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Right, so what does this do, that the venerable old Schoeps circuit doesn't (while using fewer components)?
 
I've seen / watched that series of videos several times.  So your argument is (maaaaybe) 3dB more signal level? Poooossibly a bit more headroom on the output?

I could very well be wrong, but most of the time, those might not be issues you run into, with condensers. More often than not, they'll be more sensitive than you need, hence the attenuation switches you often find in the non-bottom-of-the-barrel ones.

If anything, it would be interesting (if possible) to measure some waveforms at various SPLs both at the mic output, as well as, say, right off the JFET source in a Schoeps circuit, and see if and where the signal starts clipping.
 
"Fully twisted P1" doesn't really mean anything, in itself - you usually want to bias the gate in order to obtain maximum unclipped signal amplitude (regardless of where the potentiometer cursor happens to be).

Not to mention, simulations live and die by the accuracy of the models. I've just run a few LTspice sims on a Schoeps circuit, and with an optimally(?) biased J305 JFET, it's showing me 0.37% THD with a 1.8Vpp input signal, resulting in a 3.1Vpp output signal.

And when was the last time a condenser mic was "too quiet"? Keeping in mind that on the receiving end there's a preamp supplied at 24-30V (or +/-15V), capable of at least 50dB of gain...

By the way - that screenshot does indeed show that the output signal is severely clipped. But is that the fault of the output PNPs, or is the signal getting clipped by the FET itself, earlier in the signal path?
 
That, too, could be a simulation artifact (model parameters, etc). My version, with my models, in LTspice, shows no peaking whatsoever, just flat gain up to 17KHz, where it very gently starts rolling off to a -3dB of 180kHz or so.

I'm sure if i iterated with various JFET / PNP models and biasing conditions, i could make the Bode plot peak somewhere, but... How about testing that with a real circuit? Otherwise this all is just an arguably pointless exercise :)

Sure, "in theory", lots of things may or may not happen, but that's of no use if it doesn't agree with reality, right?

I'm not saying the Schoeps circuit doesn't have limitations - of course it does, all circuits do. I'm only asking, how likely are you to hit those limitations, in real-world (and/or "normal") use? :) Is it infamous for low headroom, by any chance?

dima_k85 said:
Let's look at the Bode diagram and the output noise for Schoeps (in the attachment).
The circled area is not valid for high quality amplifiers.
 
Fine. Here's a screenshot of the AC sweep.

PS: Microphone preamps have relatively low input impedances, usually up to 5Kohm or so, so that 47k in your version might be inaccurate / unrealistic. There's even a chance that might be part of the reason for that HF gain peak in your sim, but that's just speculating on my part.
 

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And here's a transient sim, with the THD result of the Fourier transform. It's a bit higher at 0.43% with 2N4403 PNPs; the previous one was with 2SA970 PNP models.
 

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Khron said:
How about testing that with a real circuit? Otherwise this all is just an arguably pointless exercise :)

'Real circuits' rarely seem to trouble the super keen 'I've made a sim' brigade....

Describing the Schoeps circuit as ' a wretched circuit' is a comment I've not read before though? .. a very unusual take on a classic circuit!

It takes all sorts of course  :)
 
My experience is that the Schoeps circuit is a reliable circuit, that has low distortion when the FET is properly biased (on a 'real world' circuit I usually get distortion figures of 0.02%, even at high output levels) and can have very low self noise.
 
Now let's talk about this "wretched" impedance "balanced" CM-1A circuit which is only "balanced" as long as you use it on an low impedance transformer balanced input.  If you use this circuit on a modern electronically balanced microphone preamp (which are the majority today) there will not flow any current through the "balancing" resistor (R15) and therefore the microphone will be in fact unbalanced.  This is ok if you use the microphone with a 2m short cable on your desk, but not if you run the microphone over a 50m long cable in an environment with dimmers and let's see which circuit behaves better.  The "wretched" CM-1A circuit or the Schoeps circuit ?

Oh, you can't find a dimmer pack in your simulation program ?  How sad...... but that's real life....
 
Looks good! There are more shortcomings from the body than either wretched circuit.
To be clear, this is copy of akg 414xls not schoeps?
 
1) Check the title.
2) Read the first post in this thread: https://groupdiy.com/index.php?topic=74818.msg947939#msg947939

shabtek said:
Looks good! There are more shortcomings from the body than either wretched circuit.
To be clear, this is copy of akg 414xls not schoeps?
 
dima_k85 said:
OK, let's talk about the CM-1A if you have anything to say on the case.
The balancing circuit is bad, doesn't suit you? Have you seen the AKG C414 XLS microphone balancing circuit? - So, my friend, it is exactly the same as that of the CM-1A! Maybe C414 a bad microphone? Is it poorly balanced? Maybe AKG engineers doesn't earn their keep (their daily bread)? - NO!
To talk about what currents flow to where you need to analyze the CM-1A circuit not only for DC, if you did not know about it. But you do not seem to need this knowledge, so don’t be clever, your knowledge at the elementary school level, pull it up, and then teach me, okay?
"There is a sucker born every minute" - and I don't know why so many are trying their luck in the audio industry.
 
I did a similar BM800 mounting for an 'end address' version - which works pretty well....

https://www.shapeways.com/product/EFE6MUJYM/34mm-ldc-mic-bracket?optionId=123657963
 

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