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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 17th May 2017, 8:23 pm   #1
Trevor
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Default FAL amplifier

Yet again I am working on a pair of FAL amplifiers
One is a FAL 100 watt
The second is a FAL 300 watt, does anyone on the forum have a circuit diagram.
Regards Trev
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Old 17th May 2017, 8:44 pm   #2
AC/HL
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Default Re: FAL amplifier

Does this bear any resemblance to the 100?
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Old 17th May 2017, 8:57 pm   #3
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Default Re: FAL amplifier

This is just what I am after thank you so much !
Can ask how did you come across the schematic
Are Fal still trading ?
Now I wonder about the 300 watt unit it seems similar but with a baxendall diode and more sophisticated protection
Many thanks Trev
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Old 17th May 2017, 9:10 pm   #4
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Default Re: FAL amplifier

I wouldn't be surprised if some circuit features were similar, this is quite common with Manufacturers, but it's quite a step up. I'm afraid I can't remember where or when I came across the circuit, it's just a single paper sheet.
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Old 17th May 2017, 9:23 pm   #5
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Default Re: FAL amplifier

its an exact match for the 100 watt but i have noticed an error in the protection circuit the protection diode bases should be connected at the junction of the 1k resistor and the 68 ohm not as shown but i am really thankful for this
Trev
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Old 19th May 2017, 7:52 pm   #6
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Default Re: FAL amplifier

Futuristic Aids Limited (FAL) were formed in 1959 and in the 70s and 80s produced low end disco equipment aimed at the mobile DJ.
The company was dissolved many years ago.
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Old 19th May 2017, 8:17 pm   #7
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Default Re: FAL amplifier

There's something weird in the diagram Bill's posted.
D4 clamps the base of Q11 to ground looking at how that vertical line symbol is used elsewhere on the diagram. But the emitter of Q11 is on the output terminal and can swing up close to the positive supply rail, reverse biasing the B-E junction with tens of volts and no current limiting as the B-E junction avalanches. The same thing happens with D5 and Q12 in the other direction. I think the junction of D4 D5 must really go to the output node "CL" otherwise the thing will destroy Q11 and Q12.

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Old 19th May 2017, 9:24 pm   #8
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Default Re: FAL amplifier

Quote:
Originally Posted by Trevor View Post
its an exact match for the 100 watt but i have noticed an error in the protection circuit the protection diode bases should be connected at the junction of the 1k resistor and the 68 ohm not as shown but i am really thankful for this
Trev
Should read protection transistor bases not diode.
Trev
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Old 22nd May 2017, 8:41 pm   #9
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Default Re: FAL amplifier

Amp repaired this circuit is to a mk 2 I have a mk 1 but it was near enough. I have improved the amplifier by fitting an extra Baxandall diode and modified the bias to suit. Distortion is now down to 0.05% at 1 khz and at 0.5 watts. Only did it because I could.

These amplifiers were a bargain when they were sold, not the best amp available but good enough for most duties that they were pressed into.

Trev
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