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Capacitor comparisons

206.158.165.40

Posted by Steve on May 19, 2001 at 14:15:28

We performance a test of capacitors in a coupling setting on a vacuum tube preamp. The goal was to find which was closer to neutral in this setting. Since the system was common, we were looking for any sonic changes that occurred when inserting a capacitor in the circuit path verses a straight wire connection. This doesn't necessarily mean that in all uses these results will apply, but I got the feeling, with 40 years of experience working with tubes, and 21 years in audio, that they will have similar results in most settings. Remember that we are looking for deviations of sonic character verses with the straight wire as the reference.

First, I must mention that terminations seem to be important as in a couple of cases, the terminations described appear to follow the sonic footprint of the cap. For instance, the Hovlands, from a pictorial I have from several years ago from a catalog shows soldering the leads only across one end of the foil (as opposed to across the entire edge of the wrapped foil) and wraps it over and over. If this pictorial is true, I would have to surmise it has alot of inductance designed in, like a coil and would be tweeky, which is what was observed.
The brands tested were Hovland, MIT multicap, Auricap, Infini "D", and Solen against a straight wire (switching back and forth), both with voltages applied (we won't mention without voltages applied here). Since the entire system is common for both with and without the caps, we are looking for minimum sonic change when adding the caps. In the circuit, we used whatever value we could to approach as close to neutral as possible. The input load to the amp was 100k. Although none were perfect there seemed to be a clear winner.
The Hovlands were bright compared to the straight wire, lacking bass which we just couldn't get no matter how many we used (I think we got up to 10uf across 100k load).
The Auricaps had more bass but were still just slightly bright.
Inner detail was excellent, but there was some loss of foundation in the instruments in the middle range on down.
The MIT multicap, metalized, was more neutral than the Hovland and Auricap, but couldn't get the amount of bass we needed to be neutral in that region (again we got up to 10uf). It also lost a little focus.
The Infini "D" cap was the most neutral although it is not perfect. The bass was slightly bloated and it is possible, with enough capacitance, to become bass heavy. So it is critical to get the right value in coupling circuits.
The Solens were interesting in that they were closer to the Infini "D" cap in tonal/frequency balance but lacked inner detail and slightly on the highs.
We haven't tested the oil/paper caps because the DA is higher, similar to mylar DA factor and is known to lose inner detail.
We hope this is helpful as if a speaker/driver design sonically leans, you may be able to compensate with the right cap for you.
As mentioned above, this test isn't exhaustive, but we feel does give and indication of the sonic qualities that would apply in different situations.

Steve Sammet
SAS Audio Labs

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