Help with a DIY Boom Box

[dbolt71]

I am building a DIY boom box and I need some help figuring out how to build a charging circuit and a few other questions. I am using a lot of off the shelf parts acquired from Amazon and other sources. After much research I decided to go with a 12 volt system due to the commonality of parts and compatibility with 12 volt systems. I may one day tackle custom building a PCB audio system but I wanted to start simple this time. I have the source, pre-amp, amplifier, speakers, and the enclosure already. I went with a nice 24” DeWalt tool box I found for $20 at Home Depot. It is very sturdy and has lots of room.
Here are a few of the questions I need help with:

1) Would I need to use any Ground Loop Isolators?
2) Are there any components I need to consider?
3) Should I baffle the speakers or not? What are your thoughts on molded foam baffles?
4) The biggest issue I need help with is how to build a charging circuit.

The amperage I expect to be no more than 5 amps at max volume which I really do not care to endure anymore than just showing this thing off to friends. I will normally use it at lower volumes so the typical draw should be between 2-3 amps at my best estimation. Weight is not a concern. The toolbox I am using is very sturdy and I don’t plan on rocking around the neighborhood with this thing on my shoulder. I found a 12 volt 12 Amp Hr AGM Mighty Max Battery on Amazon for a good price.

At first I did not care about being able to use this plugged in to AC power. If I only want this to be rechargeable there are many charger options I could use. It has been pointed out to me that making this Boom Box to be used while plugged in may be a smarter way to go. So therein lays the problem. Can someone either tell me how to go about that or point me in the direction of some instructions?

I have a rudimentary schematic to show what I have come up with so far. I did not think it was necessary to list all the parts by name and model number but I can provide that if someone needs them to assist me. All the parts are 12 volt.

Some of you may want to know my skill level. I have been a certified Master Mechanic for 16+ years. I have an Associate’s degree in Automotive Technology. I am a licensed Amateur (Ham) Radio operator. I specialized in a lot of electrical trouble shooting and repair on automobiles. I have installed a few aftermarket stereo systems, assorted electronics, and Ham Radios in vehicles. I can repair electronics well but this is my first attempt at actually making something from scratch. Somewhat from scratch anyway.

 

[JMFahey]

Go straight to this thread, more useful data and cool construction projects than you'll ever need :
http://www.diyaudio.com/forums/class-d/104402-boominator-another-stab-ultimate-party-machine.html

 

[rpi]

I recently completed my own boombox. Probably you will find anything interesting in the document which I prepared about making process:
https://github.com/project-owner/Peppy.doc/wiki

 

[OffGridKindaGuy]

Attempting to operate separate units from a common power source (Battery) is going to cause you headaches. Audio line isolation between all three units may be necessary, especially between the Bluetooth unit and the preamp.

You might get away with connecting the preamp to the amp without isolation but I would test that first.

I can almost assure you that there will be issues between the Bluetooth unit and a common ground. (Because of voltage regulation on the Bluetooth board)

I've been using these for portable 12 v.d.c. units. Built in overcharge/discharge protection and will easily operate a 15 watt/ch. amp for many hours. Only comes with an EU type plug on the charger but adapters are cheap.

New Super Protable 15000mAh Lithium ion Super Rechargeable Battery + Power Charger EU Plug Wholesale-in Rechargeable Batteries from Electrical Equipment & Supplies on Aliexpress.com | Alibaba Group

 

[dbolt71]

First thank you for the response. This is the kind of feedback I have been looking for. To OffGridKindaGuy. I guessing you're saying I may get a hum from using 3 components with a common ground. If I am on battery power only is that an issue or only if the system is plugged in and charging? Would ground loop isolators solve the issue? I have some shielded audio wiring I was going to use for the audio signal from device to device. As far as the voltage regulation for the Bluetooth what is it that concerns you? Are you thinking a voltage drop may cause loss off operation? If that is the case I could make or buy a small voltage regulator to power it or the other devices.

I am still unsure of how to go about the charging circuit. Like I said before if I do a charge only circuit and only use this on battery power that is easy. Having it plugged in and charging while in use is where I get lost.

Any thoughts on baffles for my speakers? Should I port the box? I am making a box for the power amp to have a grill to allow airflow for cooling but that will be sealed off. I was considering the baffles in this link below. I have used them in car audio and was pleased.

Amazon.com: XTC 4" Foam Baffle Pair: Sports & Outdoors

 

[dbolt71]

JMFahey the pictures on your thread for the Boominator are not working. To RPI that is a very nice little Peppy you made!

 

[OffGridKindaGuy]

To OffGridKindaGuy. *1_I guessing you're saying I may get a hum from using 3 components with a common ground. *2_If I am on battery power only is that an issue or only if the system is plugged in and charging? Would ground loop isolators solve the issue? I have some shielded audio wiring I was going to use for the audio signal from device to device. *3_As far as the voltage regulation for the Bluetooth what is it that concerns you? Are you thinking a voltage drop may cause loss off operation? If that is the case I could make or buy a small voltage regulator to power it or the other devices.

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*1 Not only hum, but very distorted audio and perhaps equipment damage! The first test I would do is connect all devices to the common battery for power (Bluetooth, Preamp, Power Amp) and get the VOM out. No interconnects to any units at this time via audio cables. Just the three items on their own little island, powered up, and with no audio interconnections whatsoever..

Start doing voltage tests between the units. Start with the audio shield connection of the audio in/out between the Bluetooth unit and the preamp. If you find any D.C. voltage potential difference above zero, I would highly advise total isolation. If there is a potential difference on the shield, it's highly likely there's a difference in D.C. potential (if any) in the audio signal paths. Electrolytic capacitors will pass small amounts D.C. if they are used in the audio circuits..

*2 This is the risk of trying to operate 3 non isolated items from a common power source, especially if one of the units has voltage regulation to a different voltage in it to operate part of it. The Bluetooth receiver itself on that board doesn't directly require 12 volts to operate. I'm almost certain there is some on board regulation going on there. Total isolation would cure it.

If you experience hum while charging, check the charger. That's a totally different circuit..

*3 If you use a 12-12 volt isolated power supply to operate the Bluetooth unit alone, no audio path isolation should be needed. It would then be on its own little power island all by itself..

I'm not as concerned with the connection between the preamp and the final power amp. They are usually designed to be used in this fashion for direct connection to a power amp but I would check anyway..

The most simple method of charging is to have a easy removable battery and charge off board. Perhaps 2-3 batteries, use one, and replace with a fully charged battery when needed..

Keep us updated..