500 Series Tube Vari-Mu Compressor. After having shocked and impressed the audio industry with the HERCHILD Model 670 & Model 660, Heritage Audio has now turned to the 500 series format to offer something extremely rare… An analog stereo Variable Mu tube compressor in a two-space 500 series module! The GRANDCHILD 670/500 is stuffed with 4 6BA6 (5749) NOS tubes, three exclusively designed transformers (one per channel & and one for the Sidechain) and the necessary select components and circuitry to capture that elusive sound. For the first time ever it is possible to achieve that sought after tone and response in such an affordable package. In common with its big brother, there is an INPUT GAIN control with an adjustable range of 20dB, the AC Threshold, 5 Attack and Release selectable times, the DC Threshold which gives access to the progressive ratio, which is a unique curve adjustment combining control of the ratio and knee, soft stepped from hard limiting to a very smooth and transparent, light compression. There is also a 3 position high-pass Sidechain filter to reduce the lower frequency´s influence on the detection circuit, a must have nowadays for current productions. As this is a stereo unit, a sum of the two channels will determine the overall dBs of gain reduction for both channels ensuring a stable stereo image. All built into a solid 2 space unit for the popular 500 series format with an attractive age-referencing front panel complete with a beautiful, informative VU meter that not only indicates Gain Reduction metering but also informs the user of the unit’s 3-position Active/Bypass /Off switch confirming the status even from a distance. It’s not easy to achieve that classic warm, hugging, intimate sound that just seems to effortlessly glue together a MIX in a musical way, but the GRANDCHILD 670/500 does it perfectly.