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 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
Soundlab Mk2 LFO Issue
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NicolaLeonardi



Joined: May 20, 2016
Posts: 3
Location: Seattle, WA

PostPosted: Sat May 21, 2016 5:02 pm    Post subject: Soundlab Mk2 LFO Issue
Subject description: Square output is not square
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Hi folks, been lurking on your forum trying to see if anyone else has had this problem but came up empty.

I am in the process of designing a guitar pedal that would incorporate some circuits from MFOS. First of all I needed an LFO with sqr, tri, and saw so I decided on the Soundlab mk2 LFO as it is fairly simple and versatile.

So I breadboarded it out and have a nice triangle wave, but my square wave is well, not so square. At higher frequencies it isn't noticeable but as you go to the low range the square becomes more and more sloped. What I mean is the top of the square is angled downward, and then it drops and the bottom is angled up. Would post scope traces but it's currently ripped apart.

I have checked the schematic and tested every component and re built it several times now and every time ended up the same. I tried changing the values of various components around the op-amps and for the most part the only thing affected seems to be the frequency.

From reading the circuit description I believe the issue lies in the threshold of hysteresis, but have had no luck with different values for R174. Ray says "C60 helps to square up the output of the comparator" which he gives as 10pF in the original schematic and 4.7pF in the LFO optional modification to make saw/ramp waves the same frequency. I have tried both values as well as various values up to 100pF and noticed no change. I am using standard ceramic capacitors and 1% resistors.

Think that I might be going crazy, I have a clean +/- 12v. Could it be the breadboard? Could I be misunderstanding the circuit description? Maybe I'm just overlooking something little? What could cause the circuit to behave this way?

Sorry, didn't mean to rant, was up all night messing with this, might just need to look at it tomorrow. Maybe someone who has built one of these before knows a little something I don't.
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blue hell
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Joined: Apr 03, 2004
Posts: 24079
Location: The Netherlands, Enschede
Audio files: 278
G2 patch files: 320

PostPosted: Sat May 21, 2016 5:07 pm    Post subject: Re: Soundlab Mk2 LFO Issue
Subject description: Square output is not square
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NicolaLeonardi wrote:
but as you go to the low range the square becomes more and more sloped. What I mean is the top of the square is angled downward, and then it drops and the bottom is angled up. Would post scope traces but it's currently ripped apart.


Sounds like a scope on AC .. it is a software scope you use?

http://www.ee.usyd.edu.au/tutorials_online/topics/labintro/acdist.html

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Jan
also .. could someone please turn down the thermostat a bit.
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NicolaLeonardi



Joined: May 20, 2016
Posts: 3
Location: Seattle, WA

PostPosted: Sat May 21, 2016 8:07 pm    Post subject: Re: Soundlab Mk2 LFO Issue
Subject description: Square output is not square
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Blue Hell wrote:

Sounds like a scope on AC .. it is a software scope you use?


Wow, I feel dumb... Digital scope, switched it over to DC, perfect square coming out of that thing now, great design Ray. I learned to use a scope in physics at university, didn't really talk about things like that... Thank you so much for that little tidbit of information that makes everything so much more clear. Definitely chose the right place to ask this, will post update when I get this all working.
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blue hell
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Joined: Apr 03, 2004
Posts: 24079
Location: The Netherlands, Enschede
Audio files: 278
G2 patch files: 320

PostPosted: Sun May 22, 2016 2:49 am    Post subject: Reply with quote  Mark this post and the followings unread

Great, glad that got solved :-)

Oh, and welcome of course!

_________________
Jan
also .. could someone please turn down the thermostat a bit.
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