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: more so in "power" caps versus "boutique" caps, but to a certain extent in both.
The basic Millett, and also the MAX, MOSFET-MAX, and MiniMAX, uses Wima film caps as bypasses.
These work very well and constitute the basic BOM. They are the economical choice of one of the "Can't Miss MiniMAX Builds" in the revised Tweaks-Boutique section. Using the Wimas as bypasses can make the MOSFET-MAX 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."
NOTE: the 0.22uf Vitamin Q's will not fit the MiniMAX in the recommended cases.
Use the 0.18uf VitQ's, instead.
However, the Wimas retain a certain graininess and minor squeek 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 (perhaps only limited by your choice of tubes and output caps). So, only the most linear and neutral caps should be used as bypasses, or the MiniMAX's frequency response is noticeably impaired. For instance, the MiniMAX's often intimidating bass is noticeably curtailed with classic "blooming mids" boutique film caps. In the cathode bypass positions by the tubes (CA9), such a cap can completely wreck the MiniMAX's bass.
Some caps live up to the hype, however, and at the same time provide an extended frequency response in the MiniMAX. Vitamin Q paper-in-oil (PIO) caps have always been the preferred choice in the case of an upgraded MiniMAX. Unfortunately, the genuine name-brand Sprague Vitamin Q's in the desired ratings are too large to completely clear the heat sinks on the MiniMAX PCB. So, they require a special technique for installation. That said, you will find the procedure for installing the genuine Sprague 96P-series 0.18uf 100V VitaminQ's is very simple. (The VitaminQ caps are available at Beezar.com.) The information, drawing, and photos below will guide you with this installation technique. Once installed, you will find that the 96P-/196P-series VitQ's are among the finest, if not the best, film cap bypasses that you could install for your MiniMAX. There is literally no film cap available at this performance and at these prices. ($2-$3 at beezar.com)
Referring to the detail above and using the leads the VitQ's are born with, bend them according to the template above. It's best to start with a sharp right angle bend at the rear nipple. Pull the lead through the back pad so that the cap edge presses firmly against the board. As you do this, the lead will attain a similar shape as shown in the detail.
The leads are heavy enough that they provide some structural support, but the whole assembly is quite rigid. The trick is to pull the one lead through the bottom of the PCB until the edge of the can is resting firmly on the board. Ideally, you may want to insulate the forward lead where it bends under and down to the front pad, but it's not really necessary. Installed as pictured, there is plenty of clearance with Also pull through the front lead. The top edge of the cap should be somewhere between 1/16" and 1/9" above the top surface of the caps. This is the recommended clearance if you are using 1" sinks and wish to install the PCB in the 3rd slot from bottom of the standard Hammond case.
Continue to pull until they are at the desired height. If needed, remove, straighten out the leads, and try again. Since the leads are providing structural stability, try not to force the top edge of the cap down, but continue to pull thought the bottom of the board, instead. Once soldered in the position shown, they are very solid. Nothing could be simpler unless they could somehow actually fit horizontally on the pads. As you see them in the bird's-eye pic above, they are not blocking any test points or trimmers. Even if you end up a little close with this method, the top most part of the cap end is the outer edge, not the center lead with the electrical contact.
We heartily recommend these caps for your MiniMAX builds using ES's or Black Gates! When bypassing with 196P-/96P-series VitaminQ's, performance with ES's can come very close to that of Black Gates.
file last changed:Saturday, May 23, 2009 7:00:00 AM
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