#6B. OPA861 zero feedback balanced I/V board

Introduction
OPA861 is a very special operational transconductance amplifier. It has super-high slew rate up to 900V/us over a wide bandwidth extended to 80MHz. The OPA861's performance is pretty much like a super transistor. In current input voltage output mode with zero feedback, the input impedance can be less than 10 ohms. This very low input impedance (closed to short circuit) and the ultra-high speed make it almost the perfect solution of an I/V converter. Actually, OPA861 was confirmed very successful as the SE I/V stage for TDA1541 DAC.
This is the first OPA861 I/V stage running in fully balanced mode. Different from all other active OP amplifier I/V stages, OPA861 I/V is more closed to passive I/V stages such as a resistor I/V or Transformer I/V but with much better dynamic performance.

The sound style is also totally different from a traditional I/V stage. According to my own listing test, it brings the best clarity so far I have experienced. The sound is very detail and at the same time is also very rich. The soundstage is widely open and focused. The music is vivid and dynamic. It doesn't color the music but just makes it more close to the original. I cannot say it is the perfect I/V stage, but I have to say it's the most impressive one.
This OPA861 would be a great option for the high-performance current mode DACs in balanced configuration such as the ESS9038 Q2M Dual mono, the ES9028Q2M, and ES9038Pro, AK4499, PCM1704, TDA1541 and so on.

Features and specifications

• Zero feedback
• OPA861 transconductance amplifiers work in two channels fully balanced configuration
• True current input mode with impedance less than10 ohms
• 80Mhz high bandwidth and 900V/us slew rate. This ultra-high speed performance would be great for an ESS DAC running by high frequency MCLK from 20MHz to 100MHz.
• Power supply: External +-5V power supplies
• Balanced output levels: 4VRMS @ 0dB
• Current input DC offset voltage: 1.65V
• High precision low noise thin film metal resistors
• Connection-compatible with Ian’s ES9038Q3MPi dual mono and ES9028Q2MPi DAC HATS

User's manual

Documents

https://github.com/iancanada/DocumentDownload/tree/master/RPiDacHAT/IVboards/OPA861IV