Is Schoeps Schematic "noisy"? Or better: Where I'm wrong ?

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Violinist

Well-known member
Joined
Oct 4, 2011
Messages
80
Location
België
reading this forum, and following many arguments, I wanted to try to build my Mic  :)
What I did is to find the the schematic I needed and I found the Schoeps one and the Alice one.

Ok good, i realized the schematic you find here in attachment.
I have not a TSB capsule yet, so that I used a normal Elected from "shop". Its quality is not certainly the TSB but it works (jsut to see if everything is up and running  ;) )

Well: the circuit works and I'm happy.

What is not what I expected is: the noise. The "ffffffffffff" to be clear.
It's not enormous but it is up there.

Initially I thought it was the capsule. So that I tried to connect the point C to B instead of to A.
No way out.

At this point I tried to short circuit C to ground bypassing the capsule. No way out. The "ffffffff" stays.
I compared it with my SE2200A. Connecting the SEc the "space is opened". Connecting the circuit of the schematic, the "ffff" is like "mist in the space" ...

I mean: the rustle is present. It's not unmanageable but its higher than the noise of my SE2200A.

I'm wondered if there is anything in the schematic that can lead to the fine bue hearable "ffff" in my realization

I'm wondered if anybody can help to solve this issue please.




[EDIT] Edited message for rephrasing. Sorry for my English[/EDIT]

 

Attachments

  • Noisy mic.JPG
    Noisy mic.JPG
    30.2 KB · Views: 141
Are you measuring the noise with the circuit in a shielded box?

How much louder is the noise compared to your SE2200?  You can check this by recording some voice and then also some quiet parts in Audacity & look at them using Analyse - Plot Spectrum

After you have done this, while you are investigating this further, remove the 6k8 & capsule and short your 100n to earth so the capsule has absolutely no effect.

I can't see anything in your circuit that might give more noise than usual.
 
@David-p: sincerely I haven't tried another 2SK170 yet. I was confident that it works.

@Ricardo: I will do what you suggest for the noise analysis. About the noise level compared with the SE220A: it's quite higher to be hearable the difference.

I have short circuited the input as you suggested, and fully disconnected the capsule, without having any improvement. That's why I'm quite down in the mood.
 
If you need help you should post transistor voltages
JFET drain and source
PNPs emitter, base and collector voltages

How clean is the gate to 1meg? connection area is there any flux or dirt?

Next very simple lift one side of the coupling caps(220nf) to the PNP bases (this removes the JFET drive, keep the JFET in the circuit)do you still have the noise?  If not it is the JFET stage.  If you still do it can still be both stages.

I am not a fan of the simple schematic you posted.  It looks simple but you need to match the PNPs and select the JFET.  Look at the real Schoeps CMC schematic you can find on the web for some hints.
 
I came to a solution. It was the FET as David-p suggested. That's incredible to rme but I admit it was so.
I just tried to change it with a new one.
now short circuiting the point C to ground as also suggested by Ricardo, the noise level is very low.

The "hiss" reappears when I connect the capsule but now it's clear that the capsule generates its own one. I'm not worried about because it's my intention to buy the TSB165A.

About this capsule: do you suggest to eliminate the internal FET or keep it?

@Gus: I was posting my thread when I saw you're one :)
Yes I got the Schoeps schematics and I've almost copied it (see please the attachment here below). The only one part missing (I will add now) are the 2 Zeners between each Emitter-Collector.
I didn't fully understood the function of these Zeners, I just think (please correct me if I wrong) they are for protection
 

Attachments

  • Schoeps.jpg
    Schoeps.jpg
    134.8 KB · Views: 102
You're in luck with the TSB165A capsule, because they do not have an internal FET. I have used them and they sound quite nice, to my muso's ears.

By the way, the hiss you mentioned when you connected your capsule, as far as I understand it, is the ambient air noise interacting with the diaphragm. I think that is what you are hearing.

Kindest regards,

zephyrmic
 
zephyrmic said:
You're in luck with the TSB165A capsule, because they do not have an internal FET. I have used them and they sound quite nice, to my muso's ears.

Oh that's great, I will order one, I'm really anxious to try it.

zephyrmic said:
By the way, the hiss you mentioned when you connected your capsule, as far as I understand it, is the ambient air noise interacting with the diaphragm. I think that is what you are hearing.

Kindest regards,

zephyrmic

Well, but why not with the SE2200A? The environment is the same: my room. The only things is changed is the mic.
Is this due the bandwidth of the capsule? The little one I used is 100 Hz -12 kHz, or there i some other reason?
 
Violinist said:
Well, but why not with the SE2200A? The environment is the same: my room. The only things is changed is the mic.
Is this due the bandwidth of the capsule? The little one I used is 100 Hz -12 kHz, or there i some other reason?
Capsule noise depends on size: when you increase the size by let's say a factor of 2, like going from 1/1" to 1/2", the level increases according to the surface, so by a factor of 4, or 12dB, but noise increases only by a factor 2, or 6dB. The difference between you small 4mm capsule and the SE2200's 25mm accounts for about 30dB more noise.
Other factors are the FET's noise performance and the arrangement of the head amp.
 
abbey road d enfer said:
Violinist said:
Well, but why not with the SE2200A? The environment is the same: my room. The only things is changed is the mic.
Is this due the bandwidth of the capsule? The little one I used is 100 Hz -12 kHz, or there i some other reason?
Capsule noise depends on size: when you increase the size by let's say a factor of 2, like going from 1/1" to 1/2", the level increases according to the surface, so by a factor of 4, or 12dB, but noise increases only by a factor 2, or 6dB. The difference between you small 4mm capsule and the SE2200's 25mm accounts for about 30dB more noise.
Other factors are the FET's noise performance and the arrangement of the head amp.

Thus the little capsule is 30dB more noisy than the SE2200A if I understood correctly.
Following this logic, I suppose that the TSB165A should be necessarily less noisy than my capsule.

Let's see if I correctly understood.
Being the TSB165A almost 4 times bigger than my little one, the noise will be 4 times higher while the Out Level is 16 times higher.
Regulating the volume to have the same Out Level on my headset as the one I have with the little capsule, it increases the S/N ratio and I will hear less noise.

Is my assumption correct?
 
abbey road d enfer said:
Correct. But remember, this is theory; in practice, the difference may not be exactly as expected.
Thank you very much, Abbay road. I order in the next days a couple of TSB165A :)
 
Back
Top