An Op-Amp IC For Your Hi-Fi Needs?

Given that they’ve been used successfully in a number of excellent sounding hi-fi applications, is there really a right op-amp for your audiophile needs out there?


By: Ringo Bones


Yes it’s true, there really is such a thing as an audiophile grade integrated circuit operational amplifier or IC op-amp. And most of them are not necessary manufactured by Analog Devices like the AD845 and AD843. Or those by Burr-Brown which their dual op-amps that are specified to be fast enough to handle the RF energy present in Red Book CD digital to analog conversion are often used in bridge configuration in left / right analog outputs.

The quest for finding the best off the shelf IC op-amp probably started during the early 1990s. When major CD player manufacturers discovered – either by theoretical introspection or trial and error – that those high-speed op-amps made their 500 US dollar or so CD players sound closer to entry-level audiophile grade vinyl LP replay.

From the electronic engineer’s design standpoint, high-speed op-amps are a necessity in Red Book specification CD players. Sufficient slew rate ratings are a necessity to handle the quite large amounts of ultrasonic requantization noise - which is an unfortunate by-product of converting your 16-bit 44.1-KHz digital data into a reasonably smooth analog waveform that could sufficiently past muster as music. In my experience with the most widely used up-market “hi-fi” op-amps – namely the LM318 and the LF356 – which have very different personalities when used in an audiophile context. Although I used audiophile grade ceramic IC sockets with silver connectors to allow me to easily replace both op-amps for comparison.

Over the years, my countless experiences with the high-slew rate (50 volts per microsecond) LM318 suggests that this IC op-amp is well suited to audiophiles who like to listen to Classical Music - Or wants to reproduce the recorded hall acoustic of an opera recording accurately played back in his or her listening room. It even enhances – or exaggerates – the Classical Music-like hall acoustics of some tracks of The Gathering’s “How To Measure A Planet?” album.

One drawback of the LM318 op-amp though is that it doesn’t like very much the “relatively” high-capacitance interconnects often used in entry-level solid-state audio gear. Like Monster Cable’s mellow sounding M850i interconnect often used to tame the harshness of cheap solid-state audio systems. Resulted in a high-pitched squealing sound on rare occasions (guaranteed more than once) during turn on. Although easily remedied by turning off and turning on again your entry-level solid-state amp.

Even though from a technical standpoint, the LF356 has a much lower slew rate rating (12 volts per microsecond) in comparison to the LM318, it does audiophile-oriented things that the LM318 can only aspire to. The very high input impedance – about 1 trillion ohms - of the JFET input stage of the LF356 allows it to have a bass response that Rock Music aficionados since the time of Elvis strive for. The LF356 is also capable of driving large capacitive loads – up to 10,000 picofarad or 0.01 microfarad – with ease. Which makes it more suitable for driving high-capacitance mellow sounding interconnects used in entry-level solid state gear.

Sound quality wise, it is as if the designer of the LF356 op-amp want it to sound like what recording engineer Andy Johns wants the first four album of Led Zeppelin to sound like – i.e. the “John Bonham snare sound”. The LF356 also sound as if it is the first op-amp with a very musically ideal loudness control. It defeats the Fletcher-Munson contour curve characteristic of the human ear that makes us less sensitive to the bass and treble frequencies when listening at reduced sound volume levels. With the LF356, you’ll get the full works whether you’re playing at 65dB or 95dB sound pressure levels - not unlike the sound of Electro-Harmonix versions of 12AX7 preamplifier tubes.

Surprisingly, the LF356 does room sound too - Although not like the Classical Music concert hall portrayed by the LM318. The room sound produced by the LF356 is the “normal” unadorned type – typical recording studio or just a spacious venue. The LF356 also has better low-level sound retrieval in comparison to the LM318 because the LM318 tends to exaggerate the dynamic range of CDs that are recorded without Tom Lord-Alge levels of compression. Like Lunachick’s Binge and Purge album which the LF356 still manages to retrieve low-level details that are played back even softer by its higher slew rate counterpart.

Both can still benefit from a well-regulated plus and minus 15 volt split supplies though, given the inherent RF corruption of our contemporary power lines. Despite both IC op-amps often rated with a power supply rejection ratio of over 100dB at 50 to 60-Hz AC. Boutique capacitors like Rubicon Black Gate capacitors or Philips sourced French Blue capacitors also help improve sound quality to no end.

So there you have it, two op-amps that I have extensive experience with that could past muster as being audiophile certifiable. Although it is somewhat over simplistic to conclude that one prefers Rock, while the other op-amp prefers Classical. The sound quality of one is sufficiently different from the other that it is worth noting. Although the LF356 also has a gorgeous presentation with Orchestral Classical Music recorded during the Golden Age of Stereo.

Are Integrated Circuit Operational Amplifiers Hi-fi?

In the current fashion “revival” of vacuum tube and discrete transistor usage in the hi-fi scene, are audio designs that use integrated circuit op-amps still considered hi-fi?


By: Ringo Bones


Integrated circuit – or IC – op-amps have a myriad of advantages over their discrete component-based counterparts other than space. Like extremely high input impedance, high common mode rejection ratio and high power supply noise rejection ratio just to name a few all in a very compact package. But in terms of ultimate sound quality, many top designers in the hi-fi world find the sound quality of most IC op-amps wanting.

Richard Fryer, founder and owner of Spectral Audio – one of the top manufacturers of cutting edge solid-state audio gear, who as recently as 1998 still insist on using discrete circuitry. As opposed to integrated circuit chips much of the time. Fryer and his design team at Spectral Audio had found out over the years that for critical signal applications, integrated circuits – or IC chips to you and me – simply don’t meet their quality standards. Although he and his design team had been constantly evaluating new integrated circuits and, to everyone’s credit, the IC chips are getting better and better through the years. Still in the rigorous evaluations that the design team at Spectral Audio does these “improved” IC chips simply can’t pass the microphone feed accurately. There’s so much musical information and life that is lost – according to Fryer. Even with the most premium integrated-circuit amplifiers, these integrated circuit packages are just not up to Spectral Audio’s needs in critical signal applications.

Even though most audio designers in the hi-fi world still insist on using discrete components, there are those who are adventurous enough to use IC op-amps in their cutting edge audio designs. Ron Sutherland is one of those high-end audio gear designers who isn’t afraid to use IC op-amps in his almost 7,000 US dollar Sutherland PH-1 phono preamplifier. Maybe it is because Sutherland has a degree in both electrical engineering and physics that made him courageous enough to use a number of Analog Devices instrumentation integrated circuit op-amps on his somewhat “pricey” but very good sounding phono preamplifier.

Another upmarket high-end audio gear that uses IC op-amps is Reflection Audio Design’s 4,700 US dollar (550 US dollar extra for a phono stage) OM1 preamplifier. The OM1 preamplifier is a high-speed, super wide-bandwidth design based on very high slew rate IC op-amps rated at 2,000 volts per microsecond slew rate. It is purported to be flat to 2 megahertz and able to maintain an absolute phase of plus and minus 0.5 degrees across the audio bandwidth (20 Hz to 20,000 Hz). The OM1 preamp by Reflection Audio Design is a very pretty two-chassis affair – if you include the matching 1,550 US dollar battery unit – with a high level of attention to detail. Like the use of curved circuit traces to avoid high-frequency signal reflection.

There are also budget high-end audio designs that used IC op-amps. Like the Super Pas 4 i preamp kit which famed Dynaco tube amp tweaker Frank Van Alstine sold in the early 1990s. Though this preamplifier is somewhat unique because it is a tube and op-amp IC hybrid. Comprising of two 12AX7 tubes and two AD845 (AD843) FET input op-amps in the output stage. And it is surprisingly affordable – in high-end audio terms – at 595 US dollars back in 1993.

In my personal experience, op-amp IC chips – when used properly – can achieve excellent results sound quality wise. Sometimes I wonder why all brand-name boom boxes being flogged in the “high-street” can’t achieve excellent sound quality that matches even cheap DIY hi-fi that uses op-amp chips. Even DIY-ers had achieved excellent results with these lowly audio devices. Most of these serving as a gateway to the wild blue yonder of high-end audio. Next time, I’ll be discussing my experiences with the most touted op-amps for audio use, the LF356 and the high slew rate LM318 in a DIY hi-fi context – replete with unapologetic tweaks.