Connection problem

[lvercaut]

Hi,

 

there is zero noise or distortion when i connect my imac to my Audient ID14 audio interface and then to my Neumann KH80 studiomonitors.Everything perfect so far.

When i connect my Nordlead A1 synth to the Tascam mixer and then to te KH80's, again no single problem. Everything perfect.

But...when i connect the soundcard to the Tascam LM8ST line mixer and then to the studiomonitors, the noise and distortion from the imac is not to endure. I use balanced cables all the time. What am i doing wrong ? Is this a ground loop problem ?

Any help is much appreciated !

[Markyboard]

Hi-

 

Just looked at the Tascam. Which inputs are you using for the sound card? Try the Bus inputs which appears to have a ground lift switch on the rear panel. I just can"t tell if this is for the inputs or outputs. But still it may give you some indication whether it"s a ground loop problem or not.

[lvercaut]

I did and the noise was at minimum now but also the volume was. Mayby i must buy a professional powersupply ?

Anyway, thank you Markyboard.

[Mike Rivers]

Let me see if I got this straight. Wiring diagrams, you know, are really handy for tracing down problems, so here's my attempt at a virtual one,

 

 

there is zero noise or distortion when i connect my imac to my Audient ID14 audio interface and then to my Neumann KH80 studiomonitors.

 

OK, so with the interface connected to nothing but the computer and the speakers, everything is quiet. Nothing else connected to the interface?

 

Computer -> Interface -> Speakers

 

.

When i connect my Nordlead A1 synth to the Tascam mixer and then to te KH80's, again no single problem.

 

So the with the synth connected to the mixer (to a stereo pair of line inputs?), and the mixer output (Stereo 1-2) connected to the speakers, it's quiet (except when you play the synth, of course).

 

Synth -> Mixer -> Speakers

 

 

But...when i connect the soundcard to the Tascam LM8ST line mixer and then to the studiomonitors, the noise and distortion from the imac is not to endure.

 

When everything goes to pot, is the synth still connected to the mixer when you put the mixer between the interface (soundcard?) and the speakers? Is the interface still connected to the computer?

 

[here's where the drawing might get messy due to the variable pitch font, but use your imagination]

 

Computer -> interface -+-> mixer -> speakers,

, , , , , , , , , , , , , , , , , , |

, , , , , , , , , , ,Synth ->-+

 

What happens when you disconnect the interface from the computer? Does that get things quiet?

 

What I suspect is that noise from the computer is carried to the mixer via the USB ground connection. You might be able to fix this by disconnecting the shield of the cables going between the output of the interface and the input of the mixer. And just for kicks, if you don't already have everything connected to the same AC power point, like with a multi-outlet strip, try that.

[Dr Mike Metlay]

Thanks for the detailed followup, Mike! All good advice. USB cables are notorious for carrying noise, so much so that Arturia has started throwing USB ground isolators into the box with all of their higher-end controllers.

 

I run all power from my studio from a single outlet with a single ground point, and I have no idea how much hassle I'm avoiding. I just wish that more of my hardware had balanced outputs... unheard of in a synth not long ago, now gradually popping up.

[Mike Rivers]

I just wish that more of my hardware had balanced outputs... unheard of in a synth not long ago, now gradually popping up.

 

Balanced outputs are easy to make - all it takes is a resistor of the correct value and probably a new jack. Why doesn't everybody do that? Well, Mackie did, and then a whole lot of other manufacturers followed their lead in spite of much poo-pooing by people who don't know what a balanced connection is. But it may be difficult for a novice to determine the proper resistor value and, what's probably more difficult, replace the connector. YOU could do it. For sissies, there are plug-in transformers.

 

What's harder to make, and more expensive, is a differential (I keep trying to get people to stop saying "balanced") input for the balanced output to connect to. Without that, you can't have a balanced connection. But it's relatively easy for the manufacturer to make a differential input since he's probably going to use a differential op amp IC on the front end anyway. But it's mechanically difficult to add after the fact, particularly with new hardware with PC boards and surface mounted components. That's why a lot of new gear has - oh, I give up - "balanced" inputs.

 

You can read about it in some old issue of Recording.

[Mike Rivers]

One other thing I'll add here.

 

A good way to troubleshoot a noise problem is to take the whole system apart (or if it's not built yet) and start assembling it from the output end back to the inputs. In Ivercaut's case, he has powered speakers that will ultimately be connected to the monitor output of his interface. So make that connection first, power it up, and listen for noises. If you have a problem there, it's either a bad cable or broken hardware.

 

So next there will be a mixer connected to the interface, so hook that up, and again check for noises. If you hear some noise and it goes away when you disconnect the mixer, check the cables, and check for ground loops (another article).

 

If there's to be a synth connected to another set of inputs on the interface (this wasn't clearly stated in the original post - it may simply have been connected to the interface a troubleshooting aid), then connect it and again listen for noises. If the synth is connected to a mixer input, which I believe was the original intent, and THEN you hear the noise, as was described, then look for cables or a ground problem. This may involve disconnecting the interface from the computer, or disconnecting the interface from the mixer. There are two possibilities here, so explore them both.

 

The idea is that you want to start with the simplest system and add to it until you encounter a problem, then fix that problem before moving on. If you hook up the whole system as planned and have noise, you don't know where to start looking for the problem.

.

[lvercaut]

Thank you so much Mike for all this professional advice. I gonna try all what you wrote when i have time to rebuild my equipment.

[Dr Mike Metlay]

The idea is that you want to start with the simplest system and add to it until you encounter a problem, then fix that problem before moving on. If you hook up the whole system as planned and have noise, you don't know where to start looking for the problem.

This is one of the many basic thinking structures of a good science education that isn't being taught very well below the graduate-school level these days. It is so tempting to change everything and see if the new layout works, but if it doesn't, you have no idea where the problem lies. No matter how long it takes, no matter how boring it is, only change one thing at a time before you retest. Doing it in a logical order as Mike has suggested will speed the process along, but if your rig is already assembled, you can at least change one thing at a time and trace the problem that way.

[Mike Rivers]

Changing only one thing at a time is another prime directive. Sometimes, though, you can't really do that because you don't have an appropriate substitute, and if you just bypass one piece you've changed the signal path.

 

By starting with the place you can hear and work backward, adding a new piece at a time, you eventually build up your signal chain until you find what's causing the problem. The practical way to do this, if you already have your system hooked up and humming along in a way you don't want it to hum, you don't need to replace the mixer or the interface, just disconnect the cables starting from the speaker end working back toward the source and see how far back you go before it starts humming.