Modding MS12-B so CD/DVD comes on by default instead of RIAA?

[EarToday]

Hello

I want to put it on a wifi plug and turn it on and off remotely to play music through chromecast, so I need it to default to the CD/DVD input rather than the RIAA.

Has anyone done this mod? Is it possible/easy?

I've previously done the basic upgrades on this a few years ago, so have been inside and tinkered in the past, but thought I'd ask first!

Thanks

 

[BinaryMike]

I don't know what equipment you're referencing, and many other folks won't know, but it's sometimes simpler to put an inverse RIAA network on the phono input and be done with it.

 

[vaathi]

Mike. He is referring to input selection defaulting to CD/DVD in MS-12B which it does the way he explained. I have not seen any mod referring to that...

 

[gadget73]

I don't suppose the company that makes it will provide that kind of info?

 

[I LIKE MUSIC]

IIRC and at my age and level of health that may be a stretch...

The input selection is controlled by a 2 transistor mono-stable flip-flop controlled by the front panel push buttons. The push button source selection switch switches function by grounding the appropriated transistor's base. This controls the voltage that goes to the relay that does the actual source selection. The default function select is performed by a capacitor connected to the base of the appropriate transistor.

It may be as simple as just moving this capacitor to the base of the other transistor in the mono-stable flip-flop circuit.

 

[EarToday]

IIRC and at my age and level of health that may be a stretch...

The input selection is controlled by a 2 transistor mono-stable flip-flop controlled by the front panel push buttons. The push button source selection switch switches function by grounding the appropriated transistor's base. This controls the voltage that goes to the relay that does the actual source selection. The default function select is performed by a capacitor connected to the base of the appropriate transistor.

It may be as simple as just moving this capacitor to the base of the other transistor in the mono-stable flip-flop circuit.

Thanks I LIKE MUSIC - that's the sort of answer I was hoping for (and thanks to the others for the replies too of course). I'll open it up tomorrow and take a look!

 

[Hi-Q]

Yep, just swap C18 over to the other switch, observe correct polarity! Present RIAA position at bottom left on photo.

 

[EarToday]

Yep, just swap C18 over to the other switch, observe correct polarity! Present RIAA position at bottom left on photo.View attachment 1166445 View attachment 1166446

Perfect! Thank you! I knew it would be worth asking here Wish me luck!

 

[EarToday]

Thanks everyone. It works perfectly!

I've attached a PDF with some photos and basic instructions. Easy enough without, but just in case someone else ever needs to do this and finds this thread, it can't do any harm.

All went well except 1) screwing down the board and finding I'd left one connector underneath... and then 2) losing one of the channels... didn't take too long to see I'd managed to short one of the tubes by splashing a bit of solder on the board! Oh well, par for the course for me and soldering - at least I didn't burn myself this time!

Anyway, most importantly it now does the job - so when I turn it on and off with a wifi plug, it defaults to the input I want the most (Until I can get Google Home to put a record on for me, it makes senes for it to be this way around!)

Thanks again everyone!