First of all, forgive me if I have not posted this in perhaps the correct forum, but my question is about a tube DIY kit (I hope!)
I collect and listen to lps and 78s. Most of my 78s are from the 1918-1925 era, and are acoustically recorded (no recording curve used.) Does a kit exist which would give me both the RIAA and a flat curve (switchable,) so that I could enjoy both types of discs to the fullest? Also, I would like the kit to include tubes--I feel it would take my record listening to the next level.
Would a kit also permit me to include a mono switch, and a vertical switch (reverse phase on the left channel, and mix to mono to play Edison Diamond Disc records, for example)?
Thank you for your help and your time.
Not a kit, but a well documented and (seems like it would be) easy to build phono stage is here:
It has a flat low-gain section for ceramic carts and switchable hi-gain RIAA MM section. If you're using an MM cart, it looks real easy to switch out the RIAA circuitry as that is an isolated module. Interesting design too.
Mike, Did you work for Mitsubishi Pro Audio Group in the late 80's?
I don't see why a switching arrangement could not be added to any diy riaa preamp, that would bypass the R/C compensation network, and provide straight gain for your 78's.
I am not familiar with 78's, so I assume the groove modulations only need to be amplified linearly, without time constants in the circuit.
A switch to sum the left and right channels for mono would be easy to add also.
To reverse phase on the left channel, you might need an additional inverting stage that could be switched in or out for the left channel.
I would say pick your favorite diy , riaa phono preamp, and modify it with switching, to customize it to your needs.
Many gifted people at this site could help you with the technical aspects of your project.
Diego Nardi was kind enough to author a DIY phono section for just about all of the available curves.
Be careful when bypassing an RIAA section, there will be a huge increase in gain.
I don't know of any kit avaliable for 78s. If you're into building from scratch or restoring vintage gear then look for an Altec 440C preamp or a Webster Electric Model 97-0. Also the McIntosh C7 or C20 or the Marantz mono consolette. The McIntosh and Marantz units have special one of a kind selector switches that would be hard to duplicate but the Altec and Madison Fielding units are reproducable. I have the achematics for both and would be willing to share. All the best! James
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