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VK Tech Tim Mead Revives ADR Compex F760X-RS For A New Generation

Posted on July 2, 2014 by Eric There have been 0 comments

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As the head technician at Vintage King, Tim Mead has spent over ten years perfecting his craft and working to revitalize unique pieces of vintage gear under our roof. In addition to his work at VK, Mead has been making waves with engineers and producers by faithfully recreating a classic studio compressor/limiter, the ADR Compex F760X-RS, under the banner of Q2 Audio.

Tim's obsession with recording and gear predates his time at Vintage King."I got into music in high school playing keyboard. I eventually wanted to go to a recording school," Mead says of his start in music. "They required some minimal knowledge of schematics and I knew nothing. So, I took 'DC Electronics 101' at the community college and the next thing I knew I had a degree in electronics."

Taking his "serious DIY problem" to the next level, Mead spent his time developing his passion and working on gear like the Compex for the locally-owned Rust Belt Studios. Upon first getting his hands on the F760X-RS, he wasn't exactly thrilled. "I didn't really play with it much, I somehow managed to find the bad component and sent it right back," Mead states. "My impression at that point was 'I hope I don't see one of those again!'"

During a recent chat, Tim talked about his change in view of the Compex and what made him decide to bring back this incredible studio tool to the market. Read on to discover more about the classic features, new additions and future plans for Q2 in the upcoming year.

What was it that drew you back to the F760X-RS Compex and made you want to recreate this piece of gear?

After restoring a number of them at VK I found that they had "something" that I liked. I couldn't quite put my finger on it then and I'm not sure if I can now, but they have a sound unlike any other compressor out there. Recently I discovered they they were used to all over the Love and Rockets' record Seventh Dream of Teenage Heaven (along with the Compex II and I'm sure other comps as well). I always really liked Love and Rockets' sound and I wonder if I hear it somewhat in the way the Compex treats instruments. I'm still searching for answers to: "Who used it on what?"

Talk a little about the process of tearing something apart, investigating what’s inside and then building it from scratch. What are the pain points and the highlights of this process?

I had a couple of choices: remake it exactly as it was and charge much more than it currently sells for (tons of labor would go into it), or try to find a way to make it easier to manufacture while maintaining the mojo. I have at least two other mechanical/PCB designs that I did not use. I had to get nearly to the end of the process before I could see that it was not going to work for some reason. The original Compex changed over time from a 3U hand wired monster, to a 2U version of the same thing and then it lost a decent amount of the hand wiring and went to more PCB's. Even the last iteration, which was much more reliable than the earlier versions, was difficult to service due to the construction and that was my main problem with it.

I have to say this, when I started out I thought it was going to be much easier to improve on the design than it was. The guys who did the original design were much smarter than I. It was very well done. I managed to consolidate it down to a single main PCB per channel connected via 40-way ribbon cable to a front control PCB. It's now much easier to service the parts that need service the most often: pots, switches, etc. The biggest pain of the design process in getting certain components in small quantities. I waited 13 months for prototype pots from a very well known manufacturer and when I got them they were shit. Start the search over. It does seem that every adversity that I encountered ended up making the outcome better... Sounds a lot like life in general.

What new elements did you include into the Compex to help move it into a more modern era?

On the outside, the most obvious thing is the addition of side chain access. This lets you insert an EQ to modify the frequency response of the audio feeding the rectifiers and timing components that create the DC control voltage. The other option is to use a different audio signal to control the side chain, which is called "ducking" in the broadcast biz. This has been pretty standard in certain VCA comps for a long while, but the Compex never had it.

Someone sent me a vintage unit to service and they asked if I could add side chain access. I thought about it for a bit and said "Yes." I had never thought of it before. It works quite well and I also discovered that a simple passive filter can be built into a 1/4 TRS plug to create a HPF - no fancy EQ needed if someone wanted to dedicate a unit to mix bus, etc. I keep meaning to post a list of mods and extras like that. There are a few other things done in the circuit to help keep the calibration from drifting like the vintage units do. Mostly just a few more modern components, better voltage references, multi-turn pots and things like that.

In a few of the reviews for the F760X-RS, some have said that the Compex is complex. Do you have any advice for better understanding this tool’s capabilities? 

That's a tough question. The thing has a ton of knobs for sure, but if you turn any of them, or flip any switch you can hear the change. That can't be said of a lot of other boxes where you have to convince yourself that whatever you just did made a "difference."

The biggest problem seems to be gain staging; input level vs comp threshold. The threshold control is fed by the output of the preamp stage, not the input to the unit as it might seem at first. On a box like an 1176, the threshold is preset for you when you select a ratio, whereas on the Compex you can mess with it. If you aren't careful you can end up running into the ceiling and it doesn't always sound good.

The best method is noted in the original ADR manual which says to set the comp ratio to 1:1, turn limit on and then increase the input level until the limit LED is blinking (how much? you decide!), this kind of lets you know that you are feeding the electronics the proper level and now you can engage the compressor by turning the ratio to 2:1 or higher and setting the threshold to get the amount of compression you want.

Experimentation is king with this box... And don't forget to use the expander on your drums.

There has been talk of a 500 Series version of the Compex. Is this still in the works? How do you feel it will translate over to the smaller module?

It is still in the works. I spend so much time building the 2U that I have not had time to dedicate to the 500 but, it is moving along in recent weeks. I have found some awesome little rotary switches that feel totally professional. I'm excited to get it done!


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