Oakley ADR30 User manual

Oakley Sound Systems
Analogue Delay – ADR30
User Manual
V1.3
Tony Allgood
Oakley Sound Systems
CARLISLE
United Kingdom

Introduction
This is the User Manual for the A R30 Stereo Ensemble module from Oakley Sound. This
document contains an overview of the unit and goes into some detail regarding the operation
of the module. It also contains the calibration instructions.
For the Builder's Guide, which contains a basic introduction to the circuit board and a full
parts list for the components needed to populate the board, please visit the main project
webpage at:
http://www.oakleysound.com/A R30.htm
For general information regarding where to get parts and suggested part numbers please see
our useful Parts Guide at the project webpage or http://www.oakleysound.com/parts.pdf.
For general information on how to build our modules, including circuit board population,
mounting front panel components and making up board interconnects please see our generic
Construction Guide at the project webpage or http://www.oakleysound.com/construct.pdf.
The ADR30 built into a Takachi YM300 case with Schaeffer engraved panel overlay
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The Oakley Sound A R30
The Oakley Sound Systems A R30 is an analogue delay module that processes audio signals
to create echo and chorus effects. It uses two Xvive MN3005 bucket brigade delay (BB )
integrated circuits to produce a very distinct 'vintage' sound. Classic companding noise
reduction circuitry further add to the sonic characteristics.
elay time is controlled by a single control on the front panel as well as a built in low
frequency modulation oscillator and/or an external control voltage. With short delay times
using the modulation oscillator can create both subtle and deep chorus effects. A front panel
switch controls whether the signal runs through one or both MN3005 devices. Anti-aliasing
filtering is achieved by two 6-pole discrete switched capacitor low pass filters that track the
delay time, altering audio bandwidth depending on the delay time so that short delays remain
reasonably bright sounding.
The unit is mono but features separate outputs for the wet/dry signal and the delayed signal.
The audio input and outputs are balanced but are compatible with non balanced connections.
A two LE level meter helps you keep signal levels at optimum ensuring a respectable signal
to noise ratio without clipping. The unit will not be damaged by driving the unit into overdrive
and interesting sounds can be obtained by deliberately doing so, either by turning up the input
level or by allowing the feedback to build up to self oscillation.
Although the unit does feature noise reduction circuitry the delay line devices are inherently
noisy and have a very restricted bandwidth. The signal will deteriorate in an interesting manner
as the delay time is increased and/or feedback is heavily applied.
elay time can be controlled continuously from 15ms to 300ms with one delay stage engaged,
or 30ms to 600ms with both stages engaged.
Audio bandwidth of the delayed signal varies with delay time. The upper cut off frequency
being 10kHz at the shortest delays and 1.5kHz at the longest delays.
The internal triangle wave low frequency oscillator has an approximate range of 0.11Hz to
26Hz.
An external control voltage (CV) can be applied via a dedicated socket on the rear panel to
alter the delay time. A positive voltage will decrease the delay while a negative voltage will
increase the delay. The CV will add to the effects of the internal LFO if applied and the delay
control knob. However, the maximum and minimum delay times of the unit can only be
extended a little in this way.
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Operating Instructions
INPU LEVEL and LED signal metering
The input level controls the signal running through the A R30. It affects both the wet and dry
signals. With the pot fully counter clockwise the signal is completely shut off.
The two LE signal meter shows the audio signal level going to the bucket brigade delay
(BB ) circuitry. If the signal is too high then the BB s will be overdriven and produce
significant distortion. If the signal is too low then the inherent noise produced by the BB
circuits will become very noticeable. The aim then is to have as large a signal as possible
without introducing too much distortion.
The input level should be set so that the green OK LE is always on when there is signal
present. If the red PEAK LE lights up the BB s will probably be distorting. However,
depending on the signal that is going through the A R30, overdriving the BB s for very
short intervals may be acceptable. Indeed, sonically this can produce some interesting
artefacts. No harm will come to the unit if the unit is run continually in the red.
It should be noted that the input signal is compressed prior to be being sent to the BB s to
reduce the likelihood of overdriving the BB s and to improve overall signal to noise ratio.
The signal meter is monitoring the signal after it has been compressed, so the A R30's meter
will behave slightly differently to normal LE meters such as that found on your audio mixer.
Any compressor takes a certain time to react to the input signal so very fast transient signals
will cause the higher signal LE s to light even when the apparent volume is quite low. Since
the signal meter monitors the signal going into the BB s it may be necessary to set the input
level lower for, say, drum loops, than for synth pads, to avoid any unwanted distortion.
With the input level control at maximum the A R30's limiting circuitry will start to have a
noticeable effect on the audio quality once the input signal rises above 1V(peak to peak). For
most signals the red peak LE will be lit up by then.
DELAY IME
This controls the delay time of the unit and works in conjunction with the internal LFO and
any external CV. The longest delay time is at the most clockwise point of the control. In other
words turning up the pot increases the delay time. With no external CV and no LFO
modulation applied then the range of this control is either 15ms to 300ms in 'short' mode, or
30ms to 600ms in 'long' mode.
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FEEDBACK
The output of the delay circuitry can be passed back and mixed with the input signal. This
creates repeat delays. Increasing amounts of feedback will increase the volume of the repeats.
It is possible to have the repeat volume louder than the original signal. This creates an rolling
snowball effect – often called self oscillation – by which the final output signal gets louder and
louder until the A R30's built in signal limiting circuitry takes over. At this point the sound
becomes heavily distorted and develops an interesting character.
An internal trimmer can control the maximum allowable amount of feedback.
It should be noted that the delayed signal's volume is somewhat affected by the delay time.
Therefore, self oscillation may be more readily encountered at certain delay times.
The A R30 can be produce flanger like sounds with the delay time short and fairly large
amounts of feedback.
RANGE (Switch)
This two position toggle switch determines whether the effected signal runs through one
MN3005 BB or two MN3005 BB s. When two devices are selected the signal is delayed
for twice the amount of time it would have been with just one device. LONG selects both
MN3005 devices, while SHORT selects just the one.
For chorus and flanger type effects, which require only small delays, then the short setting is to
be used.
As the signal pathway through a BB is long and tortuous the audio will be slightly distorted
on the way out. Passing a signal through two such BB s one after an another will increase
that distortion. Greater fidelity will normally be obtained using the A R30 in the short setting.
However, it is not quite that simple for longer delays.
The available signal bandwidth, that is, the range of audio frequencies passed by the delay
lines, is controlled by the delay time for each BB and not the overall delay time of both
devices combined. For example, if you wish to have a 300ms overall delay, then the maximum
bandwidth will be obtained when you have the switch in the long mode. That is, both BB
devices are being used but being run at half their maximum delay times.
LFO RA E
The A R30 features an inbuilt low frequency oscillator (LFO) which can modulate, or
control, the delay time. The speed at which the LFO cycles is controlled by this knob. The
speed can be varied from a slow 0.1Hz (one cycle every 8 seconds) to around 26Hz at its
fastest.
Like many famous chorus units the output waveform of the LFO is triangular. This means it
rises in a straight line and falls in a straight line. The rise and fall times are always equal.
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