Change of Plan

It is difficult to accept but I will need to completely rebuild the power amps and control circuitry.  That is what this stage of the build is all about, finding out what is wrong and how things can be improved.

The right-hand power amp is drawing a lot more current than it should be and although I have been through and found a fault the problem is still there.  The difficulty I have is that it is incredibly difficult to fault find the power amps because of the way they are constructed; air-wired.  Without the rigid form that PCBs give, it is very easy to lose where one is in the circuit.  Plus the lack of rigidity means that shorts between components are all too easy.  I had intended to lock the components in place by using hot-melt glue when the circuit has proved itself to work.  However, it won’t work without the hot-melt glue because of shorting.

There are implications for this problem too.  If it takes me lots of time to construct, fault find and correct, the cost of construction will rise rapidly as my labour time increases.  So I have to find a way of construction that is quick and accurate plus easy to fault find and correct.

I have decided that what I need is to use a substrate that will show me where components should be and hold them exactly in place, much like a PCB would do.  What I will do is layout the components, to scale, on the computer, complete with hole positions and fix that to some flat sheet, probably something like Tufnol.  This should solve all the above problems and also speed up construction as I can drill a few sheets at a time, drilling through say 10 at once.


About Matal

Hand made HiFi, photos, a friends poetry.
This entry was posted in Construction, Control Circuits, Power Amplifier. Bookmark the permalink.

2 Responses to Change of Plan

  1. Paul of Lustleigh says:

    Hi Matt,

    Not good. I would be tempted to go for some pcb solution with very short or screened signal paths to get the power amps operational. Once established and proven then you can do the air connection method. I agree with your thoughts that this a very labour intensive process and very difficult to get right but good labeling and lots of concentration I am sure you will get the hang of it.

    Have you considered a two (or even more) grades of construction. Say, very good but PCB’ed power circuits and then excellent which is air connected? Costs could match performance. Still bespoke and hand made… What do you think?


  2. Liquiphonics says:

    Hi Paul,
    Agreed, I need to lower my sights a little. I now have some Vero board with holes only, no track. It will give me the rigidity I need and I can enlarge the holes so I can fit more than one component lead through – that will allow me to have the components really close to each other. This should be a workable solution I feel. And you are right about the labelling – I’m at the computer now laying out the circuit and making sure the labelling works so I can construct a lot easier.

    Construction grades: great idea and one I will use. The ‘air-wired’ circuit can be used for the Level 3 amps, they will be the top of the range versions.

    Good thoughts Paul, thanks for the input 🙂



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