x0xb0x Etudes - pt 3

VCO (that's Voltage Controlled Oscillator, if you missed it) is now complete.
VCF (filter) is also complete.

Ruminations:
Either a) My scope is weird or b) I don't know how to use my scope.

When I check the waveforms, first square looked a little off...not entirely symmetrical along the y-axis, nor on the x-axis (ie pulsewidth looked off). Changing the tuning seems to make the wave look better though, as if the PW changes with the tuning somewhat.

Also, if you follow the fabrication manual exactly, then they forgot to mention you need to have R46 soldered in before you test the square wave.

Then I built the filter, and while it didn't look ENTIRELY correct on my scope, I'm chalking it up to either a or b above. Turning the cutoff definitely produced a much more sine-y waveform, and all the way open showed a square/saw with lots of high freq harmonics going on.

Now the biggest bummer I had though, is I'm feeling all high now, and so I decide to move on to the Envelope section. Much to my dismay, it makes a note that out of two transistors, which had previously been referred to as the same piece, they are not the same and you need one particular one in this instance. Sure enough, I had already soldered that one into the VCO earlier, thinking they were the same piece. Literally HOURS spent trying to desolder that sumbitch and in the end I totally broke / hosed the damn component. Of course, this is one of the 'rare' vintage parts that you can't just order from mouser. Luckily, I find this pedalhacker shop on ebay and I've got two replacement 2SK30A-Y K30A in the mail to me now, at a reasonable price (read, $1, $4.20 w shipping).

So production is somewhat on hold as I wait for the missing link. I will consider doing mods now, even though I initially forgot to do them on the VCF, and then qualified it by saying it's too much a pain in the ass right now, and I'll do it later.

In other news, I feel like I can solder ANYTHING now.

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x0xb0x Etudes - pt. 2

Power Supply completed last round.
VCO section is what I am working on now, and glory be, I got a sawtooth.



It didn't come without a bit of pain though.

First problem, in my attempts to be overly organised to make the process smoother, I made a mistake and put all the schematic part numbers for a couple of similar looking transistors under the wrong batch. This was not a huge problem once I realised that a set of 10 transistors probably didn't go in 24 different places. Anyway, thought I'd mention it as it could have completely derailed the project.

The second problem was a total new one to me: CONTROL VOLTAGE. How did I miss the part of the prep guide that said I would need a variable power supply to test the thing?!
Anyway, I got my sawtooth generator all put together, and when I went to test, I was getting very strange results. Weird waveforms, a lot of incorrect DC offset, on and on. I figured, incorrectly, that you could test this stage WITHOUT the variable power supply (supplying control voltage) applied. Boy was I wrong.
So, a quick trip to 'The Shack', as they are very obviously trying to rebrand to now, picked up a voltage regulator, and using parts I had lying around I managed to build a working variable power supply running off a 9 volt. It supplies between 1.25 and 7 volts.
Once I got that in place per the fabrication manual, things started to look exactly right. That saw wave is beautiful, and the tuning pot and the PS adjustment all change the frequency of what I see on the scope.
So I learned that you really shouldn't try to skip steps. I thought, CV, who cares? I won't be messing with it anyway. What I failed to realise is that the CV circuit seems to be integral to the proper functioning of the saw tooth generator.
I was hoping to have the entire VCO finished last night, but a lack of adjustable power supply and a wicked case of allergies has left me OVERLY pleased with my little, buzzy waveform.

Next time, the square wave + VCO completion.

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x0xb0x Etudes - pt 1

Howdy everyone
Do you know the 303?
It's a bassline synth made in the early 80s, vaulted to cult status via acid house, and now firmly seated in the uber-expensive realm of high profile gear lust.

Well if you can't afford one, why not build one from scratch?

Having finally exhausted my excuses to procrastinate (no oscilloscope, no iron, no sockets), I have recently begun doing just this using a kit I bought years ago from Ladyada's site above.

Tonight I did the power supply.
The fabrication guide was immensely helpful, if you are going to do this yourself, READ THE MANUAL AS YOU GO!!! It provides all sorts of insight into which resistor is what, what color codes you are looking for, and common mistakes.

So these posts pertaining to my progress will be more about my personal mistakes.

First, I think sockets are a must. You don't want to fry the ICs with your shitty soldering hand, so just spend the 50cents and get sockets (you need 1 6pin, 3 8pin, 2 14pin, and 9 16pin).
Second, test as often as the manual suggests; no fun flipping the switch and no boomboom.
Third, the only mistake I made on the power supply, check your connection names! I soldered some jumper wires to the wrong set of three jumper holes (j6 vs j4 I believe) and really had a hell of a time desoldering and removing those hos. In hindsight, I probably should have chilled and just left them because I will probably end up needing to put them back anyway.

ON MODS:
I only did one modification to the power supply and that is adding a power switch. It is a real PITA to 'cut the trace' between the bottom most pin on the power jack and where it connects to, but anyway thats where you put the two wires which will eventually go to a spst switch. For now, I just twisted them back together. If you know a good way to 'cut the trace' on a pcb, please comment and let me know. I just used a dull knife tip and scraped the shit out of it repeatedly (not recommended, but doable).

I will return, hopefully sooner rather than later, with pt 2 on building the VCO (I will need to set up my huge scope for this, so that's a reason to procrastinate).

-J

edit:
let's hope it goes something like this -

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