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Aurora (Legacy)

Based On
Ross / Dyna Compressor
Effect Type
Compressor, sustainer
Build Difficulty
Intermediate
Project Summary
The original guitar compressor, still a favorite of guitarists after over 40 years. The Aurora makes several improvements to the original circuit as well as adding a few new features.

Legacy PCB

Designed for the 1590B enclosure with side-mounted jacks, which some builders prefer. Bypass PCB (optional) sold separately.

$10.00

In stock

Updated Version

The same circuit, but updated for the 125B enclosure format for a more streamlined build. The bypass switch PCB is integrated.

$12.00

In stock

Project overview

The Aurora Compressor is a Ross Compressor or MXR Dyna Comp clone with a few modifications: a treble switch to control the amount of high-end attenuation after the compression; an attack/release control that can be wired either as a knob or a switch; and an internal trimmer that allows attenuation of the input.

CA3080 availability

This project uses the CA3080 OTA, which was obsoleted in 2005[1]. There was still plenty of old stock available, but then a company called Rochester Electronics purchased the fabrication equipment from Intersil and began producing it again, primarily for the hobby & repair industry. These days, if you buy a CA3080 from Small Bear Electronics, you will get a new-production CA3080 from Rochester Electronics.

At $4.95 each, they aren’t cheap, but if you need them in any kind of quantity, I’ve had very good luck buying them from Chinese sellers on eBay in lots of 50 or 100. These are usually pulled from old equipment. You can get them for pretty close to $1.00 each. The usual disclaimer applies that there are a lot of counterfeit NOS parts on eBay, so check the seller’s ratings before ordering.

The LM13700 is a current-production OTA that can be used in place of a CA3080 in the Dyna circuit with no sonic difference, and in fact is the chip of choice in the Ibanez CP-9. The only trouble is that the LM13700 is a dual OTA in a 14-pin DIP package, so the PCB must be designed around it—it’s not a drop-in replacement.

Notes & references

  1. Last of the OTA’s — Don Tillman’s blog

Documentation

Project Documents