What amps do you know of that...

...are current drive?

I know of the Pass First Watt but that’s about it. Please let me know any you can think of, just looking at what is out there!

 

Hi,

Comemrcial amplifiers practically NEVER use current drive becuase commercial speakers do not work with current drive, sadly.

I experiemnted a lot with usch things as negative impedance, current drive, motional feedback and so on in the 80's. Using normal drivers in normal sealed (or vented boxes) with current drive is not useful, current drive causes major issues around the resonance (no electrical damping so Qt becomes Qm).

In my main research active speaker project I ended up using current drive for the midrange and tweeter and eventually motional feedback based around electret mikes with normal voltage output amp's in the bass.

Midrange was a 5" Fullrange driver with 50Hz resonance build in and a 3rd order highpass crossover around 300Hz, tweeter was a 1" suprynol dome operated above around 6KHz (again 3rd order HPF) IIRC and dual 8" woofers in the bass, all drivers east german with the Fullrange being a Fa. Schulze device and the rest from RFT, crossovers used the "subtractive derived lowpass" version which made sure all driver outputs summed reasonably well back to flat and a decent impulse shape.

These speakers did okay eneough and certainly where more to my liking than normal HiFi speakers but failed to justify the extra effort next to my own double Schulze KSP215 reflex boxes (8" Fullrange driver), the Schulze TH315 (12" Coaxial) and my old EV based 15" Woofer (B15), 8HD & T35 based DIY monitors. Probably the drivers where the limiting factor as well as lobing etc. from the driver spacing.

Anyway, it is very easy to make any funloving amplifier "current drive" as long as it uses negative loop feedback. Back in the 80's my active speaker used voltage and current boosted A2030 (East German copies of the SGS TDA2030) Chip Amplifiers with a suitably arranged feedback network and serendipiously (as I needed a summing junction for the subtractive crossovers) inverting operation, which made the sound quite acceptable with decent power levels. These days my choice would be the Nat Semi LM3875 in the same job.

Ciao T