Right I might have let this blog go to pasture a bit, but I HAVE been making progress. A friend got me looking at microcontrollers and what you can do with them, and I felt to post such digital folly on here would be blasphemous, but rest assured a full update is coming on my foray into the world of ones and zeros! The latest news is that I've finally got a VCO etched and working (mostly), a VCA that works (back to front, for some reason) and an ADSR (which might be broken now).
Currently working on a complete VCO redesign and a couple of ideas about VCAs and VCFs.
Full update coming this week I promise!
Watch this space...
Sunday 29 April 2012
Monday 16 January 2012
Powering ahead
Hmmm, I seem to have let the blog fall by the wayside a bit.
Not to worry, I'm here again now with a fresh batch of information!
The power supply has been a resounding success. I built the new version of the board into its shoddy case after considerable faffing about with dodgy connections and misjudged cable lengths, to produce this:
...Told you the case was shoddy.
Looks aren't important in this case though, as it's only going to live under my desk to power my experimentations. Inside the box is the power supply circuit depicted in the last post, with the indicator LEDs taken on wires to the front panel (such as it is) and also the the rather large 60VA toroidal transformer I picked up on eBay. The transformer takes the 230v AC and gives two lots of 18v AC nd a 0v connection. These go to the input pins on the power supply, which converts the 2x18v AC to +15v, +5v and -15v, all DC.
I had issues deciding on connectors for the power output, as the sexy 4 pin mini XLR type connectors I like are rather expensive, and cheap standardised power connectors don't seem to be an easy thing to find in relatively small quantities. In the end I settled on Molex power connectors as used for PC hard drives etc, mainly because I still had the cable from the PC power supply I was using and because they're pretty easy to get hold of. couldn't find a panel mount one anywhere though, so this supply just has a Molex cable trailing out the back of it.
With that job out the way I got back to thinking about my VCO. all my attempts at combining designs to make something that could potentially in some way be said to be mine had met with abject failure, so I decided to use someone else's schematic and PCB layout. My first inclination was Thomas Henry's VCO-1, but I didn't like the idea of using the completely obsolete CA3080 chip. The LM13700, which is more cheaply and readily available, is effectively two 3080s with bells and whistles. I toyed with the Idea of using this instead but I had no idea what to do with the other half, and it seemd a waste to not use it all.
Thomas Henry to the rescue! For he has designed another VCO with this in mind, the LM-VCO. unfortunately the schematic for this module is not available online, you must do as I did and purchase his book "An Analog Synthesizer for the 21st Century" which contains schematics for various modules which can be put together to form a fully featured modular synth. The book is available from Magic Smoke Electronics here, along with some others by the man himself.
I found a layout for the module here on the electro-music.com forum. I don't know if I already mentioned it, but this place is a goldmine for information. The people there are all pretty cool, and the forum just has masses and masses of helpful posts, layouts, schematics, theory stuff, the lot.
I decided at this point that it was time to up the ante in the PCB production department. I had been ironing on toner transfers to produce my boards, but I felt like having a go at using the UV photoresist method. With this technique the transparency is placed over a special pre-sensitised board and UV light is light is shone on it for a certain peroid, then the board can be developed like a photograph, with the UV-exposed portions of the coating dissolving away leaving nice clean tracks.
It's a simple little adapter board that allows half of the THAT 340 quad monolithic transistor array I have to fit the 5 pin design the circuit called for. Once the board was etched and drilled and the chip was in place, it was just a matter of solering some leads I snipped off LEDs into the end row to connect into the main board. It doesn't fit very well and I've had to mount it on a bit of a jaunty angle, but it does the job! The sine and triangle waves now look perfect and the 1v/oct tracking is good for about 4 octaves (nearly). At this point I connected the pulse and ramp pins to try out the other waveforms and found they didn't work. Hours of troubleshooting revealed a couple of errors in my soldering, but I'm still no closer to fixing them. I think there's either a break in the circuit somewhere that I can't find, or that general shoddy workmanship and the fact that some ofthe pads are half missing cos I used too big a drill bit for the holes is causing it te not work. Either way, I don't think it's getting fixed any time soon.
It's progress though! and in the name of progress I then moved on to another modules I've been meaning to get built properly; the sequencer!
Not to worry, I'm here again now with a fresh batch of information!
The power supply has been a resounding success. I built the new version of the board into its shoddy case after considerable faffing about with dodgy connections and misjudged cable lengths, to produce this:
...Told you the case was shoddy.
Looks aren't important in this case though, as it's only going to live under my desk to power my experimentations. Inside the box is the power supply circuit depicted in the last post, with the indicator LEDs taken on wires to the front panel (such as it is) and also the the rather large 60VA toroidal transformer I picked up on eBay. The transformer takes the 230v AC and gives two lots of 18v AC nd a 0v connection. These go to the input pins on the power supply, which converts the 2x18v AC to +15v, +5v and -15v, all DC.
I had issues deciding on connectors for the power output, as the sexy 4 pin mini XLR type connectors I like are rather expensive, and cheap standardised power connectors don't seem to be an easy thing to find in relatively small quantities. In the end I settled on Molex power connectors as used for PC hard drives etc, mainly because I still had the cable from the PC power supply I was using and because they're pretty easy to get hold of. couldn't find a panel mount one anywhere though, so this supply just has a Molex cable trailing out the back of it.
With that job out the way I got back to thinking about my VCO. all my attempts at combining designs to make something that could potentially in some way be said to be mine had met with abject failure, so I decided to use someone else's schematic and PCB layout. My first inclination was Thomas Henry's VCO-1, but I didn't like the idea of using the completely obsolete CA3080 chip. The LM13700, which is more cheaply and readily available, is effectively two 3080s with bells and whistles. I toyed with the Idea of using this instead but I had no idea what to do with the other half, and it seemd a waste to not use it all.
Thomas Henry to the rescue! For he has designed another VCO with this in mind, the LM-VCO. unfortunately the schematic for this module is not available online, you must do as I did and purchase his book "An Analog Synthesizer for the 21st Century" which contains schematics for various modules which can be put together to form a fully featured modular synth. The book is available from Magic Smoke Electronics here, along with some others by the man himself.
I found a layout for the module here on the electro-music.com forum. I don't know if I already mentioned it, but this place is a goldmine for information. The people there are all pretty cool, and the forum just has masses and masses of helpful posts, layouts, schematics, theory stuff, the lot.
I decided at this point that it was time to up the ante in the PCB production department. I had been ironing on toner transfers to produce my boards, but I felt like having a go at using the UV photoresist method. With this technique the transparency is placed over a special pre-sensitised board and UV light is light is shone on it for a certain peroid, then the board can be developed like a photograph, with the UV-exposed portions of the coating dissolving away leaving nice clean tracks.
I didn't have an expensive UV exposure unit, so I decided to give it a whirl with my mum's facial tanner - You know the sort of thing... like a mini sunbed for your face.I wasn't sure about what distance away to have the light or how long to do it for, so I just placed the transfer on the board with a sheet of glass over it to keep it held flat, then just stuck the tanner face down on top of it with the bulbs a couple of inches away from the board. I had a smoke and got the tray with the developer ready, took maybe 5-8 minutes? Miraculously it worked perfectly first time. The only slight problem is that my original transparency had little pinholes in it and these came out on the final board. Some of the traces are quite thin and looked almost broken withthe tiny holes, but I pushed on regardless, as is my way, and soon I had a fully etched, drilled and populated VCO board!
...It didn't work of course.
Well it did, just not very well.
The problem was that I didn't have the 5 pin monolithic transistor pair that the layout was expecting, so as botch I just used two random transistors with the emitters tied together. This resulted in an asymmetrical wave with no temperature compensation whatsoever. Even my breath on the transistor pair was enough to make the pitch fly about wildly!
A fix was needed, so I came up with this:
It's a simple little adapter board that allows half of the THAT 340 quad monolithic transistor array I have to fit the 5 pin design the circuit called for. Once the board was etched and drilled and the chip was in place, it was just a matter of solering some leads I snipped off LEDs into the end row to connect into the main board. It doesn't fit very well and I've had to mount it on a bit of a jaunty angle, but it does the job! The sine and triangle waves now look perfect and the 1v/oct tracking is good for about 4 octaves (nearly). At this point I connected the pulse and ramp pins to try out the other waveforms and found they didn't work. Hours of troubleshooting revealed a couple of errors in my soldering, but I'm still no closer to fixing them. I think there's either a break in the circuit somewhere that I can't find, or that general shoddy workmanship and the fact that some ofthe pads are half missing cos I used too big a drill bit for the holes is causing it te not work. Either way, I don't think it's getting fixed any time soon.
It's progress though! and in the name of progress I then moved on to another modules I've been meaning to get built properly; the sequencer!
Friday 30 December 2011
Power to the pins!
Ladies and gentlemen, I give you...
The WickVoltz Mk II:
Okay so that's not much to look at, but allow me to to elaborate...
After my previous power supply cock-up I decided the time had come to build my own. I based my schematic on (ahem...copied exactly) the schematic on Ken Stone's modular synth site and created my own PCB layout for it, which was this one:
The eagle eyed amongst you will spot that my circuit is missing two diodes that Ken Stone's has, and there is a very good reason for this; I couldn't fit them into the circuit and still have it look as nice as it does. Besides, they're only for protection in case some fool bridges the outputs, and who would do something like that?? (nervously kicks remains of old, dead power supply under the bed).
At this point I feel I need to talk about CadSoft Eagle. This is the the software I used to draw the lovely pictures you see above, and it really is a must for anyone who wants to design their own PCBs. It has a massive component library and the ability to download more component libraries from their website, and even create your own components. it can find flaws in your schematic as you design it and has a nifty auto-routing feature when it comes to the actual PCB layout stage. The only drawback I've found is that the UI is often a bit counter-intuitive. You'll find yourself scratching your head in the beginning looking for the most basic functions, butt they are there I promise you! And once you get used to it you'll find it fairly simple to create what you want. It comes in pro and freeware versions, and I've found the freeware version pretty easily takes care of my needs.
...I don't work for them or anything, it's just good!
So yeah, I created my PCB layout in eagle, printed it onto transparency film and ironed it onto a copper clad board to come up with this:
one acid bath later I had this:
Then I drilled holes and put all the components into place, to give me the final product:
Drop in image quality due to the batteries dying in my camera.
I connected the circuit to the 2x18v ac transformer I bought on ebay and to my immense surprise and delight it worked first time! Filled with excitement I began making a case to house the board and transformer. I don't have a pic of this at the moment, but it's basically the top part of a DVD player case bend round into something about twice the height but a third of the width. I then made front and back panels out of chipboard and fitted a switch to the front.
I connected up the circuit with the case wiring in place, ready to give a little smug smile and finish the whole assembly process, butt to my shock and horror it didn't come on properly and the transformer buzzed horribly! It seemed like there was a short somewhere in the positive regulator half of the circuit.
Long story short, I chased the fault around the whole circuit, and every time I thought I'd nailed it and the setup worked again, it would stop working straight away. My only explanation is that it was a faulty track, something I think was confirmed late in the day when I connected the transformer already switched on and the small spark this produced was enough to visibly blow a section of track off the board!
And so it is that I sit here patiently waiting for the Mk II to be etched, with fatter tracks and an extra regulator for a 5v line, it should be a winner. Also this time I'm going to tin the tracks with solder to protect them and aid conductivity. I'll post the results of this venture in the new year, along with a more detailed build guide with schematic and PCB layout and also a tutorial on etching.
Right now though I do believe the etching is done. There seem to be a couple of slightly dodgy tracks, but I'm gonna plow on regardless, maybe the tinning will save them!
Watch this space...
Tuesday 13 December 2011
Still alive!
I'm still here, still thinking about synths!
The project has taken a bit of a back seat for a bit to make way for the festive period, but I still found time to have a think about power supplies. I've been using the ATX supply so far but I've heard switching power supplies are bad for synths and linear is much better. I built the expo converter for the VCO and sort of got it half working, but the pitch drifted wuite a lot and it can't quite manage 1v/oct tracking. That's when it hit me that the circuits i'd based my design on were all designed for +/-15v power suppplies and I was only using +/-12v!
Scouring the internet for solutions I got to thinking about the old broken alesis mixer I took apart to scavenge passive components from. Turns out its power supply distributes +12v, -15v and +3.3v, but the +12v and +3.3v are tkaen from 15 and 5 volt regulators and then brought down, so it was a simple matter to cut the trace going to the power distribution connector for the 12v and 3.3v lines and run wires straight from the outputs of the voltage regulators to bring them up to the voltages I needed.
Needless to say I was massively pleased with myself, but then I noticed that I actually had +14.85v and -15.25v. I'm 99% sure that this is close enough to being right and would have made no difference to any circuit I was trying to make with it, but being a perfectionist I could I would have a go at adjusting it.
Several ill advised resistors later the whole thing is bricked. One of the capacitors on the power supply board has bulged out and deformed underneath and the transformer itself has given up the chase. All is not lost though! I've ordered a new transformer which I believe will do the job, and can probably scavenge another capacitor. If it turns out that the circuit still won't work, then this also not a problem as I have more voltage regulators etc so I can use the transformer to build a new supply from scratch.
...after christmas.
The project has taken a bit of a back seat for a bit to make way for the festive period, but I still found time to have a think about power supplies. I've been using the ATX supply so far but I've heard switching power supplies are bad for synths and linear is much better. I built the expo converter for the VCO and sort of got it half working, but the pitch drifted wuite a lot and it can't quite manage 1v/oct tracking. That's when it hit me that the circuits i'd based my design on were all designed for +/-15v power suppplies and I was only using +/-12v!
Needless to say I was massively pleased with myself, but then I noticed that I actually had +14.85v and -15.25v. I'm 99% sure that this is close enough to being right and would have made no difference to any circuit I was trying to make with it, but being a perfectionist I could I would have a go at adjusting it.
Several ill advised resistors later the whole thing is bricked. One of the capacitors on the power supply board has bulged out and deformed underneath and the transformer itself has given up the chase. All is not lost though! I've ordered a new transformer which I believe will do the job, and can probably scavenge another capacitor. If it turns out that the circuit still won't work, then this also not a problem as I have more voltage regulators etc so I can use the transformer to build a new supply from scratch.
...after christmas.
Friday 25 November 2011
Exponentially Challenged
Despite my best efforts, I can't seem to get a working exponential converter hooked up. The majority of the designs I can find online use OTAs and have an output current rather than a voltage, so are useless. The one useable design I have found is this one on the EA site, but I can't seem to get it working. I'm using a TL084 quad op amp for it rather than having an OP-7 for the final stage, so maybe that's the problem, though it does look like any standard kind of op amp should fit in there!
I'm considering a full redesign of the VCO now using OTAs. Saw a triangle/square VCO schematic in the LM13700 Datasheet that looks promising:
If I can make that work then I can keep my existing triangle-to-sine circuitry and find a new exponential converter design. Then I can design the PCB, get two of the damn things onto a board and be done with the VCO section! THEN I can finish my sequencer!
I'm considering a full redesign of the VCO now using OTAs. Saw a triangle/square VCO schematic in the LM13700 Datasheet that looks promising:
If I can make that work then I can keep my existing triangle-to-sine circuitry and find a new exponential converter design. Then I can design the PCB, get two of the damn things onto a board and be done with the VCO section! THEN I can finish my sequencer!
Wednesday 23 November 2011
Hmmm...
Thinking about it a bit more, I should probably finish the VCO first, as really I want to use 12 position rotary switches hooked up to resistor ladders for the steps on the sequencer, and I won't know what values of resistors to use or be able to test and fine tune it until I have the VCO built with a proper 1v/oct input.
Also here's a test vid of the original 4 stepper:
Gutted I didn't think to record a vid when I switched in a smaller capacitor and went into hyperspeed!
Also here's a test vid of the original 4 stepper:
Gutted I didn't think to record a vid when I switched in a smaller capacitor and went into hyperspeed!
Sequence me uppah!
Right, so the VCO is finished design-wise; I've got the thing laid out half on stripboard half on breadboard and the schematic is done in Eagle. Now I just have to design the PCB and I'm off and away!
In the meantime I've decided to expand my little sequencer. As I said in the last post I breadboarded a little 4 stepper to play with. Here's the whole setup as it was looking:
So I've now done a stripboard layout based on the Same schematic, added some resistors for the LEDs and an 8 position rotary switch to select the number of steps by connecting the reset pin to one of the the outputs, which gives me this:
Apologies for the sideways-ness. As you can see I've left plenty of room on the board, as I'm planning to add another chip and upgrade to 16 steps.
I was a bit short on potentiometers so I just wired up the first four as a tester, and the whole thing seemed to be working perfectly, apart from the fact that I couldn't make a four step sequence! 3 steps worked fine, and when i turned the switch to 5 that worked fine, but for some reason 4 gave me the whole ten steps! not even eight! the full TEN! I triple checked all the connections and decided maybe I'd static damaged the 4017 chip, so I swapped it out for another one but must have had a wire touching the underside of the board or something because then something went bang. After much chin scratching and another 4017 replacement I realised it had been the 555! swapped that out and the whole thing is working fine now. Just need to buy a few more potentiometers and find a box to put it in and we're rockin'!
It may seem like I've neglected the VCO a bit to work on this, but it doesn't matter how nice my sine wave is if I don't have any way to make music with it. having this sequencer set up will help me get more of an idea of how stuff will sound as I progress through the rest of the project.
Also, I just realised that by giving it an external clock input hooked to an audio output from my computer I can send a pulse to it on every beat (or 1/2, or 1/4, etc) so that the sequencer will be in time with a midi track.
HOW BLOODY COOL IS THAT!
In the meantime I've decided to expand my little sequencer. As I said in the last post I breadboarded a little 4 stepper to play with. Here's the whole setup as it was looking:
So I've now done a stripboard layout based on the Same schematic, added some resistors for the LEDs and an 8 position rotary switch to select the number of steps by connecting the reset pin to one of the the outputs, which gives me this:
Apologies for the sideways-ness. As you can see I've left plenty of room on the board, as I'm planning to add another chip and upgrade to 16 steps.
I was a bit short on potentiometers so I just wired up the first four as a tester, and the whole thing seemed to be working perfectly, apart from the fact that I couldn't make a four step sequence! 3 steps worked fine, and when i turned the switch to 5 that worked fine, but for some reason 4 gave me the whole ten steps! not even eight! the full TEN! I triple checked all the connections and decided maybe I'd static damaged the 4017 chip, so I swapped it out for another one but must have had a wire touching the underside of the board or something because then something went bang. After much chin scratching and another 4017 replacement I realised it had been the 555! swapped that out and the whole thing is working fine now. Just need to buy a few more potentiometers and find a box to put it in and we're rockin'!
It may seem like I've neglected the VCO a bit to work on this, but it doesn't matter how nice my sine wave is if I don't have any way to make music with it. having this sequencer set up will help me get more of an idea of how stuff will sound as I progress through the rest of the project.
Also, I just realised that by giving it an external clock input hooked to an audio output from my computer I can send a pulse to it on every beat (or 1/2, or 1/4, etc) so that the sequencer will be in time with a midi track.
HOW BLOODY COOL IS THAT!
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