The Sound One

bijlevel

Yesterday I received the SX-150 Mark II and I discovered I was misinformed about this device being based on SN76477N chip. A bit of a disappointment, but the SX-150 has a Line In and so I connected the Sound One. This yielded many interesting sounds because it seems that the Line In audio is modulated by the SX-150. How exactly I have yet to find out. I'm also working on MIDI to CV to control the Sound One with MIDI, but I have found out that the world of MIDI to CV has a lot of pitfalls. The software approach of Silent Way (http://www.expert-sleepers.co.uk/silentway.html) seems promising, but I have to dive deeper into this subject.

bijlevel · Posted: Wed Jan 28, 2015 6:17 am Post subject: CV for SoundOne

I want to apply a CV to the SoundOne. From the datasheet of the SN76477N I understand that pin 16 accepts this CV, but (and here it shows I'm still rather inexperienced) in the schematic of the SoundOne I see that this pin is already in use. Also the datasheet describes an alternative method for applying CV, namely using pin 21. But again this pin is also in use in the schematic of the SoundOne. So in short, can someone tell me how to adapt the schematic to accept CV, but keeping the original design intact? Thanks a lot in advance!

elmegil · Posted: Wed Jan 28, 2015 8:10 am Post subject:

In this circuit, Thomas is controlling the VCO frequency with R4, which is sinking current from pin 18. I don't know enough about the theory of operation to give you a definitive answer, but I would suggest possibly something to experiment with:

Your CV source needs to be inverted (between ground and -9V), so go through an op amp inverting buffer, and then connect the output to the -9V side of R4 if you want to be able to attenuate it after the buffer.

You need the 4.7k to keep some offset more negative than ground, so the transistor continues to conduct. So don't connect the op amp directly, or even through a 39k resistor. You might try summing to the transistor emitter, however, if you're sure you can .

bijlevel · Posted: Wed Jan 28, 2015 9:45 am Post subject: CV for SoundOne

Thanks for the input! Maybe I didn't express myself clearly. By keeping the original design intact I mean I want to be able to switch between controlling the VCO frequency by external CV and the way Thomas Henry designed it. This means probably disabling (by means of a switch) the circuits connected to pin 18 and pin 16 and "just" feed the CV to pin 16. But I am, because of my inexperience, quite unsure if this will work. Of course I just can experiment, but a solution from experienced people seems preferably, isn't it?

Thomas_Henry · Posted: Wed Jan 28, 2015 6:30 pm Post subject:

Hi,

Pin 16 is worthless for voltage control, having a range of a piffling 10:1. On the other hand, by employing an exponential current sink from pin 18, you can achieve voltage control over a 10,000:1 range. This is what I did for the SN-Voice. See:

http://www.birthofasynth.com/Thomas_Henry/Pages/SN-Voice_main.html

Messing with pin 16 also upsets the pulse width business. There is a tradeoff between frequency range and pulse width range.

Thomas Henry

bijlevel · Posted: Thu Jan 29, 2015 6:31 am Post subject: CV for SoundOne

Thanks for the link! I did find in the schematics the part that deals with the CV. I will try to build this part as a kind of separate interface for the SoundOne. Maybe there is even room for it in the case I have build for the SoundOne.

Starspawn · Joined: Jun 14, 2013 Posts: 85 Location: Oslo

Thanks! Ive got a spare SN Chip after building the SN Voice and Controller.
Also built the Quadrature function genereator, VC Phaser, LFO controller and working on the 8038 LFO (Good value in that 21. century book Wink

)

If it wasnt for people like Thomas sharing their schematics I would never have learned stripboarding or the little circuit functions I know now.

bijlevel

I finally constructed the Sound One. Designing and making a front panel and also a case took also a long time. But everything is working now, maybe not always exactly as expected but every control does 'something' and the sounds variations this device is capable of are almost endless. I still have two SN76477's left. I'm thinking of building two SoundOne's, but wonder if there are interesting ways of combining two Sound One's, besides combining the audio output. Maybe some of you experts can suggest better or interesting ways! Thanks in advance!

bijlevel

My 'one shot' (gate switch) does not consistently fire just one shot and I wonder why this is. If I touch the button just very briefly sometimes it fires just fine, but also very often the sound continues, therefore not reacting to the Att/Delay settings. If I keep the button pressed down and then release the button, again sometimes the sound 'dies' according to the delay, but also it happens that the sound continues. I'm pretty sure my button is OK, just a simple momentary switch, so what could be the cause. Has it to do with the transistor or the values of the resistors and/or the capacitors in this particular part of the schematic? Thanks for any input!