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 Forum index » DIY Hardware and Software » Developers' Corner
any working masa921 Micro VCO??
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cyclic



Joined: Mar 15, 2015
Posts: 95
Location: hobart

PostPosted: Mon Mar 23, 2015 4:31 am    Post subject: any working masa921 Micro VCO?? Reply with quote  Mark this post and the followings unread

TL;DR:

has anybody out there got this super simple VCO to work:


http://masa921.sitemix.jp/image/kairo/microvco1.gif

http://electro-music.com/forum/viewtopic.php?highlight=masa921&t=16600




excessively verbose version:

hi,

i've been teaching myself electronics this last year by finally doing something which interests me - making weird bleepy counds. Don't forget that this is a learning project for me, not just a bleepy noise making one!

I'm making what I guess would be called a noise box, and although some of you may think this is ridiculous, I'm doing so out of at least partly recycled materials. A good part of my resource base is a couple of old stereo amps which I stripped down.

Anyway, thats just the background to what I'm working on now.

I need some more VCOs and LFOs, and I would also like to play with more complex rhythms.

So from what I gather, the thing for me to do is get myself some logic gates, chuck an LFO stream of PWMed squares (ie gates) and triggers into them and see what comes out the other side.


To this end, I plan to build myself an 'oscillator bank' of 3 or 4 LFOs. Does it have another name? I figured that if I could have dual purpose VCO/LFOs that would be considereably more useful in the long run, as I've also decided that I need more than my current grand total of one VCO! So I allowed myself to feature creep into a bank of 3 or 4 VCO/LFOs. It then occured to me (only after looking at lots of simple VCO schematics) that having a hard sync would probably be quite useful to keep the beats from getting too all over the place by injecting a slow reset pulse spread across the entire bank.
I'm not really worried about tracking or stability.

I still want it to be SIMPLE, as far as possible, and I want to be able to use as much salvage as possible. I certainly DONT intend it to be a solely salvage job as I quickly learnt that this is impossbile. But this principle WILL guide some decisions which other people may not understand or appreciate...

To this end, my current front runner as VCO core is Masa921's microVCO. There is a very 'robust' reason for this. I have a HEAP of 2785 and 1175s in my box which I pulled from an old amp, and his is the first analog synth project I have seen which actually specifies these particular parts. Woot! It would please me immensely to use up a huge chunk of them on this kind of thing.

I have just ordered some (very overpriced) J-FETs as he specifies. Maybe I could have used something cheap and local but I don't actually understand them enough to work that out without trial and error.



If Masa fails me, I will be next going for the 'simple saw VCO' which I already have built as a bench test unit, or if that fails too maybe the 40106 simple saw VCO or 'last resort' the 3046 arp axxe clone.



Once I've got a vco core sorted, if a capacitor swap will do a decent LFO range as well I will then use a comparator on it to get my square and PWM, and also probably give one or two of the units a triangle and maybe even a sine.


Does anybody out there have anything to say about me plans afoot? Does anybody have any more schematics to throw my way and make me rethink the whole project yet again?

sorry if that was waaay too long!
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m.o



Joined: Jul 05, 2014
Posts: 44
Location: Sweden

PostPosted: Wed Mar 25, 2015 3:48 pm    Post subject: Reply with quote  Mark this post and the followings unread

I can't seem to get that first link to work...
One possible objection to a very compact discrete design could be that it can possibly be harder to understand and 'debug' than a 'traditional' design, but as said I don't know about this particular circuit.

It sounds like you are well on your way so no objections to that, just keep building and learning!

You have a whole list of different VCO-schematics here on electro-music:s wiki.
For simple ones maybe take a look at the VCO 4069 by Rene Schmitz, also check out his own webpage it has quite a few more simple:ish designs that I find very inspiring.
Also check out musicfromouterspace.com he has very good (text) circuit-descriptions that go along with the various circuit schematics there.
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cyclic



Joined: Mar 15, 2015
Posts: 95
Location: hobart

PostPosted: Thu Mar 26, 2015 4:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

yes,
I've seen those archives, and was very tempted by the 4069 oscillator, which is still on my b-list, but I'm trying to use componenets that I have, rather than blindly buy components and copy schematics..

As I said, its so I can learn about it too, and move on from rote copying...

Right now I'm just waiting for JFETs,then I'll try out Masa921 and Takeda's designs, before moving on to other possibilities.

I've also since realised that I have 4 2SA798s (dual NPN trannies) which would make another kludged up thomas henry 555-VCO much simpler to build (or at least, take the transistor matching routine out of the equation.) I should have used one last time, but didn't understand at the time what I had, nor what I was doing.
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donpachi



Joined: Jul 16, 2009
Posts: 81
Location: Marburg
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PostPosted: Fri Mar 27, 2015 11:12 am    Post subject: Reply with quote  Mark this post and the followings unread

2SA798 is a dual PNP! But you could probably trade some for LM394, SSM2210 or 2SC1583, which are common matched dual NPNs. Or build a Thomas Henry VCO-1 Cool
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donpachi



Joined: Jul 16, 2009
Posts: 81
Location: Marburg
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PostPosted: Tue Mar 31, 2015 7:03 am    Post subject: Reply with quote  Mark this post and the followings unread

Whoops! The TH 555 VCO actually also requires matched PNP transistors, so your 2SA798 is indeed fine for this purpose.
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cyclic



Joined: Mar 15, 2015
Posts: 95
Location: hobart

PostPosted: Thu Apr 02, 2015 4:25 am    Post subject: single 40106 with triple oscillator, NAND AND NOR
Subject description: oooh! logic!
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Oh yep, I've already built a TH 555VCO, it is my main VCO presently, and I considered building a stripped back version for this project but it is just too complex for what I am after.
I did it on stripboard and it took me a looong time, but fortunately worked first time.
I wish I'd realised what I had when I did my first one as matching the transistors was pretty time consuming for me, and I didn't get a great match with what I had on hand..
If/when I make another case to fit it I may well build another later.

Anyway, back to the project on hand:

I got my 2sk118s in the mail (at $2+ a pop, aii!) so got around to properly testing the masa921 micro vco... I couldn;t get it to work, I don;t know why AND I had some really good magic smoke coming out of 5/6 transistors all at once, so I pretty much canned that one!
I was trying to build it with a split +_12v, as oppposed to his single supply and midpoint reference so I don;t know if I screwed up there.

So then I moved up a peg and built up takeda's version which is available if you search for it here. I just did one VCO to test it, and it certainly works fine and as advertised, BUT even with a bit of capacitor juggling I could only get a useful range of about 20-3.5khz from it with about 3-4v p2p. With very careful pot turning I could get to about 5.5khz but the peak to peak dropped off to <2v p2p.
I also had crack at LFOing it with a big capacitor, and although it provided the rate, the capacitor discharge was way too rapid to provide a useful lfo curve. Even if I had chucked the main ramp into a comparator it still wouldn;t have given me a particularly useful output at these rates.
I don;t actually know what else to try to drag a VCO down into an LFO range.

I've got one of the single op-amp saw VCOs already sitting on my bench as a bare stripboard test unit, and it also only gives a similar range, so I'm not going to bother breadboardingthat one either for my use.

So, my next option is the simple 40106 oscillator. I haven;t breadboarded it yet, but it claims to have a very wide range, so thats a good start, and hopefully it will go to a useful LFO rate with a bigger cap.

If not I'm not sure what to do next: simple non VC-LFO? suboctave generator/pulse divider to bring my rates down with a secondary module?

ANYWAY, because, fundamentally this is both a learning process and a weird noise making one, I thought I'd better actually try out something to test my basic assumption: that I want logic gates!

so, with Ray's help on the MFOS mickey mouse logic page I kludged together 3 40106 oscillators with different caps - full audio range easily done on each, although very rapid in the upper end (need log pots I think) and then popped on a NOR gate and NAND AND combo.
AWESOME!
I'm very happy with the basic concept and I have certianly convinced myself that logic gates are what I am after here. I also realise now that as well as three separate LFO/VCOs I am going to want a pulse divider so I can have some calm amongst the crazy logic storms.

SO.....

plan now: test out the 40106 VCO for LFO rates (easily found elsewhere on em) and put three of them on a breadboard, along with some blinky lights,
be a bit more planned with some logic gate tests (more blinkies too!)
maybe along with a 4024 for /2-/4 /8 /16 even?

I've got a nasty sample of my first playtime which I'll pop up too.
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