The Helios Type 69 input module is a reissue of the input section found on the rare, silver Olympic mixing desks which were designed in the 1960s by Dick Swettenham. Mr. Swettenham was the in-house genius of Olympic studios who, like many studio technicians of those days, had the challenging task of designing the audio gear that was to be used in their studios. Why was this necessary? There weren't many choices of off-the- shelf mixers, and the ones which were available (mostly suited for radio stations) were rarely workable for such discerning engineers as the ones found at Olympic studios. Legendary Olympic engineers like Keith Grant had a symbiotic relationship with the folks down the hall who designed the equipment. That's why gear of this ilk is unsurpassed in sonic quality-even today. People spent time designing and listening to audio equipment in the closed loop environment of a great studio.
While most new audio gear doesn't even equal the legendary Olympic silver modules in audio quality, the new Helios Type 69 does. The most difficult part of reproducing a vintage input stage with EQ is to get the inductors correct. I've been fortunate to have used different Olympic desks and input modules from Olympic desks over the years, so I was very skeptical that the folks at Helios Electronics could get an input transformer to work as well as the original, but they did. Not only that, they got the EQ spot on. I didn't need to trust my memory since I had a rack of Olympic modules handy at Bomb Factory Studios in Burbank. I first swept all the EQ curves of the original, then I swept the Helios Type 69. They matched exactly. There was less than a fraction of a dB difference. This variation is less than I'd expect between different silver modules, much less a reproduction. I should note that the new Helios has a 16 kHz position in the midrange band which the silvers don't have. While I probably wouldn't have use for a response peak or valley at this frequency, it functioned as advertised. Next, I did a blind A/B test with music played through a silver module and the new Type 69, both set to various but identical EQ settings. I couldn't tell which was which. I checked the distortion. The new units had a little more headroom (probably due to the modern transformer). The characteristics of the distortion were the same for both units, some 2nd, 3rd, and 5th harmonics.
The really big test lay ahead. How would it sound with various microphones? I picked three microphones to represent three broad categories of microphones: A Sennheiser MD 421 dynamic, a Coles 4038 ribbon, and a Neumann U 87 condenser. I've found that human speech works really well for checking out microphones and preamps. This is probably due to human hearing being highly adapted to speech. The difficult part of doing this test is saving the results for listening later. I've tried recording these tests to various digital formats including sampling at 192 kHz with rather poor results. The digital recordings seem to "homogenize" the sounds of the tests. However, a 3M M-79 two-track recorder seemed better able to preserve the differences in the tests. I'm still trying to figure out this one. I encourage everyone to try this at home and report back. Anyway...
Here are the results. The Type 69 did not act exactly as the original silver module. It actually surpassed the fidelity of the silver module for the Coles and Sennheiser microphones but fell a bit short on the U 87. This was based on the perceived bandwidth and flatness of the frequency response to a voice. Two out of three is really a great score for this test considering the Type 69 is being compared to the mighty Olympic module.
Besides having a 16 kHz midrange frequency available, there is also the much welcomed addition of a phase switch on the Type 69. All in all, this is about as good an input stage as you can buy in terms of sonic quality. It's not stiff sounding like a lot of the expensive, ultra-low distortion, solid-state mic preamps on the market, and it's "faster" than the tube mic preamps on the market. Now if only the rest of one's studio could measure up to these standards. ($1395; www.helios-electronics.com)