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 Forum index » DIY Hardware and Software » Thomas Henry designs
Mankato self oscillation
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inlifeindeath



Joined: Apr 02, 2010
Posts: 315
Location: Albuquerque, NM

PostPosted: Sat Apr 12, 2014 6:10 pm    Post subject: Mankato self oscillation Reply with quote  Mark this post and the followings unread

hey all,
i'm having an issue with getting my Mankato filter to self-oscillate properly.
With the res pot and trim cranked, I can get a high frequency Sine wave out, but when I reduce frequency below a certain point the oscillation dies out.
I've verified that the feedback trim and resistor (R35) are 10k and 18k respectively, would the answer be to reduce the 18k?
Thanks for any and all assistance,
Brad

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elmegil



Joined: Mar 20, 2012
Posts: 1509
Location: Chicago
Audio files: 14

PostPosted: Mon Apr 14, 2014 8:49 pm    Post subject: Reply with quote  Mark this post and the followings unread

That just doesn't sound right. My Mankato took no extra coaxing and I got oscillation way down deep before it would cut out. Any chance there's a wiring problem with your resonance pot? Or perhaps value? In some ways being a voltage divider, the value won't matter a lot but i could see it mattering for oscillation. ??
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inlifeindeath



Joined: Apr 02, 2010
Posts: 315
Location: Albuquerque, NM

PostPosted: Tue Apr 15, 2014 7:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

i've double check all wiring and pot values. Did you use an SSM2164 or a Cool Audio V2164? What type of caps did you use?
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elmegil



Joined: Mar 20, 2012
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Audio files: 14

PostPosted: Tue Apr 15, 2014 8:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

I used an SSM, actually. I have another built that I'm pretty sure has the coolaudio in it, but I don't have a panel or any good way to test it without ripping the older one apart.

The important caps are all Polystyrenes. So that's C3, C4, C6, C7, C9, C10, C12, C13.
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inlifeindeath



Joined: Apr 02, 2010
Posts: 315
Location: Albuquerque, NM

PostPosted: Tue Apr 29, 2014 4:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

Alright folks! I've gotten all the bugs worked out and have a fully oscillating Mankato!
As I proposed in my initial post, the solution was to decrease the feedback resistor. It's 18k stock on the schematic, I swapped in a 10k with great success.

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