Sunday, January 3, 2016

Hand-me-down Parts and Pieces from Family and Friends

What do you know, I finally finished a project!

I have this tendency to work at a project until I have solved all the questions/problems in my mind, and then set it aside.  Or, I will get the project working, but not put the finishing touches on it.  For example, I built some speakers in 1998 that have been my main living room speakers since then.  In the meantime, I have rewired them inside and created an updated crossover, but I never got around to finishing them.  They are still surfaced in raw MDF and the maple veneer is sitting in my basement.

This time, I had to finish the project because it was a Christmas gift for my niece who recently purchased a house.  The project was a small stereo (music always warms a house, in my opinion).  The idea was to use as many parts as possible that were leftover from friends and family.  Personally, I like the idea of knowing that something in my life has a history thru people that I know, especially from those that have passed.  I guess it's an engineer's way of remember those people.

10 or more years ago, I made a little amplifier for my friend, Bob.  When he passed away a few years ago, his ex-wife sent it back to me.  When we moved my father out of his house, I collected his DIY speakers.

Those components were the key ingredients of this project, but along the way, I was able to use parts from my brother-in-law's disassembled electronics, electronic parts from my parts bin, my father's parts bin, even the metal for the amplifier enclosure and the wood for the speaker boxes were already in my house.

The result was an 40 Watt per Channel integrated amplifier with 3 inputs (2 RCA rear and 1 for plugging in a smartphone on the front) and a volume control with an old volume knob of the 40's era.  Key components in the sound path were upgraded to provide cleaner sound and the coupling capacitor was chosen to match the sound of the speakers.  I got the word that lighter color and less shiny surface were preferred, so a satin, off-white paint finished the aluminum box, along with wood accents.

The speaker drivers are about 30 years old and came from a project that my father built when he first retired.  He had built them to go with a subwoofer, but we didn't have room for that in this system, so new boxes were designed and built to provide full range performance to the old tweeter and woofer.  The tweeter is a Dynaudio D-28AF from Denmark and was first class 30 years ago.  It still sounds and measures as if it were new.  The woofer is a Focal 5N401 from France.  30 years had aged the rubber surround so that it was cracked and in need of replacement.  Happily, I found new surrounds built to matching specs in the Netherlands.  The pair was put in a damped, bass reflex design with a bass cutoff of 55 Hz and a crossover specific to these drivers.

A little 2D CAD of the speaker box design.  Magnets from an old iMac to hold on the grille cover

 My niece already had her father's excellent turntable, but no way to play it because they lacked a phono preamp.  I brought along a DB-8 phono preamp built by a guy in NH.  Not handmade by me, but close enough.

Combine that with a Grace Primo to bring in music from the internet and the system was complete.  I have to say that I am please with the resulting sound.  In my niece's small living room, the speakers do a great job of filling the room without any strain.  The end result was clear, dynamic, and detailed.

Now, if I could just finish one of my own projects.


  1. Thanks, but it wasn't anything that special. Just like in motorcycles, I wish I knew enough to design these things from the ground up.