Make Mono Phonograph into Mic Preamp?

[Big Pete]

I have a nice little mono tube phonograph in its cabinet; the output goes to a speaker and it has an additional speaker out. The schematic is pasted inside the cabinet. It has small tubes.

Is it a good idea to try and turn it into a mic preamp?

I'm not sure what mods to make to the input and output. I'd probably run it into a soundcard with unbalanced i/o, but I don't really have to. The phono's amp goes into an 8-ohm speaker right now.

At the phono arm, there are 3 wires, but I don't know yet what they're for. I have some diy balanced, phantom powered mics to plug into it, and have already made a p48 supply.

To sorta hear it, I replaced the phone arm with a 1/4 inch jack, and ran a mic pre into it; the mic sounds pretty good thru the speaker, with some hum, though.

Anyone tried to do this before? Is it like I should identify a power amp section and not use it?

[stratus46]

Originally Posted by Big Pete

I have a nice little mono tube phonograph in its cabinet; the output goes to a speaker and it has an additional speaker out. The schematic is pasted inside the cabinet. It has small tubes.

Is it a good idea to try and turn it into a mic preamp?

I'm not sure what mods to make to the input and output. I'd probably run it into a soundcard with unbalanced i/o, but I don't really have to. The phono's amp goes into an 8-ohm speaker right now.

At the phono arm, there are 3 wires, but I don't know yet what they're for. I have some diy balanced, phantom powered mics to plug into it, and have already made a p48 supply.

To sorta hear it, I replaced the phone arm with a 1/4 inch jack, and ran a mic pre into it; the mic sounds pretty good thru the speaker, with some hum, though.

Anyone tried to do this before? Is it like I should identify a power amp section and not use it?

If it has a ceramic or crystal cartridge you'll need to add more gain for a magnetic mic. If it has a magnetic cartridge you'll need to disable the RIAA equalization but the gain would be in the ballpark.

Personally, I built a stand-alone mic preamp many years ago that is similar to Elliot Sound Products project 66. 27 years later I had to add output level controls because some PC sound cards are VERY intolerant of overloads. In audio before processing it's possible to get IMMENSE levels which may even destroy the inputs of the sound card as the preamp can output 25Vp-p. The old analog and digital recorders I used had the input level controls _before_ any active circuitry so controls on the preamp weren't needed.

G²

[Big Pete]

Thanks - good information.

It has a little assembly with a crystal piece holding the needle; it rotates with a little lever on it that says "78" on the flipside. The tonearm is cast aluminum, too heavy for vinyl records.