That is not really a mic pre amp, that is just a common emitter amplifier with a Sziklai transistor arrangement, if you really want a mic pre you should start by having a differential input.
That is better, I still think the 10k resistor is not needed. It is bootstrapped, which means that practically no current flows through it, bootstrapping is useful when you want to raise the input impedance, but not in that manner. The 22uF cap is too small, raise it to 100uF at least. The 6.8pF cap might not be needed, an engineering premise is not to add something which is not required. The Falstad simulator is very lame to model things like parasitic oscillations, build the thing in a protoboard and, if you notice oscillations, then you can think about adding that cap, otherwise, don't. Something important to keep in mind is that the 6.8pF cap experiences the Miller effect, with the gain you have, it presents an effective capacitance value of 172 pF, which is still ok, but, again, might be completely unnecessary. In your first circuit, since it had more gain, the cap had an effective value of around 3.3 nF due to Miller effect, which forms a pole with the 1.7k resistor at roughly 28 kHz, which is unpleasantly low, producing 1.8dB of attenuation at 20 kHz, 1.1dB at 15kHz, and 0.5dB at 10kHz; not good.
Thank you for taking time and explaining. Learning a lot, and stuff that i need to learn more about. I will tinker some more.
The best Sims I've used, and still use (thanks to the University) are Keysight ADS and Keysight Genesys, particularly the former is in a whole different league, both in terms of price, power and accuracy. However, you know that any Sim is as only as good as its models. I believe I heard that you can load SPICE models into Falstad, but I am not entirely sure about this. I've know the Falstad sim since like 2008, and it has somehow progressed from being simply a cute Java applet, to being a more complex Java applet; but it is still a Java applet. Whenever someone shows me his/her circuits in Falstad, I know they are beginners.
I've heard a lot fo good stuff about Micro Cap, but with all the free sims available by big companies like TINA or LTSpice, I think it hasn't got much attention. However, there is a free simulator that is at a whole different level called Qucs-S. You should also download Xyce with it, since they work together. Qucs-S is a SPICE simulator but it goes beyond SPICE, it can do S parameters and Harmonic Balance analysis. You can couple it with Octave for co-simulation. I just started using it and I was blown away. It is like the free version of Genesys or something similar, minus the EM simulation.
I must say that quite a lot of times I just prefer the "quasi-balanced" option of adding one resistor in series with the output for stability and an identical one from the cold terminal to ground.
I've always been fascinated by this method used by Soundcraft; anyone seen it used anwhere else?
Seems to be some sort of ground sensing circuit. Perhaps it is mentioned in Douglas Self's book, since he used to work at Soundcraft.
Not to quibble about terminology but that topology is called "impedance balanced". Some remarkable bang for the buck when a couple cents worth of resistors allow the marketers to call the output "balanced"
. Not only that it works.Impedance balanced with a simple differential output where the signal is referenced to the external ground. This (differential) is widely done for unbalanced insert points. The impedance balanced outputs are widely used on value products (because it's cheap).
Yes, however, if being completely anal, impedance balanced is whatever topology that has both impedances balanced with respect to ground.Not to quibble about terminology but that topology is called "impedance balanced". Some remarkable bang for the buck when a couple cents worth of resistors allow the marketers to call the output "balanced"
In my experience in the mixer business (decades ago) "impedance balanced" was the terminology used to describe that very specific topology where you add one equal value resistor in series with the - output lead connected to ground to convert an unbalanced output to (cough) balanced.
