Apart from an architecture which is attractive to program in, I also have several other demands on the checklist for the digital toys I'm going to pin my colours to. Ease of entry into the game and low cost development tools are a must.

Arduino is a phenomenon I did a little research into. Its become jolly popular over the past six years or so since its inception and I wanted to understand some of the reasons for its acceptance. One of the reasons has to be its open source nature. Another is the well written materials to get you going - they've put quite a lot of thought into the practical issues, even inventing their own vocabulary for elements in the process - 'sketches' springs to mind. If there's a weakness in what they're doing its this - its tied to Atmel as they're the vendors of the chips used. There are no second sources of the parts to my knowledge. This vendor-specific approach doesn't sit at all well with the open-source side - Atmel's architecture is unique...

When I began writing real-time code for the 68k, the price of entry into the development game was rather high. My first project was a tachometer processor which my boss was applying on a patent for: US patent 4924420. In order to develop this we purchased a hardware emulator which became my pride and joy - it cost a sum equivalent to around two months of my salary at that time. This was a considerably more expensive solution than the other commonly used development technique in those days - EPROM emulators - it did though provide a much faster development path by virtue of providing a window into the interior of the CPU as well as a history in its trace buffer of everything it had done. During the course of this and subsequent projects which also used the 68k (later we added a 68020 too) I became a confirmed devotee of the architecture. One of my nicknames in the company was 'the cycle stealer' - if someone had some 68k code that wasn't running fast enough, I'd find some way to get it...

My first brush with a micro as programmer was as a schoolboy - my maths teacher had a National Semiconductor SC/MP board with LEDs and toggle switches. It could be programmed in binary. I was hooked.

About a year later Science of Cambridge came out with adverts for their Mk14, using the same SC/MP. This though had a real hex keyboard and calculator style 8 digit 7 segment display. I ordered one almost immediately I saw the ad. Trouble is, it seemed to take an age to come. Someone joked that Clive Sinclair's approach was to gather up the cheques and when he'd got a few thousand pay someone to do the design! I dialled SoC's number so many times chasing my order that its still engrained in my memory over 30 years later: 0223 311488.

When I got to uni, it was clear my room-mate was in a league above me - he'd designed a system with a Z80. That was a real man's processor, compared to my little boy SC/MP. I felt a tad threatened by his prowess. Science of Cambridge...

The 1.8mm iron wire arrived and it did indeed have a 1.2mm internal diameter which is perfect for winding small chokes. I built a second box with steel chokes in but the third box I tried with the iron wire coils. Having insulated wire means the coils are smaller and I was able to fit the second tier filter into the same box.

I wound a couple of NiZn toroids with iron wire, but not as common mode chokes. When I did the sums I found that for the currents I'm running at (under 3A total draw) the toroidal core isn't close to saturation. Hence I decided on separate inductors to gain some differential mode filtering on top of the common mode.

The next stage of development has been trying to wind multilayer iron wire air-cored chokes. For this I've had trouble finding formers which allow more than 4 layers. The reason for wanting more layers is - this makes the chokes much more lossy. Proximity effect helps concentrate the higher frequency currents only in areas...

...

So I have almost all of the parts (yeah I know) for my YARPS power supply. As part of the order I got myself a prototyping breadboard.

I've knocked up one half of the yarps power supply, ie the positive side, and hooked it up to my old model railroad transformer which has a 15V output.

Parts still to be ordered are the dual secondary 15V transformer and some 50K trim pots. However I had enough to make one side of the dual rail supply.

It didn't smoke, and the CRCRC part of the PS works very nicely Pics attached at the end.

I need to do a further test with BC560c's with different HFE's to see whether this affects the output voltage (my suspicion is that it will). I put a 36K resistor (which I had at hand) in place of the 50K pot and only got 8.6V even though spice said I should get 9.13V with that value resistor so something isn't working as per the sim, the use of a pot certainly seems to be required to get the desired voltage...

i remember ads L810 sounding better years ago, but alas my hearing in not what it used to be, how i check the cap in the crossovers, what value should it measure, what replacements would compliment the speakers?

Finally the engraved top-, front- & backplate arrived.



Surely you are asking yourself, why i made a 1mm deep square around the place for the transformer...

...now here is the answer



I´ve got a perfect aluminum transformer housing and now it sits perfect without an air gap.


Now it´s time to assemble the parts.

re: KENWOOD L-09 amp MODS :

Have interest in mods to improve these DC mono block amps. After 32 years of service, a RECAP job of electrolytics ( 2) is in order for my pair (electroylics caps dry-out and BURST/ FAIL - and will take-out 24 output transistors and probably your speakers also ) So while the IRON IS HOT ..... I noticed the following possible mods to improve these amps' performance :
MOD #1- Replace 6 foot # 16/2 ' zip cord ' AC power cord....with 2 foot of # 8/2 ( amp pulls 1200 watts @ full power each ) note; a # 10/4 stranded copper power cable can be wired in 2 pairs ( red+black / white+green ) which eliminates DRILLING chassis opening LARGER to accomadate # 8/2, but will NET #8/2 gauge AND provide added shielding with 4 conductor spiraling ! THIS IS A NO BRAINER AND SHOULD MAKE THIS AMP BREATH a bit easier
(note : factory issue AC cord has NO ground conductor-and I would suggest NOT adding a grounded conductor to new 15 amp plug either-...