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echolevel / open-amiga-sampler

Open source schematics, parts lists and documentation for building generic mono Amiga sampler cartridges
MIT License
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Add phono preamp? #7

Open kikendo opened 4 years ago

kikendo commented 4 years ago

Hey guys, interesting project here!

I just thought it'd be neat to have a phono preamp in here to be able to sample straight from a turntable without the need of a phono preamp in the middle. Since there's really not many ways to improve sampler functionality in the Amiga, I thought this'd be a neat idea.

Feel free to throw it in the trash xD

PS: how do I label this as enhancement?? Doesn't let me.

echolevel commented 4 years ago

Thanks! I do like this idea, and I'm wondering how best it could be done. I guess it would need a built-in RIAA filter, and I'm not sure whether there are single-chip solutions for that (at least, ones that can run on ~5v). I've seen lots of DIY phono preamps that are built like tanks and powered by enormous switching PSUs but that might be a red herring - the designers and hobbyists building those things might have other requirements in mind, in terms of SNR or power output.

But this also reminds me that I haven't got around to just sticking a turntable right into the OAS yet. I'm sure it'll sound a bit grim without the RIAA curve compensation, but I'm curious! It would be nice to save on a power outlet and free up some phono cable runs by being able to go turntable direct to sampler...

(Oh and I'm not sure how to label this as an enhancement - my GitHub-fu isn't great. I'm happy for it to sit here as an issue for now!)

kikendo commented 4 years ago

You managed to change the label now, cool! ;) And yeah just a wild idea, but if you can pull it off, it'd definitely give it an edge over any other sampler ever made.

j0hnlittle commented 3 years ago

Maybe as a starting point, there is this application note from Maxim: USB-POWERED HIGH PRECISION HI-FI PHONO PREAMP

This design idea shows a 3.3V powered phone preamplifier with RIAA equalization curve. The advantage is the low power, low voltage single supply solution. It is done with a MAX4478, a quad, low-noise, rail-to-rail op amp.

The schematic

A small linear regulator, the MAX8877, regulates the noisy +5V from the USB supply down to +3.3V

3.3v regulator