Quad 34 pre amp

Quad 34 Pre Amps. Well, what can we say? Yes they are lovely but can have some annoying faults. I am sure a lot has been discussed, but here is my input for what it’s worth. These go back to the early ‘80s and still have hang over features from the Quad 22s of the ‘50s and Quad 33s of the ‘70s. Things like balance slider pots, tone controls and filter shapes. Anyway. If you have one of these pre amps and you are suffering with the following, read on. The Radio input should be selected upon power up. Sometimes, other inputs, settings are selected. LEDs chatter about and glow half on and off. Various inputs bleed over each other, left and right channels sound different, balance out of kilter and so on. The amp uses CMOS analogue switching ICs (4016s) and other CMOS logic discrete devices. I replace the analogue switches with HI201s. All these control signal routing, tone filter circuits etc. Also lovingly employed are loads of small value electrolytic capdensors in the audio coupling stages. These, in time, become incontinent and spill their internal corrosive jollop all over the PCB. Now we have a conductive schmoo on the PCB causing the CMOS logic to suffer from ADHD. Add to this, a double sided PCB with poor through hole connection. These were never good from the start and rely on the component leads for inter-side connection. Add to this the damaging leakage and we have a right royal mess. Very time consuming. Replace all these small value electrolytic capdensors, give the board a wash in detergent, finish with a wash of IPA. Rework as many of the through hole connections as you can before you loose enthusiasm. You will probably will be rewarded with a nice working toy. Be careful of the balance slider pot going short circuit to ground, causing a channel to vanish. I normally cut and hardwire the slider out of circuit. Who wants a balance control? Oh, watch the mains fuse holder crumble away. Sorry not to have included photos of the insides on the Quad. My camera caught Covid. Plenty of pictures on the interweb.

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