Hi
Some suggestions about buildt in solutions for Beogram 4002 / 4004/ 6000 :
The solution from "Beolover" is very impressive, plug and play you can buy it on the E-B .... auction platform, search for:
Beogram 4002 and 4004 Phono RIAA Pre-Amplifier - Easy No Soldering Installation.
For more information look on Beolvers Blog.
Have not heard it so far but there are some points where you could adjust the RIAA to you favorite sound I guess, would be very interesting in my opinion.
The second solution for a build in preamp is like this from danish Soeren Claudius:
https://claudius-elektronik.dk/designs-og-l-sninger.html
Have alredy mounted 5 of these for several projects and it'sworking great.
A little bit of soldering needed but no big deal and a good value for the money my opinion.
The third I know about is from Jacob Rungwald, member of facebook group Beogram 400/4002....
https://www.facebook.com/groups/1499233306805847/permalink/6809783595750765
This is a plug and play RIAA version and has implemneted a IR remote function via DataLink
(Beomaster 4500 or similar is needed) so you could controll the Beogram with a BEO 4, Beolink 1000 or similar.
You have to get in touch with Jacob and ask for avaiability and price.
Thousands of extern Preamps a avaiable quality from crap to high end, like the prices from a few Bucks up to somewhere ;-))
So it's your choice
Kind regards
Christian