Hum and pickup noise in combination M-audio preamp with shure KSM109 mics

TheJackAttack

Well-Known Member
Joined
Mar 20, 2008
Location
currently Billings
Be that as it may, on my properly grounded equipment and power supply, I do not ever receive any hum from any Shure KSM series or Oktava. In fact there is no hum in my system at all. Boswell has much more working knowledge of the guts of these devices than I do, so I'll let him give particulars but basically any piece of equipment is capable of causing a ground issue if it is not properly designed or it's design has been compromised. If done properly, it is possible to wire an entire studio with only a single ground wire and still not have hum. EM hum can be introduced by your equipment or it can be induced through your neighbor's power mains or neon lights or......using your gear as an antenna. If your gear is just the antenna then yes, you touching a bit of metal can affect that hum as you are adding yourself into the EM circuit.

If the KSM 109 caused hum problems with even 10% of it's purchasers, it would not still be on the market or it would be priced like an MXL mic.
 

djmukilteo

Well-Known Member
Joined
Nov 23, 2008
Location
Rainy Roads WA USA
You have an open ground lead somewhere in your signal chain.
If your equipment does not have a chassis ground connection then everything is floating above the ground plane.
Any metallic object you touch creates an antenna with you as the probe. It's not a flaw in the mics....you have no ground to keep the audio signal balanced from the microphone!
That's why the Shure guy told you it won't work without a ground....that's not a flaw in there stuff he's just pointing out the flaw in your stuff!
You can create a ground for your equipment by running a heavy gauge copper wire 8-10AWG to a grounding clamp attached to an iron water pipe that goes into the ground with no breaks or plastic insulating fittings....a cold water pipe where it comes directly into your building from the street is the best bet and location. Connect that copper wire to the chassis ground connection of your preamplifier and/or other equipment in your signal chain either using a provided chassis ground screw connection on the box or by using a sheet metal self tapping screw fastened into the sheet metal enclosure itself....
I would seriously consider getting yourself an autotransformer with center tap (CT) which can be grounded on the secondary side and provide correct grounded power to your electronic equipment isolated from the main electrical service. From your posts and broken English, it appears you live someplace where they have poor electrical service and it is 220V 50Hz.
I would also suggest making sure you are using the proper power supply converter settings for 220V 50Hz. Modern electronics relies heavily today on proper shielding and chassis ground for proper operation and safety!
 

ymed

Member
Joined
Sep 2, 2010
Be that as it may, on my properly grounded equipment and power supply, I do not ever receive any hum from any Shure KSM series or Oktava.

If the KSM 109 caused hum problems with even 10% of it's purchasers, it would not still be on the market or it would be priced like an MXL mic.

You should know that:

1. "ground connection" is necessary for safety rather then it is "а must" for clear audio recording.

2. At times grounding is free from radio noise at other times grounding can be a source of noise and work like an antenna (e.g. in multi-flat house with many electrical equipment connected to the common grounding).
Because 1-pin in XLR connected to the grounding you can accidentally record a pickup noise from your grounding connection. Some mic's preamps has a "ground lift" button to forcedly disconnect earth grounding from your audio recording equipment.

3. Whereas earth grounding is not required for clear audio recording, the so-called "chassis ground" must be properly connected to pin 1 in XLR connection. Any mic MUST work properly with PORTABLE RECORDERS that work on batteries without wall outlet and earth grounding.

My both Shure KSM 109 mics (that I have obtained with 1 year time interval) work with 50 Hz hum when I touch the attenuator even I run them with portable recorder.

Shure service center engineer checked and said: "For proper operation these mics must be connected to the grounded wall outlet. For proper recording with portable recorders my advice is to move away an attenuator."

I have asked engineer:"Why there is not any information about it in the user manual?"
He answered that: "I do not know why, but this is a circuit technique fault INSIDE the mic. We can ask Shure via e-mail."

I have answered: "Yes, please, ask them if they advise any other solution"

1 month passed from that time, but Shure did not reply any info to its authorized Service center!
 

djmukilteo

Well-Known Member
Joined
Nov 23, 2008
Location
Rainy Roads WA USA
How are you powering your equipment on batteries?
This is DC not AC....there could be no hum using strictly batteries on say a battery powered field recorder?
Hum comes from the 50-60Hz cycling of an AC power supply not a DC battery. If you are using a UPS box and calling that a battery...that is not strictly speaking a DC battery power supply it is a battery backup system powering an AC inverter circuit.
This box also needs proper grounding to eliminate any AC frequency hum...
no matter what you do.....you still operate with an open ground path....
AC cause hum....if you can't find and fix ground path then you will be using attenuators or locations where the hum is minimized but it will never go away completely...
Good luck!
 

ymed

Member
Joined
Sep 2, 2010
How are you powering your equipment on batteries?
Yes, you are right - this is UPS battery.
So, I have tried several preamps and all they run identically with these mics.
The Shure service center has an expensive stend.
When they connected it to ungrounded wall outlet, my mics started to catch hum pickup noise.

This box also needs proper grounding to eliminate any AC frequency hum...
Give me a link to tech document or specification that says that grounding is necessary for hum free, clear recording.
Wall outlet grounding is necessary only for SAFETY.

if you can't find and fix ground path then you will be using attenuators or locations where the hum is minimized but it will never go away completely...
Good luck!

You did not carefully read the history of my posts - I have wrote that the hum is maximal near an attenuator switch.
 

djmukilteo

Well-Known Member
Joined
Nov 23, 2008
Location
Rainy Roads WA USA
I have 2 Shure KSM 109 mics that are connected to M-audio DMP3 preamp.
Preamp is connected to PC sound card.
I have found then that there is NO HUM when I run my PC and preamp from wall outlet WITH GROUNDING.




I don't understand why you are using an attenuator?
If there is no hum when you use a grounded wall outlet why aren't you using a grounded outlet?

maybe you can find the answer here..
[="http://en.wikipedia.org/wiki/Mains_hum"]Mains hum - Wikipedia, the free encyclopedia[/]
Hope that helps you
 

ymed

Member
Joined
Sep 2, 2010
I don't understand why you are using an attenuator?
If there is no hum when you use a grounded wall outlet why aren't you using a grounded outlet?
I do not use attenuator. It works like an antenna and catches noise even from microphone stand and my hands.
Unfortunately, I have no grounded wall outlet in my studio.
maybe you can find the answer here..
[="http://en.wikipedia.org/wiki/Mains_hum"]Mains hum - Wikipedia, the free encyclopedia[/]
Hope that helps you

In the link you have provided there is no any info that earth grounding is a requirement for hum free audio recording.
 

djmukilteo

Well-Known Member
Joined
Nov 23, 2008
Location
Rainy Roads WA USA
Whatever....I guess your bound and determined to find another way to fix your problem and not interested in any standard recommendations from anyone here....
like I've said before Good luck in your quest to reinvent....
 

Big K

Well-Known Member
Joined
Jan 16, 2002
Location
Munich / Germany
How are you powering your equipment on batteries?
This is DC not AC....there could be no hum using strictly batteries on say a battery powered field recorder?
Hum comes from the 50-60Hz cycling of an AC power supply not a DC battery.

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Just for the technical records: of course there can be hum with a battery powered device.
 

djmukilteo

Well-Known Member
Joined
Nov 23, 2008
Location
Rainy Roads WA USA
yes agreed....still if you were able to power your equipment from a pure DC source like a battery which is typically unlikely with audio preamps and computers or interfaces it would be radio wave interference or magnetic inductive interference from transformers and the like and the cause would be improper shielding connections or direct magnetic coupling into the electronics.
I would surmise a battery powered recording device with a microphone properly connected to it to be free of noise or hum in open air...short of standing next to an electric motor.....or radio tower....but a DC power source itself couldn't produce anything on it's own...the OP's problem appears to be poor grounding between pieces of equipment which are interconnected to each other....in his case unless he eliminates power line ground loops first I suspect he will continue to have hum in his signal path...but for all I know he's set up next to a neon sign or ungrounded fluorescent light fixture....who knows?!
 

MrEase

Well-Known Member
Joined
Jan 19, 2006
Location
West Suss ex, UK
Can I suggest that it might be useful for some to read the following. [="http://www.douglas-self.com/ampins/groundloops/grndloop.htm"]groundloops[/] This is written by a very well known engineer for systems that would normally use a ground but also considers a system without a ground.

Follow this and you won't go far wrong!
 

ymed

Member
Joined
Sep 2, 2010
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Just for the technical records: of course there can be hum with a battery powered device.

I had no any classical portable recorder.
But today I have called to AT&Trade Service Center (where one of mics) and service engineer said me the next:
"I have found Shure FP23 preamp and there is no hum when it runs from battery". One month before the same engineer said me that: "These KSM 109 mics have attenuator that works like antenna without grounding."
I have said to him: "You have tried on your professional preamp and there was a hum without grounding."
He answered: "Yes, but your and my preamps had no SYMMETRIC TRANSFORMER (balanced transformer) for XLR inputs INSIDE PREAMP. But Shure FP23 has this type of transformer. Try to finde preamp with the same transformer type inside! "

Is it normal answer of service center? Why I must buy preamp with special transformers inside?

This is the preamp that was recommended: SoundClick artist: Fingerprint NZ - page with MP3 music downloads
 

Boswell

Moderator
Joined
Apr 19, 2006
Location
UK
Unlike a dynamic microphone, a phantom-powered capacitor microphone cannot have a floating capsule circuit, since d.c. power has to flow from the common-mode of XLR pins 2 and 3 to the ground on pin 1. Despite this, it is possible to achieve a balanced circuit at audio frequencies provided the microphone output is fed into a pre-amp that maintains a truly balanced input whilst supplying the phantom power. A balanced circuit is largely insensitive to external fields such as magnetic or electromagnetic hum, as induced fields are coupled into both signal conductors, inducing common-mode potentials.

Without inspecting the diagram for the internal wiring of the KSM109 it's not possible to say whether the switched 15dB attenuator has been implemented as balanced or unbalanced. My guess is that the Shure engineer was acknowledging that it is an unbalanced configuration, and therefore may be more susceptible to external fields. Taping over the attenuator switch with conductive tape could well be a practical solution to the problem of electromagnetic hum. It will have less effect on magnetic fields, so operating the microphone near to motors or mains transformers could well continue to give trouble.
 

ymed

Member
Joined
Sep 2, 2010
Unlike a dynamic microphone, a phantom-powered capacitor microphone cannot have a floating capsule circuit, since d.c. power has to flow from the common-mode of XLR pins 2 and 3 to the ground on pin 1. Despite this, it is possible to achieve a balanced circuit at audio frequencies provided the microphone output is fed into a pre-amp that maintains a truly balanced input whilst supplying the phantom power. A balanced circuit is largely insensitive to external fields such as magnetic or electromagnetic hum, as induced fields are coupled into both signal conductors, inducing common-mode potentials.

Without inspecting the diagram for the internal wiring of the KSM109 it's not possible to say whether the switched 15dB attenuator has been implemented as balanced or unbalanced. My guess is that the Shure engineer was acknowledging that it is an unbalanced configuration, and therefore may be more susceptible to external fields. Taping over the attenuator switch with conductive tape could well be a practical solution to the problem of electromagnetic hum. It will have less effect on magnetic fields, so operating the microphone near to motors or mains transformers could well continue to give trouble.

Thank you Boswell,

Shure support from Germany has replied right know: "Dear Mr,
we always recommend using balanced inputs. Usually it doesn't matter if it ins a transformer balances input or an electronically balanced input."

Can XLR input on preamp be unbalanced? If I see preamp with XLR input on preamp how can I determine is it balanced or not?

Very strange... Why I must know what inside the preamp?
 

MrEase

Well-Known Member
Joined
Jan 19, 2006
Location
West Suss ex, UK
ymed,

I strongly recommend you look at the link I posted earlier. Hum loops are something that always happen, normally when you least expect them. You ask "Why must you know what's in the pre-amp?", the only answer to that is because you have a problem with hum! As hum loops keep cropping up, it is always good to have some knowledge of why they happen and that link will explain. Also, if you have queries on balanced inputs etc., if you browse around the site on that link, you will also find a very good guide to balanced connections, their advantages and disadvantages (not many!). Having the knowledge in your own hands will help you understand both what is happening to your system now and serve you much better if it ever happens again.
 
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