CMoy Headphone Amp

I've decided to build a headphone amp (blame Dennis!) so that I can maximize my almost ten-year old Sennheiser HD495 phones.

Anyway Alexan doesn't have the OPA2134 but they do have the much worse (but still orders of magnitude better than the LM358!) TL072. About $1.50 apiece (67 pesos). Not so bad..

I use the "Gwado" design which is very similar to the CMoy but with lower gain and a series resistor to drive low-impedance cans. The Sennheiser is 32 ohms which is difficult to drive, more so with a lowly TL072. But, the TL072 is pin-compatible with the OPA2134, so if this is a success, I can get some of those and drop them in.

So far all I have is a protoboard layout. Because I don't have 3.5mm jacks, I can't pipe in a signal or pull out any output. All I can do so far is measure the DC offset. It's about 11mV on one channel, and 20mV on the other channel. Not small, but not fatal.



I'm using the virtual ground design with two 470uF capacitors, as in the original CMoy design. The clerk at Alexan failed to include any 0.1uF capacitors (which are power supply snubbers) and I didn't check. So I used some humongous 0.047uF, 600V (!) capacitors from one of my past photo-flash projects. These caps are even bigger than the 470uF electrolytics!



Once this build is validated, I will transfer it to an Alexan PC201 veroboard, which I've cut down to fit inside an HC101 plastic case.

Pentax A Mod

Old Pentax manual-focus bayonet lenses are divided into K, M, and A types. The K and M only have mechanical aperture coupling, so on the "crippled KAF2" or "crippled KAF3" mounts, which are the mounts of modern Pentax SLR's and DSLR's, K and M lenses won't meter except in stop-down mode.

"A" lenses have a pattern of contacts on their bayonet which communicate their maximum aperture, which allows full program operation, P-TTL flash mode, and so on (basically everything except autofocus).

There's a mod floating around which supposedly tricks the camera into thinking any lens mounted on it is an "A" lens. This is easy to do because "A" lenses have a recessed pin which pops out when the aperture ring is moved to the "A" position. The moving pin is called the "A" pin. So to dupe the Pentax DSLR into thinking any lens mounted on it, is an "A" lens, all we have to do is short the "A" pin on the camera mount.

Here's your typical crippled KAF3 mount:



The "A" pin is the semi-recessed one that is third in line from the left along the rank of pins next to the lens release button. It's distinctive because it's flat and recessed, unlike the rest of the pins which stick out and are round. We need to short this pin in order to "tell" the camera that the lens attached is an A lens.

After getting the metal bayonet off. Note that there's a very thin metal ring which must not be molested or removed; there is a thin wire soldered to this ring and that wire had better not get cut!



This is the metal bayonet, stuff a piece of aluminum foil into the "A" pin hole.



Another approach is to put a tiny aluminum foil "cap" on top of the "A" pin itself:



Put the metal bayonet back (don't force it if it doesn't go in nicely, the metal washer underneath must fit neatly in for the bayonet mount to go down nicely). Torque in the screws as if it were a tire, opposite screws at a time, finger-tight only.

This is what the mod looks like:



An ancient K-mount Vivitar 90mm macro:



And as we can see, the camera thinks it's an "A" lens!



Now for a few caveats: fixing the lens at "A" doesn't really do anything. P-TTL metering results in massive over-exposure. The camera thinks that the lens is an f/1.2 lens (the fastest K-mount built) because your SMC-K or SMC-M doesn't have the aperture-setting pins, so program modes also result in massive metering errors.

Green button no longer works because the camera doesn't try to stop-down the lens anymore (it's an "A" lens, right?)

So the only benefit I can think of, is that aperture data is now recorded in the EXIF. But you have to make sure that your aperture set on the camera, matches the aperture ring on the lens. Also, since "A" lenses have a differently-designed diaphragm from K- and M-lenses, there will be exposure errors.

Overall, not a worthwhile mod but heck, it takes ten minutes.

Update: after a bit more testing, it seems that P-TTL flash does work, but only with wider lenses. I'll try to see if this mod is actually worth keeping, before I dismantle it.

Nikon DK-21M

I fortuitously found a Nikon DK-21M eyepiece magnifier at Infomax in Market! Market! while looking for some computer parts. Which is a good thing because the computer-assembly exercise has turned out to be a disaster.

Anyway it was around $35 which is expensive as this is a sub-$30 item in the US, but one would have to deal with the hassle of shipping so it ends up about the same.

Here are three viewfinders: Canon EOS 350D, Pentax K20D without DK-21M, and K20D with the DK-21M. It's a usable magnification. Not quite a 5D-class viewfinder, but not too shabby.

Saturday Afternoon at the Manila American Cemetery and Memorial

The Manila American Cemetery and Memorial is the largest cemetery in the Pacific for U.S. personnel killed during World War II, with 17,206 graves, 3,744 of which are "known only to God." It is also the largest American military grave site outside the United States, with more personnel buried than any of the American memorials in France.


Pentax P3, 50mm SMC-A, Konica Centuria 100 film

It is located in Fort Bonifacio, and I have driven past it literally thousands of times, not realizing it was there.

The headstones are made of marble which are aligned in eleven plots forming a circular pattern. Each plot has a alphabetic marker, to ease finding a particular grave.


Pentax K20D, 16-45mm SMC-DA


Pentax K20D, 200mm SMC-M


Pentax P3, 16-45mm SMC-DA, Konica Centuria 100 film


Pentax K20D, 16-45mm SMC-DA with circular polarizer

The chapel, a tall stone structure with a sculpture on its front and religious mosaics inside, stands near the center of the cemetery. The memorial is eeriely quiet, the only sound being the distant traffic, muffled by the trees, and the bells of the chapel, which toll every hour.


Pentax K20D, 16-45mm SMC-DA with circular polarizer

In front of the chapel are two large hemicycles with rooms at each end.


Pentax K20D, 16-45mm SMC-DA with circular polarizer

On rectangular Trani limestone piers within the hemicycles are inscribed the names of 36,282 of the Missing, both American and Filipino, who gave their lives in the service of America and who rest in unknown graves.


Pentax P3, 50mm SMC-A, Konica Centuria 100 film


Pentax K20D, 100mm Vivitar Macro

The missing are from all the States of the Union, as well as five hundred-odd Filipinos, from the US Army, Navy, the Coast Guard, Marine Corps, Army Air Forces, and the Philippine Scouts.


Pentax P3, 50mm SMC-A, Konica Centuria 100 film


Pentax K20D, 16-45mm SMC-DA with circular polarizer

A rosette is fixed next to the name of a missing soldier when his body is found. It's sobering to see that more than sixty years after the end of the Pacific War, probably less than one percent of the names on the limestone have rosettes next to them.


Pentax K20D, 100mm Vivitar Macro

Carved in the floors of the hemicycles are the seals of the American states and its territories.


Pentax P3, 16-45mm SMC-DA, Konica Centuria 100 film

The Saturday I was at the Memorial, there were almost no people on the grounds, just a handful of Filipinos and one or two elderly American men, perhaps the comrades of the soldiers whose names are on the walls.


Pentax P3, 16-45mm SMC-DA, Konica Centuria 100 film


Pentax K20D, 100mm Vivitar Macro

Some of the names on the walls are outlined in gold, and have a star next to them: the Congressional Medal of Honor, the highest military award that the United States can confer. There is a whole story behind these gold letters:


Pentax K20D, 100mm Vivitar Macro

Willibald C. Bianchi was a twenty-seven year-old Captain in the Philippine Scouts from New Ulm, Minnesota.

On February 3, 1942, he was cited for the action that would earn him the Medal of Honor:

For conspicuous gallantry and intrepidity above and beyond the call of duty in action with the enemy on 3 February 1942, near Bagac, Province of Bataan, Philippine Islands. When the rifle platoon of another company was ordered to wipe out 2 strong enemy machinegun nests, 1st Lt. Bianchi voluntarily and of his own initiative, advanced with the platoon leading part of the men. When wounded early in the action by 2 bullets through the left hand, he did not stop for first aid but discarded his rifle and began firing a pistol. He located a machinegun nest and personally silenced it with grenades. When wounded the second time by 2 machinegun bullets through the chest muscles, 1st Lt. Bianchi climbed to the top of an American tank, manned its antiaircraft machinegun, and fired into strongly held enemy position until knocked completely off the tank by a third severe wound.

Captain Bianchi survived the Fall of Bataan and the Death March to Capas, Tarlac. On December 13, 1944, with the Americans closing in on Manila, he along with 1,600 other prisoners of war from Bilibid Prison were loaded onto the hell ship Oryoku Maru, which was sailing for Formosa and then Japan. On December 15, the Oryoku Maru was sunk by bombers from the USS Hornet while it lay at Subic Bay, Olongapo.

He survived this sinking, and was transferred to the smaller Enoura Maru at San Fernando, La Union. On January 9, 1945, the Enoura Maru was sunk by five 500-pound bombs from US Navy bombers, once again from the USS Hornet, while it lay at Kaohsiung Harbor, Taiwan. Captain Bianchi was one of the 250-odd men who were killed instantly in the bow cargo hold when one of the 500-pounders fell in. His body was probably one of those buried in a mass grave on the Kaohsiung harbor spit and re-interred in 1946 at the National Memorial Cemetery of the Pacific in Honolulu, Hawaii.


Pentax K20D, 100mm Vivitar Macro

That's a good deal of history for one afternoon! I actually went to the memorial to try out my RAW processing workflow. It's been instructive. Also, I will not use the 16-45mm on the P3 anymore, it is prone to way too much vignetting on the film body; I thought I could tolerate some vignetting to have a super-wide field of view, but I've changed my mind.

DIY Beauty Dish

Ingredients:

One aluminum pie tin (about $1 at SM Department Store):


Mark the outline of your hot shoe flash head on the underside, I used a white board marker:


Cut an H-shaped slot in the pie tin using a Dremel with emery cutting wheel:



Bend the tin outward along the H-cuts (I also used a screwdriver to poke the two screw-holes):



Second ingredient: the lid from a KFC Bucket Meal (free if you eat the chicken!)


I taped a circular aluminum foil cutout to the KFC Bucket Meal lid, this bounces the light from the flash back toward the pie tin, and eliminates the hot spot in the center:


Bolt the KFC Bucket Meal lid to the pie tin (it's easy to poke holes in the plastic using a heated screwdriver or similar):


The metal tabs formed on the underside of the pie tin are for fastening the pie tin to the hot shoe flash. Make sure to cover everything with tape to avoid accidents and so as not to scratch your hot shoe flash. I used a very thick rubber band to hold everything together (logo optional):


Here's what it's supposed to look like:



Nice ring flash effect:


I don't have any post-worthy portrait photos with the DIY Beauty Dish yet, but here is a close-up photo with direct flash:


and with the DIY Beauty Dish. Note the groovy circular highlights in the lens, and the much softer shadows:


I also noticed that on human subjects, at portrait distances, the Beauty Dish produces far more interesting lighting than ceiling bounce, let alone direct flash. It doesn't have the shadows under the chin of ceiling bounce, and it works even when there is no ceiling! (or if the ceiling is too high or too dark).