• Wide dynamic range
• Wide gain range
• Exponential (linear dB) gain control
• Low distortion:
~ 0.0025 % (2181A)
~ 0.005 % (2181C)
• Wide gain-bandwidth
• Dual gain-control ports (pos/neg)
• Pin-compatible with 2150-series

Datasheet Download

Datasheet Download
2181 Series Datasheet (384 kB)
Trimmable Blackmer VCAs


• Faders
• Panners
• Compressors
• Expanders
• Equalizers
• Filters
• Oscillators
• Audio consoles
• Automation systems
• Automatic mixers
• Teleconferencing systems
• Exponentially voltage-controlled current sources


THAT 2181-series trimmable Blackmer voltage-controlled amplifier (VCA) ICs are very high-performance current-in/current-out devices with two opposing-polarity, voltage-sensitive control ports. They offer wide-range exponential control of gain and attenuation with low signal distortion.

The parts are selected after packaging based primarily on after-trim THD and control-voltage feedthrough performance. In-circuit adjustment is required to achieve the guaranteed distortion and feedthrough performance.

Key Specifications(see 2180 Series datasheetfor complete specifications)
2181A Typical
2181B Typical
2181C Typical
Dynamic Range
Gain Range
< -100 to > +40
Total Harmonic Distortion
1V 0dB gain
Control Constant (both positive & negative- sense control available
± 6.1
Supply Current
Power Supply Voltage
± 4 ~ ± 18
Output Noise
0 dB gain
Model Grade % THD at 1V 0 dB gain Package Order Number Pricing (1000) Min Order Quantity Reference
2181 A 0.0025 Typ. 0.005 Max. 8 pin SIP 2181AL08-U $7.26 25 Request Samples
8 pin SO 2181AS08-U $6.17 98
8 pin SO Tape & Reel 2181AS08-UR Contact us 2000 per reel
B 0.004 Typ. 0.008 Max. 8 pin SIP 2181BL08-U $4.58 25
8 pin SO 2181BS08-U $3.92 98
8 pin SO Tape & Reel 2181BS08-UR Contact us 2000 per reel
C 0.005 Typ. 0.02 Max 8 pin SIP 2181CL08-U


8 pin SO 2181CS08-U


8 pin SO Tape & Reel 2181CS08-UR Contact us 2000 per reel
2181 Demo Board 2181-DEMO $100.00 1
All 2181-Series parts are RoHS compliant. Minimum order quantity (MOQ) is one tube or one reel. Parts must be ordered in multiples of the MOQ. Samples are available to qualified applicants. Pricing is subject to change.
Design Notes(as PDF files) Design Note 00A Basic Compressor/Limiter Design (113k)

Design Note 01A The Mathematics of Log-Based Dynamic Processors (64k)

Design Note 02 Digital Gain Control with Analog VCAs (106k)

Design Note 03 Signal Limiter for Power Amplifiers (95k)

Design Note 04 Improving Loudspeaker Signal Handling Capability (217k) Design Note 05 A Low Parts Count, Two-Slope Compressor (78k)

Design Note 100 A Fully Adjustable Noise Gate (69k)

Design Note 102 Adjustable Ducker using the THAT 4301 (76k)

Design Note103/104  Improving VCA Performance I (56k) Design Note 106 What to look for when the Distortion in 2180s Doesn’t Match the Specs (57k) Design Note 107/111 A Simple Effective Soft-Knee Compressor / Limiter (81k) Design Note 110 Improving VCA Performance II and III (73k) Design Note 112 LED Bar-Graph Compression Indicator (83k)

Design Note 115 Fully Adjustable Compressor/Limiter (46k)

Design Note 116 Techniques for Stereo Volume Control (126k)

Design Note 117 Input Limited for ADCs (120k)

Design Note 118 High Performance Stereo AGC (90k)

Design Note 119 Wide Ranging dB Meter (177k)

Design Note 120 VCAs in a Pan Potentiometer Application (127k)

Design Note 121  VCA Symmetry Auto-Trim Circuit

Design Note 122 5.1 Channel Volume Control (67k)

Design Note 125 The “One Knob Squeezer”  (90k)

Design Note 128 What’s a PTAT Temp. Coefficient, & Where Does It Come From?  (64k) Design Note 129 A Low-Cost VCA Limiter (47k) Design Note 130 VCA-Controlled 1st Order State Variable Filter (174k) Design Note 131 Dealing with the PTAT Coefficient (75k)

Design Note 132 Alternate Method of Indicating Compression (52k)

Design Note 137 Substituting THAT 218x VCAs for 215x VCAs in Existing Designs (68k)

Analog Secrets Your Mother Never Told You (1528k) Originally presented at the 123rd AES Convention, this seminar provides tips and techniques to achieve optimal performance in the analog signal path. Topics covered range from inputs (balanced line and mic level) to outputs (balanced to single-ended), and include analog signal processing (VCAs, RMS detection, and Analog Engines).

Related Products
Other Voltage Controlled Amplifiers (VCAs)
THAT 2180 Series Pre-trimmed Blackmer VCAs 2180 Series Datasheet
THAT 2162 Dual Blackmer VCAs 2162 Datasheet
Analog Engine® Dynamics Processors
THAT 4305 Low-cost basic Analog Engine for dual supply voltages 4305 Datasheet
THAT 4320 Low-voltage, low-power versatile Analog Engine for single supply voltages 4320 Datasheet
THAT 4315 Low-voltage, low-power basic Analog Engine for single supply voltages 4315 Datasheet
THAT 4316 Very Low-voltage, low-power basic Analog Engine for single supply voltages 4316 Datasheet

Additional Resources

2181 Series Device Model
Our SPICE macro models allow modeling of the important parameters of our ICs.

2181 Series Demo Board
– The THAT 2181 Series Demonstration System (US$100) allows the engineer to test the performance of a THAT2181 quickly and easily. The 2181 Demo Board is self-contained circuit board with XLR connectors for signal input and output and a 3-pin header for connection to an external regulated DC power supply (not included). See the 2181 Demo Board Datasheet for more information.

Harsh Environment Packaging
– TT Semiconductor repackages THAT Corporation’s IC products in ruggidized plastic for the medical, aerospace, defense, and heavy industrial marketplaces.

The History of VCAs
– THAT Blackmer® VCAs are the successors to the original dbx® line of VCAs. Their development for professional audio use has a long history, and can provide some insight into the care and feeding of these essential devices.

2181L Material Data Declaration Sheet (SIP Package)

2181S Material Data Declaration Sheet (SO Package)
Material Data Declaration Sheets (MDDS) disclose the hazardous materials in our integrated circuits as required by the European RoHS directive.