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 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
Common places for shorts in a SoundLab
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Antimon



Joined: Jan 18, 2005
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PostPosted: Sat Apr 18, 2009 4:12 am    Post subject: Common places for shorts in a SoundLab Reply with quote  Mark this post and the followings unread

So I've made a second attempt at doing a SoundLab (ordered two PCBs a couple years back), and once again I am enjoying the silence as I hook it up. This time around I noticed that the batteries became to hot to touch, so I checked the resistance between + and - and it's something like 25 kOhm, which I guess is too little. So, a short somewhere I am guessing.

The first question is: will this have broken some component on the board?
Second: any other experience with short circuits in a SoundLab? Is there some position on the board that is more prone than others for shorts?
Third: should I take up knitting instead? (I actually saw this low resistance between + and - early on while doing the VCOs, since I've painstakingly measured the contacts of every component directly after soldering it. My procrastinating brain told me I could deal with this later - the logic of a moron).

/Stefan

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Antimon



Joined: Jan 18, 2005
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PostPosted: Sat Apr 18, 2009 8:49 am    Post subject: Reply with quote  Mark this post and the followings unread

Never mind! Very Happy I pulled out the wires from the front panel and resoldered them again, component by component, checking each in my new scope as I finished it. Now I got sound! too much coffee

Everything's not sounding exactly as I thought it would, and the envelope is really really slow, but this is as much of a success as I ever hoped. Wohoo! Very Happy Very Happy

/Stefan

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seraph
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PostPosted: Sat Apr 18, 2009 11:30 am    Post subject: Reply with quote  Mark this post and the followings unread

shorts Question

Posted Image, might have been reduced in size. Click Image to view fullscreen.

you want to play a SoundLab wearing shorts Question

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Antimon



Joined: Jan 18, 2005
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PostPosted: Sat Apr 18, 2009 1:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

Of course! That's the official SoundLab uniform, you know. Wink

Anyway, I fixed the envelopes - misread 500 Ohms as 500 kOhms (duh!). It's sonic mayhem here! The LFO is doing stuff it probably shouldn't do, but I like it so I'm going to leave it as it is. Only thing left fixing is the noise generator, but I rarely use those anyway...

Attaching some pics of my patented crows nest soldering technique, the finished item (built into my mother's cookie can) and a sample. Can you tell I'm happy I finally managed to pull off (sort of) an electronics project? Very Happy

/Stefan

Edit: missed adding the final glorious picture Wink


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RF



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PostPosted: Sat Apr 18, 2009 6:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

Great Job, Stefan!
Looks good in that cookie box - and I'm glad you were able to solve the problem.
Knitting is overrated - you might as well build more stuff.
You mentioned the 'silence' on the attempt a couple years back...did you ever get that one working?

bruce

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Antimon



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PostPosted: Sat Apr 18, 2009 11:49 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks! Very Happy

The silence (and most of all really hot batteries) was solved by desoldering all the wires from the lid on the board, and the resoldering them more slowly component by component. So I started with the wires for the batteries and the VCO1. When I had those on, I hooked the scope to the output from VCO1, turned the thing on and looked at the wwaveform, which looked like an ok sawtooth with a little spike at the top.

Then I did the VCO2, and checked that in the scope, then the filter, EG, Noise, LFO and the rest. All the time feeling the batteries to see if they were going hot, which they never did. After a bit of headscratching and some small fix I had the thing making sound.

I still a bit confused about the EG. Ray says in his specific troubleshooting tips that I should se 8 or 9 volts at pin 1 of C2 and the ground, but I only see like 1 volt. At first I thought that was why the envelopes were so slow, but I traced that to the resistor mentioned earlier - it's still a low voltage there, but it works just like I would think it should: a clear envelope ramp wherever I try it out (VCAm VCO etc), with reasonable values for time and amplitude.

A similar confusion is there when I troubleshoot the noise generator. It says I should see a positive voltage on the emitter of Q7, but it's negative.

The LFO is behaving a bit strangely, but I don't think I want to troubleshoot that one, since the sounds are pretty cool.

/Stefan

Edit: typo

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Pehr



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PostPosted: Sun Apr 19, 2009 12:14 am    Post subject: Reply with quote  Mark this post and the followings unread

Antimon wrote:
The LFO is doing stuff it probably shouldn't do, but I like it so I'm going to leave it as it is.


how is it behaving?

note that the attenuation of the LFO and envelope is a little special so you will not get the expected result when connecting them to the oscillators. This is due to that they attenuate towards -9V instead of ground. I've modified those to choose either.

Also, regardnig the LFO, you have to have the ramp/tri/saw switch in 'tri' position in order to get 50/50 squares out of it.

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Antimon



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PostPosted: Sun Apr 19, 2009 8:35 am    Post subject: Reply with quote  Mark this post and the followings unread

When I tweak the LFO amplitude, the pitch of the oscillators slides upwards and starts to sound like it's modulated by something. Turning the LFO frequency mostly does nothing, sometimes (when I am having a complex sound so it's difficult to hear exactly what's happening) I hear a very weak change up or down in pitch somewhere.

I think I'm going to open it up again and see if I can find what this is - esp. since the CV in for oscillator 2 doesn't work.

I'll leave it for a day or two though.

Stefan

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PostPosted: Mon Apr 20, 2009 10:00 am    Post subject: Reply with quote  Mark this post and the followings unread

Tried out some CV from ChucK, and now the noise generator has decided to come alive all by itself! Instead, the resonance in the filter has decided to close down Confused Well, well. Anyway, if anyone's wondering what a simplistic marriage between ChucK and a slightly broken MFOS SoundLab looks/sounds like, here it is. I love this! Very Happy

Code:
SqrOsc cv1 => dac.chan(0);
SqrOsc cv2 => dac.chan(1);

0 => cv1.freq;
0 => cv2.freq;

[0.5,0.5,0.6,0.4,0.5,0.7,0.4] @=> float pitches[];
[1,0,1,0,0,1,0,1,1,0,1,0,1,0,0,1] @=> int gates[];

0 => int pitchIndex;
0 => int gateIndex;

while (true) {
        0.05::second => now;

        pitches[pitchIndex++] => float pitch;
        gates[gateIndex++] => int gate;
        if (pitchIndex >= pitches.cap()) {
                0 => pitchIndex;
        }
        if (gateIndex >= gates.cap()) {
                0 => gateIndex;
        }
        gate => cv1.gain;
        pitch => cv2.gain;
        0.05::second => now;
        0 => cv1.gain;
}


/Stefan


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Antimon



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PostPosted: Fri Apr 24, 2009 9:45 am    Post subject: Reply with quote  Mark this post and the followings unread

Just reporting that I now have the thing working perfectly! Very Happy One switch was slightly defect, meaning that it was always 'on' even though I flipped the switch. I noticed that pushing the wires changed the sound, and traced the source by push fewer and fewer wires until I noticed that it was the wire connected to that switch that changed the sound when I pushed it, or rather the pin on the switch needed to be pushed a bit to open the circuit. I solved it by pushing some elastic plastic in between the pins. This resolved the problem with oscillator 1 always being modulated by the LFO.

My final worry was that the LFO frequency knob didn't seem to change the frequency much - just a little. I traced this to the R94 resistor, where I had done the exact same error as with R6 and put in 500 kOhm instead of 500 Ohm. I only had a 470 Own resistor in my cache, and put that in, and now I have a working, nice sounding SoundLab in the can.

Now, what project should I take up next... I'm starting to get hooked on this - it's actually possible to do stuff and make it work! Smile

/Stefan

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