Odp: [sdiy] A440 -- almost

[Roman]

well... I tune sunths this way :-P
It's actually AD9850 running at 120MHz. It's controlled by PIC16F84,
has numeric keypad, 8-digit display, tuning dial (endless rotation), and
80dB range attenuator. If I get some more free time (what's that?)
I'll put schematics and firmware on the web someday.

And it wasn't expensive at all, since I was able to make it being poor
student back then.

Later I got a sample DDS from AD, can't remember a number but it was
300MHz device with built in modulations. Nice.

Roman

----- Original Message ----- 
From: Tim Ressel <madhun2001 at yahoo.com>
To: Michael Baxter <mab at cruzio.com>; synthDIY <synth-diy at dropmix.xs4all.nl>
Sent: Sunday, October 20, 2002 6:52 AM
Subject: Re: [sdiy] A440 -- almost


> Hiya,
> 
> Of course, the ultimate COOL way to do this is with a
> DDS chip a la AD9830 from Analog Devices. This
> solution gets you to within a few PPM of the actual
> frequency and is very adjustable. The down side? Well,
> as you know, 'cool' is Greek for 'expensive'.
> 
> --TR
> 
> --- Michael Baxter <mab at cruzio.com> wrote:
> > Hi all synthDIYer friends,
> > 
> > I'm designing and building a modular system, and I'm
> > very excited to see 
> > all of the activity and innovative designs in this
> > community! As I get 
> > circuits designed and built, I'll post them
> > somewhere. I did of lot of 
> > this kind of design in the 1970's, so I'm hoping to
> > contribute to "module 
> > diversity," if you will. More later.
> > 
> > In this first post, thought I'd share some quick
> > notes on the A-440 
> > reference frequency or calibrator thread that came
> > up recently.
> > 
> > I discovered that the NTSC color burst reference
> > frequency is very close 
> > to a necessary superharmonic. 3.579545 MHz / 8134
> > yields 440.07192 Hz.
> > 
> > Compared to a true 440.0 Hz, this is still pretty
> > close. The "correct" 
> > reference frequency would need to be 585 Hz lower,
> > and this is probably 
> > out of the the crystal adjustment range, esp. as the
> > NTSC frequency is 
> > supposed to be within +/- 10 Hz. However,
> > quantitatively, the actual 
> > difference seems small compared to a +/- 1-cent
> > interval above A4.
> > 
> > The hack to "adjust" crystal mechanically is very
> > interesting, I had not 
> > seen that before. It definitely has the feel of
> > amateur radio hints 
> > and kinks lore, and probably works. Starting with a
> > cheap crystal, one 
> > could try several times, to eventually get it right.
> > Not so different than 
> > Vbe matching transistors, :-).
> > 
> > I did see the later posts on the 4.40 MHz crystals,
> > which would be of 
> > course "spot-on." But I was very surprised at how
> > close one could get with 
> > the garden variety NTSC crystal, the kind laying
> > around in your junkbox.
> > 
> > Kindly yours,
> > Michael Baxter
> > California, USA
> > 
> 
> 
> __________________________________________________
> Do you Yahoo!?
> Y! Web Hosting - Let the expert host your web site
> http://webhosting.yahoo.com/