[sdiy] Integral scope on VCO

[Scott Gravenhorst]

You might want to think about building the module in a way that it is easy to
remove it and place it in it's own separate box, just in case it makes life
miserable.

If it were me, I'd buy an economic scope and stick it next to your rig.  That
way, all of the technical problems with circuitry and shielding are solved for
you by people who build these things professionally.  It comes precalibrated,
properly isolated and registered with your government as a safe product.

Thomas Dunker <dunker at invalid.ed.ntnu.no> wrote:
>On Fri, 16 Apr 2004, KA4HJH wrote:
>
>> Thomas, you're in good hands on this list. Take it from the "old"
>> timers--having a small scope in your modular synth is cool looking--and
>> even useful--which is why you probably shouldn't build it into another
>> module such as a VCO. Avoid the issues Harry and others have raised and
>> make it a module all by itself. That's why we call them MODULAR synths! If
>> you want to you can normalize the output of a VCO or a VCF to it behind the
>> panels.
>
> Sorry about the late reply, been putting in lots of hours at work over
>the weekend, preparing for a field test/demo the company's having with
>lots of military brass tomorrow (tuesday).
>Lots of antenna gear and power supply stuff for automobile use had to be
>built, prepared and packed.
>
> Anyway, yeah, I can build a separate scope module, but it would still be
>within inches of something else, so we'll see how it works out. I would
>have liked to use toroid transformers to keep the stray fields as minimal
>as possible. I'll have to dive into my junk stash to see if I can find
>something I can use.
>
>> This is IMHO more useful and will let you concentrate on getting the scope
>> working and eliminating any problems with RFI, EMI, etc. It will also move
>> the high voltages even further away the rest of your modules, reducing the
>> possibility of a catastrophic short.
>
> Well, I am used to working with tubes, it's what my DIY electronics
>projects have mostly been about up until the more recent synth related
>projects. I haven't had any actual disasters yet. I have learned a thing
>or two about the wisdom of adding fuses in strategic parts of the circuits,
>however... And about the poor reliability of high voltage electrolytics -
>some components are definitely not meant to be recycled...
>
>> Finally, if you get it all working and post the design then anyone can
>> incorporate it into their modular in any way they chose. I'm sure lots of
>> people would love to have one.
>> All this is purely my opinion but I think you'd be better off in the end.
>
> It would certainly be adaptable to any modular however I choose to do it.
>I have been discussing some issues with a friend of mine and think I have
>come up with a good scheme for the X sweep. Since I will be generating suboctave
>signals, I would want to be able to display multiple fundamental VCO
>cycles on the scope, so as to get the full picture of the waveform
>including suboctaves. I think it will be most convenient to derive
>suboctaves and X sweep signals from the same frequency divider fed by the
>sync output of the VCO. The square signals from the divider can
>simultaneously be used as suboctave audio outputs and be fed to saw
>shapers to provide selectable saw sweeps at 1x, 1/2x, 1/4x and 1/8x the
>VCO frequency.  These signals can also double as suboctave saw audio
>outputs from the VCO. All this circuitry will be located on the VCO
>module with just the sweep saw signals internally wired to the
>scope module and suboctave audio brought out on jacks on the VCO's panel.
>
> In addition, the scope will have an internal sweep generator. A saw
>output LFO with the appropriate frequency range should be sufficient.
>Whenever the sweep freq. is locked to the VCO frequency, there will be no
>need for triggering circuitry to provide a stable image. In my case, there
>is the matter of how much front panel space I can allow for the scope,
>since whenever I add something I have to drop something somewhere else.
>(I chose to build a portable synth with a finite number of modules, so
>there's no "extra space" for the scope, really. I'll just have to see if
>adding the scope still allows me to keep everything else that I think the
>synth should have.
>
> At the moment I am most concerned about having enough room for mixer(s).
>Ideally I'd like to have separate "input mixer" and "output mixer", both
>with pannable 2 channel outputs. Since the synth has two different VCFs,
>two VCAs and a number of LFOs, I hope to be able to simultaneously process
>two different signal mixes (say for instance splitting the suboctaves from
>the fundamental VCO signal and filtering/modulating/processing the sub
>signals and fundamental VCO signals independently, and mix or pan them into
>separate output channels at the output, that sort of thing).
>
> On the other hand, I have a decent
>Soundcraft Spirit Folio mixer that will probably go into the rig anyway,
>so maybe I can keep it down to a single mixer module on the synth itself,
>and just a small master 2-in-2-out volume/panning and headphone amp output
>mixer at the output, taking up only a half module.
>
> Anyway, I just got the missing parts I needed for the VCO (tempcos
>and the CA3046 transistor array) I ordered from Tony
>Allgood (thanks!), so that's one of the first things to complete now.
>
>> BTW, I don't know if anyone else mentioned it but Eric Barbour used to have
>> a collection of old schematics that had a lot of useful info on building a
>> small scope just like this. He's not on the list right now but you can
>> email him at synth at metasonix.com. I have a copy myself but I'm not sure
>> where it is right now...
>
> I have been in touch with Eric in the past on tube audio stuff. I tried
>to mail him about the tube synth stuff out there (the thyratron VCO, and
>pentode based VCA and VCF) a while back but just got a reply from some
>secretary at the metasonix address above.
> I can always do a little Googleing and see if I get any more ideas...
>
> In the mean time I'm waiting for a reply from that Norwegian ham who
>built the X-Y scope (for RTTY tuning purposes) with the CRTs I have.
>
> Anyway, thanks for the suggestions. I think you may be right that I
>should just as well make a separate scope module (otherwise a combined VCO
>and scope module would take forever to complete, I imagine).
>
> Probably the single most pleasant thing about modular construction is how
>there isn't a point of "completion" way ahead in the distance, but the
>whole job is broken into a number of manageably small projects that are
>completed one at a time. It ensures a good sense of steady progress and
>the fact that modules can be put to use as they are completed, multiplying
>the number of possible sounds each time, is also very motivating.
>
> I've also found that the nicest mounting/construction work I've ever done
>has been on this project. My tube amps always look like a total mess
>inside once they've been through the usual number of tweaks and
>experiments.
>
> Oh, on the topic of mumetal shielding the CRT - I have no experience with
>mumetal, but I do have at least one scope that I can cannibalize for parts
>(unless somebody can help me find the manual for a Dumont 190) including a
>big mumetal CRT shield that could conceivably be recycled somehow...?
>
>Thomas
>

=========================================================  
- Where merit is not rewarded, excellence fades.
- Hydrogen is pointless without solar.
- What good are laws that only lawyers understand?
- The media's credibility should always be questioned.
- The only good terrorist is a dead terrorist.
- Governments do nothing well, save collect taxes.

-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
-- Linux Rex         | RedWebMail by RedStarWare
-- FatMan: home1.gte.net/res0658s/FatMan/
-- NonFatMan: home1.gte.net/res0658s/electronics/
-- Autodidactic Master of Arcane and Hidden Knowledge.