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 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
Soundlab Minisynth MKII No Self Oscillation
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qp



Joined: Jan 02, 2013
Posts: 2
Location: Chicago, Il

PostPosted: Wed Jan 02, 2013 12:06 pm    Post subject: Soundlab Minisynth MKII No Self Oscillation Reply with quote  Mark this post and the followings unread

Hey all!

I've been a long time user of MFOS, but first time posting here.

So, I completed the SLMS MKII a couple of months ago. I had some issues that were easily fixed (power supply under voltage, a couple miswirings but nothing critical). Everything works like a champ and it scales perfectly but the one thing I cannot figure out is the SVF. It will not self oscillate. I have checked, rechecked and checked again this section of the board but cannot find where the issue is. I have swapped out the 13700 with a known good one and still no selfosc. All solder joints are good and there are no shorts anywhere. I've gone over the schematic and tried to figure it out, but I'm not familiar enough with the circuit to make an educated decision of where the issue is. I'd rather pick someones brain than start pulling parts and "guessing". My only though is maybe there is an issue at Q5? I ordered the MPF102's from MFOS, so I have spares.

Other than that, the filter is 100%. Resonance is gravy.

Any thoughts?

Thanks,
Adam
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qp



Joined: Jan 02, 2013
Posts: 2
Location: Chicago, Il

PostPosted: Fri Jan 04, 2013 3:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

Well, I went over to another forum and got an answer in about 2 minutes. Turns out the problem was at R20. I lowered the value a bit and got oscillation. It's pretty dirty. Im going to mess with some values and see if it will clean it up. other than that, I was tipped into possibly adding a pair of back to back 5.6V Zeners to ground at U2 pin 8 or U2 pin 7 to smooth the oscillation out. Gonna give it a whirl next Mouser order.
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elmegil



Joined: Mar 20, 2012
Posts: 1449
Location: Chicago
Audio files: 14

PostPosted: Fri Jan 04, 2013 11:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

E-M isn't dead, but it's not checked as continuously and obsessively as some other forums out there. Glad you found a solution, thanks for posting it here for someone to find again someday.
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