Flying cows (was Re: [f-cpu] Something new to play with :))

[Yann Guidon <whygee@f-cpu.org>]

hi !

Ben Franchuk wrote:
> Y> "flying calf" is a 20-bit stereo A/D SPDIF (coax) converter from Midiman
> > (i got two of them in a bargain).
> > however, minidisc recorders have an optical input. so i have to hack
> > an optical output to the Midiman converter. With this stuff, i finally
> > can record with 60db SNR :-))) portable minidiscs suck when you push the
> > sensitivity of the microphone input. My MZR-30 has decoupling problems,
> > the internal A/D is not protected from the electric motor power noise.
> > Now, all the conversion will be done externally, which removes the
> > other limitation : once you started to record a track, you can't change
> > the sensitivity. And the flying calf has a 6 LED level indicator per channel,
> > it's more practical in the dark ;-)
> > did i say i'm an audio freak ?
> So do you have a TUBE amp too!
no, a bunch of LM741 connected in "impedance adapter" mode.
well, that's the usual stuff i do : one 8-pin IC per channel,
one pair of batteries and some capas for decoupling. However
the analog stage of the "Flying calf" (that i'm turning into
a real flying elephant :-D) has Motorola 33078 AOPs, and i am
trying to find the correct resistors because the current setting
eats up almost 30db. i need _very_ sensitive inputs :-)

Up to now, i have sawed some part of the PCB away, so i could
fit the TOTX173 (opto-electronic output module)
in the slot of the metal case where the 9V power supply comes.
i didn't want to make holes in the metal. I have also placed
the LEDs in an individual PCB to avoid the stress on the pins (which
can break easily). I removed the RCA connector and now i'm sawing away
the location of the 2 JACK input connectors (i'm putting a stereo jack and
a variable stereo resistor in the freed round slot of the metal case).
One sad thing, however : there's no room in the case to fit one 9V battery :-(
I'm doing this mad brain surgery on one piece, i got a spare device in stock
(who knows what could happen). And IF it works, i'll put the PCB of the
two devices inside ONE plastic case :-) [one 4-channel 20-bit A/D]

mmmm yes, i know, i should be currently installing Cadence's soft, but when the
soldering iron is hot, we have to use it ;-)

> Ben.
yeah :-)


Michael Riepe wrote:
> On Wed, Sep 26, 2001 at 05:23:19PM +0200, Yann Guidon wrote:
> [...]
> > My MZR-30 has decoupling problems,
> > the internal A/D is not protected from the electric motor power noise.
> *ouch*
right. You can't even filter it out because the frequency changes with time
and the spectrum is rather wide... What the point of going digital when the
analog side is badly designed ? OTOH the "line in" is correctly decoupled but
there is still the problem of the sensitivity tuning during the recording.
An external converter is the best solution.

> > Now, all the conversion will be done externally, which removes the
> > other limitation : once you started to record a track, you can't change
> > the sensitivity. And the flying calf has a 6 LED level indicator per channel,
> > it's more practical in the dark ;-)
> > did i say i'm an audio freak ?
> No, but I get the idea... ;)
hmmm and what if i say that i have a Aria Pro II bass guitar that i equiped
with a pair of _big_ Bartolini pickups ($$$) and a mini internal amplifier
(2*9V batt. + 2*LM741 + 1 stereo jack + 1 dual switch) ? Given the fretless
handle and the flatwound strings, can you imagine the sound ? :-))))))))
And now do you understand why i could not resist hacking into the flying cow ?

The next step in the audio path will be to have 4 synchronised tracks.
I can do 2*2 tracks (i have a pair of MDs) but the synchro is not OK.
having all converters in one box and a single push-button to make the "clap"
will help the resynchronisation step.

>  Michael "Tired" Riepe <Michael.Riepe@stud.uni-hannover.de>
WHYGEE, who has a life beyond F-CPU ;-P
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PS : i'll take pictures when the slaughter is over :-P
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