negative Feedback in a Schoeps circuit?

[RuudNL]

I am really interested in the circuit you are using!

 

[maye4]

experiment the whole day...exhousted...results will be tomorrow...sorry for the delay

 

[RuudNL]

I'll be back! 

 

[MagnetoSound]

We are all agog. 

 

[maye4]

folks。。。here are audios of two mics,one is well konwn top class mic,one is my mod.change .jpg to .mp3.

 

[maye4]

another one.
share your thougts.
they are recorded in one take.so the souce is almost identical.
change .jpg to .mp3.

 

[RuudNL]

I have the impression that Mic1 sounds a bit 'darker' than Mic2. Not a big difference in the top end however.

By the way: I think if you would put this on CD, you could have a bestseller! 

 

[maye4]

those are tests of my final results.
One is re20.Which is voted the best broadcasting mic in a recordinghacks test.
One is my chinese Schoeps mod.
Which do you prefer?
change .jpg to .mp3

 

[maye4]

MicB.mp3

 

[maye4]

This is what a Diy porject should look like!

 

[maye4]

The circuit.
I added a feedback circuit.There is a high pass filter in it Which will be reflected in the
D and S of jfet as low pass filter.For some reason i don't know,it will act like a high shelf in reality.It will tame the high mid,but not the high.
The high end will be tamed by bigger the C4 and C5.
And bigger the c2 and C3,more the bass,vise versa.
So we have 3 filters.One is high shelf I added,Could be adjusted by C23; One is Low filter,c2 and C3;High filter  C4 and C5.
Values of these capacitors showd in the diagram are not typical.My stock mic has a 34mm capsule which is full of bass...For tipical values,see Zapnspark's GenChinaMic and GenChinaMod.

 

[maye4]

The Frequency response in emulation.
In reality, the low filter is far less efficient.That's why I made c2 and c3 so small.

 

[maye4]

The noise floor is around -110db(noise from my computer,preamp and sound card are added) :

 

[RuudNL]

Great stuff! I am going to do some experiments along the same line!

BTW: I see you replaced the 'smoothing' capacitor at the output of the DC converter by a series circuit with C16/R23.
This would mean that there is some HF from the converter injected into the capsule.
Personally I would connect a capacitor between the junction of R12/C11/D1 and ground to kill the HF ripple.
The source impedance for the polarisation voltage would then still be 1 M.ohm, so I don't think that would influence the frequency response.

 

[maye4]

Great stuff! I am going to do some experiments along the same line!

BTW: I see you replaced the 'smoothing' capacitor at the output of the DC converter by a series circuit with C16/R23.
This would mean that there is some HF from the converter injected into the capsule.
Personally I would connect a capacitor between the junction of R12/C11/D1 and ground to kill the HF ripple.
The source impedance for the polarisation voltage would then still be 1 M.ohm, so I don't think that would influence the frequency response.

ha,interesting enough,the stock circuit don't have the decouoling capacitor.So I don't bother with it.
After all,if you look close,you don't need a decouoling capacitor here.For DC coming into the capsule,c23 and c16 are open circuits.so it will be fine(I add c16 to block DC).
For AC generated by capsule,they can't go through those diodes and caps of the DC converter to affect the rest of circuits.So it will be fine.
For capsule signal and feedback signal,they are interacting each other.And I stil believe they acts like a dynamatic eq.That's the fist place why Nuemann design this circuit.Mybe I'm wrong. ???

 

[HellfireStudios]

The negative feedback in a Neumann circuit is used to reduce the high frequency lift that is inherent to the K-67 capsule design and the high frequency hiss that was inherent in the head amp (two birds with one stone). It is static in its operation. What is dynamic about it?

-James-

 

[maye4]

Great stuff! I am going to do some experiments along the same line!

BTW: I see you replaced the 'smoothing' capacitor at the output of the DC converter by a series circuit with C16/R23.
This would mean that there is some HF from the converter injected into the capsule.
Personally I would connect a capacitor between the junction of R12/C11/D1 and ground to kill the HF ripple.
The source impedance for the polarisation voltage would then still be 1 M.ohm, so I don't think that would influence the frequency response.

I get it。you mean the 2mhz HF generated by converter.Sorry for my misreading,I took HF as high filter...
In that case, c16 is in it's positon.And i believe It's better than original chinagenmic circuit,cause 2mhz HF must go through 3caps to get to the jfet.
You can't connect a cap directly to the ground in that position though.That would change the filter.

 

[RuudNL]

In fact C11 already shorts the HF ripple from the converter.
But even if this point would be 0 ohms for AC (which it certainly isn't for audio!), the impedance as seen by the filter is 1 M.ohm, because of R11.
The (audio) AC impedance for the filter is then lowered by C23 (with the drain impedance) and C16+R23.
Since the impedance of C23, C16+R23 is always lower than 1 M.ohm, the 1 M.ohm can be neglected.

(BTW: I think a value of 1000 uF for C9 and C14 is an overkill, although it does not hurt...)

 

[maye4]

(BTW: I think a value of 1000 uF for C9 and C14 is an overkill, although it does not hurt...)
[/quote]

Yes，it's an overkill.I use 680uf actually.everything above 220uf is ok.

 

[ricardo]

I did spice the Schoeps circuit often times. The fact that the output Z of the two FET legs is not exactly equal does not automatically create an unbalance in the output Z. Output Z is determined by the EF stage (including buildout resistors and output caps), and as long as the BJTs are matched (as well as some other components) output Z is equal for both pins.

Can you post the SPICE *.asc file and your transistor models please.

My simulations show quite a lot of difference in relative Z though the absolute difference is small.  Differences become more important at LF cos the coupling caps see different impedances.

The point in question is, if the drain resistor bypass mod does not compromise its performance.

No they do not.