Real Line In on Sony CFS devices ?

I am currently working on the restoration of two SONY boombox, a CFS-47L and a CFS-77L.

After some tests and the analysis of the service manual, it appears not only that the line input is a phono input, but also that it is not possible to bypass the RIAA (preamp) because all the signals pass through it (radio and cassette too).

Does anyone have any idea how to get around this problem?
Is the installation of an anti RIAA (attenuator) mandatory?


Thanks in advance

Dan

I would just use a line level to phono adapter similar to this:

https://www.amazon.co.uk/INPUT-PHONO-LEVEL-AUDIO-CONVERTOR/dp/B00131E0E2

Dancorp, this Line IN on that Sony is not exactly Phono input, neither it has got RIAA equalisation.
To be more precise, that is standard DIN connector (input/output connector). As far as levels are concerned, you are right, the DIN socket does need lower level of signal.
Manual of Sony CFS-47L gives several points where you could inject the signal (R115 for Left ch, R215 for right ch, or connection between R125/R112 (L) R224/R210 ( R ) or on the negative lead of C114 (L) or C214 ( R ) ).

However, I would suggest either making an attenuator (1:10) or buying the one. You can use one double logaritmic potentiometer or just 4 resistors since the voltage should be up to 0.1V compared to 0.775V as expected on RCA connectors (line). That is still not so low as Phono input expects!

Basically, you just have to turn the volume down, or you will see what happens "when you turn the amp all the way, over 10".
Service manual is available here.

Thanks for the message. I didn't see it. Your analysis is interesting.
On the CFS 77L, it has two inputs: DIN and Phono (with a switch). Both are preamplified but the phono input has an additional filter circuit.
On the CFS 47L, only the DIN input is present. It is closer in level to a Line in.

I bought the Monacor attenuator and disassembled it. It is simply composed of 4 film capacitors and 6 resistors. I think I'll make myself a few, the price will be lower. It works like a charm on the phono input of the CFS 77L.

I will study the DIN input of the CFS-77L to see if an attenuation based simply on resistances could work.

https://elektrotanya.com/sony_cfs-77l_stereo_radio_cassette.pdf/download.html

ps: i'm lucky with Sony SM, most of them are in french