Many amps use a buffer so they can be used in balanced mode to unbalanced to the first stage
The input stage is often not so low impedance so most preamps could drive the amps without these buffers
Why many manufacturers still use buffers often made with cheap op amps to good circuits ?
Is it only a commercial fashion to use XLR inputs which in reality is not a totally balanced amp ?
Thanks
The input stage is often not so low impedance so most preamps could drive the amps without these buffers
Why many manufacturers still use buffers often made with cheap op amps to good circuits ?
Is it only a commercial fashion to use XLR inputs which in reality is not a totally balanced amp ?
Thanks
I think you mix differential and balanced impedance transmission line:
https://www.sweetwater.com/insync/impedance-balancing/
Fully differential have merits into an amplifier, balanced impedance ( it's the full name that should be used as it is not misleading if you have basis on electronic imho) have too but both have differences ( and similarity).
Balanced impedance lines are used mainly for noise immunity reasons.
Fully differential bring second harmonic cancellation and amplifying ( if needed).
Commercial designers inplement buffers at input because they don't know what is going to drive the unit and it solves issues that could happen.
If you have an asymmetrical drive and know what you do ( know the drive capability of previous stage) then you can skip the buffer stage.
https://www.sweetwater.com/insync/impedance-balancing/
Fully differential have merits into an amplifier, balanced impedance ( it's the full name that should be used as it is not misleading if you have basis on electronic imho) have too but both have differences ( and similarity).
Balanced impedance lines are used mainly for noise immunity reasons.
Fully differential bring second harmonic cancellation and amplifying ( if needed).
Commercial designers inplement buffers at input because they don't know what is going to drive the unit and it solves issues that could happen.
If you have an asymmetrical drive and know what you do ( know the drive capability of previous stage) then you can skip the buffer stage.
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Yes I meant differential (+ and - balanced inputs) to single output that goes to the first amp stage.
One fine example is the Accuphase M-6000, see service manual / input assy, regardless of cinch or xlr input, the signal passes a lytic cap without film bypass cap and a NJM4580D...
This M-6000 is fully differential but as mentioned . Some amps like Classe DR 15 have an awful buffer made with a TLO72 that goes to the first amp stage
The Class
e amp is not fully differential as the M-6000.
The Class
Professionals use XLR cables for physical reasons and generally don't care if the input is actually balanced or not. They don't want cables coming out during a performance or a connector breaking when the cable is yanked sideways. They may have ground voltage differences which a balanced connection helps, but that would be between the mixer and the crossover, not at the power amp. The power amps are in a rack with the crossover so they will have the same ground voltage. Any input buffer op-amps may not be the latest trendy audiophile part, but they are adequate for the job. I expect that a modern system would use a digital connection? It's been 35 years since I worked on such equipment.