08
Jun
12

Bits & Pieces 4

I wasn’t expecting to add this post just yet, but I had a stroke of luck which has enabled me to complete the scheme for my mono mixing section which I started writing about when I described the Red Dragon the other day.

I bought a job lot of small SoundLab mixers off eBay which were said to be faulty returns.  I thought I might be able to salvage some parts from them, use bits of them in some way, or even repair them – but it turned out that several of them appeared to be in working order.

Two of them were straightforward 4 channel mono mixers – an updated version of the one I had used before, I presume – so these were immediately used for the left and right channel inputs to the mono mixer, as I described in the previous post.  Generally speaking, I wanted to have the lower tones to the left and higher tones to the right, so my ‘double bass’ stylophone was the first thing to be plugged into the left mixer; the treble stylophone and the SoftPot Stylophone in the right.

More interestingly, the two other working units were the G105C version with ‘microphone effects’ – a delay circuit which I guessed was probably based on a PT2399.  I opened up one of the dead ones, and found that this was the case.

The circuitry was very different from the original SoundLab mixer I’d acquired – all surface-mount components; everything, pots and sockets included, firmly fixed to a single circuit board – and I’m not sufficiently skilled or equipped to be able to repair something like that.  Not only was it not functioning, it seemed to short out the power when the on switch was pressed.

I sawed out the part of the circuit with the PT2399 on it, which didn’t short the power when used by itself, but didn’t do anything to the input sound either.  This section is permanently in circuit when the mixer is operating, so maybe that was why the original unit didn’t work.  In any event, I decided to put the broken ones away for another day, and concentrate on the ones that worked.  The case would find a use later on.

First of all an echo unit is a really useful thing to have – and 2 echo units with 4 inputs is a bonus!

My initial arrangement with these is to have the outputs connected to the new Left and Right Mixers.  The left echo unit is used for instrument input and the output is divided: one half of the output going directly to the Left Mixer, the other half going to the right echo unit, and from there to the Right Mixer.  As the delay time and feedback (number or length of repeats) are separately adjustable on the two units, some interesting stereo effects are possible.

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andymurkin

June 2012
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