[sdiy] Integral scope on VCO

[Ken Stone]

If all the integral scope was going to do was to play lisajous patterns, an
alternative would be to use a small laser with a couple of guide mirrors,
and project it onto a translucent film from behind. No high voltage, and a
couple of relatively simple, low voltage DC amps to drive the mirrors.

Ken

>Thgat would take a HELL of a lot of diodes and
>capacitors... and some pretty high voltage ones at
>that.
>
>That's why the voltage doubler, tripler trick is not
>played often.
>
>I would NOT try the scope in a VCO project. Keeping
>the
>EMI from the scope from interfering with the VCO will
>be the major design challenge.  I'd probably get one
>of those tiny scopes that NonLinear Systems used to
>make...
>and just modify the package to add it to the synth.
>The
>metal box, shielding etc are all in place, and its
>sort
>of instrument grade already !
>
>I agree it would look cool, and possibly be useful.
>Prlly not as useful as an external scope....
>
>H^) harry
>
>
>
>--- Theo <t.hogers at home.nl> wrote:
>> ?? Assuming you got some (12V?) AC hanging around,
>> won't a simple diode/capacitor cascade do the
>> trick??
>> 
>> Theo
>> 
>> 
>> 
>> ----- Original Message -----
>> From: Thomas Dunker <dunker at invalid.ed.ntnu.no>
>> To: Tony Clark <clark at andrews.edu>
>> Cc: <synth-diy at dropmix.xs4all.nl>
>> Sent: Wednesday, April 14, 2004 1:07 AM
>> Subject: Re: [sdiy] Integral scope on VCO
>> 
>> 
>> > On Tue, 13 Apr 2004, Tony Clark wrote:
>> >
>> > >    It's quite possible to make very tiny high
>> voltage supplies for your
>> > > application.  I just finished designing just
>> such a thing for a product
>> > > my company is making.  I was able to come up
>> with a design that
>> > > will generate a good 1200V DC (approximately)
>> and fit in a 2x2x0.5
>> > > space.  It runs on 12V at 120mA and the best
>> part is the total parts
>> > > cost is less than $10.00 (in quantity, probably
>> about $15.00 for a
>> 1-off)
>> > >    Don't know what kind of current the CRT
>> requires, but the power
>> supply
>> > > will definately give you a good zap!
>> >
>> >  As far as I can tell from the data sheets on the
>> CRT, the beam current is
>> > virtually in the microamps range, but I also need
>> a reasonably high
>> > voltage supply for the deflection amplifiers (need
>> about 250V pk-pk for
>> > full deflection on either axis) and it seems most
>> realistic to get the
>> > supply voltage for these amp stages from the same
>> supply. The deflection
>> > amps can be high impedance things so don't really
>> need to take a lot of
>> > current. I just emailed a Norwegian ham who built
>> a scope module with this
>> CRT,
>> > so it'll be interesting to find out how he did the
>> deflection amps. I
>> thought
>> > about using diff stages with 12AX7 type tubes
>> which work fine at 0.5mA per
>> > section, so two diff stages would typically draw
>> about 2mA. But for the
>> > sake of saving space it would be nice if I could
>> use transistors in the
>> > deflection amps. I don't know precisely how that
>> would work out in terms
>> > of current consumption. I may have to sink some
>> current into a voltage
>> divider
>> > and some pots and things on the same supply,
>> unless I can get a HV
>> > transformer with sectioned secondary and make a
>> stacked supply. In any
>> > case I will be needing something like -50V, 0V,
>> 500V and 800V taps.
>> >
>> >  It's not like I don't have high voltage
>> transformers in my stash, but
>> > they do take up a lot of space (relatively) and so
>> do high voltage filter
>> > caps when they have to take care of 100Hz ripple
>> current. It's cool when
>> > it's a classic tube amp for the stereo where size
>> and weight doesn't
>> > matter (to me, anyway) and one can liberally build
>> pi filters with 10
>> henry
>> > iron core chokes and that sort of thing, but this
>> is a little different...
>> >
>> >  I was looking at some high output voltage DC-DC
>> converters in Farnell's
>> > catalog, but they were far too wimpy on the
>> current for my purpose. We're
>> > probably looking at a 10-20W supply, whereas the
>> module available from
>> > Farnell was good for 1 watt...
>> >
>> >  A buddy at work says I'd probably have to use a
>> flyback type converter if
>> > I want to go that way. I'm just a total idiot when
>> it comes to switched
>> > power supplies, since I've always avoided them in
>> audio apps, but for the
>> > scope they'd sure come in handy. It would be a
>> good excuse to learn a
>> > little more about them... I guess if I need
>> multiple voltage taps I could
>> > feed like three separate ferrite core transformers
>> from the same switcher
>> > thing? Oh, and it would definitely be most
>> convenient for me to make an
>> > AC/DC supply with 230VAC input at this kind of
>> power, otherwise I'd eat
>> > away at the synth's low voltage supply's available
>> current real fast.
>> >
>> >  Can you say a little more about the type PSU you
>> had in mind?
>> >
>> > Thomas
>> >
>> 
>
>
_______________________________________________________________________
Ken Stone   sasami at hotkey.net.au or ken at cgs.synth.net
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