[sdiy] problems going from breadbaord to pcb/solder

[Jay Schwichtenberg]

Dan,

I've played with LM13700 based LFO cores some and have seen the same
problems. Maybe the cases are the same ones that I've seen. I'm assuming
there is an expo converter in there too. If not what is said applies to
whatever is supplying the current to the OTA Iabc pin.

The overall problem sounds like the current that controls the OTA gain (ie
freq) is going down to the point where it is shutting off the OTA completely
or to the point there isn't enough signal or slew to trigger the comparator.
Also when the current gets really low (ie low freq) the offset of the OTA
becomes a factor and that effects the symmetry. Some people had symmetry
problems when the op-amp they used in the ASM1 LFO had a large offset. So
I'd check the expo converter out and make sure that it was working properly
and all the right resistor values are in there. If there is a current
limiting resistor in between the expo and Iabc pin check and make sure that
is the correct value. For a LFO I wouldn't suspect there would be any issues
signal feed through in the wiring effecting the circuit. Might also add an
offset trim to the OTA integrator for more dynamic range if it is an expo
controlled LFO.

Best of luck.
Jay S.

> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl
> [mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of Dan Snazelle
> Sent: Saturday, August 15, 2009 3:36 PM
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] problems going from breadbaord to pcb/solder
>
>
>
> a friend of mine has been working on a vclfo partially based on
> the ray wilson VCLFO.
>
> it uses a triangle core with a lm13700, an integrator, and a
> tl072 comprator
>
> it worked without ANY problem on the breadboard
>
> however, when he soldered it up on perfboard the following problems arose:
>
> 1. the symetry is off. mainly as the oscillator gets slower and
> slower, the symmetry falls out of line. it is fine at higher speeds
>
> 2. at lower speeds, the oscillation dies. (at speeds which work
> on the breadboard)
>
>
> I told him to try changing the hysteresis resistor value and cap
> on the comparator and this DID help somewhat (it kept the osc from dying)
>
> however, things are still not quite right.
>
> IS THIS due to the difference between the capacitance on a
> breadboard and the capacictance on a soldered board?
>
> or could it be something else?
>
> anyone have any ideas on how to save this?
>
> i am very interested in the results as I will soon be moving some
> of my projects from breadboard
> to finished pcbs
>
>
> thanks so much
>
>
>
> --------------------------------------------
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>
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>
> (updated monthly)
>
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>
>
>
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>
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>
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>
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>
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>
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>
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>
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>
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>
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>
>
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