The Sound Modifications
are an extension of what I first installed in the early 1980s, with new
pots and knobs, three small pots for the Tom/Conga Decay function
(instead of toggle switches and trimpots) and three additional functions
marked * below.
The features are:
- * The Bass Drum decay range
is extended to include self-oscillation, so any decay time from the
normal minimum to infinity can be achieved with the Decay knob.
- * The Bass Drum Tuning knob enables higher and lower tuning. (Top white knob.)
- The Snare sound is changed in a number of respects:
- Sharper attack for the Snappy noise pulse.
- Reduced cutoff frequency in the Snappy noise pulse high pass filter, to make it gutsier in the lower mid-range.
- The two tonal components of the sound are boosted in level.
- The Snare sound is composed of the Snappy noise pulse and the ringing
of two Twin-T resonators, with the Tone pot controlling the mix of the outputs of the two resonators. There are two Snare Tuning pots,
one for the upper resonator (blue knob) and one for the lower (yellow knob). Tuning
is at the normal pitch when these pots are anticlockwise (ACW) and is
reduced by around an octave when they are clockwise (CW).
- The Cymbal Soft Attack switch (above the three small pots) gives more of a ride cymbal sound, compared to the normal crash sound. The attack is soft and the decay is somewhat extended.
- The Toms have a pulse of filtered noise, which is barely
perceptible, but gives them something of a rumbling sound. These
pulses are shortened somewhat. (In Conga mode, there is no such
- The Tom/Conga circuits each have a Decay
pot, where ACW is the normal decay time and CW is a much shorter decay
time. These are the three small pots with silver indicator lines.
- The Hand Clap sound is composed of a series of close-spaced
pulses of filtered and distorted noise plus a softer pseudo-reverb
exponential decay pulse of softly filtered noise. The Clap Reverb Disable
switch (below the three small pots) turns off this pulse, leaving the
dry, stark, and potentially extremely loud main pulse-cluster of the
- The Hand Clap Density pot
(red knob) controls the density of this cluster of pulses, from being very light
(ACW) through normal, to each pulse being bigger, to all pulses being
much louder and joined together (CW).
- The Noise Level pot (white knob) controls the
output level of the internal White Noise Generator. ACW creates a
somewhat lower than normal level of noise. 12 o-clock creates a
somewhat higher level. 3 o-clock creates a much higher
level. Fully CW produces an extreme level of noise such that the
Tom "rumble" circuits are occasionally overloaded, even when not being
triggered, so there will be sporadic crackles through each of whichever
of the Tom/Conga channels are in Tom mode.
The internal White Noise Generator runs from a noisy transistor and is genuinely random broadband noise. It is used for:
- The Snappy pulse of the Snare Drum. Increased noise levels make this a very strong pulse indeed.
- The Rumble pulse of the Toms. High noise levels lead to
more rumble to the point of completely unphysical rumbles and muffled
- The Maracas sound is based on this signal, but it is hardly affected by the noise level.
- The Hand Clap sound, both the pulse-cluster and the
pseudo-reverb, is based on this noise source. Higher noise levels
lead to gutsier and potentially very loud hand-clap sounds. It is
generally best to disable the Hand Clap Reverb when high noise levels
are used. The resulting clap sounds, especially with the Density
control turned somewhat to the ACW and with the Noise Level pot set to
about 2 o'clock, are a unique and gusty discrete sound. Since
these are generated from real analogue noise, no two Hand Clap sounds
are the same.
- * The Accent Button
forces Accent on even if the internal sequencer's pattern has no Accent
on the current beat. This Accent state also drives the 4 Level
are three audio signal inputs. (6.5mm mono sockets on right
side.) When an audio signal is plugged into one of these, that
signal takes over the
role of an internal noise signal. These are not to trigger drum
sounds - they are signals from which drum sounds are made.
- Cymbal / Hi Hat Alternative Noise Input.
Normally the Cymbal and Hi Hat sounds are created from a mix of 6
square-wave oscillators. This signals is filtered, distorted in a
gating circuit (which controls the volume) and filtered
again. By plugging an audio signal into this socket, the 6
square-wave oscillators are no longer used and the Cymbal and Hi Hat
sounds are made from the input signal instead. Bright, high,
chord sounds are an obvious choice of signal - they cause the Cymbal
and Hi Hat sounds to be metallic shimmering (low level) or mashed and
splattered chord-related sounds. Playing a single pitch into this
signal results in single-pitch square-wave Cymbal and Hi Hat
Playing a continual cymbal sound (such as from a large
cymbal hammered softly with a mallet) results in realistic sounding
Cymbal and Hi Hat sounds, depending on the level. (I did this in
the 1980s. If someone can send me a suitable long, constant
level, recording of a ride cymbal being hammered reasonably gently, I
will use it in this way in another sound demo.)
The Cymbal and Hi Hat circuitry is beautiful, inspired and completely
unique to the TR-808 and TR-606. This Alternative Input enables
the creation of many bright, delicate and potentially wild
sounds. It is my favourite part of the TR-808.
Each TR-808 has a unique tonality to its Cymbal and Hi Hat sounds, due
to each machine's six square wave oscillators having a unique set of
frequencies. As demonstrated in one of the sound recordings sounds/
it is possible to use this socket as an output for this mix of six
square waves - by gently inserting a plug until it touches the tip
contact of the switch, but not hard enough to lift the contact from the
normally closed contact. Then, it is possible to record a few
minutes or whatever of this mix of square waves. This can be
played back into a second TR-808 via this Input, and the second
machine will have the tonality of the first machine, assuming the
playback level is adjusted to match the required signal level. Of
course, this recorded signal could be subject to manipulation by
changing its playback pitch, but distorting it, by adding reverb,
random vibrato or whatever via audio editing software, so the original
tonality could be used in the same machine, with various modifications.
- Hand Clap and Maracas Alternative Noise Input.
Whatever signal is input here replaces the internal white noise
generator in the Hand Clap and Maracas circuits. Random mid-range
to high frequency noise, chords, distorted and/or reverberated chords
or various other signals result in staccato Hand Clap sounds which
are unique to the Modified TR-808 and would never result from
conventional synthesis techniques. These can be musically dramatic - please check out the recordings in the sounds/ directory.
This socket (and the next) can be used as an output for the internal
noise source, with the same technique as described above for the CY/HH
Alternative Noise Input. It is (in audio terms) "white" noise -
real noise from a reverse-biased transistor junction going into
avalanche breakdown. There are many other sources of noise in the
modern world, but this is a source and it might be handy. The
volume and to some extent the character of the noise will vary with the
setting of the Noise Level pot. There's no significant difference
in the audible quality of the noise between one TR-808 and another.
- Snare Drum Alternative Noise Input. This signal replaces the internal white noise generator for the Snare Snappy noise pulse circuit.