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 Forum index » DIY Hardware and Software » Thomas Henry designs
AS21C "Super LFO" PCBs available
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davebr



Joined: Jun 09, 2007
Posts: 198
Location: portland, or
PostPosted: Sun Feb 21, 2010 1:20 pm    Post subject: Reply with quote  Mark this post and the followings unread
b-funk wrote:
OK, got it.
Anyways, it's working now. After I calibrated the waves, I had an issue with the gate output, the gate low phase was completely distorted, and just dropped to 1 Volt. A 2M2 resistor in parallel to R74 (also a 2M2) fixed this problem.

Tobias


Glad you got the ramp working.

R74 sets the hysteresis level for the comparator U4A. You shouldn't be that close to the reference level to have to change that value.

Make sure D7 and D8 are oriented correctly.
Check the value of R16. It should be 2K2.
Check the value of R20. It should be 4K7.
Check the voltage on pin 2 of U4A. It should be ~-7.5 volts.
Check the waveform on the side of R16 that connects to the two diodes. That will be the square wave output through one of the diodes. The amplitude should be from about -14V to ground. The comparator is set at midpoint so there should be no need to have changed R74. Something else is going on.

Dave
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davebr



Joined: Jun 09, 2007
Posts: 198
Location: portland, or
PostPosted: Sat Jun 26, 2010 10:49 am    Post subject: AS21C Super LFO
Subject description: Finished TH-301 module		 Reply with quote  Mark this post and the followings unread
I finally completed a front panel for my TH-301 module using my Rev1 PCB.

I changed the panel design by incorporating the ramp polarity into the waveform switch. I also incorporated the foot switch function into a more general gate function.

I used a 3 pole 4 position rotary switch for the waveform selection switch so it selects Sine-Tri-Saw-Ramp.

I changed the 3 position Gate-Delay-Foot switch to a Gate-Delay switch and a Gate-Polarity switch. I eliminated the Foot Sw jack by using the Gate jack with the polarity set to negative. I normalled the Gate jack to ground so the LFO would operate when set to a negative gate with no input.

Updated construction and panel images on my TH-301 page at
http://modularsynthesis.com/magicsmoke/as21c-lfo/th-301.htm

Dave
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