More Phoenix Gold ZX Modifications

ZX had been in for cap upgrades a year back, then changed hands. New owner wants SQ tweaks which includes high bias. Previously we added individual heatsinks to the predrivers for this but it’s a fiddly job.



Skills learned in 4 years of Metalwork at High school have come in handy. Piece of ally bar cut and tapped to allow fastening to end drivers. Green goo is thermal gap filler which transfers heat and holds the bar in place.


Ally bar soaks up heat from predrivers and it’s then transferred to the cooling tunnel by thermal gap filler. Middle predrivers bonded to the bar and have thermal compound to ensure good heat transfer. This keeps them cool and the bias stable.


Usual underbiased distortion waveform that we see with ZX amps as they arrive with us. If the bias is turned up they can go into thermal runaway as the predrivers get warm, so the factory sets it low.



After optimisation, and the bias is now completely stable. That’s less than a tenth of the previous figure.




If I could get these anodised it would look totally stock. Even as it is, it doesn’t seem out of place. This is now better than new SQ wise, and should give many years of listening pleasure.



4 thoughts on “More Phoenix Gold ZX Modifications

  1. Hi Sarah
    Last year you did some SQ tweeks on my zx450, would the modification posted on July 25 2013 be a worthwhile addition, can it be done to all zx amps as I have 5 I want to use on an install
    Thanks Allan

    • Hi Allan

      Yes some of these modifications would be advantageous, although you wouldn’t really benefit from the sub mods. The cost for Bias upgrade would be £50 and the preamps would need to be quoted for one the amps was here.

      Hope this helps


    • Hi TKarl,
      The main thing on these would be Cap upgrades and bias stability. We sort the bias stability when we do a service which for the 0.3 would be £169.00 and the 0.5 service £229.00
      Cap upgrades would be an additional £44.00.
      All of the work would come with 1 year warranty, power sheet and include cost of return courier.

      I hope this helps and look forard to hearing from you if you would like to proceed.

      Kindest regards