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Old 11-04-2017, 06:45 AM   #10
Join Date: Nov 2015
City & State: Saskatoon, SK
My Country: Canada
Line Voltage: 120VAC 60Hz
I'm a: Hobbyist Tech
Posts: 27
Default Re: TC Impact Twin mods

Originally Posted by Khron View Post
I guess that's a possibility, but i have no idea. I don't think i've ever scope-probed the power supplies to see what frequencies they work at (and/or it wouldn't surprise me if that was even load-dependent, since they're self-oscillating). "They", because the two are independent - the smaller transformer's for the 5v & 3.3v digital rails, while the bigger transformer's for the +/- analog rails and the 48v phantom power.

Interesting that they seem to be present on only one channel(?), though...

<bad joke> But hey, what do you care about measurements, if the sound's so much more "transparent"? Don't those peaks provide some more "air" to the sound?

Actually, the noise is present in both channels, but stronger in the right channel. The second peak appears to be a multiple of 2 times the first. Given that they are -120dB, perhaps it doesn't matter, but they shouldn't be there. If they were audible, I doubt that they would be adding anything desirable to the sound. More air would likely be something like a gentle boost in the highs with a shelving EQ. I've looked at quite a few RMAA tests of other interfaces and most of them are pretty clean at the noise floor. That said, the noise has been decreased somewhat by the various modifications, I'm guessing that the Panasonic FR replacements in the power supply are the biggest factor.

It is unfortunate that you live so far away... otherwise I'd be happy to loan you the interface so that you can listen for yourself and compare it with your other TC interfaces. The larger caps on the microphone input noticeably deepened the bass response and the polypropylenes added some transparency. Not sure why, but TC used much smaller input caps on the preamp than recommended in the THAT 1512 design notes, which is likely the reason why they sound a tad thin stock.
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