Monday, September 7, 2009

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.

7 comments:

Ricardo said...
This comment has been removed by the author.
Ricardo said...

Maybe Fryer and his team of designers should count how many op amps are inside the mixing boards in the recording studio which might also affect the quality of the microphone feed. Or simply put, discriminate against all music recorded with mixing boards which employ op amps regardless of any other factor. If their ears are so good they should be able to notice the difference. Let's take into account that most recording studios use mixing boards which are full opamps and very few use discrete or tube based ones.

I have listened to excellent sounding, discrete, tubes and op amp preamplifiers and I have listened to horrible sounding ones regardless of price, company name and designer.

We tend to think equipment sound is related to high price and complicated topology. It's all about the right implementation. At the same time we must remember that every human being listens differently and what to me sounds good to others might sound horrible. An example of this is the tendency I have noticed on some people to highly regard a piece of equipment because it produces a certain amount of bass which isn't existent in the original recording to begin with IMO. But that's only my opinion.

To each their own.

Cheers.

VaneSSa said...

The problem with good IC op-amps is that they are often discontinued before they earn best buy status in mainstream electronic DIY stores like Radio Shack or Circuit City. I've already heard gripes that the "audiophile sounding" LF356 JFET input op-amp is already very scarce in our post 9 / 11 world. And given the "aggressive on-line marketing" strategy of distributors of Electro-Harmonix sourced tubes like the 12AX7, it is getting more and more likely for most DIYers to opt using tubes as opposed to the latest IC op-amps rated at 1 million volts per microsecond slew rate with the looming certainty that such op-amps will no longer be manufactured in 6 to 8 months time.

Ringo said...

As to state "just the facts" on fears of I might attract further criticisms of my current viewpoints on the subject matter. My personal experience on fixing, servicing, and maintaining mixers either in recording studio or FOH use, mixers that are specified to have a signal-to-noise ratio greater than 100dB A-Weighed often tend to be made with discrete devices - like those 2N series JFETs as active gain devices.
Ten years ago (back in 1999), I successfully repaired a Peavey 16-channel mixer that met with an unfortunate mishap with a cupful of beer. I forgot the specific model, but I remembered it being one of those 24-bit 96-KHz ready analog mixers with a manufacturers rated signal-to-noise spec close to 130dB A-Weighed. Fortunately for me, only of the two of the 16 microphone inputs were damaged by the beer spill mishap and thankfully Peavey managed to supply ten spare 2N series JFETS with the mixer when they sold it to their customers. I found out a few days after successfully repairing the unit that these type of JFETs are no longer sold by our local electronics parts stores. Even their handy ECG parts replacement guides only show that these particular JFET were discontinued back in 1995.
Looking back on these repair incident, I think in order for Peavey to make this particular mixer to achieve a signal-to-noise ratio close to 130dB, discrete JFETs are a necessity - especially when paralleled up for applications requiring gain as in microphone inputs. The circuit topology did remind of a very expensive DNM 3B preamplifier. Those particular JFETs might be considered state-of-the-art in a circa 1977 Penton Publication's Electronic Design magazine, but those JFETs unavailability in our local electronics parts suppliers only highlights my gripes against "modern" manufacturers of solid-state devices and very high slew rate op-amp ICs is that these tend to get discontinued before they became widely available or even obsolete. That's why everyone is jumping into the "retro" bandwagon of using tubes. Electro-Harmonix 12AX7 and 12AT7 peramplifier tubes are more plentiful on-line than very high slew rate IC op-amps.

Sherry Rashad said...

IC op-amps are good enough to be used as a unity-gain buffer. But in applications requiring very high gain, they hiss like crazy. Even the low-noise LM387 op-amp when used as a moving-coil preamp for vinyl LP reproduction can't manage better than a 70dB signal-to-noise ratio.

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Sans Ferdinand said...

The only mixing console I know that extensively uses integrated circuit op-amps is the Soundcraft Ghost. Which fortunately I had the good fortune of "peeking" into. Though the op-amps are found only in the stages were they are used as a unity gain buffer. The Soundcraft Ghost sounds gorgeous though, having a fat British tone. Probably due to the JFET input op-amps they are using.
Another mixing console I had the good fortune of peeking into is the Peavey SRC 4034FC which uses discrete discrete transistor summing amps instead of off-the-shelf op-amp ICs found in most mixing consples. Peavey even claim that there low-noise microphone preamplifier stages - which uses discrete transistors - deliver a noise floor on the order of 1dB from the theoretical. I don't have test instrument gear that costs thousands of dollars to prove Peavey's claims. But Peavey's mixers do have less hiss - in my actual usage - compared to other mixing consoles. Although Peavey mixing consoles have a much thinner tone compared to the Soundcraft Ghost. Tone-wise, it is like comparing the Arcam Alpha 1 CD player with the HDCD-capable Alpha 8 SE CD player.