MOD for the David Eden WT800 bass amp

We discussed in a much earlier blog that we provide service & repairs for the David Eden brand of bass amplification. In today’s blog we are showing the “World Tour Series” WT800 model as an example, but this blog probably applies to most of the range at this time.

We recently implemented a MOD to this amp at the request of our good customer, Mr Paul Disspain. We can’t claim any originality for this as the idea came from an example on the David Eden user forum. Initially we thought the idea was a bit overkill, but now wholeheartedly agree this is a MOD that greatly enhances long term reliability.

Commercially made amplifiers often have little design short cuts or oversights where the design team momentarily dropped the ball, and David Eden is no exception. Specifically, the low voltage power supply in this model has been done “on the cheap”. Rather than design dedicated low volts supply rails from their own transformer winding, the design simply drops the power amp volts supply rails by way of inserting series resistors, designated R62 & R64.

The end result of this technique is that the voltage dropping resistors generate a LOT of heat, even though R62 & R64 each comprise a pair of 5 watt ceramic body components. We are talking about enough heat to desolder the connections over a period of time. This heat is constant, the whole time the amp is powered on. The resultant poor connectivity gives rise to intermittent faults – not necessarily a total loss of signal, but unpredictable drops in signal level and functionality which mysteriously correct themselves.

The intention of the MOD is to get the low voltage supply dropping resistors off the printed circuit board altogether. No more heat being absorbed into the board represents a big improvement in reliability. The next obvious step is to up the power dissipation rating of the resistors. If we use aluminium clad resistors, then these by design are suitable for mounting onto a heatsink. A pair of 15 watt resistors each for R62 & R64 (ie, four in total) mounted to an aluminium heatsink, suitably mounted to the bottom section of the amp chassis, in the space between the front board and the toroidal transformer will require only short lengths of hookup wire to connect back to the board.

You can see in the photos that we have to strip out the front board completely from the chassis. Removing & replacing the printed circuit board without introducing any additional problems is a time consuming element of this work. We need access to the solder side of the board to clean up any problems, remove the old solder and possibly repair any heat damaged tracks & pads.

While we have the board out of the way, we can mount the heatsink, taking care to leave enough clearance to actually be able to reinstall the board. This task is fiddly enough as it is, without the resistors in the way. We don’t want the heatsink hard up against the transformer or the interconnecting wiring.

The final photos show the board reinstalled and the interconnections between the aluminium clad resistors and the former positions on the board for R62 & R64 completed. The final arrangement still creates some heat, but nothing at all like the original design. With one channel only driven into a 4 ohm resistive load at a time, the power amps deliver 480 watts, which translates into a nominal 400 watts per channel with both channels driven into 4 ohm loads.

The whole job takes at least 2 hours to complete. It is a worthwhile improvement in reliability for those owners of the original David Eden amplifiers who intend to keep their amps for the long term.

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8 Responses to “MOD for the David Eden WT800 bass amp”

  1. Stanley Whitehouse Says:

    Hi Ivan …
    It’s pretty cool that you have taken & improve the Eden WT 800
    and as an owner that has had hicks fixed am interested what the cost Wouk be for you to MOD my amp maybe one day ..
    Where are you located?

    Just an enquiry
    Regards
    Stan W

    • ivanrichards Says:

      hello – we are located at Gosford on the NSW Central Coast. Workshop address: Ivan Richards Audio, c/o Eagle Business Park, 1 Frances Parkes Close, Wyoming, NSW 2250, Australia. To maintain the highest level of customer service, we prefer customers to attend the workshop by appointment. Phone 0418 862 034. International 61 (0)418 862 034.

  2. Dan Says:

    Did you just use aluminum angle stock for the heatsink for the power resistors, or did you find a ready-made heatsink predrilled for the 4 power resistors?

    Thanks!

    • ivanrichards Says:

      it’s just a suitably sized chunk of aluminium which would mount in the limited space available and which I drilled to suit the resistors – it was quite experimental but it worked and the amp is still performing after what must be several years now; IR.

      • Dan Says:

        Thank you, Ivan. It looks like my WT-300 has plenty of chassis room to mount the resistors to it, without having to install a separate heatsink. Do you foresee any problems with attaching the resistors right to the chassis?

        Thanks for sharing your wisdom with the rest of us.

      • ivanrichards Says:

        if I were you I would employ a heatsink, the reliability of this MOD is proven over time, but also we cannot comment on hypothetical questions – that is beyond the scope of the blog; thanks, IR.

  3. phillip jameson Says:

    Hi There Ivan,
    Phil here I have a 1999 WT800 D model I think . Anyway I used your tutorial followed your instruction and did this resistor mod to my amp . I took a build it your self kit for a electric car kit i found at a big electronics store called Fry’s here in california. it was a big so i just cut it half and bolted it together so it was l shaped .this gave me the perfect shape and size to make a heat sink to mount the new resistors i got from mouser electronic supply on line .

    the solder work was easy and getting the new ones installed ad hooked up was not too bad at all . i AM IN A METAL band so i play loud and before this mod it would kick the fan on a fart out at shows here and there . I did that and also flipped the fan around and now its working perfect and with a hotter preamp tube not the eden tubes they say you need to use it’s a great amp . lots of power and never ever over heats and sound great .

    thank you for posting this . At least you know at least one person figured it out . I used your photos to figure out what resistors to order . I think the where like 4.00 bucks each US .

    phil from Lipshok the band bay area california http://www.lipshok.com

    • ivanrichards Says:

      great work phil !! the original MOD was done 5 years ago now, and the amp hasn’t missed a beat for customer Paul Disspain; thanks for sharing your achievement, which gives the story a happy ending; IR.

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