Project "Frankenstein"

Re-inventing The Yamaha NS-6390


3-22-2016 - Project start

So I was picking up some gear from a local Customer and he gave these to me as he was about to throw them out.  These were his 'out-door' speakers that he tried to weatherize.  This is one of those situations where you put on a pair a gloves, take these to a sand pit and start a bonfire. What possessed me to keep these and decide to restore them is simply beyond me. Call this a pet project of sorts but my plan was to use these as a test to see exactly how far I can go with a restoration.  It has already been an experience.  As you can see from the pictures, these were wrapped in roofing material, nailed to a piece of plywood and the front used a porch screen mesh.  One of the woofers had been replaced (and I use the term loosely) with one clearly bigger than what was there before. After peeling off the roofing material, removing the mesh and plank...they started to resemble speakers again.  Ironically, the cabinet did not look to be in horrible shape; but it was not very pretty either. after pulling out all the drivers, terminal/crossover; I was able to get a good look inside. Not too bad.  Some of the corners were water damaged and needed to be fixed up. I tried to keep the original vinyl covering; but that did not work very well....so I stripped it down to the MDF. all the bad corners and areas of the faceplate were repaired and now I am in the process of figuring out what to do with these.  Here is what I have in mind:


  • Hardwood Oak Veneer.  I am thinking of a mahogany or dark cherry stain with a satin clear coat finish.  This will go on all 4 sides.  The front of portion is rounded so it is going to making the joints a bit of a challenge.
  • Faceplate, I am think of contrasting the hardwood with a black coat of textured Duratex. (Back panel I'll just give a coat of black paint...nothing is needed there.
  • Internally, I am going to beef up the walls with hardwood trim.  This will give the MDF a bit more rigidity and reinforce the areas that needed repair.
  • Change out the normal spring terminals with a dual banana plug style interface.  
  • Build a 2nd order three-way high power cross over (or may buy one...not sure yet.)
  •  Going to make a basic custom grill; nothing special but not like the original with the curved front/base combination.
  • Have not determined if I am going to keep it as a sealed enclosure or port it; but I am leaning to a single, or possibly dual rear ports.
  • Driver selection is still up in the air, but I have some JBL's that should work; but I may go with all new GRS high sensitivity drivers.

Optimus Prime

Resurrecting a pair of Optimus-50's from the garage stash


Project start date: 12/5/2016

So this was set of speakers i grabbed a while back and has been sitting in the garage waiting for their turn on the bench. A number of weeks ago, I was having a conversation with a Customer about availabile loudspeakers.  I invited him out to take a look at my inventory to see if there was anything that caught his eye....and these Optimus 50's did just that. Generally speaking, they were already in pretty good physical condition, but have obvious signs of wear, chips, scratches, etc.  The grills were ok, but had some rips/tears and they were pretty dusty/dirty.  The biggest problem with them was that both the main 12" woofer and midranges were suffering from foam rot.  As you can see in the pics below, they needed to be replaced.  So we agreed to move forward with their restoration.  As a result, here is what was done:


  • Pull main woofers and midranges as well as tweeters and check to make sure nothing was blown.
  • Ensure coil movement around pole piece was free and clear.
  • Inspect magnetic structure to ensure adhesive/epoxy are solid and not showing signs of failure
  • Clean off and replace foam surrounds on woofer and mid-range drivers.
  • Clean and re-apply gaskets.
  • Check and verify crossover (capacitor) function/values.
  • De-Ox and lube L-pad pots on front panel (for tweeter and mid-range)
  • Check and verify cabinet insulation is good and properly affixed
  • Clean/restore cabinet finish
  • Replace grill cloth with new, acoustically transparent black fabric (from the original brown)
  • Pull off rear mid-range vent and ensure metal grill is securely in place.


As the projects name suggests, these certainly transformed into something special. Although there are still some dings/scratches on the cabinets, they actually cleaned up very nice. The hardwood veneer has a beautiful pattern and depth to it and it just glows. The new black grills look much nicer with the color of the cabinet now compared to the old brown ones that were on there. Both speakers have been power checked and sound great. I am actually going to be sad to see these go....but knowing who they are going to, I know they will have a good home and be well cared for.