{"product_id":"heritage-audio-herchild-660-mono-tube-compressor","title":"Heritage Audio Herchild 660 Mono Tube Variable-Mu Compressor Limiter","description":"\u003ch2\u003e\u003cbr\u003e\u003c\/h2\u003e\n\u003c!-- Video Section with Keyword Title --\u003e\n\u003cdiv style=\"margin: 20px auto 10px auto; text-align: center; max-width: 800px;\"\u003e\n\u003ch2 style=\"font-size: 20px; margin-bottom: 12px;\"\u003eHeritage Audio Herchild 660 Mono Tube Compressor Demo\u003c\/h2\u003e\n\u003ciframe style=\"width: 100%; max-width: 800px; height: 450px; display: block; margin: 0 auto; border-resize: 8px;\" src=\"https:\/\/www.youtube.com\/embed\/wNytp3eoMGs?si=TOG0LojUjMQ18ymf\"\u003e\n  \u003c\/iframe\u003e\n\u003c\/div\u003e\n\u003c!-- Section 1 --\u003e\n\u003cdiv class=\"par-section\"\u003e\n\u003cdiv class=\"par-image\"\u003e\u003cimg alt=\"Heritage Audio Herchild 660 mono tube variable-mu compressor\" src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0646\/4031\/9643\/files\/Heritage_Audio_Herchild_Model_660_Vintage_Mono_Tube_Compressor_scaled_view.png?v=1771550871\"\u003e\u003c\/div\u003e\n\u003cdiv class=\"par-text\"\u003e\n\u003ch2\u003eFairchild 660 Sound at Half the Weight and Price\u003c\/h2\u003e\n\u003cp\u003eLess than 1,000 original Fairchild 660s were built. A functioning vintage unit commands $15,000–$25,000 and weighs over 30 pounds. The Herchild 660 delivers identical variable-mu behavior — 11 tubes, 5 transformers (AMI input, CineMag output), all-tube sidechain — at 16.23 lbs and a fraction of the cost. Built in Heritage Audio's factory in Spain using NOS 6BA6 variable-mu tubes and custom transformers spec'd to match the original.\u003c\/p\u003e\n\u003cp\u003eFront-panel DC Threshold (original required internal screw adjustment) gives continuous control over ratio and knee from hard limiting to transparent compression. Sidechain filter with four selectable frequencies (50, 100, 200, 350 Hz) reduces low-frequency influence on gain reduction. Six attack\/release time constants exactly duplicated from the original.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c!-- Section 2 --\u003e\n\u003cdiv class=\"par-section reverse\"\u003e\n\u003cdiv class=\"par-image\"\u003e\u003cimg alt=\"Heritage Audio Herchild 660 program dependent soft knee compression\" src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0646\/4031\/9643\/files\/Heritage_Audio_Herchild_Model_660_Vintage_Mono_Tube_Compressor_rear_view.png?v=1771550871\"\u003e\u003c\/div\u003e\n\u003cdiv class=\"par-text\"\u003e\n\u003ch2\u003eProgram-Dependent Soft-Knee Variable-Mu Compression\u003c\/h2\u003e\n\u003cp\u003eVariable-mu tube gain reduction starts with a gentle ratio on small peaks and progressively increases to brick-wall limiting on loud transients. The compression curve responds to the music itself, not a fixed threshold — creating the buttery, natural dynamics that made the original a staple at Abbey Road (EMI owned multiple 660s used on Beatles vocals).\u003c\/p\u003e\n\u003cp\u003eHigh-voltage operation ensures no audible thumps. Extremely low distortion and noise: THD \u0026lt;1% up to +18 dBu output, self noise \u0026lt;-82 dBu, SNR 120 dB. Input impedance 2 kΩ, output impedance 600 Ω, max output +30 dBu. Frequency response 40 Hz–15 kHz (±1 dB). Single XLR input\/output.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c!-- Section 3 --\u003e\n\u003cdiv class=\"par-section\"\u003e\n\u003cdiv class=\"par-image\"\u003e\u003cimg alt=\"Heritage Audio Herchild 660 handwired Class A 3U Spain\" src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0646\/4031\/9643\/files\/Heritage_Audio_Herchild_Model_660_Vintage_Mono_Tube_Compressor_scaled_view.png?v=1771550871\"\u003e\u003c\/div\u003e\n\u003cdiv class=\"par-text\"\u003e\n\u003ch2\u003eHandwired Class A, Built to Outlast the Original\u003c\/h2\u003e\n\u003cp\u003e3U rackmount. Standard IEC AC power. Controls: AC\/DC Threshold, Input Gain, Time Constant (6 settings), SC Filter (Off\/50\/100\/200\/350 Hz), Metering. Hand-assembled using same construction techniques as vintage British modules Heritage Audio is known for. Modern components eliminate the maintenance headaches of 1960s units.\u003c\/p\u003e\n\u003cp\u003eAs an authorized dealer, Pro Audio Reserve ensures you receive a genuine Heritage Audio product backed by full manufacturer warranty and long-term support.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003ch3\u003eHighlights\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003eFaithful Fairchild 660 recreation — 11 tubes, 5 transformers\u003c\/li\u003e\n\u003cli\u003eNOS 6BA6 variable-mu tubes, AMI input transformer, CineMag output transformer\u003c\/li\u003e\n\u003cli\u003eAll-tube sidechain circuit for precise control\u003c\/li\u003e\n\u003cli\u003eProgram-dependent soft-knee compression (ratio increases with signal level)\u003c\/li\u003e\n\u003cli\u003eFront-panel DC Threshold: continuous ratio\/knee control (hard limit → transparent)\u003c\/li\u003e\n\u003cli\u003eSidechain filter: Off, 50, 100, 200, 350 Hz\u003c\/li\u003e\n\u003cli\u003eSix attack\/release time constants (exact original settings)\u003c\/li\u003e\n\u003cli\u003eHigh-voltage operation eliminates audible thumps\u003c\/li\u003e\n\u003cli\u003eInput impedance: 2 kΩ | Output impedance: 600 Ω\u003c\/li\u003e\n\u003cli\u003eMax output: +30 dBu (clipping point)\u003c\/li\u003e\n\u003cli\u003eFrequency response: 40 Hz–15 kHz (±1 dB)\u003c\/li\u003e\n\u003cli\u003eSNR: 120 dB | Self noise: \u0026lt;-82 dBu | THD: \u0026lt;1% up to +18 dBu\u003c\/li\u003e\n\u003cli\u003e1 x XLR input, 1 x XLR output\u003c\/li\u003e\n\u003cli\u003e3U rackmount, 16.23 lbs\u003c\/li\u003e\n\u003cli\u003eHandwired in Madrid, Spain\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch3\u003eHeritage Audio Herchild 660 Specifications\u003c\/h3\u003e\n\u003ctable style=\"width: 100%; border-collapse: collapse; border: 1px solid #ccc;\"\u003e\n\u003cthead\u003e\n\u003ctr style=\"background-color: #f2f2f2;\"\u003e\n\u003cth style=\"text-align: left; padding: 10px; border: 1px solid #ccc; width: 35%;\"\u003eSpecification\u003c\/th\u003e\n\u003cth style=\"text-align: left; padding: 10px; border: 1px solid #ccc;\"\u003eDetails\u003c\/th\u003e\n\u003c\/tr\u003e\n\u003c\/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e\u003cstrong\u003eCompressor Type\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003eTube variable-mu compressor\/limiter\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background-color: #fafafa;\"\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e\u003cstrong\u003eNumber of Channels\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e1 (mono)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e\u003cstrong\u003eCircuit Design\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003eClass A, handwired\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background-color: #fafafa;\"\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e\u003cstrong\u003eTubes\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e11 tubes (NOS 6BA6 variable-mu)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e\u003cstrong\u003eTransformers\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e5 transformers (AMI input, CineMag output)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background-color: #fafafa;\"\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e\u003cstrong\u003eSidechain Circuit\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003eAll-tube\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e\u003cstrong\u003eFrequency Response\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e40 Hz – 15 kHz (±1 dB)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background-color: #fafafa;\"\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e\u003cstrong\u003eSignal-to-Noise Ratio\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e120 dB\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e\u003cstrong\u003eSelf Noise\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003eLess than -82 dBu\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background-color: #fafafa;\"\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e\u003cstrong\u003eHarmonic Distortion\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003eLess than 1% at any level up to +18 dBu output (no limiting)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e\u003cstrong\u003eInput Impedance\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e2 kΩ\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background-color: #fafafa;\"\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e\u003cstrong\u003eOutput Impedance\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e600 Ω\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e\u003cstrong\u003eMaximum Output Level\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e+30 dBu (clipping point)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background-color: #fafafa;\"\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e\u003cstrong\u003eControls\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003eAC\/DC Threshold, Input Gain, Time Constant, SC Filter, Metering\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e\u003cstrong\u003eTime Constants\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e6 attack\/release settings (original Fairchild specs)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background-color: #fafafa;\"\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e\u003cstrong\u003eSidechain Filter Frequencies\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003eOff, 50 Hz, 100 Hz, 200 Hz, 350 Hz\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e\u003cstrong\u003eAnalog Input\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e1 x XLR\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background-color: #fafafa;\"\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e\u003cstrong\u003eAnalog Output\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e1 x XLR\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e\u003cstrong\u003eRack Spaces\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e3U\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background-color: #fafafa;\"\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e\u003cstrong\u003eDimensions (W x H x D)\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e19\" x 5.25\" x 7.87\"\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e\u003cstrong\u003eWeight\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e16.23 lbs\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background-color: #fafafa;\"\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e\u003cstrong\u003ePower Source\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003eStandard IEC AC cable\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003e\u003cstrong\u003eManufactured\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003eMadrid, Spain\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003ch3\u003eWhat's in the Box\u003c\/h3\u003e\n\u003ctable style=\"width: 100%; border-collapse: collapse; border: 1px solid #ccc;\"\u003e\n\u003cthead\u003e\n\u003ctr style=\"background-color: #f2f2f2;\"\u003e\n\u003cth style=\"text-align: left; padding: 10px; border: 1px solid #ccc;\"\u003eIncluded Items\u003c\/th\u003e\n\u003c\/tr\u003e\n\u003c\/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003eHeritage Audio Herchild 660 Mono Tube Compressor\/Limiter\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background-color: #fafafa;\"\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003ePower Cable\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"padding: 10px; border: 1px solid #ccc;\"\u003eUser Manual\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e","brand":"Heritage Audio","offers":[{"title":"Default Title","offer_id":48024187404443,"sku":null,"price":2995.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0646\/4031\/9643\/files\/Heritage_Audio_Herchild_Model_660_Vintage_Mono_Tube_Compressor_scaled_view.png?v=1771550871","url":"https:\/\/proaudioreserve.com\/products\/heritage-audio-herchild-660-mono-tube-compressor","provider":"Pro Audio Reserve","version":"1.0","type":"link"}