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 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
Weird Sound Generator - Wacky Osc & Filter Questions
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Bogus Noise



Joined: Jun 03, 2009
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Location: Sheffield

PostPosted: Tue Jan 21, 2014 11:19 am    Post subject: Weird Sound Generator - Wacky Osc & Filter Questions Reply with quote  Mark this post and the followings unread

Just been finishing up some waaaaay old projects, and dug out this WSG I started long ago (using Andrew Sharp's stripboard layout), with a view to actually finishing it. It never worked right at the time, but I know a bit more these days and have gone through the Troubleshooting section of the MFOS page, and fixed a couple of things, but got a couple of other questions remaining.

Firstly, for each voice, the Wacky Frequency acts like an audio oscillator, and disappears if I turn the knob up full. However, the Troubleshooting page says:

Quote:
1. Look at on the scope or listen to point: U1-B pin 4. Adjust Wacky Frequency pot R1 until you see and/or hear it oscillating slowly (a few hertz per second).

So does this mean the Wacky osc should be more like in the LFO ranges? Turning the pot all the way anti-clockwise only goes to something like 100hz, definitely not going to subsonic frequencies!



Secondly, the filter is really muffled. I’ve traced as much as I can but cannot find why. I’ve used a TL071 instead of an LM741, which I didn’t think would affect it. It seems like the pot isn't fully opening the cutoff frequency. The signal going into the filter is as expected.

With both problems, I’ve checked and double checked the wiring, panel wiring and schematics, but haven’t found anything wrong so far.



So yeah... any thoughts?

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elmegil



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PostPosted: Tue Jan 21, 2014 2:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

I thought Zany was the LFO, what with the 1uF cap rather than .022uF....

Unfortunately my WSG is in an enclosure that is a huge pain to open up, or I would take a frequency range measurement of just that oscillator.
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Bogus Noise



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PostPosted: Tue Jan 21, 2014 2:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yeah that's right, Zany is the LFO, Wacky is the one that gates the Weird oscillator, or can also be sent directly to the filter.

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

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elmegil



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PostPosted: Tue Jan 21, 2014 3:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

It just so happens that my battery is dead, so I will have to open up the thing anyway. I'll take measurements of all 6 oscillators and see what the min/max frequencies are. I'd swear mine went down to lower than 100Hz, but not subaudio.
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Bogus Noise



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PostPosted: Tue Jan 21, 2014 3:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ok cool, thanks for that Smile

100hz was a guess, but it's not in the area I was thinking from the Troubleshooting section, as that implies you have to turn it up to get it to cycle only a few times per second. But yeah, from the schematic the Wacky and Weird oscillators are pretty similar, just there's two 4.7k resistors either side of the pot on the Weird one and one 4.7k on the Wacky one.

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elmegil



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PostPosted: Tue Jan 21, 2014 4:08 pm    Post subject: Reply with quote  Mark this post and the followings unread

Voice A Osc 1 goes 84 Hz through 8 KHz.
Osc 2, 58 Hz through 14KHz
Osc 3, 1.1 Hz through 264 Hz

Voice B Osc 1, 86 Hz throug 8 KHz
Osc 2, 56 Hz htrough 15 KHz
Osc 3, 1.2 Hz through 271 Hz
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Bogus Noise



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PostPosted: Wed Jan 22, 2014 3:11 am    Post subject: Reply with quote  Mark this post and the followings unread

Cool, cheers! Much appreciated Smile

Will check mine when I'm back at the work bench.

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Bogus Noise



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PostPosted: Wed Jan 22, 2014 3:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ok, I'm getting the below results:

Osc 1 - pin 2 98hz - 11khz
Osc 2 - pin 4 100hz - past 15khz, then stops oscillating
Osc 3 - pin 6 <20hz - 350hz
Osc 4 - pin 12 102hz - 11khz
Osc 5 - pin 10 110hz - past 15khz, then stops oscillating
Osc 6 - pin 8 <20hz - 350hz

It probably makes me happier than it should that I guessed it being around 100hz Laughing

But yeah, similar results to yours, so I guess it's working right. Could do with 1, 2, 4 and 5 going a bit lower, though might be able to get there with a little tweaking. Also will put a couple of resistors in to limit the top range of 2 and 5.


Regarding the filter... I just found the problem there. The link connecting the two lugs of the Fine cutoff point wasn't soldered properly, so turning the knobs would still have an effect and made it seem like the filter was working but not properly, haha.

Thinking I'll do away with the Coarse tune and change the Fine tune for a 220k pot, and tweak the pot's range a bit to make it closer to an antilog.


Thanks for your help in confirming things!

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elmegil



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PostPosted: Wed Jan 22, 2014 4:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

Any time Very Happy
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Kosmo Mishka



Joined: Apr 18, 2013
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PostPosted: Tue Mar 18, 2014 6:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi, I just build WSG. And have problem with filter coarse pot. It works, but somewhere at almost full clockwise, the value jumps very significantly. Until this it adjusts smoothly.

Can it be caused because pot bodies not grounded? (build it in cardbox for testing)
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Bogus Noise



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PostPosted: Wed Mar 19, 2014 1:22 am    Post subject: Reply with quote  Mark this post and the followings unread

The cardboard won't be at fault, many people have built theirs on cardboard, myself included! (I'll be mounting it in a case once I've tested out some mods, but that's by the by)

There is naturally a bit of a steep curve at the end of the pot range on this design, presumably that's why the Fine pot was included as well. I switched my Coarse pot to a 470k in the end, as I found there wasn't much change in the lower half of the Coarse range anyway. This definitely made it feel a bit more 'playable' for me.

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Kosmo Mishka



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PostPosted: Wed Mar 19, 2014 6:21 am    Post subject: Reply with quote  Mark this post and the followings unread

Bogus Noise wrote:
The cardboard won't be at fault, many people have built theirs on cardboard, myself included! (I'll be mounting it in a case once I've tested out some mods, but that's by the by)

There is naturally a bit of a steep curve at the end of the pot range on this design, presumably that's why the Fine pot was included as well. I switched my Coarse pot to a 470k in the end, as I found there wasn't much change in the lower half of the Coarse range anyway. This definitely made it feel a bit more 'playable' for me.

Just to make clear what I mean, recorded audio. Tweaking only Coarse pot, I am almost not rotating it, and it make a very big jump, and until 0 to 1/2 of pot value, it not make significant changes. https://soundcloud.com/bmlaster/wsgfilter .
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Bogus Noise



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PostPosted: Wed Mar 19, 2014 7:09 am    Post subject: Reply with quote  Mark this post and the followings unread

Kosmo Mishka wrote:
Bogus Noise wrote:
The cardboard won't be at fault, many people have built theirs on cardboard, myself included! (I'll be mounting it in a case once I've tested out some mods, but that's by the by)

There is naturally a bit of a steep curve at the end of the pot range on this design, presumably that's why the Fine pot was included as well. I switched my Coarse pot to a 470k in the end, as I found there wasn't much change in the lower half of the Coarse range anyway. This definitely made it feel a bit more 'playable' for me.

Just to make clear what I mean, recorded audio. Tweaking only Coarse pot, I am almost not rotating it, and it make a very big jump, and until 0 to 1/2 of pot value, it not make significant changes. https://soundcloud.com/bmlaster/wsgfilter .

Yes, that's what I experienced. As I say... I found there wasn't much change in the lower half of the Coarse range. A 470k pot is half a 1M pot, so in this instance you get the 1/2 to 1 range only.

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Kosmo Mishka



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PostPosted: Wed Mar 19, 2014 7:11 am    Post subject: Reply with quote  Mark this post and the followings unread

Thank you,but Ray just e-mailed that it is not normal, it should be smooth. So I am little bit messed, I will check everything double at evening, if that won`t help, I will try 470K.
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Bogus Noise



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PostPosted: Wed Mar 19, 2014 7:17 am    Post subject: Reply with quote  Mark this post and the followings unread

Ah ok, I figured it was normal as there was a few other threads around where people had a similar result, and through experimenting that was the way that worked it out for me. Be interesting to know if there's another way around it!
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Kosmo Mishka



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PostPosted: Thu Mar 20, 2014 4:33 am    Post subject: Reply with quote  Mark this post and the followings unread

Bogus Noise wrote:
Ah ok, I figured it was normal as there was a few other threads around where people had a similar result, and through experimenting that was the way that worked it out for me. Be interesting to know if there's another way around it!

Checked wiring, pcb, and did not find anything wrong. Also I tried your solution, and placed 500K instead of 1M. It is smoother, but still there is a big difference when knob full CW. I am finding it is pretty weird, as I dig like all electro-forums WSG topics, and many peoples have problem with it, and there is no answer to it. Also on youtube, there are a lot of units with similar filter problems. Could it be that there are different versions of WSG?
Also from demos I think mine resonance not giving much feedback.
I used TL071, what did you use?
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Bogus Noise



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PostPosted: Thu Mar 20, 2014 11:06 am    Post subject: Reply with quote  Mark this post and the followings unread

Yeah, a TL071 here as well!
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Kosmo Mishka



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PostPosted: Thu Mar 20, 2014 11:08 am    Post subject: Reply with quote  Mark this post and the followings unread

Maybe tl071 and LM741 sound differently? I ordered like 3 different LM741, and one LF411. I will test them all when recieve (next week).
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Kosmo Mishka



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PostPosted: Mon Mar 24, 2014 7:42 am    Post subject: Reply with quote  Mark this post and the followings unread

Tried LM741 and no success( Still very touchy on full CW, and no bottom. It is usable only on max coarse, fine and res. Any ideas where to dig? Wiring and pcb checked.
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