibes wrote on Tue, 27 April 2004 22:24

what kind of transformers are available for this type of application?

A fully assembled off the shelf Jensen transformer box
The build it yer damn self version