EuroRack "LFO Prime"--Worked the First Time!

 I have a few days off for the Thanksgiving Holiday. Time for more DiWhy fun! 

Doepfer smokers: this time I completed a EuroRack analog LFO design from my distant past--"LFO Prime".

For more about the features and development of this LFO check out the previous post here. To summarize: I cobbled together different LFO designs back in 2002 or so, into this module, but didn't document anything. It took me a bit to figure out how the 2002 era circuit worked, but I did, and this is it. 

I figured the build would work without issue and it did....since I already built this same circuit for Frac and large format. 

Let's build!    

As they say at the dentist's office: "you know the drill".  

I laid out the boards on a Windows PC using Eagle CAD, then shipped gerbers off to PCBWAY (this blog's trustworthy sponsor) for quick fab.  

The boards came back posthaste: 

Unbagged them and inspected. Looked good.

Front panel and main PCB for a "skiff" (<30mm depth) module layout

Rounded up the parts....

From here it was like building a kit....my calculation: +/- 12V Euro power should work without issue....

I put the C3 and C4 caps and the trimmers on the back of the board.  

  

Ready for final assembly and testing

"Seems working!"

I experimented with different values for the speed pot (A25K was best--higher values for this component led to issues with the symmetry of the triangle wave at output) and "speed" caps C3 and C4 (ended up using 47uF (range = "fast") and 1000uF (range = "slow"); if you build the LFO you may want to experiment with the values of these two capacitors.

I also used a two color 3.5mm LED (green/red) and increased R8 to 10K (15K for even dimmer LED action) since the unit was racked at eye level and the LED was too bright otherwise.

Of course the LFO could be modded--how about a rotary capacitor select switch for "range" instead of a DPDT?  Variable bias offset pot instead of a toggle switch? It wouldn't be too hard to add ramp or sine wave, etc., deriving them from the triangle/square wave.  

Easy to mod, but for me it's time to move on.  

Thanks again for PCBWAY for helping the audiodiwhy blog out. You can get the boards and plans to build this puppy--gerbers, Eagle files, PDFs of the layout, and so on, at their community site: here.  

Next time on to something a lot tougher: working with very small SMT parts to create a 14 bit ADC breakout board. (Update--done, works, go here). Until then, Gobble gobble!