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Q. What do you mean by 'subsonic components'?

By Hugh Robjohns

The AEA RPQ2 — an excellent preamp but, given its primary purpose of amplifying ribbon mics, should it have included a  switchable high-pass filter?The AEA RPQ2 — an excellent preamp but, given its primary purpose of amplifying ribbon mics, should it have included a switchable high-pass filter?

I enjoyed Hugh's review on the AEA RPQ2 ribbon mic pre (SOS June 2017: https://sosm.ag/jun17aea), but I have a question: what exactly did he mean when, in the Cons section, he said, "Still has limited ability to remove unwanted subsonic components"? Did he mean low thumping thuds from touching, or floor-borne vibrations and thumps?

John Mackniskas

SOS Technical Editor Hugh Robjohns replies: I was thinking about floor-borne vibrations like foot tapping, or the very low-frequency noises that can be generated if the mic is on a wobbly mic stand and is moving gently back and forth. A more common problem on a wooden stage, perhaps, rather than a solid studio floor, but it's not a good situation as it can generate a lot of very low-frequency energy!

As I said in the review, the earlier TRP model (reviewed in SOS April 2007: https://sosm.ag/aea-r92-and-trp) included a useful high-pass filter, but that facility was omitted from the RPQ and RPQ2. I understand why the AEA designers wanted to give the preamp a flat response down to almost DC — and that can be useful in some applications — but ribbon mics typically resonate at 10-15 Hz and can generate a lot of energy under some conditions, which could potentially overwhelm the preamp by eating up a lot of headroom. A simple selectable high-pass filter would give the user the means of preventing that.

Ribbon mics typically resonate at 10-15 Hz and can generate a lot of energy under some conditions.

The absence of a switchable high-pass filter is not a huge 'con' when working in a studio with a solid floor, and it's certainly not something that would stop me buying this otherwise excellent preamp. It's also worth noting the availability of stand-alone in-line high-pass filters, such as the Shure A15HP, which would add the functionality to the RPQ2 if you needed it. But it's something to be aware of, and given how simple it would have been to implement the facility in this preamp it seemed to me a shame that it wasn't included.

Published October 2019