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Collective Custom Boombox Project?


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#91 Superduper

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Posted 15 April 2016 - 08:03 PM

Well, had a few hiccups but I make do with what I have.  The PS that I wanted to use would no longer power up so I sent that back to Instek to repair.  That was 2-weeks ago, haven't heard from them since.  So I pulled out my older unit instead.  Works fine although the slave tracking voltmeter is a bit off and needs adj.  No bigge, the primary channel is spot on and that's the supply I'll be using anyhow.

 

So first off, I tested the radio I intend to use for the project.  I have removed the housing before and it looks like relocating some switches and maybe the rotary encoder will allow the unit to be installed in my project and also retain a tuning "knob" for those that likes to play with knobs.  That includes ME.  I hate up/down buttons.

 

First test, current consumption:

 

Attached File  project_12.jpg   73.3K   4 downloads

 

Attached File  project_11.jpg   68.67K   4 downloads

 

With 12v source, consumption was 20mA in off position, and 730mA in operation.  Although this will allow battery operation, if constantly connected to power to retain memory, standard alkaline batteries will be exhausted in 21 days.  Obviously, for long term storage with batteries, this unit will need to be divorced from batteries with a hard switch or else you'll just be wasting good batteries.  In operation, this unit will consume 8.76 watts.  D cells will last only about 11.5 hours.  Luckily, this module can be powered off with it's own power button.  If used in the boombox, then this module should be powered off if the unit is operated in other modes.  At this rate of consumption, it is prudent to keep this module idle if it isn't actively being played.  Of course when on AC mode, it looks cool to be ON all the time.  Ah, such is the downside of digital gear, needs to be always in active mode.  An analog tuner would be far more thrifty but shoehorning one of those is much too challenging and beyond the scope of this project.  However, the upside is that I've found that these tuners are extremely good performers.  Far better than most boomboxes. 

 

OK, next module is this MP3, bluetooth device that can accept USB thumbdrives or SD cards.

 

Attached File  project_10.jpg   466.35K   5 downloads

 

Attached File  project_08.jpg   98.12K   4 downloads

 

I'm measuring only 30mA during operation, so this is a very thrifty module.  With amplifier hooked up and "cranking" at a good clip, I see 730mA but that is just an instantaneous photo capture.  The actual usage varies with the dynamics of the music between 40mA to over 3.0A (blips the current led on the PS). This is just a tiny flash so it doesn't dwell there very long. 

 

This module is supposed to have bluetooth but I could not get that feature to work.  Not really a problem because that's not why I got it.  Rather I wanted an MP3 module that included a working display so I would know what I was playing.  There are many that are cheap but you have no clue what you are playing and can only navigate with a Fwd or Rv button -- I didn't want those but suspect that the sound quality of those are similar since these things are almost all based on the same basic designs..  Alas, the sound quality was not good, always sounding like the circuit was either loaded down or something.  Either this unit is damaged or it needs a buffer amp to beef up the output before connection to the power amp.  That would be suprising since these amps almost all have an input impedance of around 10k ohms.  Well, I've got another one on order so I'll know later how to proceed and tackle this, but virtually all this stuff, whether it's connectors, modules, or what-not all come from China.  Meaning, at least 2-4 weeks wait every time I need to wait for something else.  I still haven't ordered everything I am considering since I'm still wishy washy and undecided about what to use and/or might work best.  Again, the challenge, except for the PS, all off the shelf parts that can be duplicated by any idiot here, hehe.



#92 Superduper

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Posted 15 April 2016 - 08:54 PM

All right, next up is the amp module itself.  This is the one I'm using.  Supposed to be 50W x2.  Well, we will see.  Here it is connected with no input signal.  Looks like quiescent current is about 40mA.  Not bad.  If you left the boombox on with D cells and forgot to turn it off but either at idle or very low output, it would drain the boombox in about 210 hours or almost 9 days.

 

Attached File  project_09.jpg   77.83K   4 downloads

 

To test the power output, I had it hooked up like this:

 

On the left is my fluke used to measure the audio signal to be injected for source audio.  The thing about music is that it jumps all over the place and you can't really measure since the reading is so unstable.  I  had it set up at 1khz and about 730mV.  This is over 50% higher than the "standard consumer line-in" of -10db or about 447mV.  Since we are stress testing the amp, why not push it, right?

 

Attached File  project_07.jpg   63.47K   4 downloads

 

The analyzer above the power supply will be used to measure the power output in watts.  I have it set to 8-ohms.  I did not bother to test at 4-ohms.  We can presume that output will be higher than the measurements obtained at 8-ohm impedance loads. 

 

Attached File  project_06.jpg   54.17K   3 downloads

 

At 12V to the amp, I was reading about 12wpc RMS.  Increasing the voltage to 16 volts results in output readings of 20wpc.  Pushing the amp further, I increased voltage to 18 volts and got 26wpc rms x2.  Remember that this is with input signal strength higher than one would normally feed it.  Although it's possible to inject this much input power and more via MP3 or external CD's with headphone outputs, I am guessing that this would lead to clipped and distorted output.  In fact, distortion is audible when input levels are pumped near max output from my iPhone into the amp.  Because I'm all about audio quality and not distorted sound, I would not operate the boombox that way, although it's clear that the amp does have enough juice to produce lots of output, even if it IS distorted.

 

Reading output, 30w left, 26w right, 100w scale so reading x10.

Attached File  project_03.jpg   388.56K   3 downloads

 

Further notes:

I tried to increase the input voltage to 1v @ 1khz, but the amp shut down.  It is unclear whether the amps internal protection kicked in, or whether the PS (this I suspect) could not provide the juice needed and over-current protection kicked in.  In fact, initially, I thought that I had blown the amp.  I found out later that it was not fried.  Speaking of which.... this amp is pretty durable.  At one point, I tried to connect speaker leads with the unit powered up.  No input at the time, but with the screw connectors, it should not have been a problem..  I only inserted one wire first (other end wasn't even connected to anything) and as soon as I started tightening the screw, smoke began to appear.  Apparently, either the wire curled inside and touched the other pad or the terminal block itself twisted enough to short.  I immediately removed the wire and checked.  Again, I thought that the amp was fried.  It was not and survived that momentary short.  I knew it was risky and took the risk for convenience of time purposes (I had a spare amp available just in case).  Still, this amp does seem quite durable.  Luckily there was no input otherwise the end result might've been way different.

 

As for distortion, that was something I am interested in.  Unfortunately, my Leader distortion meter turned out to be dead.  Ah well, another bugger thing to add to my work queue.  So what to do...  Ok, I figured I would just scope the darn thing.  By comparing input signal to output signal, I should be able to crank until I just see distortion or clipping, then register the input level it would take for that to happen.  Simple right?  Well, turns out not quite.  Although I could get good readings on the input from the audio generator, the output looked all weird.  Since the output waveform was not a clear sinewave, it was a bit hard to tell when exactly distortion occurred with the sinewave.  Then it hit me.  This isn't a class AB amp, it's a class D amp.  Unlike standard analog amplifiers that amplifies EVERYTHING and outputs a carbon copy (albeit bigger), these digital amps chops up the audio signal and outputs it via PWM (pulse width modulate).  No wonder the output looked all screwy compared to the audio signal input.  Although the ears hear it as normal sound, the scope shows the signal much differently.  Now, some people love class D/T amps.  But to me, let's just say I can hear the difference and prefer the smoother sound quality of the class AB's.  Well, anyhow, these class D's are much more efficient and the difference is not a deal breaker, especially for a boombox.  Heck, we aren't talking HiFi McIntosh stuff here.  It's gonna be a boombox!

 

Ok, while hooked up to an audio program, I watched the scope waveform and observed flattening out of the waveforms at various peaks and valleys when output was high.  By increasing the voltage incrementally, the flattening was reduced.  Normally, I would call these flattened areas clipping.  However, once again, as we are talking about PWM output, this may just be longer dwell time on the pulse signal.  The audio at the time did not sound "distorted" like one would hear during actual clipping in a standard class AB amp.  While all of this is interesting, I think I've concluded that for the purposes of this project, I'm not going to worry about clipping and just use common sense.  Distorted sound?  Back it down a bit.

 

Now, to wait for more toys to come.  Stay tuned.  Lots of modules left to complete this.  Once everything is in-hand, then comes time to construct a multi-rail power supply setup. 



#93 MyOhMy

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Posted 16 April 2016 - 08:37 AM

Awesome stuff, Superduper and waaaaaaaaaay over my head. :yes:  ;-)  :thumbsup:



#94 PostEnder

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Posted 16 April 2016 - 09:11 AM

This sounds amazing, unfortunately I neither have the skills or money to contribute in anyway.....but I wish you the very best with this very difficult project and hope it pulls off for you Norm cos it sounds like the finished product would be both unique and amazing.

"Pardon me for asking, sir, but would you happen to have any Grey Poupon?" (Just kidding)

 

A bit more earnestly -- and hopefully not being offensive -- I ask you: are you the member some website users have at times referred to as lav loo? After all, there is -- or was -- this Stereo2Go website member known as lav loo ...

 

Cheers



#95 Reli

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Posted 16 April 2016 - 09:40 AM

Would a fan be needed with that amp?  Seems like such a small heat-sink for the power it puts out.



#96 redbenjoe

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Posted 16 April 2016 - 06:06 PM

Would a fan be needed 

i am already ready to be a fan of superduper and his creation  :clap:  :hooray:  :thumbsup:



#97 jimmyjimmy19702010

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Posted 16 April 2016 - 08:10 PM

This is the 50 watt RMS per channel stereo amp I'm using for my next 24V DIY box: Sure brand gear is pretty good stuff!


#98 Superduper

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Posted 16 April 2016 - 09:56 PM

Would a fan be needed with that amp?  Seems like such a small heat-sink for the power it puts out.

Reli, no fan needed.  The heatsink is pretty substantial.  It's like 1000 times larger than the chip itself, which has the surface area of your pinky nail.  Any larger and I wonder if heat can travel that far anyhow.  During all this time testing it, I bumped it pretty hard and it never felt very warm at all.  Remember this isn't a class AB amp which can get pretty hot.  Not sure if there are any class D hifi amps out there since there is an argument regarding quality of AB vs D and I tend to think that class AB is better for hifi, but these type of amps (class D) are typically used in subwoofer and TV, soundbar, car, etc applications.  For bass applications, class D is excellent due to their efficiency, low heat generation, and the fact that bass accoustics are rather unintelligible anyhow, so it's like a match made in heaven.  As for fan, my personal preference would be to use a fan-less amp rather than one whose longevity relies on the reliability of a fan for a lifeline, not to mention potential noise introduced by the fan, both audible and electrically.  Maybe those aren't issues, but why take a chance?

 

 

 

i am already ready to be a fan of superduper and his creation  :clap:  :hooray:  :thumbsup:

Ok, but digital tuner, Ira, digital tuner.  You ok with that?  Or, but it does have a tuning knob so maybe that might be OK with you?  Seriously, these new tuners are far more sensitive than most any boombox (I checked) and can pick up stations perfectly clear that a boombox might not even sense.  The oscillators are all synthesized and rock steady, as opposed to the oscillators in older analog designs (especially simple ones like on boomboxes) that are tuned by tuning rf coils, caps, etc. and whose values frequently drift from original oover time rendering the tuner either not as sensitive or centered, or other tuning issues.

 

 

 

This is the 50 watt RMS per channel stereo amp I'm using for my next 24V DIY box: Sure brand gear is pretty good stuff!
attachicon.gifimage.jpeg

 

Jimmy, I haven't tried that one.  Got one you want to ship here for testing?  :lol: :thumbsup: :bow:

Seriously, the amp I'm using, although I purchased it quite some time back, appears to still be a current model so the design is probably solid otherwise they would've changed it.  But why mess with a design that work?  In truth, I've discovered that these chinese manufacturers simply takes the recommended sample circuits published by the IC manufacturers and clones them.  As long as they follow all the recommended manufacturers guidelines, the resulting product should be good.  As I mentioned, I was able to obtain 26wpc into 8-ohms @ 18volts.  With 4-ohm woofs, the output probably meets or approaches the 50wpc rating, although it was tested using a meter, and not an audible audition so I can't say what does it sound at 50wpc.  Ideally, the higher frequencies will be at 15wpc or less, and the 50wpc hits should only be bass transients.  That should result in best sound quality while maximizing power use.  BTW, I did review manufacturer datasheets and it appears that all these types of amps can be tailored to the expected output impedance via some changes to the resistors and capacitor values used depending upon whether 4/6/8 ohms.

 

BTW, I have some observations to share.  While operating the amp at a moderately high level, I changed the voltage by cranking the output on the power supply.  While observing the voltage rise from 12 through 18 volts, I never at any time perceived any greater loudness to my ears, nor any sound improvement.  I believe greater voltage will result in greater headroom to deal with transients that can make use of that headroom.  This makes me wonder whether it is of any practical use to increase voltage much beyond 15 or 16 volts.  I'm still debating how to power this boombox.  Most of the modules use 12V.  If I power the amp at a different voltage level, then that complicates the design.  Not so much for a single source, but rather because of the need for flexible sources (AC/DC/Batteries).



#99 JVC Floyd

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Posted 17 April 2016 - 07:24 AM

The only advantage to a class D amplifier is efficiency there are almost no class D amplifiers made specifically for sound quality

#100 Superduper

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Posted 17 April 2016 - 09:07 AM

My thoughts exactly Floyd.

The only advantage to a class D amplifier is efficiency there are almost no class D amplifiers made specifically for sound quality



#101 Reli

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Posted 17 April 2016 - 11:48 AM

How about bi-amping it, with a class D for the woofs, and a class A for the tweets?  OK, just spouting off nonsense here.



#102 mellymelsr

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Posted 17 April 2016 - 01:48 PM

Love this idea. Norm put me down as an investor and a buyer!

#103 hardmen

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Posted 17 April 2016 - 03:03 PM

Some design of a Brazilian BBoys.
Using some receiver and tape deck aluminum panels.

Attached File  IMG-20160402-WA0020.jpg   54.71K   7 downloads

But, a little BIGGER.

Attached File  IMG-20160402-WA0033.jpg   141.95K   4 downloads

Cheers.

#104 Reli

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Posted 17 April 2016 - 03:25 PM

Some design of a Brazilian BBoys.
Using some receiver and tape deck aluminum panels.

attachicon.gifIMG-20160402-WA0020.jpg

 

 

Now that's cool.  If there's a common model we could harvest for its cosmetic trim, we could achieve a classic look.  There are some boomboxes, receivers and tape decks that only fetch $20 on Ebay, yet they have some cool looking trim, like speaker grills, meters, and knobs and switches.



#105 MyOhMy

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Posted 17 April 2016 - 03:50 PM

How cool is that - a BB as big as a 'fridge!!!  :w00t:  :lol:  :lol: :lol: 



#106 caution

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Posted 17 April 2016 - 06:22 PM

I can have any pattern laser cut into brushed stainless down to 19 mil thick (26ga), it's sturdier than aluminum and looks nice too



#107 Superduper

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Posted 17 April 2016 - 06:55 PM

I can have any pattern laser cut into brushed stainless down to 19 mil thick (26ga), it's sturdier than aluminum and looks nice too

Serious?  Because THAT is what we need!  Can you also do acrylic?  Cut and then have the lettering laser engraved on the backside so they would be protected?



#108 caution

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Posted 17 April 2016 - 07:29 PM

The place that cut my replacement trims stock only metals.  But on the acrylic side, when I stopped in at Metal Supermarkets recently I noticed the business card board filled with laser engraving places. There's enough of these places around it might help to find one with a good price. Some of them market themselves as artists, which translates to "expensive"



#109 Superduper

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Posted 17 April 2016 - 07:42 PM

Actually, I wonder why that laser cutting place can't also laser engrave as well on the same piece they cut, at the same time?  From what I can tell, the only difference between laser cutting and laser engraving is the amount of power applied by the laser, or the speed of which the laser is operated at.  Slow speed = deep cuts.  Fast = shallow cuts or engraving.  Or maybe their machines are too powerful and can't be turned down far enough to engrave.  Looks like they only employ 2500 watt and 4000 watt lasers.  Typical acrylic engraving or cutting machines can make do with 60 - 90w lasers.



#110 blu_fuz

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Posted 18 April 2016 - 08:15 AM

The progress looks good. Glad to see your equipment put to good use again ;-).



#111 Lasonic TRC-920

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Posted 18 April 2016 - 11:39 PM

Finally got a chance to sit and catch up on this thread....

 

Norm as always man, so much info I am trying to find on my own. Amp selection, controller selection.

 

I have been looking at that digital display/control and you just answered a ton of questions for me.

 

I am following this thread closely even if I am short on time to comment!

 

:popcorn:  :gathering:  :popcorn:



#112 caution

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Posted 20 April 2016 - 11:51 PM

Actually, I wonder why that laser cutting place can't also laser engrave

 

Wouldn't hurt to ask I suppose. Not sure they work with stock they don't sell though. Do you have an example of what you want in the end?

That gives me an idea, I wonder if that could replicate fine-line silkscreening, just do a shallow engrave of all the lettering and fill it in with a grease pen like I used to do years ago when I made control panels for test equipment, except it wasn't a laser :thumbsdown:



#113 THAFUZZ

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Posted 21 April 2016 - 12:06 AM

Love this idea. Norm put me down as an investor and a buyer!

You beat Me to it Mel. I too would like to get in on that. Will it have Wheels on the bottom like the Helix? :-D



#114 Superduper

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Posted 21 April 2016 - 12:11 AM

Eric,

 

We aren't ready for the shell or cosmetics yet, as we aren't decided what modules to implement, the selection of which will dictate where and what controls are present, control spacing, cutouts, number and spacing of switches, etc etc.

 

As for engraving, typically, you wouldn't need to fill in any engraving unless it was bare metal.  If the metal is coated with paint or a contrasting anodizing color coat, the engraving would just etch past the coating and the native material would show through, making a permanent lettering that should wear well.  Unless it's acrylic, in which case the engraving would show up white and could be left like that.  If clear, the acrylic could either be painted on backside to set off the engraving or side lit rendering the engraved areas to "light" up.  I've read where laser engravers are able to etch at the equivalent of about 4000dpi.  Considering laser printers produce awesome output at only 600dpi, that should mean the graphics should be spectacular.



#115 riker1068

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Posted 24 July 2017 - 11:24 AM

OMG



#116 Reli

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Posted 24 July 2017 - 12:43 PM

 

I can have any pattern laser cut into brushed stainless down to 19 mil thick (26ga), it's sturdier than aluminum and looks nice too

Serious?  Because THAT is what we need!  Can you also do acrylic?  Cut and then have the lettering laser engraved on the backside so they would be protected?

 

 

 

I have been talking to a shop that can do both (laser cutting and engraving/lettering) acrylic.  Can produce multi-beveled edges, polished too.