Doepfer DIY Synth do-it-yourself analog synthesizer - Manual (Page 17)

User's Guide page 17 DIY Synth Kit
VCF CV SUM Control voltage summing
input for VCF frequency Required only if the two VCF CV inputs
of JP3 are not sufficient, serial resistor
100k required to obtain roughly
1V/octave (or ~ 47k for 0.5V/octave)
VCA OUT VCA Output Usually connected to a socket labelled
"VCA Out", which is normally the final
output of the synthesizer and connected
to the audio mixer
JP10: Tempco-Option
If the tempco option is used IC1 has to be removed and replaced by the tempco option.
That’s nothing but the former IC1 expanded by a small temperature controlled oven that is
glued to the circuit. The oven heats up the the circuit IC1 to a fixed temperature which is
cleary above the usual room temperature (sorry - the tempco option will probably not work in
the Death Valley or in the Sahara desert ☺).
The tempco option is connected to JP10.
Auxiliary terminals
Near the power supply connector JP1 some auxiliary terminals are available (please refer to
the picture on page 9 for the corresponding positionss):
• +5V / GND (JP8): output of an +5V voltage regulator (derived from +12V)
• –5V / GND (JP9): output of an –5V voltage regulator (derived from –12V)
• +12V (JP11): nothing but a terminal connected to +12V
• -12V (JP12): nothing but a terminal connected to –12V
These terminals can be used whenever a fixed voltage is required (e.g. for potentiometers
that are used to generate manually controlled voltages e.g. for VCO tuning, VCF frequency,
VCA loudness or others). If a higher voltage range is required (e.g. for manual VCF
frequency control) the "high voltage" terminal +12V can be used. If a smaller voltage range is
required the "small voltage" terminal +5V can be used (same applies to –12V and –5V). The
voltages appearing at the +5V and –5V terminal have the advantage that they are nearly
independent of possible voltage changes of the +/-12V supply. Consequently they should be
used for VCO control applications.
Trimming potentiometers
Trimming potentiometer P1 is used to adjust the 1V/octave scaling of the CV inputs of the
VCO (CV1…CV4 of JP2). If the tempco option is used the board should be powered at least
20 minutes before this parameter is adjusted. For example a control voltage with the values
0.0 V / 1.0V / 2.0V / 3.0V / 4.0V /5.0V is applied to one of the 1V/oct CV inputs of the VCO.
The CV can be supplied e.g. from a Midi-to-CV interface (e.g. A-190-2) or a CV keyboard
(e.g. A-100CGK). P1 is adjusted so that the 1V intervals of the CV correspond exactly to
octave intervals. If a frequency counter is available the frequencies can be measured, e.g.
32 / 64 / 128 / 256 / 512 / 1024 / 2048 Hz. But usually the human ear is the best frequency
counter.
Trimming potentiometer P2 is used to adjust the frequency offset of the VCO (i.e. the lowest
frequency if all VCO CV inputs are 0V). It' up to the user which frequency is chosen. Usually
a "C" is chosen when all frequency controls (e.g. coarse and fine tuning) are in the center
positions. The corresponding "C" frequencies are ~ 65 Hz or ~33Hz (one octave less).