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Alternative to Faceplate/Preamp unit for Table Radios...

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  • tomzarbo
    replied
    So, I just wanted to update this thread for posterity and additional information regarding the SWM 7805C Single-DIN car radio...

    A poster named Noah had a question on this on my other YouTube channel where I posted this review and I put it on the bench again to test it out.
    Basically he wanted to use this for a battery-powered radio and was concerned about the current draw since the screen always stays on when you turn the unit off by the power switch to display the time.
    Only if you cut the power to the red line does the screen go off and it basically goes idle (except to save settings which is powered by the yellow lead) which is what would happen in a car when you turn the car off to leave... the yellow lead always hooked up would save settings, but the screen would go out.... Not a problem in a car with a 500 amp battery, but would be an issue in a portable radio powered by a few 18650 Lithium cells.

    So here is what I found out:

    *With the unit ON (FM Radio) and the volume down it drew around 400 mA (to simulate the unit running, at a low volume)

    *With the unit OFF but still connected to power (red and yellow leads) it drew around 200 mA as the screen was still active displaying the time.

    *With the unit OFF (No Screen Showing) and the red lead disconnected (similar to the ACC being off in a car) but the yellow (memory) lead still connected, I only read between 0.01 and 0.00 mA. So the power draw was so low as to be basically nil.

    So basically, in order to use this in a boom box/table radio type of situation without killing the batteries, you would have to put a switch on the red lead and power that down so just the yellow/black leads were connected.

    I confirmed that this held the settings and drew basically no current. A bit inconvenient to have to turn a switch on and then turn the unit on, but in order to preserve power when you're not using it, I guess that's what we will have to do. Thanks for posting the question!


    So when I use this in a portable radio situation, I'll be putting a switch somewhere to kill the screen (red lead) so that's not always on. Even as a plug-in device, I don't think I'd want the screen to ALWAYS be on, there just would be no reason to have this be the case, I don't sit across the room to remote-control any of my radios basically, so getting up to turn off/on the radio isn't an issue for me either by battery or by 'mains' power.

    Here is that video on my other channel again for reference in case you're interested: SWM 7805C Car Radio Video - YouTube

    TomZ

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  • Dukk
    replied
    Nice Find! Looking at it right now.

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  • 3rutu5
    replied
    Pretty cool, I might have to invest in one and build it into a unit for the kids. They seem extremely cheap don't they, considering they have an inbuilt amplifier as well, I'll be watching this thread ')

    Leave a comment:


  • tomzarbo
    replied
    Also, on a related topic...
    I found this Double din radio for the 'Bang'-ing good deal of $31.50 shipped. Has Bluetooth, remote control, touch screen, FM radio and plays videos and audio files from USB jump drive and the small memory cards. Looks to be pretty much the same deal as the other radio, just a bigger screen. I'll know in 2-3 weeks.

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    Has pretty decent reviews and it's not deep at all, like the single din unit. Should not take up much space in a table radio. I'm going to try to design something around this player as well. I have a couple of non-brick, in-cabinet 12V power supplies so if they are not too noisy, this may be a cord-only project.

    Best of all... you can "TURN it Up!" with a real volume knob!

    Fun!


    TomZ

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  • tomzarbo
    replied
    Originally posted by Millstonemike View Post

    Remember to get the 12V version. The circuitry is the same in both. The difference is the relay coil voltage. Both have losses in a 5V linear regulator and 555 timer circuitry. But at 5 V, there's not enough volts left over to trip the relay coil control transistor. Note, I never tested the 12 V version, I just reverse engineered the 5 V and updated it. If the 12 V has the same issue, just shunt the trip trigger LED. That's where the most losses are.
    I may have already picked up some of the 12v ones awhile back.
    I have a design sketched up for this already, Curves and angles and such. Plus... white paint! Taking a break from veneer.

    TomZ

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  • Millstonemike
    replied
    Originally posted by tomzarbo View Post
    I got a few more of these radios in recently to play with. I have another boom box/table radio type of thing to make with this head unit.
    I think I'll test with the built-in amp to see if it's up to the task of powering the speaker I plan to use (a set of Wolf's Rubyk's which I have the parts for)

    If I don't go with the built-in amp, I'll use one of the 30 to 50 watt at 24 volt Class D amps I have with a delay on/off unit that Mike suggested above.

    I won't modify the head unit this time... I just don't think it's worth the risk for the small gain in space and amperage; I just don't seem to have the 'knack' to 'hack'. I think this will be a 'corded' radio for the most part. I have someone in mind that I plan to build it for, and I'll ask them if they want cordless or corded, but I'm hoping for corded.

    Anyway, I didn't forget about this, and I think there were a few of you who were wondering how it worked out, sorry I just left it there. I hope to start messing around with this thing in the next few months.

    TomZ
    Remember to get the 12V version. The circuitry is the same in both. The difference is the relay coil voltage. Both have losses in a 5V linear regulator and 555 timer circuitry. But at 5 V, there's not enough volts left over to trip the relay coil control transistor. Note, I never tested the 12 V version, I just reverse engineered the 5 V and updated it. If the 12 V has the same issue, just shunt the trip trigger LED. That's where the most losses are.

    Leave a comment:


  • tomzarbo
    replied
    I got a few more of these radios in recently to play with. I have another boom box/table radio type of thing to make with this head unit.
    I think I'll test with the built-in amp to see if it's up to the task of powering the speaker I plan to use (a set of Wolf's Rubyk's which I have the parts for)

    If I don't go with the built-in amp, I'll use one of the 30 to 50 watt at 24 volt Class D amps I have with a delay on/off unit that Mike suggested above.

    I won't modify the head unit this time... I just don't think it's worth the risk for the small gain in space and amperage; I just don't seem to have the 'knack' to 'hack'. I think this will be a 'corded' radio for the most part. I have someone in mind that I plan to build it for, and I'll ask them if they want cordless or corded, but I'm hoping for corded.

    Anyway, I didn't forget about this, and I think there were a few of you who were wondering how it worked out, sorry I just left it there. I hope to start messing around with this thing in the next few months.

    TomZ

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  • tomzarbo
    replied
    I did hook both yellow and red lines to 12V positive.
    did the amp chip look okay to you?

    I'll try to double check the nodes I've soldered to, compare against the schematic, just in case I picked the wrong nodes
    TomZ

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  • Millstonemike
    replied
    Originally posted by tomzarbo View Post

    I checked continuity between the various leads, and the respective node on the board. I figured the fuse was 'in line' with the main 12V+ feed on the big black plastic connector.
    Tom, I updated my previous post to add the "Ignition" turn on input.

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  • tomzarbo
    replied
    Originally posted by Millstonemike View Post

    Did you account for the fuse that's no longer in the power circuit?
    I checked continuity between the various leads, and the respective node on the board. I figured the fuse was 'in line' with the main 12V+ feed on the big black plastic connector.

    Leave a comment:


  • Millstonemike
    replied
    Originally posted by tomzarbo View Post
    Well, I borked it up. I'm not sure which of my recent maneuvers did it, but it's not powering up...

    TomZ
    Did you account for the fuse that's no longer in the power circuit?

    There's the constant battery power input (e.g., remember settings), and, a separate +12 V input to turn the unit on (e.g., turn the key on, the radio comes on).

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    If I still lived in Millstone, I'd have to take a ride out to the country and watch you wield the iron. Geez . To be fair, I've been soldering well over have a century. My first iron was a trapezoidal hunk of metal with a pointed end . It was attached to a wood handle via a steel rod. You heated it on the stove burner.and then quickly tried to solder a connection. Wish I still had it.

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  • tomzarbo
    replied
    Well, I borked it up. I'm not sure which of my recent maneuvers did it, but it's not powering up...

    I made a diagram by testing continuity for the power leads coming in, ground, antenna, 12 amp power-on, etc... I'm pretty sure I did that right.

    I did dig into one lead and the actual amp chip just a bit when cutting off the big plastic connector blob... I don't know if that did anything or not....

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    I also noticed in the process of getting the blob off, I think I managed to pull off a trace from the board. (see pencil mark on end of board) The other pair of connections that have that little raised bridge under the green coating between them had continuity, and this one did not, so I made a little piece of wire and jumped the connections from the other side.

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    Still, no dice. After messing with this for awhile, I feel like I need a break for today. I'll give it another crack maybe tomorrow when my eyes uncross.
    I have another unit coming from Aliexpress so I can use that to help me troubleshoot this one when the time comes. Ahhh, learning by failure!

    TomZ

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  • Millstonemike
    replied
    Originally posted by tomzarbo View Post
    I was able to get the big black plastic blob cut off without (I think) damaging the board or any components. The Dremell tool was a good idea.
    I did just touch the big cap with the cutting wheel, but it just barely broke through the plastic outer case...

    Next step, clean the rest of the leads up, and run some wires to it and make sure I didn't mess it up somehow. Onward!

    TomZ
    Nice going. I wouldn't worry about the big cap. That's the bypass cap for the power amp - reserve energy close to the amp itself to handle peak demands. It might even be removed, possibly replaced with a small axial cap to further reduce the the board height.

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  • tomzarbo
    replied
    I was able to get the big black plastic blob cut off without (I think) damaging the board or any components. The Dremell tool was a good idea.
    I did just touch the big cap with the cutting wheel, but it just barely broke through the plastic outer case...

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    If you look closely, you can see that I also nicked the board in a few places as I got rid of the last of what was there, I probably should have left that little bit on there, it wasn't taking up much space, just wanted to clean things up a bit. Looks like that part is solid copper underneath so no issues there I don't think.

    Next step, clean the rest of the leads up, and run some wires to it and make sure I didn't mess it up somehow. Onward!

    TomZ

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  • tomzarbo
    replied
    Originally posted by Millstonemike View Post

    In the absence of a Dremel cut-off, I would try a fine tooth hacksaw blade to cut it off close to the board. That might allow the individual pins to be removed one at a time.

    +1 on Neil's wire size post. I like reclaiming wire from Ethernet cables. The wire comes in twisted pairs, each pair has a signal and a ground in the Ethernet application. Seems perfect for audio line level signals to minimize noise.
    I often just use pliers or cutters and smoosh/break apart the plastic bits until it kind of comes apart in bits, but that may be dangerous with this. I do have a Dremel, maybe I could give that a go. Maybe Dremel off what I can get to and snip off the rest, whatever works and is safe.

    I was wrong, I actually used 24 gauge wire for this. I have various colors of this finer gauge for hook-up duties, so I used what I had.
    I do have some twisted Cat 5 type wire around somewhere from when I wired up my other house, but I thought multi-stranded may have a bit more durability to it.

    Thanks for the suggestions. I'll see what Dremel blades I have!

    TomZ

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