JVC RC-M70L renovation... and mods ? :)

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bugpat

bugpat

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This beautiful box arrived 2 hours ago... :clap:

I tested it, everything is working as expected, including full autostop, FM stereo reception, no cracks from potentiometers, loud sound... I recorded a song on the radio, and that's perfect too. I don't know if it has been rebelted, but I'm sure it has been opened.
There is only one mark on the faceplate under vu-meters.
The seller was saying that it has marks, but omitted (of course) to mention that the antenna support has been repaired... Maybe I'll give him a neutral feedback (eBay). The parcel was very strong to resist the french Post treatment...
I had it at a fair price, conditon is good so :thumbsup: .
After cleaning it, mods I (eventually) will do :
Led kit
Adding audio in line after the phono amplifier with a 10K resistor
Li-Po battery

M70.jpg


M70-1.jpg



The antenna broken/repaired support (will repare that later, or change the back cover ?)

M70-back.jpg



Before that, I must finish to rebelt the M9998 and to mod th CX-710ME.

To be continued...
 
Barb Bush

Barb Bush

Member (SA)
Questions:

Why are you Adding audio in line after the phono amplifier with a 10K resistor? Not really sure what this is accomplishing.

How the Li-Po battery? In place of the D Cells? With plug to recharge? - this sounds pretty cool. Let me know how you do this.
 
caution

caution

Member (SA)
Barb Bush said:
Why are you Adding audio in line after the phono amplifier with a 10K resistor? Not really sure what this is accomplishing.
Click to expand...
Hmm. I read that thread bugpat posted, and you know, I'm not really sure if Goodman calculated 10K to match proper line levels or if he just took a shot in the dark, but yeah, the value might need to be adjusted. The JW uses 27k, but it also ties into a different part of the preamp, so it may be higher for a reason. Also, there should be a DC blocking cap in series with the resistor. The JW uses 0.47uF@50V.

For the curious, line-in on the L shares the same preamp circuit the external mic jacks do. There is a switch that engages when the DIN has something plugged into it, which redirects the external mic jack's input circuitry to the DIN. Also, trying to redirect an L's line-in to enter the preamp the same way it does in a JW would be haaaaard. The function switch connections are different and the JW has a bunch of parts the L lacks.

So that leaves the phono inputs, which, from the input panel board connector onward, are identical on the L and JW. They go directly to the function switch and see identical circuitry from that point forward.
 
bugpat

bugpat

Member (SA)
Yep, I saw on the other thread that the resistor value of 10 K was a supposition, but I will test that and try to find the best value givin the better sound...
And will try to add the capacitors too.
 
goodman

goodman

Member (SA)
Yes, 10 k is minimal value, 33 k maybe is maximal.
Everything depending from volume level of SmartPhone or MP3 music player.
I agree with caution about blocking cap in series with the resistor.
Good luck with restoration.
 
goodman

goodman

Member (SA)
JVC_RC-_MJ70_Line_In_DIN_-_03.jpg



JVC_RC-_MJ70_Line_In_DIN_-_04.jpg

Find a 8 pin jack.
Solder violet cable to ground (7).
Cut the cables for L (8) and R (6) channels at 4-5 cm before jack.
Solder 8a to 3 (L channel).
Solder 8b to 1 (L channel).
Solder 6a to 4 (R Channel).
Solder 6b to 2 (R Channel).

PHONO IN - work as before modification.
LINE IN - use 3.5 mm jack for line in, phono input is disconnected.



-----
 
bugpat

bugpat

Member (SA)
No, I ´m waiting for the parts to make my led mod to arrive, and I want to finish the M9998 first...
 
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