Doepfer

> Hi,
>
> I've recently received my second A-143-9 quadrature LFO. I'll be
> using the two for creating FM spectra a lot as this module has
> such a beautifully clean sinewave and the combination with the
> A-132-2 is ideal for FM index modulation.
>
> In this context it would be interesting to know wether anybody
> has modded his A-143-9 to have linear FM inputs? Ideally, I'd
> like to add a 3-way switch that selects between the current
> exponential  modulation, DC-coupled linear and AC-coupled linear
> FM modes for the CV 2 input....
>
> Any ideas?
>
> Cheers,
> Denis Goekdag
> Surround SFX

Denis,

from the theory it should be possible to replace the fixed reference voltage
(R8 connected to -12V) of the exponential converter by a variable voltage to
obtain linear FM. The voltage has to be negative. Consequently a little bit
of additional electronics is necessary (manual control + CV input with
attenuator combined with an inverting amplifier as shown on the A-100 DIY
page). You may even modify an A-183-2 by using the internal inverted output
(pin 1 of the TL082) as new reference voltage (instead of -12V) for the
A-143-9 exponential converter.

Best wishes
Dieter Doepfer