ARP 4019
Voltage Controlled Amplifier module for the ARP 2600 synthesizer
Overview
The ARP 4019 is a Voltage Controlled Amplifier (VCA) module designed for the ARP 2600 synthesizer, replacing the earlier ARP 4010 used only in the first 2600 units. It was designed by Dennis Collins and features both linear and exponential control voltage inputs. The module requires trimmer adjustments in the ARP 2600 to prevent distortion, though the CV rejection and high-frequency rejection trims have little effect. A known circuit board error in the ARP 2600 places the exponential trim across V+ and GND instead of between -V and V+ as intended in the original Tonus 4019 schematic.
Design
The ARP 4019 VCA is a long-tailed pair with current mirror and diode buffer, built around a non-potted 4005 VCA type 1P. It uses three pairs of matched transistors to minimize VCA thump, a characteristic of the original ARP design. The exponential converter uses complementary transistors Q1 and Q2 with matched saturation currents (Is) and base-emitter voltages (Vbe), driven by an external 54.9K resistor connected to pin 4. The linear control voltage drives a 100K external resistor attached to pin 3. A Wilson current mirror (Q6, Q7, Q8) sums the currents from the two input sources, setting the operating current for the differential pair (Q9, Q10), whose collector load is a cascode current mirror (CR10, Q11, Q12, Q13). Audio is applied to both sides of the differential pair, with output current converted to voltage by an LM301 opamp acting as a current-to-voltage buffer.
Specifications
| Format | Original ARP 2600 sub-module |
| Linear CV Input | Drives 100K external resistor connected to pin 3 |
| Exponential CV Input | Drives 54.9K external resistor connected to pin 4 |
| PCB Mounting | Long gold PCB pins not supplied; 1mm gauge wire can be used |
Context
The ARP 4019 VCA module was used exclusively in the ARP 2600 synthesizer and is not a standalone instrument. It succeeded the ARP 4010, which appeared only in early ARP 2600 units. Modern reproductions, such as the New England Analog NEA-4019, are available as Eurorack modules and PCB/panel sets for repair or DIY replacement.
Market
A New England Analog NEA-4019 clone PCB/panel set is sold for $40.00.
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