ARP 2500 - 1042 module

 This is one of ARPs 2500 "lost modules"

I've never seen one of these ... even as a picture.

I don't know if any were even produced.

Please let me know if you have any info .

I have a AM Synths AM1042.

It's probably the closest I'll ever get to one of these.

There are 3 circuits using the ARP 4019 VCA circuit

in each case.

The ARP 4019 is a classic discrete transistor voltage-controlled amplifier (VCA) sub-module originally used in the ARP 2600 .

+ ARP 2600 - VCA

VCA  (4010 & 4019)

The circuits have AC & DC inputs

They are classic VCAs

Plug the audio into the AC input & the CV into the DC input.

The DC inputs are better suited for CV signals.

If you just use the 3 AC inputs (for audio) it's a good amplifier

Each circuit has a black slide switch for VCA mode (linear or expo).

So which do I choose??

Linear VCA modes provide a 1:1, natural response ideal for mixing and modulation, while exponential modes produce a "snappier," faster response suited for percussive audio, aligning with how human ears perceive volume. 

Linear is generally best for CV modulation, whereas exponential is preferred for sculpting amplitude envelopes to sound more natural.

Human ears hear logarithmically, so exponential VCA responses often sound more "linear" in volume to our ears, whereas linear VCAs can sound abrupt.

Mixing Methods: If using a linear envelope, an exponential VCA creates a natural-sounding curve. Conversely, if using an exponential envelope, a linear VCA is sufficient.

------------------------------------------

Exponential VCAs (The "Audio/Percussion" Standard)Response: 

Follows an exponential curve; slow initial response, faster later on.Best For: Audio amplitude (VCA as a volume envelope).Characteristics: "Snappier," faster, and more "natural" sounding for percussive or fast amplitude envelopes.Use Case: Percussion sounds, or creating smoother decays if the envelope itself isn't already exponential.

Linear VCAs (The "Modulation" Standard)Response: 

CV input directly maps to audio gain (e.g., 5V = 50% amplitude).Best For: Modulation, controlling other CV signals (FM, PWM), and precision mixing.Characteristics: Easier to predict and manage; sounds more gradual.Use Case: If you need subtle, precise control over modulation depth

ARP-2600 - AD & ADSR Trigger and gate inputs

The vast majority of synths made today have two primary types of control voltages : 

CVs and gates. 

The CV is for pitch & gates are used to fire envelopes.

Most Eurorack modules output a 1V/oct pitch voltage, and a +5V gate. 

Korg and old Yamahas use Hz but that's another story.

When I first bought my 2600 , I exclusively used the S/H gate

jack as my gate input.

This mostly worked as long as I had a +10V gate.

And if you had installed a gate booster you could boost those

pesky Eurorack +5v voltages to keep the ARP happy.

In most cases the AR & ADSR envelope generators are used to control the filter & VCA.

They can also be used to modulate other sections such as the VCOs.

The AR has a constant sustain (it's open as long as you press a key).

The AR envelope is not prewired to the VCOs so we need to use a patch cable to use it.

It is however prewired to the VCA.

The AR has a linear shape, vs the ADSR which is exponential.

The human body naturally perceives changes (such as in audio volume or changes in light) exponentially rather than linearly.

So if you want the volume to change "naturally" use the ADSR 

This is the basic setting for connecting a sequencer/keyboard to the 2600.

Note that the switches above the CV inputs must be UP and the switch above the S/H gate must be down.

For about 10 years I mostly ignored those two jacks next to the S/H Gate thinking they were just 

gate & trigger outputs from the ARP 2600 keyboard (which they are) since the arrows pointed out.

Actually, they are also inputs !!  ... that is they are bi-directional.

After a bit of research I learnt that the old ARP 2600 (& ARP2500) use an almost forgotten system of triggering envelopes.

They use both triggers & gates.

How does this work?

The ADSR is as you'd expect.

Here is a common envelope shape when using a a trigger & gate  

The "trigger" is the envelope's cue to start the ball rolling but it won't do anything

unless it also sees a gate (in the above drawing its the spike at zero time).

ATTACK
When a gate signal is applied, the EG's output will rise exponentially to 10V
(the rate is determined by the "attack" setting).

DECAY
When 10V is reached, the attack phase is ended, and the voltage will decay exponentially to the Sustain level. (the rate is determined by the "initial decay time" setting). In modern synths, we just call this the "decay".

SUSTAIN
The sustain level is adjustable from zero to 10V
The output remains at the sustain level until the gate is removed.

RELEASE
When the gate is removed, the voltage drops to zero volts.
This is called the "Final Decay Time".
The rate of the drop is exponential and is determined by the "Final Decay Time" setting.

If the gate signal is suddenly removed, the envelope will immediately start to decay to zero unless
another gate is inputed. In this case the envelope will then restart the attack phase.

This system of gates & triggers makes very complex envelopes possible 

If you don't have a sequencer with both triggers and gates

you can "trick" the 2600 by plugging into both the trigger & gate jacks the same gate signal.

I've tried this with a Arturia keystep and it works fine.

We are multiplying the gate signal and sending this to both GATE & TRIGGER inputs. Make sure the switch above the S/H Gate is up.

Another option is to set two VCOs into LFO mode.

I like to use a pulse for the gate, and a saw for the trigger.

It works too !

This is from the ARP sequencer manual:

Notice the triggers and gates.

The 1601 & 1613 sequencer has a unique gate bus that allows mixing of Gate and "triggers".

Another sequencer  to use is the Klee.

It also uses a bus that mixes gates & triggers.

I have a Analogue Solutions French connection.

https://www.analoguesystems.co.uk/index.php/keyboards/the-french-connection

This unusual keyboard apart from the Ondes Martenot ring controller has CV, Gate and trigger outputs. 

Other possibilites in the world of eurorack include 

ALM Busy Circuits ASQ1

Or just combine a CV/Gate sequencer with a percussion sequencer.

(plenty out there)

Links:

+ Arp 2500 - 1003, 1033, 1046 envelope generators

+ ARP 2600 - Envelope Generators

+ ARP 2600 - Sample and hold (& electronic switch)

+ ARP 2600 - Ring Modulator

+ Arp 2600 - Envelope Follower & pre-amp

+ ARP 2600 - Voltage processor

+ ARP 2600 - Filter

ARP 2500 - sync with 0-c0ntrol & AE modular

 Some personal notes of syncing the ARP2500 with external gear.

I'm using the ARP2500 sequencer as the master clock.... the 1027 module

It's sending a clock into the 0-control clock input

The clock out from the 0-control goes into 

the AE modular

Its the orange cable ... into the 4 I/O.

The 4 I/O is a great & safe way to input/output external audio and Cv

Importantly, the sockets have overvoltage protection 

(as AE modular is limited to 5V).

They can be switched between audio and DC/CV signals.

The output from the 4 I/O is driving the trigger sequencer

TRIQ164

Finally, CV and gates/envelopes from the 0-control enter the AE modular via the Master I/O

https://wiki.aemodular.com/pmwiki.php/AeManual/MASTER

I'm not sure if the input/output is voltage protected.

Though seems to work without any probs ....but if you're worried 

the external voltages might be too high, its better to use the 4 I/O

and keep things below the 5V level.

 

ARP 2500 VCOs

 The Arp 2500 has 3 "types" of VCOs

1004‑T: Single Oscillator Module
1004-R: Single Oscillator Module
1004-P: Single Oscillator Module

The 1004-P

P stands for Potentiometer.

This is a Voltage Controlled Oscillator with a range

 from 0.03Hz to 16kHz.

This module can function as a VCO or an LFO. 

It features separate outputs for each of its five waveforms 

(sine, triangle, square, sawtooth, and pulse)  and a final

mixed output.

There are 6 CV (control voltage) inputs (3 at the top and 2 at the bottom of the module)

 

Input #4 is a CV input for Pulse Width Modulation.

 

The pots allow for gradual shaping of the waveforms.

You can easily mix different volumes of each waveform with one another to sculpt your sounds

The 1004- T

T stands for Toggle

This is a Voltage Controlled Oscillator with a range

 from 0.03Hz to 16kHz.

This module can function as a VCO or an LFO. 

Its core is identical to the above 1004-P.

 

It features separate outputs for each of its five waveforms 

(sine, triangle, square, sawtooth, and pulse)  and a final

mixed output.

There are 6 CV (control voltage) inputs (3 at the top and 2 at the bottom of the module)

 

Input #4 is a CV input for Pulse Width Modulation.

 

The toggle allow for quick shaping of the waveforms.

You can easily add and remove different waveforms from the final mix to sculpt your sounds.

 

The toggle version also allows you to add/remove inverted waveforms

1004-R

R stands for Rocker.

This is a Voltage Controlled Oscillator with a range

 from 0.03Hz to 16kHz.

This module can function as a VCO or an LFO. 

Its core is identical to the above 1004-P & 1004-T

 

It features separate outputs for each of its five waveforms 

(sine, triangle, square, sawtooth, and pulse)  and a final

mixed output.

There are 6 CV (control voltage) inputs (3 at the top and 2 at the bottom of the module)

 

Input #4 is a CV input for Pulse Width Modulation.

 

The rocker switch allows for quick shaping of the final mixed waveform.

You can easily add and remove different waveforms from the final mix to sculpt your sounds.

 

This is a simplier version of the 1004-T however its the rarest of the bunch

ARP 2500 - 1047 Multimode Filter / Resonator

The ARP2500 filter/resonator 1047 module

It's a lovely sounding filter whos design evolved from analog computing.

 

 This module is a combined Low Pass, Bandpass, Highpass and Notch (band reject) filter.

All the filter outputs are available simultaneously in the lower section of the module.

This is why it's called a multimode filter.

 

I think the 1047 was one of the first multimode filters ever produced.

 

Resonance or Q, controls filter shape.  

Low Q settings give wider and smoother filter shapes.

They result in a gentle effect on the sound.

 

As you increase Q, the filter shapes become narrower & sharper. THis helps in focusing on narrower frequency bands.

As Q goes even higher "pinging" may occur, esp if you trigger the filter with a gate.

This is good for percussive sounds.

 The filters start to peak boosting some frequencies into overload territory.

 

 

 

 

 

 

 

 

 

 

These are the outputs and inputs

 

There are two audio inputs, two filter cutoff frequency control voltage inputs and two 

resonance inputs for CV control. The 6 pots are attenuators for these inputs .

 

What's really interesting about this filter is the bandpass section.

The 1047's band pass filter mimics that of a natural acoustic resonator.

Typical examples of natural resonators include strings, pipes, horns, drums.

The bandpass is a single pole 6 dB slope.

This gentle 6dB slop which lies on either side of the frequency cutoff point makes it

ideally suited for replicating things like drums, violins, etc

The filter can self oscillate as the resonance (Q) is turned up.

 

So you can patch a trigger into the filter and make it "ring" at very high resonance levels.

The input for your trigger is in the top right corner of the module.

 

The decay time of the ring is set by the resonance control. 

 

This filter design is how many analog drum machines

emulate sounds like Kicks and Toms.

You use the frequency knob to set the pitch.

I like to use a sequencer to automate varying the pitch while pinging the filter with a trigger/gate signal.

This ringing occurs as it's design is similar to mechanical resonators which ring when struck by an impulse of energy.

 

 

 

 

Turning the "Keyboard Percussion" switch to "on"  will connect the trigger output of your keyboard (or whatever other module is producing the trigger) to the audio input of the filter.

 

The Algorythm by Grayscale is excellent for this task.

 

 

 

Unlike earlier bandpass filters which simply combined LP & HP filters, 

The 1047 filter is an analog computing circuit consisting of summers and integrators.

 

If I'm reading the schematic correctly it looks like a State Variable filter.

 

 The state variable filter is a type of multiple-feedback filter circuit that can produce all filter responses simultaneously from the same single active filter design.

 

In programming a state variable filter/resonator on an analog computer, we'll need two integrators and one inverter connected into a loop.

 
You can see 3 op-amps (A1,A2,A3)
The last two use capacitors in a negative feedback loop -- they are RC integrators.
The first opamp is a summing amp.

Tapping the output of the first amp gives you the HP output.
Tapping the second gives you the BP output.
This BP out is fed back into the 1st op-amp, (non-inverting input).

Tapping the output from the third OP amp gives you the LP output.
This is fed back into the 1st opamp (the Summing amp)... the non-inverting input.

 

Filter frequency can be set both manually & with control voltages. 

The center frequency Fc of the band-pass output is the
cutoff frequency of the high-pass and low-pass outputs.
F c may be set by the coarse and fine frequency knobs
over the range of 16 Hz to 16 kHz.

There is also CV control over resonance.

With the resonance (Q) knob at minimum and the resonance switch set to "norm," the band-pass output has a gain of 0.5, and attenuates 6 dB per octave above and below Fc

 

 

 

 

 

 

 

When triggering, watch the overload light.

It indicates excessive input

 

Note that there is a resonance limit switch.

Setting it to "LIM" prevents signal overload when high levels of resonance are used.

 

 

 

 

Or the INPUT attenuator knob can be turned down

if the input source is the cause of the overload.

 

The switch effectively limits the height of a filter’s resonant peak. 

The LIM setting is preferred for signals which possess a strong harmonic or fundamental frequency.

 

----------------------------------------------------

The Notch Filter

This notch Fc knob is used to offset the notch filter’s center frequency (“fc”) set by the COARSE and FINE frequency controls. 

 

 The filter passes lows and highs, cuts out frequencies somewhere in the middle

 

 

The default setting for the notch filter is 1. 

 

In the pic above, the dial is fully counter clockwise. 

Thus the Notch frequency is shifted significantly below the filter's frequency cutoff (fc).

In effect, the notch filter is a copy of the high-pass filter. 

The reverse occurs if the dial is fully clockwise (ie past 4). 

The Notch frequency is shifted significantly above the filter's frequency cutoff (fc).

In effect, the notch filter is a copy of the low-pass filter. 

Notch filters can be used to create a faux phasing effect by modulating the cutoff with an LFO.

The notch filter is kind of like a high pass & low pass filter in parallel. 

The sound is quite cool, esp when sweeping noise

----------------------------

Links

+ EG & G Selective Amplifier model 189

+ Dennis Collins paper

 

For more info google:

 

stand-alone Analog Computation equipment used for Electronic Music

North America based companies EG&G (Edgerton, Germeshausen & Grier) and PARC (Princeton Applied Research Corporation) of New Jersey (Princeton roughly between New York and Philadelphia),


EG&G PARC model 121

 

 

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ARP index

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ARP 2500 & Make Noise 0-control

 Patch notes using the MakeNoise 0-Ctrl.

The zero-control seems to be really good for controlling the ARP2500.

The +8V gates seem to be fine for triggering the 2500's EGs  

The Pitch CV is OK too.

The ARP 2500's sequencer is the master clock.

It's clocking the 0-control.

The 0-ctrl's pitch is controlling the pitch of the 1023 VCO

The 1033 EG is triggered from the 0-ctrl.(I've used its gate inputs).

EG left is triggered from CV (strength channel).

EG right is triggered from #6 gate out

 To trigger the gate, the strength knobs need to be fully clockwise.

 

 

 

 

 

 

 

 

 

 When the 0-control is receiving an external clock, the time knobs don't influence the step time anymore, but they are still outputting a CV. 

 

This can be used to control things ... like trigger the 1033 envelope.

 

 

 

 

 

 

 

 

Both the 1033 & 1046 EG modules work well with the 0-ctrl.

Possible combinations:

Use "strength" to control one EG and "time" to control the second.

If there are 4 EGs, then  use the individual gate outputs.

Of course the 1027 sequencer can also make more gates.

 

 

Links

+ 0 cONTROL - bASIC pATCHES
+ 0-Coast - Basic Notes 

+ Arp 2500 - 1003, 1033, 1046 envelope generators

+  ARP 2500 - 1046 envelope generator & eloquencer

ARP 2600 - Envelope Generators

 The 2600's & TTSH's Envelopes

 

 The ARP 2600 has two envelope generators.

The first is a full four-stage (ADSR) Attack, Decay, Sustain, and Release Envelope. 

 

 

The second EG  is a simpler AR offering variable Attack and Release only. It works really well for making percussive sounds.

The Manual Start button allows both the Envelopes to be retriggered at any time, without using the keyboard. 

 Usually, however, the EG is triggered with a +15V spike of voltage (trigger pulse) from the keyboard. As soon as the key is pressed, the keyboard also begins generating a gate signal.

The cord that connects the keyboard is on the left side of the tolex cabinet. It has six prongs.

 

 

The envelope module also provides both Gate and Trigger outputs for patching to external modular gear.

The S/H Gate jack is an input.

It's wording is rather misleading. 

When nothing is plugged into the jack, the internal clock (that is used in the sample & hold circuit) triggers the envelopes if the switch is in the lower position.

It seems that the 2600’s designers considered the electronic switch, the internal clock and the sample-and-hold units all part of the “Sample-and-Hold module.” Hence the label on the jack below the EG’s. However, it is really the internal clock which is responsible for causing the EGs to fire, not the sample-and-hold unit. (Fundamentals of Music Technology  by Samuel Ecoff)

Thus when the S/H switch is in the lower position, the envelopes will self trigger. Like a LFO.

The rate of the trigger will be controlled by the 2600's internal clock.

If you wish to externally trigger the ADSR or AR envelopes, connect a clock (+10V  pulses) or a +10V gate.

The switch should again be in the lower position.

The eurorack Winter Modular Eloquencer triggers these envelopes perfectly.

I've also had success with the Music Thing Modular Turing Machine. (mk II).

 

 

The internal clock’s connection to the EGs can thus be broken by returning this switch to the upper position.

You can now trigger the EGs with the keyboard.

 

The ADSR EG is normalled ( hardwired) to FM inputs on each oscillator and one of the control inputs on the VCF.

The VCA has two control envelope inputs .. the first normalled to the AR envelope, and the 2nd normalled to the ADSR. 

Thus, the EG’s can be used to raise the filter’s Fc every time a key is pressed. 

 

They can also be used to modulate the VCA.

You of course can override these hard wired (very west coast connections) and modulate the VCOs

or Filter with an AR envelope.

Both envelopes in-fact have their own outputs which to can patch to any place your heart desires.

 

Another module you can incorporate to make the envelopes more interesting is the inverter.

The ARP 1601 sequencer is a great device if you can get your hands on one.

Quite rare these days, though I understand there is a clone available.

 

This is a basic patch for connecting the 1601 with a 2600.

The quantized CV outs of the 1601 are connected to VCO 1 + 2's CV inputs.

The 1601's "clocked Gate 1 Out" is connected to the 2600's S/H GATE input jack

 

A second way to connect is just plug the clock out into the  2600's S/H GATE input jack.

The Clock out is a +10V pulse.

 I have also tested a ARP2500 sequencer with the 2600.

This basic patch works very well.

Clock out of the 2500, to the 2600's S/H GATE input jack.

 

You can also connect the gate outs (of the 2500) to the 2600's S/H GATE input jack.

 

 

 

 This is only a brief introduction but. should get you started. I'll cover more features of the 1601 in later blog posts.

ARP 2500 - 1026 Preset Voltage Module

The 1026 is a rare module. I think only a few were produced and Ive never seen a original

though there are a few reproductions around.

Probably the year of production of the originals was about 1970 ???  

 

There are 16 preset voltages : 2 rows of control voltages 

each holding 8 individual CV values.

You set their value with the pots.

You trigger the CVs by pushing the associated momentary button

or with a 10V gate. (at lines 1 to 8).

The output voltages appear at lines 9 & 10.

Pretty simple.

The manual suggests using this with the 1027 sequencer or 1050 Mix-sequencer.

There is a socket at the rear of the unit to connect to a 1027 or 1050.

 

Specs:

Output voltages: 0 to +10V

Output impedances: 1K ohms

Input impedances : 100 K ohms

Power requirements: +/- 15V @ 20ma , regulated to +/-0.1%

 

 

 

 

 

 

It reminds me very much of the Serge programmer.

I have of course, rotated the pic to illustrate my idea.

I wonder which module came first?

The programmer has evolved into many forms today.

Think Makenoise pressure points & 0-control 

or Synthwerks 4x4