DBX 160xt …….under pressure….as Freddy would have had it.

The DBX 160 compressors are definitely a cut above average. They use a chip called a VCA chip. These have been used in analogue synthesisers, more or less from their inception.

You might be wondering at this point why I might want to use the word ‘inception’. Apart from it being a wondrous bullshit word, it reminds me of the Jenson Interceptor, a car with more carburettors than sense. I always thought of it as a sort family saloon AC Cobra. A great way to get rid of your ears, as it would rip them off at the first dab of the gas.

The VCA chip stands for ‘Voltage Controlled Amplifier. There were also, of the same ilk, the VCF and VCO. They were/ are respectively ;Voltage Controlled Filter’ and Voltage Controlled Oscillator’. They all worked in basically the same way. A dc voltage (the control voltage) is applied to the control pin of the chip (Before the advent of chips there were….fish. No, no! Come on, get a grip.) Let’s try that again. Before the advent of chips these devices were built up from discrete transistors. Before that, they were built from valves.

I remember a valve analogue computer at Chesterfield tech college. It had six operational amps and they shifted it from room to room on a fork truck.

The output of a VCA is proportional (I don’t know a car of that name…..wait a minute…..a pro Porche…nal. That’s relief, I thought I was turning sensible.) to the input dc control voltage. In other words, its output amplitude goes up as the dc control voltage increases. On a VCF the filter effect frequency rises or falls according to the voltage, and with the VCO the oscillator frequency rises or falls similarly.

What has any of this to do with the DBX 160xt? Well, this compressor has a VCA chip in it. The control dc voltage is sensed from the input level, and also from the setting of the compression level.

This probably won’t help to fix it, but might help a bit to understanding it.

Here’s a practical fix it bit. The DBX160 xt compressor uses a six pole push switch to bypass the compressor. If this goes bad, it won’t work, and you can’t buy one. I have heard there are plentiful stocks on Calisto, but DHL don’t ship from Mars. But you can get four pole push switches (alps switches). You can use these if you know how to a) solder and b) not panic when tracks peel off.

Take the original, bust, switch out. Tricky, but not impossible. A good desoldering device is advisable. Put the new switch in so that it occupies the 12 holes furthest from the front. Solder it in. Get a piece of heat shrink sleeving, and cut it so that the front bypass switch will push the switch operator forward. I also used a bit of the pipe from an aerosol can inside the heat shrink to make it more solid to the touch.

This will work and also switch in/ out the bypass function. What it doesn’t do is switch the led on the front which remains on. If you can live with that, you’ve fixed it.

I’m now going to phone somebody on this macaroon. It is, of course, my hermit-o-phone for the week. Last week it was a Tesco radish.




Comments are closed.