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

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Old 18th Jun 2018, 10:25 pm   #1
george1960
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Default How do you feed a signal into an HF43 MK2/3 amplifier?

Sorry another newbie question, but how do you feed a signal into an HF43 MK2/3 amplifier?
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Old 18th Jun 2018, 10:50 pm   #2
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Default Re: How do you feed a signal into an HF43 MK2/3 amplifier?

Presumably a Fidelity HF43?

What signal sources do you have?
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Old 18th Jun 2018, 11:17 pm   #3
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Default Re: How do you feed a signal into an HF43 MK2/3 amplifier?

Easiest would be to add a DPDT switch before the volume control. One position for the deck cart and one for the proposed line in. Might be worth adding a series resistor to the line in for attenuation, as it will probably be a bit more signal than that coming from the X5M or whatever medium output cart is fitted.
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Old 19th Jun 2018, 10:28 am   #4
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Default Re: How do you feed a signal into an HF43 MK2/3 amplifier?

i just wanted to test the amp before plugging into the mains really and wondered if there was a way of doing this.
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Old 19th Jun 2018, 10:47 am   #5
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Default Re: How do you feed a signal into an HF43 MK2/3 amplifier?

Well I'm afraid you can't really. The amplfier needs to be powered up before you can fully test it under the correct operting voltages. It's a 1973/4 transistor amp which has a mains voltage down to c.20V power supply, so I can't see what harm can be done. Without this, it means you need to passively test each component for values against a circuit diagram.
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Old 19th Jun 2018, 10:50 am   #6
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Default Re: How do you feed a signal into an HF43 MK2/3 amplifier?

Feeding in a signal with no power applied won't tell you a lot.

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Old 19th Jun 2018, 1:31 pm   #7
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Default Re: How do you feed a signal into an HF43 MK2/3 amplifier?

I was thinking the OP just wanted to be able to connect external devices like a phone or mp3 player through the record player's amp. My mistake! As said above, I would just go ahead and plug in. If you suspect there might be a short, just be ready to pull the plug if any distress or smoke is noted.
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Old 19th Jun 2018, 7:11 pm   #8
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Default Re: How do you feed a signal into an HF43 MK2/3 amplifier?

like that
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