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Nov 29

Attempting to repair my FAL Phase 44 amplifier

FAL Phase 44 Amplifier

FAL Phase 44 Amplifier

Sometime last year my old Kenwood hifi amp stopped working due to the speaker cutout relays not working. The speakers would never switch on, making for a fairly useless amplifier.

While my cousin was sorting out his mess before moving to the US he found this old “FAL” brand amplifier. A spot of Googling reveals this was made by a company called “Futuristic Audio Limited” who also seem to make guitar amps. He didn’t want it, I needed an amp, so it came home with me.

Due to its age I noticed quite a lot of noise when trying to adjust the volume so decided today to take it apart and attempt to clean the insides out. I also bought some switch cleaner to spray in the potentiometers.

The insides were very simple. Here is a photo of the main circuitboard which contains nothing but through-hole mounted resistors and capacitors. The most complex electronic components in this are the four transistors bolted to a piece of metal. There are also some large looking capacitors, and an interesting looking network of diodes.

Unfortunately I think cleaning the contacts on the potentiometers and switches might have messed the electrical characteristics of the amp up. Since this isn’t an IC based amp, I have a feeling there’s a fine balance between the components that makes the thing work, and squirting a load of switch cleaner into things has altered this. When I power the amp up, only the left channel works and the volume goes really loud then distorts – all by itself, without me moving the volume knob. I’ll leave it for a few hours to see if the cleaner evaporates off. It’s no great loss if it is broken, the reason I took it apart was because the sound wasn’t correct and the volume kept wandering between left and right speakers, so maybe it’s finally packed in.

Looking at the electronics inside, part of me wonders if it’s repairable.

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3 comments

1 ping

  1. Johny Davies

    Hey

    I have just started on a FAL 100 mono amplifier. The capacator youa re talking about are the smoothing capacitors, and the network of diodes is the bridge rectifier. This converts the AC coming out of the power supply into DC. The capacitors are there to give 2 smooth voltage rails as the rectified voltage will jump between 0 and whatever the full voltage is.

    They are fairly simple amps. Tho mlooking at your photo of the transistors you have different ones to me. the amp is fundamentally 2 identicle circuits. One amp for the left speaker, one for the right. With 2 transistors per channel, it is a push pull amp or class B amplifier. As the voltage sginal going in increases in the positive, one transistor will draw voltage from the positive power supply rail. When the voltage comes back down and goes into the negative, the other transistor will draw voltage from the negative rail. hence the push pull. A lot of the other ciruitry is to smooth the crossover between one transistor and the other. Anyways, if you are having problems fixing it and there is anything I can help with, dont hesitate to email me :)

    All the best

    Johy

  2. Johny Davies

    HeyI have just started on a FAL 100 mono amplifier. The capacator youa re talking about are the smoothing capacitors, and the network of diodes is the bridge rectifier. This converts the AC coming out of the power supply into DC. The capacitors are there to give 2 smooth voltage rails as the rectified voltage will jump between 0 and whatever the full voltage is. They are fairly simple amps. Tho mlooking at your photo of the transistors you have different ones to me. the amp is fundamentally 2 identicle circuits. One amp for the left speaker, one for the right. With 2 transistors per channel, it is a push pull amp or class B amplifier. As the voltage sginal going in increases in the positive, one transistor will draw voltage from the positive power supply rail. When the voltage comes back down and goes into the negative, the other transistor will draw voltage from the negative rail. hence the push pull. A lot of the other ciruitry is to smooth the crossover between one transistor and the other. Anyways, if you are having problems fixing it and there is anything I can help with, dont hesitate to email me :)All the bestJohy

  3. James

    Nice write up. Pioneer and Kenwood always make decent products (IMO). You can’t really go wrong with either brand. Pioneer and Kenwood products are also inexpensive.

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