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Modern Condensers with 'Classic' Preamps, Should We Pad?
Old 18th December 2010
  #1
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Modern Condensers with 'Classic' Preamps, Should We Pad?

I was browsing the Josephson website, and came across this tech note:

http://www.josephson.com/tn9.pdf


In summary it says that vintage preamps (those with input transformers) were generally designed for use with mics having lower impedance, and lower output levels. They recommend using an H pad to lower the impedance and the level when using a modern condenser with a vintage preamp (or, presumably, those based on vintage preamps.)

I'm curious whether anyone follows this advice, especially with very loud sources.

If I recall, many vintage preamps have a rotary switch at the input, with varying combinations of pads built into them. I'm not sure whether this would alleviate the impedance issue, but I suspect it might. My preamps are mostly old, though I hesitate to call them vintage (PM1000, Yamaha M406, a Neve 1084 clone) and all have the rotary selector input pads.

Anyone care to comment? Anyone regularly use an external pad when tracking with condensers? What's the difference between an external pad and the one in most condenser mics? I imagine the built-in pad would alleviate overdriving the mic's internal electronics, but I haven't studied the schematics of many mics!
Old 19th December 2010
  #2
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It really depends on the mic.

The very low output impedance of David's mics can interact with the complex reactances of input transformers, and there are others on the market with similar amplifier topologies.

Usually the result is a rising high frequency response at the top of the audible range.

This is damped by adding the build out resistors or an H-bridge, but it usually
isn't a severe effect.

I can measure it, but it hasn't bothered me. That may have something to do with having 55 year old ears that have seen a lot of mileage, but I wouldn't
sweat it, try the pads and see if it matters to you.
Old 19th December 2010
  #3
I think a lot of the reason for padding mics when using vintage preamps is so that you can use more gain for more colouration. I see where you're coming from with the old mics having lower outputs though, I couldn't comment on the impedance. Another bump for a good question.
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