Good morning Friends!
I need your help again. Yesterday I met a master who can assemble a preamplifier for me. But he doesn't know of any truly balanced preamp circuits. He says that all existing dump circuits are pseudo-balanced circuits. And there is no real balance. I do not believe in this. Can you help me and give me a balanced preamp circuit? And, importantly, the XLR output must be less than 50 ohms. Is this even possible?
I need your help again. Yesterday I met a master who can assemble a preamplifier for me. But he doesn't know of any truly balanced preamp circuits. He says that all existing dump circuits are pseudo-balanced circuits. And there is no real balance. I do not believe in this. Can you help me and give me a balanced preamp circuit? And, importantly, the XLR output must be less than 50 ohms. Is this even possible?
The under 50 Ω O/P impedance is easy enough. 25 mA. drain current IRFBC20 source followers get things done.
DC couple the FET gates to the plates of a high gm/low μ twin triode differential gain block whose "tail" is constant current sink (CCS) loaded. 15 V. Zener diodes connect the plate side of the FET gate stopper resistors to the corresponding FET source electrode. The Zeners provide protection against power on transient over voltage trouble.
DC couple the FET gates to the plates of a high gm/low μ twin triode differential gain block whose "tail" is constant current sink (CCS) loaded. 15 V. Zener diodes connect the plate side of the FET gate stopper resistors to the corresponding FET source electrode. The Zeners provide protection against power on transient over voltage trouble.
There are quite a few options. How much, if any, gain do you desire? Input transformer, with split secondary, into two grids, series feed or parallel feed output transformer. Choose your triodes (or pentodes if so inclined) and OPT ratio to get the output impedance and overall gain you desire.
Why would you need "balanced"?
An honest answer to that will define what "balanced needs to mean.
My Fisher tube amp would put 16 Volts in 16Ω with ease. If driving 50 actual Ohms (not just Rout=50Ω) would be 1/3rd the THD (which you have not quantified even roughly).
An honest answer to that will define what "balanced needs to mean.
My Fisher tube amp would put 16 Volts in 16Ω with ease. If driving 50 actual Ohms (not just Rout=50Ω) would be 1/3rd the THD (which you have not quantified even roughly).