EFM VCO3D as LFO

[Dave Kendall]

Hi gang.

Am about to build an EFM VCO3D, and would like one half (it's a dual, based on the moog rogue VCOs) to be able to run at slow LFO speeds.
It would only need to be run as an LFO, it won't need to do dual duty as a VCO.

Setting T2 or T5 to it's lowest would help obviously, but as it was designed as a VCO, that may not be enough.
Points A and I are 1V/octave inputs, B and J are freq mod inputs, and C/K and D/L are fine and coarse tune respectively.
FWIW, I'm only really interested in the saw outputs.

Anyone got any ideas?

The schemo is below.

cheers,
Dave

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[yusynth]

Use a 0.1uF for C3 instead of 0.01uF and it should do the trick

[Dave Kendall]

Merci Yves!

Will try it out.
I'm going for the chip-heater version this time.....


cheers,
Dave

[Dave Kendall]

Thanks, your tip worked Yves
I went up to 0.22uF, and may go larger.

One weird thing, the Saw output appears to be ramping from +15V to +5V on my scope. I rather hoped it would be + somethingV down to 0V......
Does anyone else's do this - Yves, Matthias?
The square wave is nicely centred around 0V.

(BTW, I dug out my beaten-up old VCO3D tempco option that has seen better days, and am using it for testing before a new board build - but that shouldn't affect the waveforms surely..... )

cheers,
Dave

[yusynth]

[fonik]

on mine both waveforms show an offset of 1.5V. the saw is going from 4V down to 1.5V, the square goes from -1V to 4V.
this VCO was the 3rd module i ever built, so i don't know if i attenuated one or the other output.

i will have to tweak it a little bit. what about AC coupling on the output (just a cap and a resistor)?