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While in the process of considering upgrades for an Aragon 18k MkII preamplifier, I finally came around to inspecting the output coupling capacitors, since I had a matched pair of premium 10uf V-Cap OIMP (Oil Impregnated Metalized Polypropylene) capacitors going to waste in my audio parts collection. Photos of both the 18k and the 18k MkII often show a pair of yellow MKP caps, but some show a pair of white MKP caps. From what I gather, the white MKP cap is considered highly desirable and labeled as a Mondial Designs Phi Beta Kap (manufactured by an unknown maker). It was nice to find my 18k MkII features the Mondial branded cap along with the desirable Penny + Giles volume pot, but I had to rub my eyes since the value of the caps are labeled 100uf, with no decimal point indicating "10.0uf" as one might expect.
But after contacting Chris VenHaus of VH Audio/V-Cap, I was told it's not so surprising that a solid state preamplifier design might involve such a large value output coupling capacitor. So I asked Chris if the 10uf V-Cap OIMP cap might serve well as a bypass cap for the stock 100uf MKP, and while I was told a 4.7uf OIMP cap might be a better option to consider, the 10uf OIMP should be a worthwhile thing to explore. I took that as a green light, since the modification simply involves soldering the bypass caps to the exposed leads of the base caps, rather than if I had to remove the PCB in order to entirely replace the stock caps.
My first impression of the modification indicated that the OIMP as a bypass cap for the particular application did no harm, which is an audiophile credo that tends to be a golden rule, IMO. As time passed during the burn-in process of the OIMP bypass caps, the influence of the MKP base caps seemed to be less readily apparent, with the beneficial characteristics of the superior OIMP bypass capacitor becoming a more dominant factor, especially a notable decrease in what I identified as dielectric coloration, if not a sense of a faster sounding signal purity. The betterment I'm finding is a gradual thing to observe, not something that hits it right off the bat, which is not an unusual thing when it comes to audiophile upgrades, especially issues having to do with high-performance parts that involve a dielectric affect.
Years ago I modeled the roll off of my pre-amp into the 50k of my power amp. I found that 220uf was as good as DC. Just something to think about. On another note, looking at the photo of your unit I would as I always do increase the power supply filter caps by X10. This includes the pairs at each channel. Do it and hear your bass improve. Good Luck, bobwire
Duster, since you apparently like what the OIMP is contributing to the sound, you should try removing the MKP and running the OIMP alone. A 10uf output cap should be more than enough for even a low 10K load. In my experience, a single high quality coupling cap always sounds better than a mix of different caps especially in terms of coherency.
I have never heard a V-Cap OIMP but I am a big fan of their TFTF and CuTF caps.
If the white capacitors shown in the photo are the MKPs that the OP bypassed, I wondered whether those actually might be only 10uF value, maybe labeled "10.0 uF" with a faded decimal point. So they appear to be 100uF. (They look too small to be 100uF, unless the voltage rating is very low.) In which case you certainly don't need both the MKPs and the OIMPs in parallel. You could ditch the MKPs entirely.
I appreciate both Salectric's and your perspective, but as mentioned, there is definitely no decimal point within the 100uf markings on either of the base caps, and the cap features an atypically low 100V voltage rating for an audiophile MKP cap, so the somewhat small size for the large value MKP cap is understandable. In some cases, I don't mind going against the intent of a designer, but in this case Mondial may have had a clear reason for implementing such a large value cap, and I trust Chris VH would have recommended pulling the stock caps from the PCB in order to replace them with the OIMP caps.
I don't doubt what you say for a minute. It's just that I have some 10uF/100V metallized polypropylenes that I bought from Mouser, and they are about the same size as the capacitors I see in your photo. This means very little, of course, compared to your direct eye-ball examination of them. I have a trusty old Sencore capacitance meter that I use to resolve such issues when they occur on the odd occasion.
I've been advised that if there is a feedback line after the caps in my unit, and if there is a 100uF value in there, to move to 1/10th the value on a whim would be foolish, without first getting more info from the manufacturer. I've submitted a request for information from Indy Audio Labs who seems to be involved in Aragon and Acurus since Klipsch dropped their support.
"but in this case Mondial may have had a clear reason for implementing such a large value cap"
Only if there's a feedback line after the cap.
Otherwise the 10uf alone should be fine.
It won't hurt anything to try the 10uf alone just to hear what it sounds like.
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