Semi Active upgrade of the Yamaha NS1000
I've been a huge fan of the NS 1000, admiring it as a teenager, and buying my first pair 7 years ago.
I bought a second pair last year. It was in better condition, being newer (serial numbers suggesting early 90s).
The inevitable AB test showed that the newer speaker sounded just a little better.
I thought the drivers in the old pair were in good condition and surmised that the (slightly) inferior sound quality of older pair was probably due to degradation of
crossover components.
I had followed a thread by Qwin(Ken) that he started a couple of years ago as he experimented with actively drive of the NS1000.
I revisited the thread to find, somewhat disappointingly, that it ended with recommendations for refurbishment/upgrade of the components in the
complex three-way passive Yam crossover.
I PMed Ken and asked for his views on active drive, DSP and the subwoofer option.
Well he hadnt abandoned active drive at all but had come up with a semi active solution that would improve bass especially, while
retaining the character of the NS1000 ie sealed box / acoustic suspension design.
He explained that DSP was not the way to go unless one was using only digital sources as there were too many A to D and D to A steps.
He got me interested in this semi-active drive that would improve not just the low frequency performance of the speaker but also the mids and highs.
Ken had done his homework with mics and freq analyses and had identified a modern woofer that would replace the venerable Yam woofer.
We got into a long discussion and I decided to embark on this project which required these new woofers from Scanspeak, new cabinets,
a new analog active crossover, and 2 way passive crossovers using premium components.
The 2 way active drive was necessary as it would facilitate direct drive of the Scanspeak woofers which are 4 ohm and not very sensitive.
The Yam mids and tweets are 8 ohm, are more sensitive (about 93dB/watt) and would be handled by a 2 way passive XO derived from the original design.
ie crossing over at 6000Hz
This pagefrom Kens website explains the basis of the drive .
http://www.jkwynn.co.uk/YamRev_HTML/Yamrev_02.html
2 way 500Hz Linkwitz Riley analogue Active Cross over is the heart of the system.
Ken had identified this device , designed by Rod Elliot of Australia, and assembled as a kit .
The predetermined XO freq, in our case 500Hz, is achieved by selecting the correct values of crossover resistors and capacitors.
Passive XOs were assembled on acrylic boards using rather expensive Jantzen Superior Z-capacitors and inductors
I used components nearly identical to Ken's.
Scanspeak 30W/4558TOO: 4 ohm, sensitivity (2.83V/1m) 89dB
Substantial things these - they are used in commercially built subwoofers
They work best in a 55L sealed box
I built cabs to Ken s design. Base dimensions are similar to the NS1000 cabinets but they are 13 cm taller.
The panels are MDF on the outside , ply on the inside.
On my build i used 16 mm MDF and 12mm Malaysian 'marine' ply bonded with adhesive.
There is a substantial inner brace, and the whole thing is bonded together into a rigid box.
When I had done all the panels and sanded bits so that they all fitted nicely it was time for the assembly.
Each cab a frantic 4 minutes of glue slopped on, excess wiped off,whacks with rubber mallet, quick fastening of straps quickly tightened to compress the thing together.
I had a lot of help for the whole project. Ken and i must have exchanged well over 100 emails.
I had friends help with sourcing timber, finishing them after i had veneered ( a first for me) the cabs,
and I had help with the electronics and preparation of the aluminium chassies for the electronic cross XOs.
Oh and I made up 2 pairs of speakers ie double of everything. The other set for my pal Ranjit who had blind faith in me who had previously only done some basic
soldering, not ever done veneering before.
The project consumed me for over 6 months. All done now.
I use a Nak CA5 preamp, pre out goes to the eXO, High Pass ie >500Hz goes to the power amp section of Sansui AU111 (abt 45 wpc push pull 6L6GC amp) that feed the tweeters and midranges via the passive XO (inside the cabs)
Low Pass (<500Hz) goes to Nak PA7 amp that feeds the woofers directly.
The 'balance' between thw High Pass and Low Pass is adjusted using variable pots for Rt and Lt channels on the eXO.
Depending on the relative Gains of the power amps the either the High or the Low Pass needs turning down.
On my set up the sound was pretty bad until i figured out that the Low Pass pots had to be turned down several turns (they are 20 turn variable pots) . Then things begin to sound nice.
Fine tune - just using my ears - to get things just right.
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