September 26, 2014 -Finally got the capacitors swapped out. Turned out to be about 800 of them. Yamaha decided to use a very aggressive epoxy to hold them on. Each one had to be loosened with a dental pick before I could desolder. Next step was to perform surgery with a Dremel tool on the spare headphone PCB. I need just the small part to convert the mono CUE and TB output into a stereo Control Room output. Lastly I’m ordering parts and trying to figure out where to fit this Midas AD/DA FireWire circuit board. It’s a little bigger than I suspected.
September 30, 2014 – So I spent a few days polishing my knobs. Sorted out the cracked and damaged ones. Glad I have a bunch of spares. I have swapped most of the capacitors and LEDs. Today I decided to take a break and work on a shielded case to mount the FireWire card under the meter bridge. I striped a pair of channel frames down to bare metal and cut them into a mating rectangle, reusing existing screw holes and brackets. Marked off where to weld them and proceeded to make a bunch of quite ugly welds. I hate welding. They cleaned up ok but didn’t break. A little jb weld to fill the crevices should finish them nicely. The brackets fit the holes with a little tweaking. I’ll wrap the back and side with aluminum tomorrow, then mount everything in the console. And possibly work out the power supply requirements.
October 8, 2014 – The headphone amp contained the last few capacitors that needed replacing. Then it was time to do some testing. I need to verify that the OPA604 opamp swap works without oscillation or distortion. While prepping for that, I decided that the even after recapping, the stock headphone amp was too noisy. Quite a lot of hiss. So I decided to mock up a replacement using a pair of Texas Instruments INA217 Instrumentation Amplifiers. While I was at it, I made a stereo unity buffer for the monitor controller and a power supply for the Midas circuit board. +/-18vdc, +5vdc & +3.3vdc with regulation and filtration. Lots of solder today.
October 9, 2014 – Finally got some serious testing done. Among other things that worked out well, the OPA604 opamp swap was a success. I used Rightmark Audio Analyzer to monitor a 1kHz sine wave in both Oscilloscope and RTA modes. As I increased gain beyond clipping, there was less high frequency distortion as compared to stock. As you can see on the screen display the green numbers are the new opamp, the red numbers are the old opamp. Then I played some music thru them and it’s a noticeable improvement in tonality and detail. I can’t wait to mod all of the summing busses. Ordering parts tonite. I finished building and tuning the power supply for the Midas. It’s ready for a case. Then I figured out I could modify one of the 11 position gain switches to be used as a control room source selector. Since it was a live mixing console, there were very limited monitoring options. In order to use it in a recording studio, you need to be able to monitor any of the output busses. That’s 4 stereo Program busses, 4 stereo Matrix busses, 1 Cue bus and 2 stereo Tape Returns. There’s just enough room beside the meters to fit the controls.