Synthesizers.com Q150 User manual

Q150/Q150A Transistor Ladder Filter
Dec 2018
Based on Bob Moog's famous design, the Q150 Transistor Ladder Filter
changes the harmonic content of signals to create new, interesting sounds
which is the basis of subtractive synthesis. The cutoff frequency can be
controlled manually and/or controlled by another signal such as an enve-
lope generator, oscillator, keyboard, etc. Frequency control signals can be
attenuated and inverted. Resonance (Q) of the filter is adjusted with a pan-
el control. Both -12dB and -24dB slopes are available.
In most ladder filters the output signal is greatly reduced as the resonance
is increased. This usually requires resetting input levels (sometimes many)
when changing resonance settings - quite annoying. Special circuitry in the
Q150 keeps the output signal level at various resonance settings while
keeping the harmonic content unchanged. This option can be disabled with
a jumper if desired.
The Q150A is a single-wide version with only one attenuated input and
one frequency voltage control. The frequency voltage control can be
changed from reversable to attenuated by moving the pot and jack con-
nectors on the pcb.
Specifications
Q150 Panel Size: Dual width 4.25"w x 8.75"h.
Q150A Panel Size: Single width, 2.125”w x 8.75”h
Low Pass Slope: -12dB/Oct or -24dB/Octave.
Cutoff Frequency: 1/V per Octave and adjustable.
Resonance (Q): 1 to self-oscillation.
Frequency Range: 20hz to 20khz.
Power: +15V@30ma, -15V@30ma.
Waveform Levels: 10V PP.

Q150/Q150A Transistor Ladder Filter
Manual
resonance (Q)
control
Filter cutoff
frequency manual
adjustment
Filter cuttoff
frequency
voltage controls.
One is reversable,
one attenuated,
one is 1V/Oct
to track keyboard.
Signal input mixer
with manual
attenuation
Slope Control
-24dB is the
classic Moog
sound.
Filtered signal
output
Dec 2018

Q150/Q150A Transistor Ladder Filter
Manual
resonance (Q)
control
Filter cutoff
frequency manual
adjustment
Filter cutoff frequency
voltage controls.
reversable is preselected,
Attenuated can be set on pcb,
Use 1V/Oct to track keyboard.
Signal input mixer
with manual
attenuation
Slope Control
-24dB is the
classic Moog
sound.
Filtered signal
output
Dec 2018

Q150/Q150A Transistor Ladder Filter
Response
The following plots show the frequency response.
Controls and Connectors
Manual Frequency and Resonance Control Section
Frequency Control
Manually controls the filter's cutoff frequency.
Resonance Control
Manually control of the filter’s resonance.
Frequency Control Section
Frequency Level Controls
Allows adjustment of the cutoff frequency control input.
One control provides inversion.
Frequency Control Input
Voltage control of the filter's cutoff frequency.
1 Volt/Octave Frequency Control Input
Voltage control of the filter's cutoff frequency at a fixed 1V/Octave.
Normally used to track the keyboard.
Signal Input Section
Signal Input
Signal to be filtered.
Signal Input Level Control
Allows attenuation of the input signal.
Output Section
Slope
Allows selection of -12dB or -24db slope.
Low Pass Output
Filtered output signal where high frequencies are attenuated.
Dec 2018

Q150/Q150A Transistor Ladder Filter
Usage and Patch Tips
Basics
Most waveforms contain many different frequencies. When an oscillator produces a sawtooth waveform, it
can be thought of as a single sine wave, and additional sine waves which are at multiples of the funda-
mental frequency and are at lower amplitudes. These additional frequencies are called harmonics and
different waveforms have different amounts. The Q150 Filter changes the way a waveform sounds by
attenuating (lowering the amplitude) of these harmonics. This effect is especially useful when changing
over time. The frequency at which attenuation starts (or close enough) is called the cutoff frequency. Cut-
off frequency can be controlled manually or by voltage control. Resonance (also known as Q, Regenera-
tion, or Emphasis) has the affect of enhancing frequencies near the cutoff frequency.
Frequency Control
The frequency control gives you about 10 octaves of cutoff frequency response. The control inputs are
added to the manual control's value to create the final cutoff frequency. All of these signals work together
at the same time to set the filter's cutoff frequency.
It's very common to have your filter track the keyboard so that the response is the same over all frequen-
cies. This is accomplished by using the 1V/Octave frequency control input. Simply patch your keyboard
pitch voltage into a multiple then out to your oscillators and to the filter.
The other frequency control inputs normally come from an Envelope Generator or from an Oscillator. You
can attenuate, amplify or invert the incoming control signal right on the filter instead of having to use an-
other module. The 0 to +5 volt outputs of the Q109 Envelope Generator will give you a total of 10 octaves
of range when the attenuator is full on.
The Sequential Controller can also be used to control the filter frequency. You could use one bank to con-
trol an oscillator and another to control the filter at the same time.
Resonance Control
Resonance is the emphasis of frequencies near the cutoff frequency and has a great affect on the sound.
The range of the resonance control is very large. If you have too much resonance the filter might oscillate
and clip. We let you decide if this is good or not. You can increase the maximum resonance possible by
turning down the input signal level control so that there is more room for resonance without clipping.
Self-Oscillation
Turning the resonance to maximum without an input signal will cause the filter to self-oscillate. This allows
the filter to act like an oscillator creating a very pure sine wave. Oscillation works best in –24dB mode.
Signal Inputs
There are 2 signal inputs which are mixed together - both are adjustable. Normally you will adjust the
input levels to 50% or less to allow larger resonance peaks.
Outputs
The output is available at the bottom of the module. A switch allows selection of -12dB or -24dB slopes.
Traditionally ladder filters have had -24dB slopes but we are also offering the -12dB slope to give you
even more sound possibilities.
A sine wave has almost no harmonics and will only respond to the filter by lowering its amplitude. Saw-
tooth and Ramp waveforms have the most harmonics and respond quite nicely to filtering. Square and
Pulse waveforms also have a great deal of harmonics and respond well to filtering.
Dec 2018

Q150/Q150A Transistor Ladder Filter
PC Board Layout
Power Connector
6 pin .1” MTA type connector made
by AMP. Available from Mouser
Electronics or Digi-Key. Modules
have a male PCB mount connector
and cable harnesses have a female.
Part Numbers:
Female cable mount: #6404416
Male PCB mount: #6404566
Pinout:
1 = +15v
2 = key (pin removed)
3 = +5v
4 = gnd
5 = -15v
Not all voltages are used on all mod-
ules.
Calibration
Calibration is accomplished with two trim pots. The Tracking trim pot is the one closest to the power con-
nector. The Resonance trim pot is near the center of the board.
* Setup
Turn resonance to 10, Slope: -24dB.
Set Tracking trim pot to center, set Resonance trim pot to full CCW
Connect an oscilloscope & frequency counter to the output
* Set Resonance trim pot
Turn frequency knob to achieve 80hz, should be around 3.
Set the Resonance trim pot to get 10v PP signal
* Set Tracking trim pot
Turn frequency knob to achieve 500hz, should be around 5.
Attach a precision voltage calibrator to the 1V/Oct jack and set to 1.000v
Turn tracking trim pot to achieve 1000hz
Go back and forth between 0v and 1v to get 500hz, 1000hz
Check the 2v setting for 2000hz. Should be within 10hz
Resonance
Trim Pot
Tracking
Trim Pot
Slope
Jumpers
Slope Jumpers
These jumpers allow you to select a 1-pole, 2-
pole (default), or 3-pole filter response when the
Slope switch is in the –12dB position. Numbered
from top to bottom #1 – #6.
3-Pole: Jumpers #1 and #4
2-Pole: Jumpers #2 and #5 (Factory Default)
1-Pole: Jumpers #3 and #6
Level Jumper
Off=Auto Level
On=Normal
Dec 2018