It replaced the input / output-buffer in the HeDo Pre. Original there where OPA2604 / NE5534 replaced with OPA627BP (double) / OPA627SM, replaced with V5 double / single. One of the single V5 break down so i replace the V5 with V6. V5 stays as input buffer (XLR) and V6 i use as input / output buffer for the RCA Line. The sound is… The OPA 627 where very good. But the V5 / V6 are clear the better OPA. No way back!