[sdiy] Aztec Revisited

[mike ruberto]

On Jan 12, 2008 10:14 AM, Ian Fritz <ijfritz at comcast.net> wrote:
> At 10:50 PM 1/11/2008, mike ruberto wrote:
>
> >Also the multiplier pulse output is a bit on the indecisive end.
> >Certain conditions lead to some very dramatic toggling. Fun to watch
> >on the scope and even more interesting to hear. While I'm sure I could
> >stableize this I'm not sure I want to. Compared to the samples of
> >Ian's 5Pulser this circuit is much less subtle and clean about
> >introducing a new octave. Yes it's something like PWM but with a bad
> >attitude.
>
> Hi Mike --
>
> Cool stuff!
>

Thanks Ian! Thanks for the inspiration too.

> I found a lot of the same "indecisive" behavior in working on the 5Pulser.
> I also saw a lot of the same HF oscillations. All this turned out to be
> caused by spurious x-coupling via radiation. These circuits splash RF all
> over the place!  On the whiteboard I had to keep all the traces separated,
> with the inbetween rows grounded.  It was also very important to keep the
> output lines well separated from the inputs.  Twisted pairs for the I/O
> lines helped a lot.
>

On the breadboard this circuit is a complete mess of flying leads all
over the place. It isn't as noisy as the original Aztec design which
had the 3914 outputs sinking 10 MA each. When I had that racked into
my old Frac system you could hear it in every other module.

> On the PC board I made, I built the digital (pulsed) part of the circuit
> over a ground plane.
> http://home.comcast.net/~ijfritz/sy_cir8.htm
> You can see the ground plane through the board. This got rid of all the
> litttle nasties.
>

I'll follow your example on this. I sure don't want to be transmitting
a blast of RF into other circuits. The worst of the hash is coming
from the CMOS chip. I'm actually using some used MC4070 from
yesteryear so I'm sure it would be in my best interest to find a more
modern device.

> Of course, I'm not saying you need to do any of this, but at least you
> know.  :-)
>
> Ian
>

Well I planned for this to be an improved design so any suggestions
for improvement are quite welcome.

Mike

>