Published On May 21, 2019 | Features

In a moment of gear epiphany, Jonathan Burnside discovered Spectra 1964’s V610 Complimiter. Impressed and intrigued by how well this very old technology solved a very modern problem, he chatted with Spectra 1964’s co-owner Bill Cheney about the V610, the history of Spectra Sonics, and more. 

Interview: Jonathan Burnside

Many times when mastering I’ve needed sporadic limiting to protect against the ‘overs’ caused by intersample peaking, as shown when using a true peak meter. These overs can cause distortion when codecs are applied for streaming or MP3s, but many of the digital limiters I’ve tried did not provide effective protection. I compared virtually every digital limiter on the market, and measured the true peak outputs, but wasn’t in love with the sound of any of them. Wouldn’t it be great to be able to pump up the volume of a master, with no intersample peaks, and remain completely in the analogue domain? 

Researching ultra-fast analogue limiters, I learned that the Spectra Sonics 601 limiter is the fastest on the planet – even though it’s an original design from 1969. It’s a fixed-timing, fixed-threshold peak limiter circuit that operates fully within a 180 nanosecond range [0.00000018 seconds], transparently eliminating voltage transients and thereby providing more headroom for any device placed after it in the signal chain. Many of these transients are inaudible except for how they affect the operation of analogue and digital processing downstream. 

Spectra Sonics is the same company that built the desks in many of my favourite studios, including Muscle Shoals, Ardent, Stax, Advision, Chateau d’Herouville and the Record Plant studios. Their 101 preamp was the soul of these desks, and many of my favourite-sounding albums were done on them. In fact, their preamp and limiter modules were used to make much of the music that has influenced me. Here’s a very abbreviated list: T. Rex’s Electric Warrior, Aerosmith’s Toys in the Attic and Get Your Wings, Led Zeppelin’s III, Elton John’s Honky Chateau and Don’t Shoot Me I’m Only the Piano Player, Big Star’s #1 Record, most of the albums Tom Dowd recorded, all the Stax and Muscle Shoals output from the mid-sixties onwards, and more. 


Intrigued by this revelation, I reached out to the affable and highly knowledgable Bill Cheney, co-owner of Spectra 1964 (makers of the Spectra Sonics analogue products, see sidebar). Bill suggested I try their flagship V610 Complimiter, which contains their 601 limiter/compression module followed by their 110 amplifier – the amplifier used for the preamps in later Spectra Sonic desks. It’s the same circuit as the 101 amplifier used in the studios mentioned above, but with more headroom, higher gain and less noise. 

The V610 has indented pots throughout, as well as improved headroom and noise specs when compared to the original 610 limiter, so it’s recommended for mastering. After waiting a couple weeks for a pair to be assembled, burnt-in on the bench and hand-matched to within 0.1dB throughout, I finally got them and put them straight to work in my mastering, mixing and tracking sessions. 


The V610 is simple to use… when you know how! The limiting threshold is fixed at a very low level of -40dB, which means operation isn’t just a matter of setting a nominal level, pulling the threshold down, pushing the ratio up and playing with the release time. Because the limiting threshold is fixed at such a low level, there is an input pad switch (with attenuation selectable in 10dB steps from 0dB to -30dB) to control how much the V610 is driven into limiting, compression or both. A large ‘bat wing’ knob follows the input pad switch; it’s labelled ‘Threshold’ but should be thought of as a finer-stepped pad switch that allows up to 11.5dB of additional attenuation to be applied in 0.5dB steps. This is important because, with a fixed threshold, finer steps than those offered by the input pad switch alone are required. On the right side another large ‘bat wing’ knob labelled ‘Output’ offers makeup gain from 0dB to 75dB. The makeup gain is provided by the 110 amplifier, and it sounds wonderful. 

There is a lot of misinformation on audio forums about the 610, with some saying it’s too wild and unpredictable for tracking. I can only assume this comes from people who do not understand how it works. Finding the right amount of attenuation on the input before limiting/compression, combined with the right amount of makeup gain on the output, is the whole ballgame when it comes to getting the desired result. While it is true that a 610 is great for smashing things on a parallel bus and sounds wonderful when pushed into distortion, it is, in fact, ultra-precise in operation. (If you want to hear what it sounds like when driven hard, take a listen to the fat, present guitar tones on all the early ZZ Top albums.) 


With a maximum gain of 65dB (the same as the venerable API 512), the V610 can easily be used as a preamp. It has separate balanced line and microphone inputs, and phantom power can be applied to the microphone input via a front panel switch with status LED. 

Using the V610 as a microphone preamplifier has been huge for me, not only because of how it sounds but because of how it’s affected my workflow. I use a mastering/mixing chain that starts with two V610s, followed by other compressors and equalisers. If I need to do overdubs for a soundtrack or band project, I can do it almost immediately without having to re-patch a thing. I keep an AEA R92 in front of a guitar amp and patched into the top V610’s mic input, which handles ribbon mics very well. Even if I’m in the middle of a mastering or mixing job, if I need to lay down a guitar track I just switch the top V610 to microphone input, adjust the attenuation to where the signal is just kissing the limiter, dial-in the parameters on any of the other units I want to use in my chain, bypass what’s not needed, and record through the mastering converters the chain is already patched into. Then I switch back to line input, match the controls on all the top units to those of the unchanged values of the bottom units, and I’m back to mastering or mixing again. Easy recall, and switching back and forth takes about a minute. 

I have recorded electric and acoustic guitars, DI bass guitars, pedal steel, vocals and percussion through the V610; it has become my favourite preamplifier as well as my favourite limiter. Recording percussion with it was especially revealing. There was no chopping of the transients from tambourines and cowbells; the details were all present, both sat well in the mix and neither sounded dulled or icepick-like. (Finally I can put more cowbell in the mix!) When you get your hands on a V610, or any of the Spectra Sonics preamps, try this test: plug in a condenser mic and record a set of car keys jingling in front of it. Now plug the mic into any other preamp in your studio and do the same thing. Listening back, you’ll probably find the V610 recording has clear, open transients and the recordings from the other preamps sound like the transients are clipped in comparison. 

The Spectra OG: Spectra Sonics founder, William Dilley, and his wife Jean at an audio tradeshow.


In 2002, a virtual instrument software company deleted the space between the words ‘Spectra’ and ‘Sonics’, then applied for and received a US trademark for the name ‘Spectrasonics’. Instead of wasting their resources in a legal battle to use the company’s original name, Bill Cheney and Jim Romney decided they would concentrate on putting Dilley’s designs into useable modern packages with the original sound and build quality. They rebranded the company with the name Spectra 1964, chosen because 1964 was the year Spectra Sonics was formed. 

In the vintage console market, the names of consoles with Spectra Sonics parts is also confusing because Auditronics built Spectra Sonics desks for awhile, as did Flickinger, and there were many custom boards built that had all Spectra Sonics parts, but were not branded as Spectra Sonics consoles. 


There’s a lot more to say about how these units can act as a limiter, a compressor or both, with a wide range of compression ratios (1.1:1 to 100:1) and release times (50ms to 10 seconds). As a preamp with a built-in limiter taking care of ultra-high voltage peaks, it has become the house favourite. After 30 years of using and owning many vintage and modern high-end compressor/limiters and preamps, the V610 is my new pack leader. 

The more I looked into the history of Spectra Sonics and what made the V610 tick, the more I realised the role they’d played in recording the music that influenced me the most. I had many questions for Bill Cheney, and he kindly answered them during several lengthy phone calls. 

Jonathan Burnside: Do you think there’s a Spectra Sonics sound? I’ve been listening to a lot of music recorded on Spectra Sonics boards and I’m hearing a certain similarity between them. For example, ZZ Top’s Waitin’ For the Bus, Aerosmith’s Walk This Way, and Hall & Oates’ Sara Smile all have guitars and drums that are stylistically very different but share the same presence and realness. The drums in Sara Smile are quite up in the mix but sound so musical that they still somehow fit, even in such a laid back and smooth song. And all that was used to record them was Shure SM57s, so we can’t credit the mics with that. 

Bill Cheney: I think the ‘sound’ you’re hearing is that of the actual instruments as captured by the microphones. Our big deal is that we reproduce what’s on the input and try to have no signature. We don’t want to have a ‘fat low-end’ or a ‘particular midrange sound’. We’re trying to reproduce the waveform, and one of the things that affects how accurately a waveform is reproduced is avoiding peak overload. You can only guess what happens to a signal when an amplifier overloads, in terms of harmonic distortion. It’s unpredictable. Whereas with our preamps, which the recordings you mentioned were made on, you can run them to +18dB output and run a thousand percent worth of peaks through them and they won’t clip. What should be understood is that all of our preamps will pass the peak, not clip it. And it’s not uncommon, even on our old desks, to get 25dB of accurate peak reproduction above the RMS average. A kick or snare will create peaks of 20dB or more above RMS. Those peaks are normally lost with a conventional amplifier, but ours can reproduce them. 

When you record a kick or snare and play it back but don’t really hear what you heard in the room, or don’t get that ‘presence’ and ‘realness’ you referred to, it is because of the time period a conventional amplifier takes to recover from overloading after a peak. There’s a given time base when the amplifier overloads and that time base is your harmonics. 

Jonathan Burnside: And this ‘time base’ is the time it takes the amplifier to recover from the peak overload? 

Bill Cheney: Yes. Let’s say we have a kick drum that’s doing 20dB peaks. The conventional amplifier won’t reproduce those peaks and you can do one of two things: you can turn it down 20dB, or you can let it clip. When it clips, the power supply cannot supply the required current so its power rail drops, or gets ‘pulled down’, for a given amount of time until it recovers. Some manufacturers get into designing very stiff power supplies – with a lot of capacitors and regulation – in an attempt to fix that problem, but there’s still a period of time when that power supply gets pulled down and the reproduced waveform is affected. When you record with our amplifiers and limiters you’ll notice a snare sounds like a snare and a kick sounds like a kick, because we don’t have the problems we’ve just talked about; our amplifier’s recovery time is less than one millionth of a second.

Jonathan Burnside: You used to work for Spectra Sonics. How did that come about? 

Bill Cheney: I was 22 years old and working for an audio equipment retailer in Ogden, Utah, near where Spectra Sonics was located. William Dilley, Spectra Sonics’ founder, was giving a lecture on solid-state design, so I attended. He was standing in front of a chalk board and he wrote: “A properly designed amplifier eliminates the cause, it doesn’t minimise the effect.”

Jonathan Burnside: That reminds me of that age-old tracking excuse that turned into a joke: “We’ll fix it in the mix.”

Bill Cheney: Yes. Eliminating problems through initial design has always been Spectra Sonics’ guiding principal. It’s why his designs don’t have these problems.


Jonathan Burnside: Tell me more about Dilley. 

Bill Cheney: Dilley was one of those larger-than-life WWII guys. He’d run missile programs, written international aviation protocol, commanded fighter squadrons, been a jet test pilot and was an organising member of ‘The Minutemen’ – an air acrobatic team flying P-51s. He was at one time the holder of both US and world air speed records. He even had his fighter plane’s ass shot off in the Battle of the Bulge – the GIs found him hanging from a tree in his parachute, and the first thing he did, before they cut him down, was point to the direction of the Nazis! 

Eventually he hung up his wings but continued working for the Air Force. He oversaw the transition of their entire communications systems and protocols from tube to solid-state in under three years. Considering how high and fast radio frequencies are operating at, and how low the margin of error is, this was quite an accomplishment. Coming from that background, moving to designing solid state circuits for the lower, slower audio frequencies used in professional recording and sound reinforcement was a piece of cake for him. 

Jonathan Burnside: What got him into audio design? 

Bill Cheney: Dilley was always a lover of audio. He had already designed tube audio circuits and written papers on tube technology. He was good friends with Les Paul, and he designed a lot of the equipment that was on Les Paul’s workbench. Not many people knew that, because Dilley never made a big deal about his accomplishments. The reason he initially designed the Spectra Sonics solid state modules was to earn enough money to buy his own airplanes; like the de Havilland Vampire, a single-engine British jet fighter. He never wanted to build consoles, just the modules inside of them. That’s why so many studios had custom consoles that were actually made from Spectra Sonics modules, like Chateau d’Herouville where Elton John did his albums. After a time, he got another manufacturer to build complete desks with our modules and specifications, but he soon got tired of fixing their shoddy workmanship! When consoles started slipping out of their backdoor, that was the final straw for Dilley. He ended the relationship and started building complete Spectra Sonics consoles.


Jonathan Burnside: So how did you start working for Spectra Sonics? 

Bill Cheney: After attending Dilley’s lecture on solid-state design, I told my mother “I’ve just met the most incredible man, who really knows what it’s all about”. And he did. So I started going out to Spectra Sonics every day and helping in any way I could, and I ended up with a job. 

Dilley was inspiring. He came from an architectural engineering background, where things had to work perfectly on paper before you ever started building. He applied that same approach to his audio designs. He would write down all the limitations of a transistor or other electronic component first of all, and then he would design his circuits taking these limitations into account and following his own strict guidelines on peak headroom, DC stability, low distortion, low noise, the whole thing… 

Jonathan Burnside: Your partner in Spectra 1964, Jim Romney, also worked at Spectra Sonics, yes? 

Bill Cheney: Jim Romney and I were high school friends; I brought him to Spectra Sonics shortly after I began working there. It was kind of a family situation where we were as much friends of the family as we were employees of the company. It was very much a family company. Dilley’s daughter Kay was the key part of production, and was renowned for her NASA-level soldering skills. His son Greg was the business interface and helped run the day to day operations. The planning and financial side was run by his wife, Jean – she was the perpetually friendly but always efficient ‘get things done’ side of the business. Life-long employee Randy Ward was a member of the ‘family team’. He was a wizard at metal and wood fabrication for our outboard products, as well as the numerous Spectra Sonics consoles that were built over a 10-year period. 

Jonathan Burnside: It sounds like you and Jim Romney go back a long way… 

Bill Cheney: We do! Jim Romney is a design genius. We’ve worked together for years in other companies we’ve started, doing things like audio, video and data integration. In 2007 we bought the Spectra Sonics company from the Dilley family. When we first purchased the company there were only sparse notes on how components were matched and selected. Dilley’s military command background meant he was used to working in very high-security environments where, for security reasons, as little was written down as possible. After buying the company we were trying to build a functioning 610, but we were really struggling to get it to meet spec – until Dilley’s son called one day to say “I’ve just found Dad’s handwritten notes on the 610!” Even with the notes and a very good prior knowledge of how the unit worked, it took us two years of chalk-boarding to reverse engineer it and meet the original specification. Dilley had given us lectures every morning on theory and how it all worked, but he did not show us the actual specifics of how he put everything together, and how he selected and matched parts. His genius was both in his design approach and how he actually implemented it. We knew the ‘what’ and the ‘why’, but the exact ‘how’ took some time to crack.

I’ve been lucky to be surrounded by geniuses! Dilley was a genius at thinking out-of-the-box. He was technical but still very intuitive, a ground-breaker. Romney’s a genius at getting it all to fit inside the box, and to work without size being a major issue. Without Jim’s expertise and tenacity, most of the products we’ve put out as Spectra 1964 wouldn’t exist. He took the core of what Dilley designed, which was the 101 and 110 amplifiers and the 601 limiter, and he set up all the parameters so we could repackage them in a way that’s most useful for recording these days. 

Our products are still made in Ogden, Utah, to the same exacting factory specs as they originally were. There’s always a debate going on in the office about what we’re going to build next and how we would do it. 

It’s fine to have great ideas and understand the technology, but it’s a totally different thing to have the skills to follow through with that and bring it into reality. During all of these processes we continually ask ourselves, “Would Bill Dilley approve of this?”, because Dilley never half-assed anything and we don’t do that either.  

Jonathan Burnside is an American/Australian mastering engineer and mixer living in the San Francisco Bay Area. He can be contacted at

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