I did this little test a while ago, but didn't get around to posting it. I may or may not do the same tests for the new T-MOD v. W-mod I just received from the Oade Bros. Anyway, FWIW...
TEST INFOI started off with a simple test to identify the gain differences between the R4 stock and Oade Transparent MOD channels, since I noticed the T-MOD offered less gain than stock. It eventually grew into the additional tests below, but here's how I did it:
- Generated a 1 kHz tone in Audacity at 24-bit / 96 kHz
- Looped playback, PC digi-out > Bel Canto DAC 1.1 > Segue Enterprises (Todd R) Dogstar RCA cables > RCA | 1/4" adapters > R4 (would've preferred XLR adapters, but didn't have them handy)
- Recorded mic-in with gain knobs all the way down
- Recorded mic-in with various "o'clock" gain levels
- Recorded line-in with gain knobs all the way down
- Recorded line-in with various "o'clock" gain levels
GAIN MAPTurns out the Oade Transparent MOD (in its original incarnation...just got my updated T-MOD today) offers less gain than stock. Here are the gain differences mic-in for the Oade T-MOD v. stock, feeding both the T-MOD and stock channels the same 1kHz tone signal:
==========================================
MIC-IN MIC-IN MIC-IN MIC-IN MIC-IN MIC-IN
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STOCK | T-MOD | GAIN
------------------------------------------
dBFS | +dB | dBFS | +dB | O'Clock
==========================================
-42 | 0 | -30 | 0 | 07:00 \
-40 | + 2 | -30 | 0 | 08:00 - I found 0 gain across this range strange, not sure how to account for it
-38 | + 4 | -30 | 0 | 09:00 /
-35 | + 7 | -28 | + 2 | 10:00
-30 | +12 | -26 | + 4 | 11:00
-25 | +17 | -22 | + 8 | 12:00
-21 | +21 | -20 | +10 | 13:00
-16 | +26 | -16 | +14 | 14:00
-11 | +31 | -11 | +19 | 15:00
-06 | +36 | -06 | +24 | 16:00
0 | +42 | -01 | +29 | 17:00
And here are the gain differences line-in for the Oade T-MOD v. stock, feeding both the T-MOD and stock channels the same signal (but obviously a slightly stronger signal than in the mic-in test in order to achieve proper dBFS levels):
==========================================
LINE-IN LINE-IN LINE-IN LINE-IN LINE-IN
------------------------------------------
STOCK | T-MOD | GAIN
------------------------------------------
dBFS | +dB | dBFS | +dB | O'Clock
==========================================
-40 | 0 | -30 | 0 | 07:00 \
-40 | 0 | -30 | 0 | 08:00 - I found 0 gain across this range strange, not sure how to account for it
-38 | + 2 | -30 | 0 | 09:00 /
-36 | + 4 | -28 | + 2 | 10:00
-30 | +10 | -26 | + 4 | 11:00
-25 | +15 | -22 | + 8 | 12:00
-21 | +19 | -20 | +10 | 13:00
-16 | +24 | -16 | +14 | 14:00
-11 | +29 | -11 | +19 | 15:00
-05 | +35 | -06 | +24 | 16:00
0 | +40 | -01 | +29 | 17:00
NOISE MEASUREMENTSI also measured the frequency response for both T-MOD and stock channels mic-in with no gain, and when adding enough gain hit -12 dBFS (15:00 Oade T-MOD, 10:00 stock). I then repeated the FR measurement for line-in with no gain, and when adding enough gain to hit -12 dBFS (15:00 Oade T-MOD, 10:00 stock), though of course the tone signal was stronger in order to achieve the proper levels using the same relative gain settings. The results:
Line-in, no gainCHAN | GAIN | COLOR
=======================
T-MOD | 07:00 | GREEN
STOCK | 07:00 | RED
http://img.photobucket.com/albums/v245/bskalinder/r4/line_no-gain_linear.jpghttp://img.photobucket.com/albums/v245/bskalinder/r4/line_no-gain_log.jpgLine-in, with gainCHAN | GAIN | COLOR
=======================
T-MOD | 15:00 | GREEN
STOCK | 10:00 | RED
http://img.photobucket.com/albums/v245/bskalinder/r4/line_gain_linear.jpghttp://img.photobucket.com/albums/v245/bskalinder/r4/line_gain_log.jpgMic-in, no gainCHAN | GAIN | COLOR
=======================
T-MOD | 07:00 | GREEN
STOCK | 07:00 | RED
http://img.photobucket.com/albums/v245/bskalinder/r4/mic_no-gain_linear.jpghttp://img.photobucket.com/albums/v245/bskalinder/r4/mic_no-gain_log.jpgMic-in, with gainCHAN | GAIN | COLOR
=======================
T-MOD | 15:00 | GREEN
STOCK | 10:00 | RED
http://img.photobucket.com/albums/v245/bskalinder/r4/mic_gain_linear.jpghttp://img.photobucket.com/albums/v245/bskalinder/r4/mic_gain_log.jpgCONCLUSIONSo what does all this mean? Well, unless my testing methodology is fundamentally flawed (which is entirely possible), I
think it means:
<01> The Oade Transparent MOD offers less overall gain than stock.
<02> The Oade Transparent MOD reduces self-noise significantly v. stock.
<03> If you can get away with running line-in, do, since it adds less self-noise than mic-in (which I wouldn't have expected, since I assume line-in is just mic-in with a pad, but...perhaps that assumption is incorrect).
<04> I don't know how much of the self-noise in the results is due to my Bel Canto DAC 1.1, and how much due to the R-4.