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Old 14th June 2005, 03:46 PM   #1
tade is offline tade  United States
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Default phono amp as headphone amp.

I bought an old record player at a garage sale. five bucks. I am chasing that tube dream in the cheapest way possible. I have no idea how do design a circuit using tubes, so i want to use the pre made one.
This amp takes a signal from the needle and plays it through two small included speakers.
I am sure that the signal coming from the needle is way way lower than a line level signal from a source like a cd player. can i just throw a large resistor in between the source and the amp then hook headphones up to it?
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Old 14th June 2005, 08:10 PM   #2
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If the phono is old enough it has piezoelectric cartridge which output is high (approx. the same as of PC). At first try to connect straight.
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Old 14th June 2005, 11:45 PM   #3
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Before you connect anything, make sure that the amp is isolated from the mains. Many cheaper units used live chassis amps with ht coming either from a tapping on the record deck motor coil or a dropper resistor. Because everything (speaker, volume and tone controls, pickup cartridge) were insulated, nobody got killed. However what you are planning might just involve connecting your ears or the source components to live mains (electric chair anyone ??)
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Old 15th June 2005, 05:23 AM   #4
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My 5-buck amp is a project likely based on something similar to what you have.

What tubes does the unit have?

community sites,, ........ commercial site planet10-HiFi
p10-hifi forum here at diyA
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Old 15th June 2005, 06:39 PM   #5
tade is offline tade  United States
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For one thank goodness the chassi was not part of the circuit! Would have found that out the hard way...
I cleaned off some oxidation and connected it up to a source. Very little amplification and tons of hum. Way more than sound levels. The hum also got louder and softer along with the volume knob.

The unit came from a magnavox tereo unit. the tubes say magnavox on them. the two tall and skinny ones have the numbers.
337 63-48 D-U

and the one fat one says.
348 III

I also have a tube fm reciever. It did an absolutely great job the five minutes it lasted. then the sound started to fade and i heard a slight pop. now all it does is light up and look pretty.
That is actually the extent of my knowledge about tubes. I like the elegant look of tube amp schematics, and I want to learn more about tubes in general. do you have any advice on that as well?
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