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  • Bantam table radio

    I'm trying to finally get to work on building a "Bantam Table Radio"
    It will consist of two 'Strengths,' Both will use the ND91 woofer along with the AMTPOD-4 tweeter same as the original Bantam speakers.

    The smaller 2-channel version will use the same Peerless passive radiator as the originals. It will use a small video player as a preamp unit with a nice remote control unit and the ability to play videos, MP3s, and Bluetooth.

    The larger 2.1 channel version will use the same Bantam drivers, likely without the PR's, and a small subwoofer, ether the Tang Band W5 5.25" subwoofer or the Peerless SLS-P830945 5.25" subwoofer, which models similarly. It will use a similar, but larger screened video player as the other one, with the same basic functions. I found a decent quality unit to use as a head-unit for these radio projects that are high-quality and decent looking, and priced right.

    The amp for the two-channel unit will be the same one I've used for a number of other projects: The TDA7492 50 watt amp. https://www.parts-express.com/tda749...2x50w--320-606

    For the 2.1 version, I'm thinking of using this two channel amp for the stereo portion:
    https://www.parts-express.com/sure-electronics-aa-ab32174-2x50w-tda7492-class-d-amplifier-board--320-301


    It's the SURE AA-AB32174 2x50W Class D amp board. The reason for the change in amp board for the 2.1 version is that this amp works well with higher voltages, it should work well with the 24V power supply that I intend to use with the subwoofer amp I sources from Amazon. It needs 24 Volts to really shine, but I think this combo may end up being a stout performer if there are no serious noise issues. If I use the first 2x50 watt amp I linked to, it may not like the low 4 ohm impedance of the Bantams drivers at 24 volts, then I'd have to reduce the voltage to it somehow... I'm trying to make life easy for myself. Some more testing will determine what will work in reality, though.

    Anyway, I'll probably be asking for a bit of advice and guidance along the way as I get started building these. I plan on making the boxes fairly easy to build as well, not like the Toni Table Radio I built a few years ago with a lot of curves. I wanted to create something easy to construct with normal wood working tools.

    initial tests indicate that this will be a good-sounding, fairly loud, and relatively small setup, at least in 2-channel form. I'm hoping for good things from the 2.1 version too.

    Just something to whet the appetite a bit if anyone is interested.

    I'll have more info and some pics in a few days to help explain things a bit better. Stay tuned.

    TomZ

    Sorry, not sure why the links are not working correctly
    *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
    *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

    *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

  • #2
    Both amps use the same chip and the chip determines the capability of the amp vis-avis the speaker impedance. The 7492 datasheet doesn't provide a lot of info at 4 ohms and that shows in the mfg's spec.'s for particular modules.

    In the end, it's the chip's thermal dissipation that determines the amp's limits at any voltage and impedance. You can use a 4 ohm driver at 24 V with the 7492. The question is the amplitude of the source - ultimate power out of the amp to speakers. The ND-91 can only handle 30 W rms. And that's below the chips spec at 50W per channel. So if your not stressing the drivers, your not stressing the amp.

    For what it's worth, the TDA7492's output impedance is 0.2 ohms where the TPA3116 output impedance is 0.12 ohms. So the 3116 has an advantage with the lower impedance.

    Question: Why not use a 2.1 amp with two chips on board, one for L & R, and one in PTBL mode for the sub? That eliminates any interference between two separate amps.

    Comment


    • #3
      Hey Mike,

      Thanks for the perspective. Just going from some prior testing of the Bantam speakers with the PE small 50 watt per channel amp. I powered it up with my 16 volt 5 amp power supply with a laptop computer as a source and the amp was starting to run out of steam before the speakers. Not by that much I don't think though. I think that using a higher voltage may cause issues with that amp per the instructions on the product page, but maybe as you say, it wouldn't.

      Yeah, It would be easiest to just use a 2.1 amp for sure, but PE doesn't have any that look to be high enough quality from reviews except for this one: https://www.parts-express.com/tps311...e-con--320-635
      And that one has Bluetooth, I guess I could just not use the Bluetooth. My source preamp/head unit has Bluetooth built in.

      I guess I'll look into that one and see if it may do the job. It does seem to have a high pass on the satellites, that's nice.

      Stuff to think about. Thanks for the food for thought.

      TomZ
      *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
      *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

      *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

      Comment


      • #4
        I'm interested in what you're using as head unit. thx

        Comment


        • #5
          Originally posted by dwigle View Post
          I'm interested in what you're using as head unit. thx
          I'll post some pics this weekend of what I'm using.

          TomZ
          *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
          *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

          *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

          Comment


          • #6
            Waiting on your usual great build pics.

            Comment


            • #7
              Originally posted by tomzarbo View Post
              Hey Mike,

              Thanks for the perspective. Just going from some prior testing of the Bantam speakers with the PE small 50 watt per channel amp. I powered it up with my 16 volt 5 amp power supply with a laptop computer as a source and the amp was starting to run out of steam before the speakers. Not by that much I don't think though. I think that using a higher voltage may cause issues with that amp per the instructions on the product page, but maybe as you say, it wouldn't.

              Yeah, It would be easiest to just use a 2.1 amp for sure, but PE doesn't have any that look to be high enough quality from reviews except for this one: https://www.parts-express.com/tps311...e-con--320-635
              And that one has Bluetooth, I guess I could just not use the Bluetooth. My source preamp/head unit has Bluetooth built in.

              I guess I'll look into that one and see if it may do the job. It does seem to have a high pass on the satellites, that's nice.

              Stuff to think about. Thanks for the food for thought.

              TomZ
              That amp was around the web before PE carried it and got good reviews back then (2.5+ yrs ago). It uses TI's 31136 series chip and they're good down to 3.2 ohms at 24 V.

              Comment


              • #8
                These are the head units I'm planning on using. I've tested both of them in several versions and they are solid units with consistent build quality. It would be great to see PE carry them, especially the smaller one as it would fit in almost as small of a space as their other Bluetooth faceplate preamp unit... https://www.parts-express.com/12-vdc...remot--320-348 I have not had good luck with that one, personally.

                Here is the bigger one:

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                It has a 4.3" screen and It comes in two versions, a 5 volt version without the rear plug panel, and a 12 volt version with the rear panel. The rear panel includes hook ups for video output audio in and out, plus power input. It has a voltage regulator on the board which accepts 8-12 volts and sends it to the player as 5 volts. I would be using the 5 volt version as it's just a bit cheaper and I don't need the plugs on the back. This player is all over AliExpress and you can get one shipped to your house for under $30.
                You'd have to search for 'Lossless video Bluetooth player' or something similar to that. The AliExpress search engine is not the best to find these.

                Here is the smaller one:

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                It has a 3" screen and comes in black and raw silver aluminum. I've only seen it in the 8-24V input version so far. It isn't very deep so I think it would be an upgrade to the PE bluetooth faceplate preamp unit linked to above. The big player needs a few more inches of depth as it has one of the daughter boards arranged so it needs more space behind the player. This one is around $30 shipped as well.

                They both use the same remote and work basically the same way.

                They will play all types of music files, video files, and pictures. They both have FM radio tuners as well, although only the larger unit has a place to connect to an antenna.
                At least on the larger one I was able to play music files on it while displaying pictures like a digital picture frame, that was nice. It's not touch screen, but the interface is well done and logical, the remote works well and takes two AAA batteries and has decent feel, not like the thin card remotes, I really dislike those for some reason.

                I believe they use the same internal chipset to operate as the screens are basically the same and they both operate the same way. The video screens are high enough quality for their size, not HD or anything, but you're not going to be staring at these things or watching a movie on them, just accessing features or maybe playing a video while you do other things... for that they are great. The screen can be easily changed to English too. They both seem to be low-noise and of decent quality. Bluetooth seems to work well, though the antenna is just internal on both of these. The USB and SD card inputs are handy if you're not a bluetooth person.

                There is another version of the larger player that comes raw without the mounting plate. Don't be tempted by saving a few bucks, I have one of those, but there just isn't a good way to mount it. That's how it was first available, it took a year or so for them to get the faceplate version up and going. I really like the look and feel of the smaller player, it's buttons are aluminum and really feel pretty good to press for something this inexpensive.

                One of the things I want to do with both of these preamp boards is find a switched voltage source so that I can connect a relay or something so that turning on the video player via remote will turn on the amp as well, that would really tidy up things a lot. My other 'Toni Table Radio' had a power button on top that needed to be switched on and off before using the unit which wasn't as nice. Once switched on, the amp would always be powered up even if you turned off the preamp faceplate player.

                I may end up ordering one of those amps Mike. Beings that this will be controlled by a head unit, I was just looking for a basic amp without all the knobs and Bluetooth, but I guess some adjustability wouldn't be bad. The other sub amp I was considering using had pots for the volume and lowpass frequency as well. Maybe put the knobs out the back so they can be adjusted, but not easily.

                TomZ
                *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
                *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

                *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

                Comment


                • #9
                  Tom,

                  There's these delay relay units from ALI (<$3). Once the relay module receives power, it'll wait the adjustable delay time then trip the relay (1 sec on up). If you can find a switched power point on the head unit to power up the relay module, the relay will switch 10 A. They come in 5 V and 12 V versions (Power draw: <100 ma power for the 5 V and < 50 ma for the 12 V). Here's the catch. Both modules are exactly the same but use relays with different coil voltages. And the 5 V version doesn't work out of the box. At 5 V, the control circuitry doesn't have enough voltage to trip the transistor that completes power to the relay coil. That circuit includes a blue LED in the series with the trip transistor. A blue SMD LED has like 3.2 V drop. I replaced the that with a red LED (~1.2 V drop) and that did the trick - enough voltage to trip the transistor. I had to buy a roll of 50 red SMD LEDs so I have extras to mod the 5 V module ...

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                  • #10
                    Mike,

                    thanks for the info on that unit. I do see a bunch of them on AliX after reading what you wrote. It's nice to hear from someone on how they actually work. I assume you use the ground from the input voltage source and just try to find a decently sized 5 or 12V source on the board that has enough power to trip it.
                    I think both of these boards use 5V so I'd have to get that one.

                    I'll probably try to power up both the big and small preamp board and see what there is at 5V.
                    Is there much danger in connecting the neg lead on a multimeter to the neg. on the 5v input and testing various solder joints on the board with the positive test lead? I wouldn't think so but...

                    Thanks for the info. I'll hopefully mess with this a little this weekend.

                    TomZ
                    *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
                    *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

                    *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

                    Comment


                    • #11
                      Originally posted by tomzarbo View Post
                      Mike,

                      thanks for the info on that unit. I do see a bunch of them on AliX after reading what you wrote. It's nice to hear from someone on how they actually work. I assume you use the ground from the input voltage source and just try to find a decently sized 5 or 12V source on the board that has enough power to trip it.
                      I think both of these boards use 5V so I'd have to get that one.

                      I'll probably try to power up both the big and small preamp board and see what there is at 5V.
                      Is there much danger in connecting the neg lead on a multimeter to the neg. on the 5v input and testing various solder joints on the board with the positive test lead? I wouldn't think so but...

                      Thanks for the info. I'll hopefully mess with this a little this weekend.

                      TomZ
                      I wouldn't think testing voltages can cause any damage (other than static electricity discharge which shouldn't be an issue if you first ground the DVM + lead before probing).

                      You may just want to use a relay with a 5 V coil and eliminate the hassle with the module I referenced (I need the delay). Just buy a small PCB prototype board (and be prepared to drill one or more holes as the relay footprint doesn't completely line up with the standard 0.1" (2.4mm) hole spacing (the center pin on NO/NC output for a SPDT). Those dual position screw down terminals do line up with the prototype board spacing and a handful are cheap. They'll take 18 gauge wire. 16 gauge requires some "massaging" - flattening the twisted strands to fit the max opening height. All on ALI for less then ~4$.

                      Comment


                      • #12
                        Cutting some wood finally.

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                        I originally drew up a 'mildly' wild enclosure with lots of angles and what not, but I decided to keep this one a bit more simple cabinet-wise, thinking it would make it easier for others to duplicate if it turns out well.

                        I decided not to go with the built-in sub version for the time being. I've been struggling to get myself going project-wise and I don't want to take too large of a bite. This project should be easy enough to keep truckin' on, and that's what I really need now is some steady progress to get things moving again.

                        Same driver compliment as the original Bantams, and hopefully the same crossover as well, although I'll have to address that later on. Peerless Passives opposed on the ends... and dang, I placed an order today and just now realized that I forgot to put the PR's in the cart. At least I have a few of them to mock up with. The ND91-4's are on sale until the end of August so I decided to pick them up today before I forgot.

                        It looks to be about 6" high, 6" deep, and 17" wide for the main cabinet. There will be a base that will be angled so as to tilt the main cabinet upwards a bit as well. I've given away my other radio's, so we are without one again -- therefore, I'm building three cabinets since they are pretty easy to construct. I have one larger video player/preamp unit, and two smaller units in black and silver. They all work pretty much the same, and are the same width even. I'll have a bit more vertical space for the smaller player in the center section. The larger one will take up almost all of the space on the cabinet.

                        I plan on doing some large round-overs on the vertical corners to make veneering a one-piece affair if I'm lucky. I may even do one in aluminum to use with the silver faced video player.

                        Not a lot to see, but it should take shape fairly quickly if I can stay on it.

                        Thanks for looking,
                        TomZ

                        *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
                        *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

                        *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

                        Comment


                        • #13
                          A little more progress gluing things up...

                          You can see two holes in each interior panel, those are for the wires for the tweeter/woofer in case I decide to mount part/all of the crossover in the middle section.

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ID:	1420048 After a light sanding the tops and bottoms are gluing up as well. I cut them a smidge oversize, like 6 1/16" and 17 1/8" to allow for an easier time gluing up. I'll flush trim on the router table.
                          Now on to the bases. The bases for these will just be there to 'lift and angle' the cabinet upwards a bit, not for extra added airspace for the drivers as in my previous project. Probably about 1.5" in the front and .75 or so in the rear.

                          The center section will be routed open on the bottom of the radio and be covered up with the base with some holes for breathing.

                          I didn't plan it this way, but the dimensions should allow for a single piece of veneer about 46" wide to cover the front/back and sides considering the round-overs that will be applied. Shouldn't take much at all to cover these, and will allow for a single 7" piece of 4x8 veneer to be used along the 4' side for easier bending around the round-overs.

                          3/4" MDF for the front and back, and 1/2" MDF for the rest. I'm liking the extra room in the middle section for wires and amps and who knows what else.

                          Stay tuned...

                          TomZ
                          *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
                          *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

                          *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

                          Comment


                          • #14
                            Sanded the boxes smooth and straight.

                            I'm hoping to get the driver cut-outs done tomorrow and maybe bases underway... But for now, here is the current progress.
                            Bottom access openings cut out and all three faceplate openings cut out and mounting holes drilled.

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                            Wondering if it's worth the effort to try and make the smaller preamp panel radio an 'all aluminum' version with an aluminum veneer to match the silver player. I think it might look cool, but maybe too much aluminum? I guess the black drivers may provide some contrast.
                            Watcha think?

                            TomZ
                            *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
                            *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

                            *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

                            Comment


                            • #15
                              Got the driver openings cut out today.

                              Almost goofed up, I drew a circle for the side Passive Radiators the size of the exterior of the frame, instead of the internal dimension. I drew the holes last night and for some reason decided to double-check that one before I cut... glad I did.

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ID:	1420162 I went in with a 3 1/8" Fostner bit for the woofer hole part-way. Most of my Fostner bits are just high speed steel and don't like MDF too much, they get dull fast. I just went in a bit to scribe the line, drilled a bunch of relief holes, went back to the Fostner bit again maybe 1/4" total, and finished with the jig saw since it's not too critical to have a perfect opening.

                              Not a lot of room between the tweeter and the side of the cabinet, may need a 3/4" roundover instead of the 1" I was contemplating.

                              Now I can really mock-up the base and see what it looks like a bit better.

                              Company arriving later today, but hopefully I can get some more done tonight, maybe roundovers, and driver mounting screw holes.
                              I gotta' say, keeping the cabinet simple really makes things move along pretty quickly.

                              TomZ
                              *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
                              *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

                              *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

                              Comment

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