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 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
Experiences with my first MFOS VCO
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friedo



Joined: Sep 28, 2013
Posts: 7
Location: Brooklyn, NY

PostPosted: Sat Sep 28, 2013 5:48 pm    Post subject: Experiences with my first MFOS VCO Reply with quote  Mark this post and the followings unread

Hi folks,

I got bit by the modular synth bug and I've been reading these boards for the past few weeks. Lately I finished my first project, the MFOS VCO!

Overall my experience with it was pretty good. I made only a couple mistakes, which were easily tracked down and corrected despite my extremely limited electronics experience. It sounds great! I put a short video demonstrating the oscillator up here:

http://www.youtube.com/watch?v=hMMRCXt91iA

I've ordered some more boards and am going to start assembling them in the coming weeks. I'm going to build a custom design with two of everything, so I can have a fully stereo signal chain.

So there will be two of each VCOs, LFOs, VCAs, VCFs, and ADSRs. Those modules will probably all come from MFOS. I also have a plan for building my own 4x8 sequencer based around an Arduino and some 16-bit DACs.

I'm doing the front panels via Front Panel Express, and my next video will show off my fully-assembled dual-VCO module.

One thing I'm curious to find out is why my VCO seems to max out at only around 14kHz. Not sure if that's due to me or maybe my crappy multimeter.

I really need to get an oscilloscope I guess. Shocked
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ashleym



Joined: Aug 20, 2009
Posts: 181
Location: uk

PostPosted: Sun Sep 29, 2013 2:37 am    Post subject: Reply with quote  Mark this post and the followings unread

Good luck with this.

If your VCO shows a maximum frequency of 14 kHz that is good and probably correct. The 14k is the fundamental frequency of the tone. Above that you will have harmonics. Concert A on a piano is 440hz but a piano will produce a lot of harmonics or overtones above that creating the rich timbre we know from a piano. Back to your 14k tone, the first overtone to that will be 28khz and beyond your hearing ( there is debate about the upper range of our hearing and how overtones affect what we hear but that's another debate!) so the 14k will be plenty good enough.

If I could comment on your plans, I would have everything in one signal path- a mono one rather than a stereo one. You will get a lot more tonal variation from mixing 2 VCOs and syncing them than you ever will with 2 mono channels. Look at ALL the classic synths and they will pile on the oscillators rather than going for a stereo chain. By all means do the stereo thing but have that as an option rather than the fundamental design

Also I think you will need a few mixers, either for the stereo out or to help combine audio or control signals. By this I mean mixing the 2 VCOs to going into a filter (or how about 1 vco unfiltered mixed with another heavily filtered etc etc) for the audio chain. And for control you might need to vary the amount an ADSR affects a filter cut off or add some LFO modulation too. And control the proportion of both or invert the ADSR output etc

Sorry if you know this already!!

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friedo



Joined: Sep 28, 2013
Posts: 7
Location: Brooklyn, NY

PostPosted: Sun Sep 29, 2013 1:33 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
Good luck with this.


Thanks!

Quote:

If your VCO shows a maximum frequency of 14 kHz that is good and probably correct. The 14k is the fundamental frequency of the tone. Above that you will have harmonics. Concert A on a piano is 440hz but a piano will produce a lot of harmonics or overtones above that creating the rich timbre we know from a piano. Back to your 14k tone, the first overtone to that will be 28khz and beyond your hearing ( there is debate about the upper range of our hearing and how overtones affect what we hear but that's another debate!) so the 14k will be plenty good enough.


Ah, that makes perfect sense of course. This is the first ever VCO I built so I wasn't really sure what to expect.

Quote:

If I could comment on your plans, I would have everything in one signal path- a mono one rather than a stereo one. You will get a lot more tonal variation from mixing 2 VCOs and syncing them than you ever will with 2 mono channels.


My plan is to make it totally modular (3.5mm patch cables) so I will be able to do two separate channels or mix things together, depending on my mood. Very Happy

Thanks for your comments - I'll post more videos over the coming weeks as I build more stuff.
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roglok



Joined: Aug 28, 2010
Posts: 159
Location: uptown

PostPosted: Mon Sep 30, 2013 7:06 am    Post subject: Re: Experiences with my first MFOS VCO Reply with quote  Mark this post and the followings unread

friedo wrote:

http://www.youtube.com/watch?v=hMMRCXt91iA
[...]
I really need to get an oscilloscope I guess. Shocked


Nice video! While your "sinewave" does indeed sound interesting, I don't think it's sine shaped at all. There seem to be lots of overtones in your sine signal. Did you try to adjust the trimmers for least harmonic content? The easiest way to do this is using a scope, but trimming by ear works quite well, too...
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friedo



Joined: Sep 28, 2013
Posts: 7
Location: Brooklyn, NY

PostPosted: Mon Sep 30, 2013 7:09 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi roglok,

Thanks for the comment. I haven't yet tried adjusting the trimmers; I figure I would need to get some kind of scope first to do it in any kind of sensible way. I certainly don't have enough experience to do it by ear.
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roglok



Joined: Aug 28, 2010
Posts: 159
Location: uptown

PostPosted: Mon Sep 30, 2013 7:18 am    Post subject: Reply with quote  Mark this post and the followings unread

friedo wrote:
Hi roglok,

Thanks for the comment. I haven't yet tried adjusting the trimmers; I figure I would need to get some kind of scope first to do it in any kind of sensible way. I certainly don't have enough experience to do it by ear.


Well, a scope will help a great deal, but as Ray himself says:

Quote:
It is interesting to adjust the waveform to where you believe it sounds best and then tweak a little. You will be suprised to see how little distortion it takes to start adding overtones to the fundamental frequency. Adjust until you hear the purest tone with the least overtones.


I think he is right. With a bit of experimentation and concentrated listening you should be able to approximate a distortion free sinewave. Keep in mind, however, that you will first have to adjust the triangle wave, since the sine is derived from that.
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prgdeltablues



Joined: Sep 25, 2006
Posts: 176
Location: UK
Audio files: 11

PostPosted: Tue Oct 01, 2013 1:38 am    Post subject: Reply with quote  Mark this post and the followings unread

If you have a computer and a way of recording audio, which you obviously do, then instead of a scope you can use one of the free audio editing programmes around (Audacity is my own choice) and zoom in on the waveform. You'll see clearly how well shaped it is. It will also give you an FFT spectrum, so you can see how strong the harmonics are. A bit cumbersome if you're trying to trim a VCO, but might be worth it as a check. But as said, the purity of a sine-wave signal is quite distinctive by ear.

Peter
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friedo



Joined: Sep 28, 2013
Posts: 7
Location: Brooklyn, NY

PostPosted: Tue Oct 01, 2013 7:56 am    Post subject: Reply with quote  Mark this post and the followings unread

Great idea! Thanks!
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