Tuesday, 10 October 2017


After many years of making do with either restricted commercial software (Eagle) or old tools long out of support (P-CAD) I am now firmly entrenched in the OrCAD camp.

Time to put mouse to keyboard and get some new designs out!

Wednesday, 8 June 2016

Done (Really)

Following some gentle prodding by a fellow AP enthusiast (thanks Andy!) I finally found inspiration and time to sort out the auto-detect capability of the AP control program S1.EXE.  It turns out I had missed off a couple of logic paths, and following careful reading of the S1 service manual (again) I found that all I needed was a simple one-line fix in the Verilog..


-- Neil

Tuesday, 16 February 2016


Next task is to make up some XLR cables.  I found a few metres of Gotham GAC-3 in my junk store and so set about an evening of soldering up some test leads:

A quick test on the SystemOne showed them to be as good as the internal "GENMON" loopback test.

On a related note, by setting the analyser input filter to 22Hz-22kHz it reads down to 0.00034% THD+N.  Awesome!


Wednesday, 20 January 2016

Done (Mostly)

So there is one wrinkle in my System One interface card: the auto-detect doesn't work for some reason.  I'm pretty sure the logic is all there, and I've tested it with QBasic test programs.  I can start the AP software (S1.EXE) from the command line and specify the interface card address with the /I option and then everything is fine.  So at this moment in time I don't fancy digging in deeper to fix this minor issue.  It doesn't stop me using this amazing machine.

A side note: after setting the SystemOne to internal loopback I measure the THD+N as 0.0014% on both channels.  That's a decent 8dB better than the 8903B (about 0.0035%).


Monday, 18 January 2016

Analyze This!

It works!  The damn thing works!!

Well, okay, there were a few bugs in the Verilog, but checking out each block soon ironed out those.

Ta daaa.... Start up screen:
Eagle-eyed readers will note the flat grey cable poking out the case - that's the ISP download cable for the Lattice CPLD.

A quick graph showing that scans are working (needed the external interrupt line wired up properly - took an evening to fix that little bug):
Note that the performance at the moment (THD+N @ 0.0033%) is about on par with the 8903B it currently sits on top of:
But that's with a less-than-ideal coax cable - I can shift the TND+N over 0.01% just by handling the cable.  I think I really need to look into replacing those BNCs with proper Neutrik XLRs.

The PC that I am using is an Advantech industrial control PC in a small case.  It has a 486 processor running DOS 5.00.

For now, this is just what I need.  Perfick!


Friday, 11 December 2015

Stuffing for Christmas

So, yesterday's post showed the bare PCB.  Today we have the stuffed board ready for bring-up:
During bring-up I'll be adding each IC in turn, making sure it is doing what it should be doing.  The last one with be the CPLD - you can see the in-circuit programming header top-left of the board (a couple of the pins are also used to set the board address).

I've also checked the board fits into the PC. The next version of the PCB will be gold-plated.


Wednesday, 9 December 2015

New project just in time for Christmas

I've started work on the next project.  Well, "started" in this case means getting the first prototype PCB back from the fab:
Took a while to get everything to fit, and the release version will be a little bit simpler.  As to what it does....I'm sure there are some folks out there who will be able to work out what this is for!