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The Millett Hybrid MiniMAX - K42 PIO Caps

Russian K42Y-2 PIO (Paper In Oil) Capacitors

Background -
As many of you know, the MiniMAX continues the long tradition of the Millett in using bypass film caps. Under certain scenarios, a small bypass cap applied in parallel across a large electrolytic can cure the issues of using an electrolytic in the signal path: high end harshness and lack of resolution. High end harshness and lack of resolution occurs in almost all electrolytics to a greater or lesser extent.
Note: Due to the small layout of the MiniMAX (compressed space as much as possible with through-hole parts), only the 0.1uf K42's (as sold on will fit on the MiniMAX. The 0.22uf size K42's are too large to fit in the space between CA7 and the volume pot (or headphone jack).
This occurs more so in "power" caps versus "boutique" caps, but to a certain extent in both.

The basic Millett, and also the MiniMAX, traditionally use Wima film caps as bypasses. These work very well and constitute the basic BOM and economical choice of one or two "Can't Miss MiniMAX Builds" in the revised Tweaks-Boutique section. Using the Wimas as bypasses can make the MiniMAX a compelling amp with just power caps in the signal positions. They also help the sound of many of the boutique caps and pair very well with the Nichicon ES's, for instance, a favorite electrolytic cap for the signal positions on the MiniMAX (CA2 and CA7). Pairing the Wimas with the ES's is another of the "Can't Miss MiniMAX Builds."

However, the Wimas cannot remove a certain edge and graininess that is slightly noticeable to the committed audiophile. In those cases, higher quality bypassing caps are desired. At the same time, the BJT Diamond Buffers enable the MiniMAX to have an extended frequency response performance that rivals many high-end amps. So, only the most linear and neutral caps should be used as bypasses, or the MiniMAX's frequency response is noticeably damaged. For instance, while Sonicap Gen II's on the output provide a spectacular high frequency response and buttery mids, the MiniMAX's often intimidating bass is noticeably curtailed. In the cathode bypass positions by the tubes, such a cap can actually wreck the MiniMAX's performance.

At left is a photo showing the commonly available relative sizes of many of these type of preferred capacitors. At top to bottom, starting with the top -
1. Russian K72 Teflon
2. Hopkins Vitamin Q (same size as 0.22 Sprague)
3. Philco Vitamin Q (used in Colin's MAX)
4. WIMA MKP10, 0.1uf (used in the Millett Hybrid and the 1st MAX proto)

It's easy to see that using one of these "boutique" caps presents some challenges.

Russian K42Y-2 PIO Capacitors -

Enter Rob Wills, aka user "fordgtlover" on the Head-Fi forum. Rob discovered a type of PIO cap on e-bay (and elsewhere), readily available with an inexpensive price. The cap, as pictured above, is a Russian version of similar construction and performance close to a Vitamin Q. However, unlike most Vitamin Q's, the Russian K42Y-2 is less than 1" long at the desired 0.22uf rating (160V). The 0.1uf size is even smaller. After extensive testing between Rob and myself on several MAX builds, it is apparent that this cap provides an improvement over the Wima box caps for use on the MiniMAX - neutral, with no loss whatsoever in the bass frequencies. They have a tad bit more glare than a genuine 96- or 196-series Vitamin Q, but can compete head-to-head with other Vitamin Q - type film capacitors.

Please make sure to review the important changes on the "Boutique" section of the MiniMAX website. As time goes on, we are finding new discoveries like these, but also learning some that don't work - even though we thought they should.

file last changed:Saturday, May 23, 2009 7:00:00 AM
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