Digging into the M9935k

MesaAZGuy

Member (SA)
So I just picked up one of my long lost childhood radios early this week. I enjoyed playing with it for the last two days and now its business time. I wanted to add bluetooth capability and a lighted dial aside from a good general cleaning and de-bugging. ( There were insect parts floating around in there!)


First was disassembly, wash, see what I have to work with and reassembly. I don't have the bluetooth module yet and it should arrive in a couple of days. The original speakers looked aged but were in good shape overall. I taped the center cone and lightly spray painted the speaker with a satin black which turned flat from absorbing into the paper. Over all, I think it came out mint and no degradation in sound. The dial light is in but I need to clean the actual dial scale and plastic window to free it of stuck on dust.
This is where it is so far. For the dial light, I used LED tape light I had leftover from a job. It it supposed to be 12v, but runs fine on the 9v mains. Having said that, I do get some slight flicker when the radio is cranking.



IMG_0076 by https://www.flickr.com/photos/153164955@N06/, on Flickr




One of the mounting pegs was broken. I used crazy glue and haven't screwed the case until I am done with the bluetooth. This will give the adhesive more time to set.




IMG_0083 by https://www.flickr.com/photos/153164955@N06/, on Flickr




IMG_0088 by https://www.flickr.com/photos/153164955@N06/, on Flickr




IMG_0090 by https://www.flickr.com/photos/153164955@N06/, on Flickr





IMG_0089 by https://www.flickr.com/photos/153164955@N06/, on Flickr




IMG_0091 by https://www.flickr.com/photos/153164955@N06/, on Flickr




IMG_0086 by https://www.flickr.com/photos/153164955@N06/, on Flickr




IMG_0087 by https://www.flickr.com/photos/153164955@N06/, on Flickr
 

Reli

Member (SA)
Dec 24, 2010
6,316
441
83
USA
Digging those speaker panels, they really braced them structurally to reduce resonance
 

MesaAZGuy

Member (SA)
Honestly, It could use more Bass at low volume. When you crank it up it comes alive, but by then the cops are being called out! I have some tapes made that have the EQ set for more bass. At that point, this radio sounds almost as good as my marshal bluetooth speaker. I am impressed by this little radio. Its really not bad. The tape belts are in excellent condition. I ordered a replacement set but will hang on to them until these crap out. There were alot of insect wings and dust in the case. A good bath took care of that.
 

MesaAZGuy

Member (SA)
I need to cut into the amplifier input which I have located thanks to YouTube University. I have a six position switch to separate both the radio input and the BT from the amplifier input. For the power I have a micro BT module from Amazon along with an adjustable voltage regulator to go from the radio's 9v source to the BT's 5v power requirements. It will be an experiment.
 

goodman

Member (SA)
Jun 14, 2011
2,321
216
63
50
Bulgaria
2 months ago, I was restoring and modifying a Sanyo boombox with a mp3 module:
https://boomboxery.com/forum/index.php/topic/28879-sanyo-c30-restoration-modification/?p=363151
I wanted to use Sanyo's power, but have some parasitic noise.
I solved the problem by using an autonomous power supply for the mp3 module.

I assume that you will use a similar module:
https://www.aliexpress.com/item/Wireless-Bluetooth-Adapter-3-5mm-Jack-USB-Music-Audio-Receiver-Dongle-for-Aux-Car-PC-for/32805373719.html
To resolve problem with parasitic noise you have 2 options:
1 - Use a second power supply 5 v. from an old phone or similar.
2 - Use an ground loop isolator like this one:
https://www.xmpow.com/mpow-ground-loop-noise-isolator-for-car-audio-system-home-stereo-ma1.html

I waiting to see next steps of your mod. :yes:
 

MesaAZGuy

Member (SA)
I got the idea from Teddy Hashee on YouTube. I reached out to him and he not only got back to me, but sent me some wiring diagrams. I ordered some more parts based on his list. Some of them are resistors, capacitors and other goodies. I think he puts those inline to cut interference. Before he got back to me, I had ordered a BT module and power supply step down converter which were different from what he uses. I hope to see if those work without additional parts. Either way, I will keep you guys posted.
\By the way, Teddy is awesome. Love his videos on BB restorations.
 

MesaAZGuy

Member (SA)
So I successfully installed the bluetooth after a couple of failed attempts. My first failed attempt was due to a bluetooth module that had a 5x5 watt amplifier which interfered with the radios amplifier. It would click out one of the speakers and introduced alot of humming noise. The second bluetooth module did not have an amplifier built in. I used a homemade simple circuit DC isolator courtesy of Teddy's drawings along with an inductor, capacitor and resistor. My radios 9v power was stepped down to 5v using an amazon voltage regulator chip. I put a switch inline to the radio tuner's power supply which would shut off the radio tuner. The BT speaker outputs were soldered to the radio tuner line out on the PC board. Once I powered it up, I heard a little jingle and the rest is history. Sounds amazing! I did add a blue 3mm LED with resistor to cut down its voltage on the side of the case to show its powered up. (Doubles as a seriously bright blue LED flashlight!) All components were hot glued onto the top of the battery case moulding inside the cabinet.


I didn't end up using the red BT module due to the interference of its built in amp with my radio's amp.



IMG_0149 by https://www.flickr.com/photos/153164955@N06/, on Flickr





IMG_0157 by https://www.flickr.com/photos/153164955@N06/, on Flickr





IMG_0150 by https://www.flickr.com/photos/153164955@N06/, on Flickr





IMG_0153 by https://www.flickr.com/photos/153164955@N06/, on Flickr





IMG_0155 by https://www.flickr.com/photos/153164955@N06/, on Flickr





IMG_0154 by https://www.flickr.com/photos/153164955@N06/, on Flickr
 

neanderthal

Member (SA)
Jan 1, 2016
167
22
18
MesaAZGuy said:
I would love another larger box but the prices are outrageous on eBay. I can’t afford those prices
Hitachi 3D80/ 88 can be had reasonably. 6 speakers of fury! It's a matter of patience.

I think it's my best sounding box of the 3 I have. (Sharp WFT380, Sharp QT73-CD (7 speakers of fury!) and the Hitachi.) Good response up top and nice lower down range as well. The 380 hits harder, the 73 has better lowdown response, but the Hitachi has the best balanced sound.

If that's your garage i'm jelly.

Edit. Just looked at Ebay. Yikes.
 

caution

Member (SA)
Mar 25, 2014
2,498
334
83
Boomboxery
I really like your bench setup! Great job getting this fella cleaned up, the BT mod and dial light mods look fantastic.
 

Beerwolf

Member (SA)
Dec 20, 2014
4
0
0
i need a set of these speakers. i found one all rotted out and the speakers are full of holes, do you recommend a good replacement speaker?
thanks