Coupling Caps:First some words to the test setup. The signal always had to pass through a volume attenuator (D.A.C.T., 10klog) and a coupling cap (1uF Mundorf MCap-ZN) in the amplifer. The input resistance of the amp is rated at 47kOhm. (-3dB at 3Hz). The capacitor being tested was added in one chanel between the DAC output and the potentiometer and was compared to the direct signal path. A/B comparisons were made by mixing my favourite songs to mono and listening left and right chanel over the same speaker.
The Caps (replacement for C5/C6):
Results: The speaker I've tested the caps with, has a low frequency extension as follows: -3 dB at 70Hz, but slow roll off. In the beginning there where two interesting things to test.
With the Epcos 0.33uF the low end extension is clearly limited. There's nothing bad about the mid and high frequencies. They are precise and uncolored, but with the thinned bass response, the balance turns a bit to the bright side. A better overall job does the Mundorf 2.7uF. The treble resolution in not as good as with the small Epcos 0.33uF but it has the same balance as without coupling cap. The 4.7uF Mundorf MCap has the same tonal balance as the 2.7uF MCap-ZN. Maybe a 1uF capacitor would just be large enough in my system. Anyway, I most like the MCap-ZN among the first five caps listed above. None of them sounds harsh, but I realised, that as bigger the capacitance value gets (or as bigger the cap itself gets), the more precision you lose. This loss in precision can first be heared at higher frequencies, but also the bass isn't that textured anymore. That's why I can't say whether an MCap could perform just as well if it were of same value. When comparing the SCR to Mudorf (both 4.7uF), I prefered the Mundorf because of the more defined sound. The Epcos MKV sounds about the same as the SCR polypropylenes, no harshness but lower resolution than the MCap-ZN.
When compared to no capacitor at the output, the MCap- ZN is too slow and offers not enough bass authority. Best bass performance I obtained by using a Panasonic FC 1'000uF. Midrange could be more colorfull and high frequencies are more liquid with the Epcos 0.33uF or with the MCap- ZN. Adding a Vishay 15nF to the Panasonic opens up the highfrequency spectrum and adding the MCap-ZN brings back the warmth in the midrange. Replacing the MCap-ZN with the 4.7uF Mundorf did not make a difference. This setup is hardly distinguishable from the direct DAC output. So decided to use the same solution as for the powersupply (except for the large BC elko).
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