preamp,high pitched sound?

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hei everyboodyy

so i got m-audio firewire 410 today,and am pretty happy with it,strange ey?
well anyway,i can hear that high pitched sound when phantome power is turned on.this sound kind of gets thiner if i set sample rate higher,and disappers when i turn off preamp,i can still hear the mic for several seconds but the sound is gone so i presume it has something to do with preamp..
i also got behringer tube ultragain mic 100 preamp and it seems to work just fine,no high pitched sound atleast.
an i also sometimes hear that sound in movies.well i hope you know what im talkin about,and maybe know any ways to fix it?

[DeadlyKungFu]

I believe that sound is coming from the power supply, "switching power supplies" can generate noises like that. I don't have any real advice than to look in that direction, try a different wall wart, I don't know.

M-Audio rides again.

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i quess its not power suply,cos its working on 6 pin wirewire port.its not connected to adapter.

[nolus]

sounds like you might have a ground loop problem, where the firewire signal has two possible return paths; the correct path through the firewire cable and an extra path via the audii cable to the mixer then via the mains earth back to the computer.
Available solutions are to remove the mains earth from the computer or mixer (potential danger unless yiu can find a double insulated supply for your computer) or install a line ballancing transformer or ground loop isolator in the audio cable.

Maplin do a cheap ground loop isolator designed for car stereos. i've not used it myself, but it always get mentioned when thistopic comes up.

you can verify if it is a ground loop if it goes away when you run the computer off the battery.

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i forgot to say that this i can hear this sound only when i turn volume to maximum..

[DeadlyKungFu]

i quess its not power suply,cos its working on 6 pin wirewire port.its not connected to adapter.

wirewire = firewire?

The power pins on the firewire port would be tied to the power supply, so it would come from the computer's power supply. It's possible there's a direct copper connection from the firewire power pin to the laptop's power supply.

Try a firewire port replicator in a store and see if you can find one that's well made enough to not have this problem, or can filter the noise out from your lappie's power supply. Your laptop's power supply is without a doubt a very compact switched mode power supply that may have been designed with size over low level high pitched hums, most PC users don't care about that, know what I mean? Us audio users have unique requirements.


Ground loops result in 50 or 60Hz hums (depending on which part of the planet you live on) which are low in pitch.

[unusable]

/. what ever you do don't touch your AC cabling. that could possibly work but you're treating the symptom and not the cause.

there's a couple things to do, google ground loop for starters.

but I'm not sure this is a ground loop. it could be the way you're setting your gain from your computer to your headphones. If you're hearing a high-pitched noise when you have your 410 @ full volume you could just be exceeding the range of your exceptionally high quality converters //end sarcasim//. try adjusting your gain stage so that what ever application you're running that's producing the audio is at 85% or so, and that the inputs to 410 are hot but not clipping. Then turn your 410 in/out volume down. Plain and simple.

Although I would investigate the ground loop problem using a 4-pin to 6-pin firewire cable and power both your computer and 410 (and whatever else you're using) off the same electrical outlet and use a power bar(we call them power bars in Canada, but they're also known as power strips) or something, that puts all the relative grounds for all your equipment on the same ground path, hopefully at that point you shouldn't have any difference is chasis ground between any of your devices. I think

[DeadlyKungFu]

unusable-
1 - nobody has suggested he touch the mains.
2 - this cannot be a ground loop problem, that's a much lower hum.
3 - clipping would not result in a high pitched hum, it would result in digital clipping which is broadband noise (white noise, static).

power bar, I like that term

[unusable]

Available solutions are to remove the mains earth from the computer or mixer

I agree DeadlyKF, I was trying to ensure /. dosen't got cutting off plugs on his power

I don't think it's a ground loop,
I never said it's clipping,

I think it's probably poor gain stage through his system. turn up the input source, and turn down the converters. apparently when the 410 is cranked it makes noise. so, turn it down, turn other stages up. I'm not surpirsed that if you jack everything up on a relatively inexpensive m-audio product makes noise. I personally don't run converters at max gain and expect it to sound pristine. I've never had the dough to get really really expensive converters though

[DeadlyKungFu]

unusable - I agree. Good points, I misread your suggestion about gain stages.

Damn electrons!!

[nolus]

...Available solutions are to remove the mains earth from the computer or mixer (potential danger unless yiu can find a double insulated supply for your computer)...

I appreciate your caution but please quote me properly.

unusable-
...2 - this cannot be a ground loop problem, that's a much lower hum...

It can be a ground loop problem. in a purely analogue audio system earth loops can cause induced mains hum, but in a mixed digital and analogue system they can cause all kinds of noises.

Using really hight quality (low resistance) cables and plugs and keeping all leads, including mains leads as short as possible helps a lot, but can't eliminate the problem completely.

The important clues are that it changes with the sample rate, therefore it does not originate in the preamp (which is independent of the sample rate) but it goes away with a different preamp (which probably has different earthing arangements / or maybe lower input impedance).


If it is the problem I am thinking of then it happens because the digital signal (firewire) has multiple return paths. Some of the current flows through the screen of the audio cable. Because the resistance of the audio cable and connectors is greater than zero ohms, this current generates a voltage drop across the earth conductor which is seen by the preamp as being superimposed on the audio signal.

I had the same problem with my firewire 410 (and a behringer USB sound card that I tried breifly). After much head scratching I fixed it by isolating my Samson power amp from the mains earth - I know - not recomended - but I feel safe because my house is protected by a residual current device - I am now in the market for another power amp that is double insulated.

When I next upgrade my laptop I will definately make a point of checking that the power supply is double insulated and not earthed. in fact add that to the checklist for any item of equipment.

[nolus]

the association with the phantom power switch is a bit confusing though - so this might be another problem - but I don't think it's the gain stage thing because with no signal, all I get from my 410, even with all gains at maximum is a slight hiss.

[DeadlyKungFu]

With the phantom power and the pitch changing with sample rate, it could be crosstalk from digital data stream. Word clock is being aliased down into the audible range, but as he goes up to 96kHz the harmonics he was hearing before are above the audibe range and fade out. If word clock got into the power supply before the 48V regulator the noise would also be amplified.

Nolus, you make a good point about ground loops showing up in weird ways, any which way you can put a voltage drop between two devices, or within a device itself, they can float around, pushed around by almost anything.

Maybe putting a wire between the bare metal casing of the pre-amp and the PC's case might help. Or just put a wire on the preamp's case and touch it to other metal surfaces to see what effect it has.

In the end, adjusting gain stages so the noise is down in the noise will probably be the easy way to go.

Interesting stuff, lots of voodoo around ground loops.


nolus - btw your signature, can you explain?

[nolus]

btw your signature, can you explain?

When I find someone who recognizes that quote then I'll know I've found a kindred spirit - I'm not holding my breath though


I think the answer to most of these type of problems is ballanced line.

(note to self - don't buy any more audio gear unless it supports balance inputs and outputs)

[unusable]

The important clues are that it changes with the sample rate, therefore it does not originate in the preamp (which is independent of the sample rate) but it goes away with a different preamp (which probably has different earthing arangements / or maybe lower input impedance).

You actually change your sample rate on your 410 converters h/w and not in s/w. When you change SR in software you're telling the h/w what you want in the form of digital audio. and the 410 is a pre-amp and has converters built in as one unit, like the other billion or so other similar products currently on the market

as described:
1) using 410 pre-amp, it is noisy on phantom powered mic when gain at max
2) when using different front-end pre-amp (and therefore using different 410 input) there is no problem

solution - don't use your 410 pre-amp at max gain, or use your behringer as the front end, that's what pre's are for. Or take it back for an exchange on a different unit (if possible)

sure it could be a ground loop, but considering that he's probably using the 410 as a converter for both situations 1 and 2, I doubt it, as I'd expect to hear it regardless of what you put on the front-end.

but hey I've been wrong before and inexpensive electronics are un-predictable

/* you might in fact have faulty pre amps or faulty 48V power supply in the unit. have you tried both XLR inputs of the 410 and do you get the same thing happening? and can you try a different unit in the store, or a friends' or somthing