Please, help with ground noise

[maurizionatoli]

Dear DIYers
I decided to write to you to ask for help on a project that got stuck:
following the advice of KingKorg (whom I respect and thank), I bought some prepolarized microphone capsules on Ali (I bought 10 of them) to be mounted in some wooden 35mm spheres that have to be set far from the amplifier unit, to minimize the acoustic effect of the mic body.
The project essentially consists of a buffer (active cable type) made in a round PCB (16mm diameter made in SMD) housed on the back of the capsule. This buffer will interface with a circuit (jfet as amplifier, BJT as buffer, transformer for balancing) which also takes care of lowering the voltage arriving at the amplifier circuit through an RC network (the last filtering stage, always RC , resides on the buffer).
The problem: the noise (ground noise) makes the circuit unusable, until I grip the outer ring of the capsule with my hands, effectively acting as a ground terminal. I checked with the continuity meter (buzzer) between XLR terminal 1 and all ground points, both buffer and amplifier, and everything seems fine, but the noise persists. Also checked that the voltages expected by the project arrive correctly in every point and everything seems OK (I thought that if there was a problem with the grounding "0" reference the voltages should not be right)
Can someone help me? Thank you in advance!

 

[gyraf]

in a microphone, it really can't be ground noise..

Perhaps you need electrostatic screening? Most mics need this.

/Jakob E.

 

[maurizionatoli]

very interesting, I will try to shield both the capsule and the preamplifier. Many thanks indeed for the reply!

 

[rock soderstrom]

Perhaps you need electrostatic screening? Most mics need this.

/Jakob E.

+1

you need a grounded faradays cage for this capsules or it will hum like hell.


View attachment 20230828_130517.mp4

 

[Newmarket]

+1 on screening.
Important to note that when you grip the outer ring, it is the mic that is grounding YOU (assuming you are not in contact with anything else that is grounded). This stops you acting a source of noise.
I get this all the time with people questioning the bridge etc grounding on electric bass / guitars etc.
To illustrate just touch the tip of an oscilloscope probe. You'll likely see a distorted waveform with the fundamental at whatever the mains frequency is at your location.

 

[maurizionatoli]

Tested, everything is OK!!!! Many, many thanks to all!!!
I'll post some audio files making blind comparison with "boutique" microphones.
RGDS and again thankyou!

 

[maurizionatoli]

... a little bit of steampunk...

 

[kingkorg]

... a little bit of steampunk...

 

[maurizionatoli]

Thankyou Sir! And thankyou for the suggestion of the capsule!

 

[kingkorg]

Thankyou Sir! And thankyou for the suggestion of the capsule!

One thing you could experiment with. The way you have it now there's a resonant chamber behind the capsule, which will for sure affect the pattern and frequency response. Yes, you have it vented, but still there's a lot going on behind the capsule. I would personally add considerably more venting on the side of the cylinder. If that PCB is still right behind the capsule, I would move it further back. Experimentation with these parameters will yield different results.

 

[maurizionatoli]

One thing you could experiment with. The way you have it now there's a resonant chamber behind the capsule, which will for sure affect the pattern and frequency response. Yes, you have it vented, but still there's a lot going on behind the capsule. I would personally add considerably more venting on the side of the cylinder. If that PCB is still right behind the capsule, I would move it further back. Experimentation with these parameters will yield different results.

Thank you sir, I will. Up to now, however, from tests carried out by ear, in comparison with American LDCs, with all the vents free (both front and side) the sound seems a little more "smiling" and the pattern is quite regularly cardioid. I'll keep you updated on developments... thanks again!

 

[kingkorg]

Thank you sir, I will. Up to now, however, from tests carried out by ear, in comparison with American LDCs, with all the vents free (both front and side) the sound seems a little more "smiling" and the pattern is quite regularly cardioid. I'll keep you updated on developments... thanks again!

Sure, if it sounds good don't change anything

 

[maurizionatoli]

Well, actually I would prefer a slightly more defined and articulated sound on the medium frequencies, I think I'll try the solution of making other vents laterally, as you suggested, and if that doesn't work I can always close them.
My main field is in recording classical music and the articulation of practically all instruments is in the mid range so the goal is to have a frequency response as linear (pleasant) as possible precisely in the mid range. All in all it's a challenge, isn't it?

 

[kingkorg]

Here's an idea for your next project. For something like classical music, and room/ambience sound in general i go for least possible reflections coming from around the capsule. You have the advantage of not having to use much physical protection around as you don't have a singer spitting/blowing directly into the capsule.

So an arrangement like this is IMHO best. Just pure capsule sound, nothing obstructing diaphragm or back vents in any way. Diaphragm and the body are in this case grounded. I installed the smd fet, and 1G resistor at the back of the capsule.

However if you are interested in midrange detail, this is probably one of the best capsules ever made in any price range. As it has the fet built in, shielded, you probably don't need any additional shielding. I would go for em204, and not the em200 as it has less noise and more gain.

https://micbooster.com/microphone-capsules/176-primo-em204n-cardioid-electret-microphone.html

 

[kingkorg]

Even though not best looking, these are probably best sounding mics i've ever made.
Primo EM204 with modified bm800 circuit.

 

[maurizionatoli]

Here's an idea for your next project. For something like classical music, and room/ambience sound in general i go for least possible reflections coming from around the capsule. You have the advantage of not having to use much physical protection around as you don't have a singer spitting/blowing directly into the capsule.

So an arrangement like this is IMHO best. Just pure capsule sound, nothing obstructing diaphragm or back vents in any way. Diaphragm and the body are in this case grounded. I installed the smd fet, and 1G resistor at the back of the capsule.

However if you are interested in midrange detail, this is probably one of the best capsules ever made in any price range. As it has the fet built in, shielded, you probably don't need any additional shielding. I would go for em204, and not the em200 as it has less noise and more gain.

https://micbooster.com/microphone-capsules/176-primo-em204n-cardioid-electret-microphone.html

Yes, the concept of "pure capsule" is what I was looking for...
Apart from the "Captain Nemo" model I already have the spherical wooden housing ready for a "M 50 like" model ("pure capsule" and remote electronics, I will publish the photos tomorrow)... A question: I saw that you plugged the rear vents to change the microphone pattern from cardioid to omnidirectional. Did you leave a vent to equalize the internal pressure? What diameter?

 

[kingkorg]

Yes, the concept of "pure capsule" is what I was looking for...
Apart from the "Captain Nemo" model I already have the spherical wooden housing ready for a "M 50 like" model ("pure capsule" and remote electronics, I will publish the photos tomorrow)... A question: I saw that you plugged the rear vents to change the microphone pattern from cardioid to omnidirectional. Did you leave a vent to equalize the internal pressure? What diameter?

1mm

 

[maurizionatoli]

Thankyou man!

 

[maurizionatoli]

... Pure capsules M50 style...

 

[maurizionatoli]

Dear diyers
As promised, here are some classical guitar tracks recorded yesterday in my studio.
As my usual, there were 2 cardioids @ 40 cm (+o-), one pointing the 12th fret from above, and the other pointing the right hand from below, and 2 omnis @ 2 meters high.
No EQ, non compression, only delayed the nears and checked the phase.
Of course a little bit of convolution reverb (and none in the tracks "no verb").
Roughly 50% of each.
The guitar is a Rinaldo Vacca.
Please let me know what do You think about it.
Again many, many thanks to the diyers who gave me some precious advices.
Enjoy!