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Easy101 fm radio mod question

Started by yamahajohn, October 22, 2016, 03:57:12 PM

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yamahajohn

model DC1, only 1 channel radio. Can I modify/change to a guitar amp? attached pics. tyvm

Enzo

Probably.  But you'd need a schematic, either from somewhere, or draw one up from it.

Anything that amplifies can become a guitar amp.

J M Fahey

What Enzo says.

It´s basically a fixed tuned FM radio, meaning it has a tuner circuit, whose audio output drives a small amplifier, a couple watts or so.
IF you can find the point where tuner feeds audio amplifier, you can disconnect tuner, add a jack and plug your guitar there, it should work.
The tuner and audio/supply sections might even be on separate boards, which would simplify your job.

I see yours has an extra "remote control" ... what does it do?
You *might*  have an external audio input (to ampify, say, a cassette player or microphone); if so plug your guitar there.
Show the back panel .

Absolute worst case, if you can´t reuse the existing FM/audio board but you have inside, say, a power supply giving you from, say, 9 to 12V or thereabouts, you can build a simple amplifier (Little Gem or similar) for your guitar, using that supply, cabinet and speaker.

What kind of power supply does it have? I don´t see it.

yamahajohn


J M Fahey

You have more than I expected there :)
Two TDA2003, probably bridged , would amount to about 16W RMS .
Or if both chipamps are independent, they can provide some 8W each; in any case very loud for a "table radio",  I suppose they were also meant for noisy workshops, or , say, a relatively large restaurant or bar.
I see you can add an extra speaker.

Or they use one TDA2003 for the internal speaker, and the "remote control" controls volume amplified by the second one driving the remote speaker.  Cool.

The third device on the heatsink seems to be a 78xx regulator, probably a 7815 or 7818 one, to feed clean power to the power chips.

I don´t see no RF parts anywhere, which is good; if tuner board is separate and feeds the audio section through a shielded wire or similar, now you know where to cut and splice an input jack.

That HA**558 is a dual op amp, probably used for tone controls and to drive the chipamps, plus maybe be some simple preamp; if you find the track which sends it audio probably a guitar can be sent there.
Try to find the path from the tuner to the HA****

You might mount a nice little Guitar Preamp there.



yamahajohn

thankyou for all your info its a big help to me ill let you know how it works out i allso have one other amp ill post in couple of weeks when i get some better pics of it its a califone 2412 25watt old school record player amp so thanks again john.

J M Fahey

Remembervthe oint here is idntifying how the FM tuner, which at the end has an audio output, sends that signal to the audio section.
You find that, you found the point to insert a jack for your guitar.

We haven´t seen pictures of the FM tuner section (is it on another PCB?) nor on its connections.

yamahajohn

ill have to take the speaker out to get that cardboard cover off the fm tuner then ill get pics of the tuner and the wires and somebody said there is a screw under the card to get a station here in ohio write now its just stadtic with an antenna too wright now picking up propane for mrbuddy heater for shop and fuelline for snowblower lol should be couple of days for sure john

yamahajohn


J M Fahey

I bet the orange wire in picture 5958 carries +V (9 to 12V?) to tuner PCB and brings back Audio.
Looking at the connector in tuner, function should be:
1: audio
2: +V
3: ground

I bet you unplug that connector and touch the white wire contact with a needle held in your bare hand and speaker hums or buzzes, depending on volume and tone controls, of course.

If so, I can tell you how to wire an adapter jack so you can plug your guitar.

I would not chop the connector off because someday you might want to use the tuner; it´s fixedtuned to the "captive"  FM station which you do not have available, but I guess it can be tuned to another by adjusting the trimmers or perhaps a ferrite core but do not touch them at random or you´ll never recalibrate them, leave aside for a while.

yamahajohn

this is weird i got 12 volts coming out of the white wire huming from the orange wire and black i guess its ground the dam plugs are so tiny needles were to tiny so i used little tacs ill have to solder wires to the tacs then just push them in and tape em tight and hope i dont get hum sound maybe with a 68k resister on the plug ? i have 6 7 great guitar amps why am i messing with this thing thank for your info it helps a lot.

yamahajohn

ok this should be my last post on this amp its all done and back together with a socket on the back and it sounds just like my gorilla gg20 amp with out the distortion and loud as hell just one more question the second speaker hookup on the back says 8ohms would a 4ohm 12inch speaker hert it or wate until i get another 8ohm speaker anyway thanks for all your help 

J M Fahey

Don´t leave us without fully telling how the story ends  :'(
With multimeter black probe touching amp (not tuner) ground, what DC do you measure on connector pins 1, 2 and 3?
Which pin(s) cause hum?

How did you wire your input jack? (which colour goes where).

I guess then white is +12V and orange is audio, heatshrinked black is ground/shield but please confirm.

As of the external speaker, IF each TDA2003 drives its own speaker (one the internal, one the external)  then you can use an xternal4 ohms; BUT now I´m guessing they are bridged (it´s a higher-power connection but more picky about impedance), in tht case you will have to respect the 4 ohms warning **or** connectbthe external 4 ohms one BUT discnnectbthe internal one.

In any case,you got a nice amp  :)