ARP Avatar for the weekend sir?.......updated

[StephenGiles]

http://img.photobucket.com/albums/v517/uncle_boko/Arp%20Avatar/ArpAv1.gif
http://img.photobucket.com/albums/v517/uncle_boko/Arp%20Avatar/ArpAv2.gif
http://img.photobucket.com/albums/v517/uncle_boko/Arp%20Avatar/ArpAv3.gif

food for thought??

The story so far:

3.5 Board E
3.5.1 PREAMPLIFIERS
Z1B through Z6B are the string preamplifiers. The trimmers on the output of the amplifiers adjust the gain from 22 to 220. Coupling capacitors C1 through C6 rolloff frequencies below the lowest note of each string for hum reduction.
3.5.2 FUZZ CIRCUITS &
FUZZ PREAMP SELECT SWITCH CIRCUIT
Z1A through Z6A are the Fuzz Circuits. They have a gain of about 20, a rolloff above approximately 2 KHz, and are soft clipped at +0.7 volts by the feedback diodes. Z7 and Z8 select either the preamplifier signals or fuzz signals which are routed to the Hex Mixer, Left Output Mixer, and the Right Output Mixer Circuits.
3.5.3 STRING SELECT LOGIC
Z15 is a priority encoder which produces a three bit binary code for the last pulse it has received from the Trigger Detector Circuit. When a pulse appears on any of the inputs of Z15, pin 14 fires Z17A which generates a TRIG pulse. R123 creates a small delay to make sure the outputs of Z15 have settled. The TRIG pulse then latches the latest three bit string code into Z16B, Z17A and Z17B. This code is supplied to the Audio Multiplex Circuit so that it will pass the appropriate guitar string signal from the preamplifier to the pitch extractor module (E'). The code is also sent to the E' module and to the Ramp


3.5.4 AUDIO MULTIPLEX CIRCUIT
Z18 is an eight channel audio multiplexer. The audio inputs (pins 5, 1, 12, 15, 14 and 13) are switched to the output (pin 3) according to the three bit string code on pins 9, 10, and 11:
3.5.5 TRIGGER DETECTOR CIRCUITS   
Z9 through Z14 are the trigger sensors. Looking at the high E channel, Z9C and Z9D form a peak follower. The negative going output is stored by C25. Z9D is a noninverting peak follower and Z9C is an inverting peak follower. Their outputs are 'wired-ored' together for full wave operation. R67, R79, and C37 form a low pass filter, with an attenuation of 2. R73 and C31 form a high pass filter, with DC offset (from TRIG SENSE) added. When the high pass output falls below the low pass output, Z9B will fire, discharging C43. C43 will recharge through R85. Z9A converts this voltage to a wide pulse and C49 passes the rising edge of the pulse to the String Select Logic Circuit. CR13 grounds the pulse when the enable line from the String Select Switch on the front panel is low.
3.5.6 E'MODULE
The E' Module accepts the guitar signal from the Audio Multiplex Circuit (MUX, pin 17) and extracts from it a pulse wave (CLK and CLK). This clock output (at the frequency of the guitar string) is sent to the D board for processing. The three bit string code from the String Select Circuit is supplied to pin 13, 14 and 15 so that the circuit can 'set up' for the open string frequency of the guitar signal it is to receive. The clock output (CLK, pin 23) is also sent to the Limit Detector Circuit to generate Transfer (XFER) and Clear (CLR) signals. The level signal from the E' Module goes high to confirm that an extracted signal is appearing on the clock output.
The CV input (pin 6) comes from the output of the D' Module and is used to adjust the E' circuit to the pitch which is being extracted. After an initial pluck, the TRAIN signal (pins 10, 12) causes the E' Module to ignore temporarily the CV input until a new pitch has been extracted and processed through the D board.
The Q GATE inputs (pins 20 and 19) instruct the E' Module to begin extraction.
3.5.7 RECTIFIER/FILTER
The signal from the Audio Multiplex Circuit (MUX) is sent to the Rectifier/Filter Circuit which is a precision full wave rectifier. C76 partially averages the output and Q3 discharges upon each TRIG pulse so that the rectified average starts from zerio on a new string pluck.
3.5.8 GATE DETECTOR CIRCUIT

The purpose of the Gate Detector Circuit is to make the gating sequence dependent upon a signal with good energy; hence, making the gating insensitive to accidental striking of the guitar string with a pick.

When the output of the Rectifier/Filter Circuit exceeds the threshold established by R205 (about .5 volts on Z27 pin 9, when A GATE is high), Z27C will go low (A GATE output). This starts the gating sequence.  The threshold  is set by R205 so the  A GATE goes low after the second cycle of a moderate level input. Final adjustment should be done with a guitar since this adjustment is to a degree a matter of preference.

3.5.9 ENVELOPE FOLLOWER

Z24 and Z25 take the rectified signal from the Rectifier/Filter Circuit and smooth it out to yield an envelope suitable for VCO or VCF modulation. Z24 controls the time constant for a fast attack and smooth decay. On initial pluck, C73 charges quickly since the TRAIN signal switches in R182 via Z24B. After a pluck, C73 follows the signal more slowly through R183. When the note dies out, A GATE turns on Z24B to discharge C73 quickly.
3.5.10 GATE LOGIC   '
The Gate Detector Circuit starts the gating sequence. When new notes are plucked, the Gate Logic circuitry is reset by the TRIG signal.
First, A GATE clocks Z30A to produce a TRAIN and TRAIN signal which is used to set up E' Module for initial new note extraction. It is also used in the Envelope Follower Circuit to create a fast rise time envelope.
Next the TRAIN signal clocks Z37A to generate a Q GATE and Q GATE  signal which is used to start the E' extraction. Once the E' has begun extraction, it sends out a LEVEL signal to the Gate Generator Circuit to hold A GATE low for the duration of pitch extraction.
Pitch Gate is generated by Z34B which confirms E' pitch Extraction. The extracted pulse wave (CLK) output from E' clocks Z33A in the Limit Detector Circuit which is in turn supplied (in pulse form) to the 'set' input of Z34B to produce the PITCH GATE and PITCH GATE signals.
As soon as the PITCH GATE signal goes high, one shot Z30A (TRAIN) is allowed to time out. Thus the time constant of the TRAIN one shot (and therefore the duration of TRAIN) is dependent upon the presence of a clock signal on the E' output (via Z33A and Z34B). The PITCH GATE is also used to enable the Envelope Follower.
Sustain Latch: The purpose of the SUSL and SUSL signals is to 'freeze' the extraction process while the sustain footswitch is held. Z30B is used as a de-bouncer for the footswitch: when the footswitch is depressed, Z30 pin 9 goes high which clocks Z32B (the sustain latch). Providing the D gate is high, (when TRIG and A GATE are both low) SUSL goes high and stops the following signals from changing: TRAIN (via Z30A pin 3), D GATE (via Z31 pin 5), Q GATE (via D GATE to CR24 and 2290), and TRIG (via Z17A pin 5 in the String Select Circuit). During the time the footswitch is held, no pitch extraction takes place and new string plucks are ignored.
3.5.11 RAMP GENERATOR CIRCUIT
The purpose of the Ramp Generator Circuit is to generate a window to determine if the extracted pitch from the E' Module is within acceptable frequency limits. The extracted signal (CLK) is compared with the ramp generator signal in the Limit Detector Circuit and determines the validity of the pitch. Anything the E' Module produces which exceeds these limits is ignored by the D board.
Upon an initial string pluck, the three bit string code is sent to an Audio Multiplexer (222) in the Ramp Generator Circuit which selects one of the resistors on pin 5, 1, 12, 15, 14, or 13. These resistor values are selected to produce a specific current (for each string) which charges C72. The Clear pulse (CLR), which is generated by Z33B, resets the Ramp Generator.
3.5.12 LIMIT DETECTOR
The Transfer Enable (XFEREN) and Clear Enable (CLREN) signals are generated by the Limit Detector Circuit. Transfer Enable transfers data from the input counters on the D board for a new number.
To generate these signals the ramp voltage from the Ramp Generator Circuit is compared to fixed thresholds in the Limit Detector Timing Circuit by Z27A and Z27B. Pin 1 of Z27B will be high when C27 is discharged and will go low after enough time has passed to account for one cycle of the highest note of the string being played. Until it goes high, both CLREN and XFEREN will be low, causing the D board to ignore transitions of the CLK signal. Z27A pin 2 will initially high also, and will go low after a time equal to the period of the lowest note of the string. Once it goes low, it will set XFEREN low, causing the D board to ignore the period measurement of the current CLK cycle, yet still allowing the D board to clear its counter when the next cycle starts. The thresholds of Z21A and Z21B are set so that pitch information will be passed only if it is between four semitones below the bottom of the string and two octaves and two semitones above the bottom of the string (21/a octave range). Any frequency that the E' produces outside of these limits is considered 'out-to-lunch' and accordingly is ignored.

3.5.13 LIMIT DETECTOR TIMING
The Limit Detector Timing Circuit generates a CLR signal and a 1st XFER INHIBIT signal. Z33A is clocked by the extracted pulse from the E' Module (CLK) and produces a pulse on the Q (pin 1) output. The Q output of Z33A clocks Z33B to produce a clear (CLR) pulse to reset the Ramp Generator.
The CLR signal from Z33B (pin 12) sets Z34A (first transfer inhibit). Until it is set, XFEREN will be low, hence disabling the first transfer of the D board since it is necessary to wait for the second clock cycle before any valid period measurement can be made. R221 and CR25 gate the 'transfer' pulse from Z33A and XFER ENABLE together causing Z34B (PITCH GATE) to be set on the second pulse.

[petemoore]

  Did you mean 'Month-end' ?
  ...or yearend ?
  Because that's what it looks like to me .

[StephenGiles]

That's something that barbers always used to say years ago to customers because they sold contraceptives!!!

[Peter Snowberg]

Thanks for posting that.

Pity it doesn't have per-channel gain controls (yet).

One mod suggestion if using stereo outputs... rather than hard-panning the 3rd and 4th to opposite sides in the final mixer with 100K resistors, I would use 200K resistors going to either side so that the strum across the space is more gradual.

[Gilles C]

Cool. A bit every weekend, and the year would be gone...

I should try a string with the G-Vox Pickup I bought but never used.

Gilles

[gez]

That's something that barbers always used to say years ago to customers because they sold contraceptives!!!

And wasn't it Oscar Wilde who replied "not with a fcuking haircut like this mate!"?..well, perhaps not.

[petemoore]

  Mighty big circuit and thanks for posting !!!
  It has my curious interest up, hope high and expectations low...that's how it is for for me circuits like that.
  Oh yeah, the curiousity...what all 'does it do.
  I see the lables, but don't know I've ever heard about or heard a passage using one that I could place.

[StephenGiles]

Original post has been updated.

[Rodgre]

I have had one of these for years (without the guitar, so essentially a keyboardless Arp Oddyssey) but have yet to get it to make a peep.

HELP!

Roger

[StephenGiles]

There's a load more circuitry for this when I have time, we're going to watch polo today and the sun is warming up to 30C!