Vox Cambridge 30 optocoupler

Discussion in 'The Projects Forum' started by jbmdisco, Jul 31, 2014.

  1. jbmdisco

    Thread Starter New Member

    Jul 14, 2014
    I am trying to source an equivalent part for the optocoupler on the cambridge amp. I can get the LT9914 but by all accounts this seems to be unreliable I have also tried to locate the suggested replacement VLT5C3 but cannot find reference to it from any of my usual suppliers (Farnell, RS etc). Does anyone have any suggestions to another equivalent part which would work as well, if not better than LT9914 that maybe I will be able to source in the UK


  2. to3metalcan


    Jul 20, 2014
    Here's the service manual.

    "Vactrol" style optos aren't much in demand, these days, outside of audio production, so mainstream suppliers tend not to carry 'em. eBay is probably a better bet.

    Option 2: pretty much any LED/CDS optocoupler will probably work okay in this circuit...the schematic shows trimpots to set both the voltage and the current across the LED! It might require a little fiddling to get the response down, but if you take your time it's totally doable.

    Option 3: it's doubtful the original part was chosen for any specific characteristics, anyway. In my shop, when I replace optocouplers in amps or electric pianos, I almost always just make them. Glue an LED to a CDS photocell and dip it in PlastiDip or Liquid Electrical Tape (just something opaque to keep external light out.) Tweak your trims a bit, and I bet you'd never know the difference.