To ensure that the PPA is free from obvious flaws, we have done quite a few tests on it. This page shows the ones I’ve done with the RightMark Audio Analyzer (RMAA). This program plays various test tones through your sound card’s line output and records them with the sound card’s line input. Then it munches on the input signal and presents the results in a very pleasing fashion. While it’s not as flexible as a generalized audio analyzer, it’s nearly perfect for this application — highly recommended!
For these tests, I’ve used an M-Audio Delta 44 pro-level sound card. I like it because its performance is excellent, and because the external breakout box makes it convenient for test bench use. I should point out that I’m using it on its lowest voltage range for technical reasons, so the noise floor probably a bit higher than it could possibly be.
Like any decent solid-state amplifier, the PPA adds nearly no noise or distortion when it isn’t driving a load. Therefore, the only tests showing the amp unloaded are done solely as a baseline for the other tests. For the most part, the faults in the baseline are from the sound card, so mentally subtract them from the test. In all other tests, the amp is run into a dummy load. (The small box in the picture above is a splitter that lets the amp drive the dummy load in parallel with the lines that run back to the sound card’s inputs. It also has a switch to break the ground connection between the input and output sides so as not to short IG to OG in amps like the PPA.)
Herewith, the tests:
10mA Bias — Standard configuration, output buffer set to 10mA bias.
20mA Bias — Same as above, except 20mA bias.
30mA Bias — Same as above, except 30mA bias.
Bias Points Compared — 33 ohm tests from each of the above, compared to each other.
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|Updated Sun Jan 18 2015 04:24 MST||Go back to The PPA Project||Go to my home page|