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DTA 2.1BT Amp LP Filter Incursion - The Movie

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  • Kevin K.
    replied
    Originally posted by tomzarbo View Post

    I know that PE has version 2 of this amp out in full force, but Mike, I really appreciate what you did with this, and the effort you put into figuring out how to alter this little amp for the rest of us.

    TomZ
    I second this Mike, much appreciated. And thanks to your efforts, PE/Dayton responded with the improved model which IMO, now gives them one of the nicest 2.1 desktop amps on the market.

    Leave a comment:


  • tomzarbo
    replied
    I just finished modding my third, and last amp and all went well. It's a game of angles with this stuff. Last two I did I half-melted the pot next to the barrel cap. This time I almost vaporized the clear LED in the same general location.

    My eyes are still crossed a bit, but it works. I still can't almost believe that a component the size of a spec of sand can be a capacitor somehow... or survive having solder-melting heat applied to it without *POOFING* into the ether.

    I'm planning on using this amp with my newly finished N.E.H.D. (No Ears Have Died) speakers by Wolf, and a passive subwoofer to be determined.

    I ran this amp with my Nano Neo's and a home built foot-stand subwoofer in my hobby room for close to an hour just getting wrapped up in various music... Love it. It really has a good deal of power.

    I know that PE has version 2 of this amp out in full force, but Mike, I really appreciate what you did with this, and the effort you put into figuring out how to alter this little amp for the rest of us.

    TomZ

    Leave a comment:


  • tomzarbo
    replied
    That makes sense; bad noises do make me turn things down...guess it's the audiophile in me.

    Yeah, I 'textured' the pot on the second one as well.

    I just now finished up the second one and I was disappointed because there was no bass output at the subwoofer...of course--not turning up the subwoofer output knob will do that.
    So yeah, the second one went fine as well...and it took less than half as long as the first since I knew what to expect. Still had trouble getting the C60 cap out of there though.

    I did kind of get away with one while modding the first board because I didn't realize until working on the second one that C60 was a polarized cap. I'm so used to crossovers using non-polarized capacitors that I never thought to look too closely at it. Luckily, I put it in correctly anyway.

    TomZ

    Leave a comment:


  • Millstonemike
    replied
    Probably louder because you can turn up the sub a little more now that the higher end is eliminated. 

    In the absence of one of those circular, lighted lamps with a magnifying glass in the middle, I use a pair of 3.00 reading glasses for this type of work.

    Hit the pot with the iron, did ya'  

     

    Leave a comment:


  • tomzarbo
    replied
    I tried my hand at doing the mods that Mike outlined above. It was a bit nervewracking for me... those little bits are tiny. If I didn't have a few magnifying glasses and good lighting there would be no way I'd be able to do it...
    But, the results are pretty dang nice. No localization of upper bass frequencies now on my little Tang Band 1138 Dual PR'd subwoofer. It seems a bit louder too? Not sure if I'm imagining that, but it sure seems so. 

    Pics in no particular order...I still have some trouble with getting my pics positioned where I want them
    :
    C47 under the heat sink and my blobbed solder job.

    Also note the melted plastic on the pot next to C60 that needed to be removed to get to C43.  I modded PE's tweezers style soldering iron to get these little buggers out. Basically filed a bevel on them so I could tweeze the little caps out at a comfortable angle... squeezed the tongs so they were flush first. It worked okay, but it's tight in there for sure.  I almost put it back together and said 'forget it' but I prodded on.  I'd just hate to bork up $79 dollars of amp because I have sausage links for fingers.

    After resoldering in the C60 cap that had to be removed to get to C43...

    That was the hardest thing for me to do believe it or not. It didn't want to come out. I had enough heat on it, but It just would not come out without a fight.  I used a solder sucker and braided wick to get out as much solder as I could.  Reinstalling it meant putting a little blob of solder on both pads, and heating them both as I pushed the cap in from behind... worked fairly well.

    Mike, thank you so much for all your help with this. You clearly put a lot of work into figuring this out as well as modding the one you did for Kevin. I personally appreciate it and all you do for us here at Tech Talk. Thanks a lot man!

    Hopefully, I can get the second one modded a bit easier than the first one with experience and all. I did practice a bit on a wrecked circuit board with similarly sized SMT bits for some practice. Really positioning your hands with the iron without melting other stuff is the hardest thing. When I used the magnifier/light I have, I could see where I was soldering fairly well, but the peripheral stuff fell out of vision and that's how I burned the pot casing and nearly a few other things.

    I'm looking forward to PE bringing out the version with the adjustable low-pass, that will make this a killer little amp. I could nearly blow my Bantams and the sub with this thing, no joke, it's got some power.

    TomZ
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  • tomzarbo
    replied
    Originally posted by Millstonemike View Post

    Forgot to mention the 0.15 uf cap is C47 (by the heat sink) and the 0.33 cap is C43 (by the white LED).
    I was going to ask but you beat me to it. Thanks.
    TomZ

    Leave a comment:


  • Millstonemike
    replied
    Originally posted by Millstonemike View Post
    Just in case I misunderstood you ... the blue slope is two 0.22 uf caps. Pink (purple) slope is one 0.15 and one 0.33 uf cap.
    Forgot to mention the 0.15 uf cap is C47 (by the heat sink) and the 0.33 cap is C43 (by the white LED).

    Leave a comment:


  • tomzarbo
    replied
    Originally posted by Millstonemike View Post
    Just in case I misunderstood you ... the blue slope is two 0.22 uf caps. Pink (purple) slope is one 0.15 and one 0.33 uf cap.
    Right.
    Thanks again sir!
    TomZ

    Leave a comment:


  • Millstonemike
    replied
    Originally posted by tomzarbo View Post

    Mike,
    I do think that the steeper purple slope will work better with the Bantams, as they are PR speakers and not sealed. So it's a .15 and .33 uf cap, thanks for the PM info, I have the hardest time figuring out how to search on that site.

    I've used the desolder braid before, and it's nice stuff. Also one of the 'sucker' desolder guns that Brian linked to above. I think the braid would work best for getting rid of all the solder. I've used the sucker for larger 'blobs' and stuff; works surprisingly good, though. I've had to 'fix' a few mistakes with some surface mount stuff a few years back and I know it's not easy... I didn't have a tweezers iron back then, didn't even know they existed. I just recently picked one up for stuff like this.

    I'll order these parts and once the amps get back in stock, I'll order a few of those too and get to work. I may even have the speakers done before the amp gets back in stock.

    Thanks a million Mike for all the help.
    Just in case I misunderstood you ... the blue slope is two 0.22 uf caps. Pink (purple) slope is one 0.15 and one 0.33 uf cap.

    Leave a comment:


  • tomzarbo
    replied
    Originally posted by Millstonemike View Post
    Tom,

    You want 2.00 mm (L) x 1.25 mm (W). The way I read your order the cap is 1.25 mm in height (which doesn't matter much).

    With two 0.22 uf caps, you are going to have a LR2 LP filter at 72 Hz (e.g., Q = 0.5). You may want a steeper roll off. When I did the mod for Kevin, he was thinking small, sealed, desktop speakers with a sub, so the higher LP Fc and shallower roll off seemed like the right way to go. But I did take note of your comment "I can still hear vocals through the sub". While I don't think that will be an issue at 72 Hz, you may want to compare the filter slopes.

    If you use WinPCD (or xsim?) you can model the LR2 roll off as well as a steeper "near" Butterworth roll off (Q=0.74). Below is the basic difference for the those two filters at 72 Hz as shown in WinISD. Once you settle that, I can pick the caps from Digikey (couple dimes each plus $3.75 USPS shipping). The steeper filter will require a 0.15 uf and a 0.33 uf cap.

    Lastly, I'm about to mod my second SMD board. But I don't have a hot air station or "Tweezers" soldering iron. It's easy enough to remove the existing SMD caps by heating up one side and then the other while to the first side is still molten with a relgular iron. But that leaves solder on the pads. So it's difficult to get both sides of the new cap flat against the PCB. So I also ordered some copper braid to remove the original solder from the PCB pads. I hope it will be like soldering the new caps to a PCB that's only been fluxed. That cost me $1.50 at DigiKey with my latest cap order.

    [ATTACH=CONFIG]n1372176[/ATTACH]
    Mike,
    I do think that the steeper purple slope will work better with the Bantams, as they are PR speakers and not sealed. So it's a .15 and .33 uf cap, thanks for the PM info, I have the hardest time figuring out how to search on that site.

    I've used the desolder braid before, and it's nice stuff. Also one of the 'sucker' desolder guns that Brian linked to above. I think the braid would work best for getting rid of all the solder. I've used the sucker for larger 'blobs' and stuff; works surprisingly good, though. I've had to 'fix' a few mistakes with some surface mount stuff a few years back and I know it's not easy... I didn't have a tweezers iron back then, didn't even know they existed. I just recently picked one up for stuff like this.

    I'll order these parts and once the amps get back in stock, I'll order a few of those too and get to work. I may even have the speakers done before the amp gets back in stock.

    Thanks a million Mike for all the help.

    Leave a comment:


  • Brian Steele
    replied
    Originally posted by Millstonemike View Post
    It's easy enough to remove the existing SMD caps by heating up one side and then the other while to the first side is still molten with a relgular iron. But that leaves solder on the pads.
    ​Would this work? https://www.parts-express.com/solder...-pump--370-030

    Leave a comment:


  • Millstonemike
    replied
    Originally posted by tomzarbo View Post
    Mike,
    would you mind double checking this for me if you could before I order these.... I think this is right for a roughly 72 Hz crossover point. I'd need two caps to do the swap... I'm ordering a few extra because I'm at least modding two of these units, possibly three. I think I got the size right too, 1.25mm?

    [ATTACH=CONFIG]n1372059[/ATTACH]


    Man, finding these parts is a little complicated... it actually took me 45 minutes to locate this believe it or not.

    TomZ
    Tom,

    You want 2.00 mm (L) x 1.25 mm (W). The way I read your order the cap is 1.25 mm in height (which doesn't matter much).

    With two 0.22 uf caps, you are going to have a LR2 LP filter at 72 Hz (e.g., Q = 0.5). You may want a steeper roll off. When I did the mod for Kevin, he was thinking small, sealed, desktop speakers with a sub, so the higher LP Fc and shallower roll off seemed like the right way to go. But I did take note of your comment "I can still hear vocals through the sub". While I don't think that will be an issue at 72 Hz, you may want to compare the filter slopes.

    If you use WinPCD (or xsim?) you can model the LR2 roll off as well as a steeper "near" Butterworth roll off (Q=0.74). Below is the basic difference for the those two filters at 72 Hz as shown in WinISD. Once you settle that, I can pick the caps from Digikey (couple dimes each plus $3.75 USPS shipping). The steeper filter will require a 0.15 uf and a 0.33 uf cap.

    Lastly, I'm about to mod my second SMD board. But I don't have a hot air station or "Tweezers" soldering iron. It's easy enough to remove the existing SMD caps by heating up one side and then the other while to the first side is still molten with a relgular iron. But that leaves solder on the pads. So it's difficult to get both sides of the new cap flat against the PCB. So I also ordered some copper braid to remove the original solder from the PCB pads. I hope it will be like soldering the new caps to a PCB that's only been fluxed. That cost me $1.50 at DigiKey with my latest cap order.

    Filter Qs.png

    Leave a comment:


  • tomzarbo
    replied
    Mike,
    would you mind double checking this for me if you could before I order these.... I think this is right for a roughly 72 Hz crossover point. I'd need two caps to do the swap... I'm ordering a few extra because I'm at least modding two of these units, possibly three. I think I got the size right too, 1.25mm?

    Click image for larger version

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    Man, finding these parts is a little complicated... it actually took me 45 minutes to locate this believe it or not.

    TomZ

    Leave a comment:


  • JohnBooty
    replied
    The AD18 already has all the user interface hardware needed. It's got a LED (OLED?) lit screen. By default the big knob controls volume, but you can cycle thru settings like "bass" and "treble" and so forth.

    SMSL's older Q5 Pro, as well as some of FX Audio's other amps, have a similar screen + settings adjustment interface, though unlike the AD18 don't know which chips those models use.

    That's why this is so frustrating. Allllll the necessary hardware (both chip level, and user interface level) there on some of these amps. =)

    Leave a comment:


  • Millstonemike
    replied
    Originally posted by JohnBooty View Post
    What's really frustrating is that a lot of these chip amps (and/or their companion chips) actually have this functionality built right in!

    But, the OEMs building these amps simply don't use/expose this functionality.

    Check out page 28+29 of the manufacturer's specs for the chip used in the SMSL AD18. Note, this is isn't the chip amp itself. It's a processor chip. $12 at Mouser.

    http://www.ti.com/lit/ds/symlink/tas5508c.pdf
    These are all programmable via the I2C protocol in real time. For sure, that is plenty of firepower. With that, you could implement crossover functionality and still have plenty of filters left over for tone controls, loudness compensation, etc.

    For me it's not a huge problem. I own several MiniDSPs that handle the job just fine. But, dropping $100 a pop on MiniDSPs is not very ideal.

    Do I need to dive into the world of I2C programming? hmmmm
    It's not the chip that is really expensive. It's everything you need surrounding it to allow end user control.

    Leave a comment:

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