#AUDIO ISOLATOR DRIVER#

PS Audio's HumZero stops ground contamination before it can enter the system. Once connected together, the dirty outside cable television grounds will mix with your home's cleaner AC power grounds and degrade the performance of both the video as well as audio systems. If your audio system has any connection to your AV system, or a cable internet modem, then you need PS Audio’s HumZero. Noise and ground contamination enter our homes and dirty our grounds through CATV connections with the cable company. More often than not, our home audio systems commingle with connections to the outside world and this can be problematic. But, most of us don’t live in perfect worlds. In a perfect world, our audiophile-grade systems would benefit from a dedicated ground, one that only the stereo system is connected to. The cleanliness of that ground has a major impact on both sound quality and noise levels. It’s where our audio signals, from the tiniest moving coil cartridge output to the largest output from our preamps and sources all reference to. Thus common op amps, such as the 741 and LM324, will likely give poorer performance in this circuit due to their high noise and distortion.Removes unwanted noise and prevents ground loops in the audio system by means of galvanic isolation.Īt the heart of every high-end audio system is ground. The opamps shown are rail-rail types but standard types could be used if dual supply voltages are available.Īny op amp type used should have good performance (noise, bandwidth, distortion) over the audio range.

Pot U2 adjusts to get the desired voltage output and compensate for the gain of the particular opto isolator you have. (A double-blind A/B listening test of music would be interesting). The simulated harmonic distortion is less than 1% at 1kHz for a 1 Vrms input, and the frequency response is 20Hz to 20kHz.ĭistortion doesn't quite meet high fidelity standards but should be inaudible in most audio applications (except perhaps to those with the proverbial 'Golden Ear'). The linearity degrades at higher operating currents due to reduction in the CTR of the opto but looks good if the maximum current is kept to no more than a couple mA or so (1.6mA maximum in this simulation). The simulation results are somewhat idealized of course, as determined by the accuracy of the models, and the real linearity will depend upon the actual characteristics of the opto coupler used, but should still be good, adequate for non-critical voice and music applications. (Note the blue trace where the output is graphically superimposed over the input so any non-linearities are more readily observed). If a symmetrical output signal with respect to ground is required, then the output can be capacitively coupled to a load resistor connected to Ocom.Īs can be seen, the output voltage plot appears quite linear with respect to the input. R2 can be increased in value to increase the output voltage in this configuration, the tradeoff being some increase in the distortion. If you have a high impedance load (>1.5KΩ) and are satisfied with an output voltage of about 1/2 the input (depending upon the opto transfer gain), then U5 may not be needed and you can use the voltage across R2 as the output. Op amp U5 is a buffer/non-inverting amplifier that amplifies the voltage across R2 to convert the opto isolator output current back to a voltage. The opto is operated Class A with about 1 mA DC bias current.

#AUDIO ISOLATOR DRIVER#

Op amp U3 is configured as a current driver for the opto input, generating a current proportional to the voltage input. (Ocom is the isolated output common and Rsim is just to allow the simulation to run with an isolated output ground).

This eliminates the non-linear LED input voltage to current relationship, with the opto isolator output current typically being quite linear with respect to the input current, especially for low current levels.īelow is the LTspice simulation of such a circuit using the 4N25, a common and representative general purpose opto isolator. There are special purpose (and relatively expensive) optical isolators available with separate feedback connections designed for high analog linearity and fidelity but, for non-critical AC applications, a standard opto isolator may be adequate if it is driven by a current source instead of a voltage.

Audio isolator