[sdiy] EFM lfo5a issues

[harrybissell]

Yes... help (some)

> Julian wrote:
> 
> Running through these modules here, and ive come to the lfo5a...
> 
> On building, my board had a square wave output that swang in the range
> of about +/- 10v whilst the other waves were more like (after a little
> messing with the saw) +/- 3v
> 
> Adding a 75k resistor to the square output has bought it down in line
> with the other outputs, however....

I'm assuming that you are patching square wave out to the clock input. 
I would normalize from the square wave output BEFORE the resistor, to
the
clock in jack. Then put the resistive divider
~after~ that connection to bring the square wave level down...

You probably just don't have enough level anymore...

> 
> I had the s&h section triggered from the square, and now, with the
> lower voltage, and, indeed any external clock, im not getting any
> 'sampling'.
> 
> Id suspect c7 and r17, but im not sure.  Im using a 1n metalised
> polyester cap for c7 (and c8?)

C7 is not critical. C8 would be better as a polystyrene, but the
rest of the circuit is not super-high performance anyway. Mylar
will be good enough for non critical (modulation) apps...

> 
> One other concern with the board is that its saw tooth output is not
> as regular as id like.  One wave is sharp, and the alternate is
> rounded and slightly different voltages.  Adjustment of the trimmer
> does not help much.

Sawtooth from a triangle is tough... one side is going to be rounded.

Adjust the trimmer for best symmetry, then play with the R37 value.
Maybe change C10 to a smaller value.

H^) harry
> 
> So then, any ideas?
> 
> Cheers, Julian
> 
>