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Poor Man's version of the Monster GO DJ (Read 7749 times)
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Poor Man's version of the Monster GO DJ
May 10th, 2020, 4:17pm
 
Project Background
 
The Monster Go DJ is one of those cool bits of technology that we'd all like to receive as a gift, but few of us would drop the $500 to buy one.
 

                                                            Monster GO DJ -- Photo from GO DJ Store
 
In most cases like this, one can normally find a far less expensive (and typically far less functional) Chinese clone.  However I haven't really found anything similar to the Monster GO DJ.
 
Of course this is totally understandable.  The Monster Go DJ, cool as it may be, is also totally useless.  One is not going to slide one into a pocket or purse and go jogging -- pausing between each song to seamlessly mix into the next song.  Similarly, no professional DJ is going to show up for a gig, and whip his Go DJ out of his back pocket.
 
It's not cloned because there's no demand for the real thing -- let alone a clone.
 
The closest I have found is my Numark MixDeck Express, which in my case, was -- in equal parts -- cheaper and less portable.  I found one on eBay advertised as not working for less than $100, and was able to repair it within about 1/2 hour of it's arrival. It works fine, and is a great product for an occasional party or perhaps for a learning or beginning DJ, but I remain obsessed with the elegance and size of the  Go DJ.
 
The other part of the story is my success (and sometimes partial success) in building other projects just by piecing various Chinese modules together.  The NodeMCU clock is basically a display module, a WiFi module, and a small amplifier wired together with a few wires.
 
So why not just buy a pair of cheap MP3 player modules and wire each output to a linear potentiometer?  - Bingo!  A primitive Go DJ for a few $20 bills.
 
 
Other Ways to Realize a Home-made Go DJ Inspired Device
 
Yes, it would certainly be possible to base something on (for example) a Raspberry Pi Zero (or 2), some very nice TFT capacitive touchscreens, and start coding away, but the amount of coding required was far more than I was willing to face.
 
Another alternative is to throw a lightweight Linux distribution on an Intel based tablet, and load up Mixxx DJ software.  But without real analog controls, it would still just be DJ software running on a tablet, it would hardly be an imitation of a Go DJ.
 
The Actual Project
 
So something pieced together from Chinese Media Player modules is never going to have the functionality of the custom hardware and software of the real Go DJ.
 
Since this is a zero-coding project, we are limited by whatever functionality the Media Player modules provide.
 
It is likely that these basic and fundamental DJ Deck/mixer functions will not be implementable:

  • Beat detection
  • Speed Control, or Pitch Bend, Brake, etc.
  • Scratching
  • While some basic player modules support A-B looping, the interface will be lacking even if the functionality exists.
  • Waveform Display
  • While most modules display the time in a given track, customization, such as time remaining may not be supported.

With these fundamental features missing, one could argue that the device is unusable as an actual DJ setup.  Of course my argument, again, is that no "real" DJ is going to use a real Go DJ either.  It can still be a fun project to build, and a cool looking device when completed.
 
Here are some features I decided could and should be implemented:

  • Physical Fader
  • Real, analog tone controls even though the module may have preset EQ modes,  as tone mixing is fundamental to some forms of modern mixing.
  • Battery power for portability
  • LED VU meters.
  • Ability to Cue either player to headphones, although the functionality may be limited.
  • Fingertip digital sample players ("Effects") in addition to the 2 main channels.  

In addition, the chosen player modules should allow the following functionality, some of which "Real Devices" such as either the Monster Go DJ or  Numark Mixdeck Express cannot do:

  • Bluetooth
  • FLAC and other formats in addition to MP3
  • Microphone input, although it will be in place of a player channel
  • Voice Recording capability. In essence it will also function as a dual digital tape recorder. (Recording of the mix output will not be supported.)

Project Status
 
This project is currently in design and parts procurement.
 
A fairly mature front panel layout is shown here:
 

Front Panel Layout - Image is scaled 50%
 
The enclosure will be custom made from Clear Lexan.  It will be painted on the inside, with the areas above the LED VU meter, and the Battery control module left unpainted (masked).  This should look cool while minimizing the number of rectangular cuts needed.
 
The battery (power switch) will completely disconnect the (2) 18650 Lithium Ion batteries, allowing the unit to be stored for months without significant battery drain. The battery board will handle charging the batteries, battery level display, and provide 5V at up to 2A.  The unit will need to be powered during battery charging.
 
The other USB micro connector will allow sample files (up to 8) to be loaded on the effects board.
 
The 2 toggle switches just above the fader control cue/live for each channel.  Cue is taken after the tone board.
 
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Re: Poor Man's version of the Monster GO DJ
Reply #1 - May 15th, 2020, 8:50am
 
I'd be remiss without mentioning a few other products:
 
The Tonium Pacemaker predated the Monster GO DJ by about 5 years. While not as elegant, and having only a single screen, its actually more pocketable.  Pace maker later became an iPad app.  It never had actual physical knobs or sliders, faders, scratching, etc. was implemented with touch sensitive areas.
 
In addition to the Numark Mix Deck Express, there are also several products by Numark sold as the iDJ -- most (all?) of which relied on an Apple iPhone or iPod Touch for the media.  Some models did have an additional built-in second screen.
 
Denon also makes at least one stand alone model.  While portable -- in the sense that it can be carried (probably in a road case) from one gig to another, and it can run from an internal Lithium Ion Battery, it's hardly pocketable.  It's cost is also in the thousand dollar range.
 
 
 
 
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Re: Poor Man's version of the Monster GO DJ
Reply #2 - May 16th, 2020, 9:53pm
 
As we slowly accumulate parts, the design begins to solidify.
 
It's finally time for a schematic:
 

 
Schematic notes:
 
The Tone control boards and op amp modules are considered components, and thus details of their circuitry -- including any changes to component values -- are not shown here.
 
Tone Control Boards come from China as unassembled kits. Building will be customized for this purpose.  Note that +/- 12VDC is furnished from a boost converter module.  There is no power transformer. As a result, the power supply portions of the Tone Control Modules will not be installed.  (Diodes, regulators and the larger filter capacitors.)
 
The same is true for the op amp (preamp) modules, although the only component that is currently planned to be removed is the LED.  Feedback resistors R5 and R6 may be replaced to adjust gain as mentioned in the page for the relevant product.
 
At this time it is assumed that all resistors shown separately, including potentiometers, are 10K ohms.
 
 
I am beginning to receive parts.  I received the Adafruit Sound Effects Module and keypads today.  I have already encountered some minor issues.
 
-- The Adafruit Sound Effects Module was not being recognized/mounted as a filesystem on my Ubuntu Computer.  It seems there was filesystem corruption on it's small built-in storage.  Fortunately, I was able to easily format it with the Linux "Disks" utility.  It is now recognized correctly when connected via USB.  Note that the filesystem on the SFX board seems very slow.
 
--  The Adafruit 1x4 membrane keyboards also gave me some problems:  1).  The pins are not in order.  The correct pinout is [GND(Common)] [2][1][4][3].  This is not mentioned anywhere on the page, but it can be gleaned from looking at the picture of the back of the keyboard with the backing removed.
 
-- 2.) One of the Adafruit 1x4 membrane keyboards had a high resistance from GND(Common) to all keys.  (about 500 ohms with a key pressed). I carefully removed the connector shell, and gently squeezed the common connection to the ribbon cable with small pliers.  This reduced the "closed" or pressed resistance to about 20 ohms (the same as the other one I received), and the SFX module now recognizes all key presses.
 
Once the above issues were rectified, I copied over 8 DJ/Party/Event sound effects (in .wav format) to the SFX board's storage, and it works as expected.  The files must be named T00.wav --> T07.wav, corresponding to buttons 1 - 8 respectively.  The included and useful T00.ogg Left-Right stereo test file was unfortunately lost due to the filesystem corruption.
 
I suppose it is possible that I am receiving counterfeit Adafruit products from the eBay vendor.
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Re: Poor Man's version of the Monster GO DJ
Reply #3 - May 19th, 2020, 9:04pm
 
Design maturation continues, as parts slowly begin to arrive.
 
Due to current delays in shipments from China, the "main load" of parts may still be weeks or months away.  Another order has not even shipped yet.
 
I will also make a trip to MRAM Electronics -- a local surplus electronics store -- in the near future.  I'm hoping they can provide the discrete potentiometers (all those not included with the tone boards), as well as 3.5mm stereo and mono jacks for the headphone jack and mic jacks, respectively.
 
Many other parts are already on hand.
 
I have added a Cue/Live switch to the Sound FX function, since an operator may not remember what sound is programmed on what key.  The cue switch allows the operator to preview the sound on the headphones before sending it live to the "house" or audience.  Note that the cue switches do not actually set cue points in the audio players.  Any functionality like that is dependent on what is provided by the player modules themselves.  
 
If you are reading this, and you would like to contribute to the conversation, provide relevant suggestions, etc.  Please see the updated notice at the top of the page.  I'm happy to create accounts for legitimate users.
 
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Re: Poor Man's version of the Monster GO DJ
Reply #4 - Jun 26th, 2020, 6:58pm
 
Update:
 
Unfortunately, I still cannot report any progress on this project.
 
Apparently, Banggood did not address my package correctly, and it is being returned to them.  This is not my 1st time having problems getting Banggood to ship me stuff.
 
In addition to the FX module, I have received a few parts I ordered from eBay.  The potentiometers not associated with the tone boards have arrived, and so have the 1/8" phone jacks.
 
I've ordered replacements for the other parts from AliExpress and eBay vendors, and expect their arrival in a few weeks.  I choose US vendors or US stock whenever possible.
 
Some of the parts are different, and will drive design changes.  These include:
 
1.  The VU Meter is different. It is slightly longer, and has a button to select the mode.  I plan to incorporate this, so I will have to allow for the button.  The VU meter is a kit, and comes with a Lexan case, which will not be used.  The VU meters ship from the US, so putting them together will give me something to do while I wait for the other parts.
2.  The Tone Control boards are different.  They are pre-assembled, and run from a single ended +12VDC source.  The +/- boost converter will be replaced with a single ended boost converter set to ~+12 to 15VDC.
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Re: Poor Man's version of the Monster GO DJ
Reply #5 - Jul 2nd, 2020, 11:06pm
 
VU Meter Trauma
 
So I've reordered all of the parts and modules that never got to me from Banggood.com.
 
I couldn't find a US seller for the same LED VU Meter module, so I ordered what is intended to be a stand alone LED VU tower display from a US eBay seller.
 
This has arrived, but I'm not sure I'm going to use it.
 
Here is the module I am referring to:
 

 
It seems to be called a "KingSong AS30" 2 Channel 30 Segment LED level display.
 
First a few notes on this product.  As I mentioned it is intended as a standalone device, and comes with an acrylic case (which I haven't assembled yet, and would not be used if it is installed in my project, although I may use some of it just as a filter.)
 
It is not for the inexperienced to assemble.  It is mostly SMD (Surface Mount Device) and none of the parts are soldered for you.  Usually these "DIY" modules come with the SMD parts installed, and only require the hobbyist to solder the thru-hole LED modules, and perhaps a connector.  If you do not have Surface mount rework soldering equipment and skills, you'd never make it through this one.
 
Also, don't expect much help from the "manual".  The sheet is written with some of the worse "Chinglish" I've seen.
What is "LED flat tube tail India R on behalf of the red" even supposed to mean?!. No -- it really says that!
 
Fortunately, the board is well marked, and good quality.  Between that, and a table on the "instruction" sheet, you can figure out where each of nearly 40 chip resistors go.
 
That said, once assembled, it works really nicely.  It's very bright and very responsive.  While the picture above shows how bright it is (notice reflection on my hand), it doesn't do justice to how nice it actually looks.
 
It also has an assortment of basic modes and settings, which I won't get into here.  It was in it's most basic VU mode when I snapped the above picture, but it has options for peak indicators, and several other modes -- some of which aren't particularly useful for a "real" audio engineer, but just are there as another cool visualization of the music.
 
So if it is so pretty and crisp, why can't I use it in my "Poor Man's GO-DJ" project?  The problem is that it is much longer than the previously selected 12 segment VU module.  I can trim about 10mm off the top by sawing off the section with the mode switch,  it will still force the fader to the very bottom edge of the chassis.  Access to the functions should still be included, so the switch would have to be mounted elsewhere, and hard wired back to the board.
 
There is a US vendor selling a dual 12 segment VU module, but it has the opposite problem.  It's half the size of the originally intended one.  It's possible that once I have the other parts on hand, the entire unit could be made smaller by using a smaller VU meter, but there is a risk of the VU meter looking "chincy" or like an afterthought.  That said, lot's of even "pro" DJ mixers have pretty minimal VU meters.
 
Obviously, the other option is to order the originally intended module from a different Chinese vendor, and hope that it arrives -- someday.
 
For now, I'm going to wait for the other parts to arrive, and then evaluate if the whole project is worth it, and see if it can be made smaller.
 
This VU meter will still be used in one form or another.
 
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Re: Poor Man's version of the Monster GO DJ
Reply #6 - Jul 3rd, 2020, 12:50pm
 
So my comment yesterday about "...evaluate if the whole project is worth it..." should be worrisome to anyone (that is not a 'bot) who is following this.
 
As I continue researching this project and parts, I've come across a number of alternatives in addition to those already mentioned.  The first and most obvious is  actual Monster GO-DJ's for sale on eBay.  There is currently a used one for only $260.  I certainly hope that Banggood is going to refund my money for the order that got shipped back, but if they don't, I've already got more than that in this project.
 
There's also GO-DJ Plus's available for around US$ 500.
 
Lastly, I've also discovered the Stanton SCS.4DJ.  While not really portable in the sense that a GO-DJ or this project intends to be, it is smaller and lighter than my Numark Mix Deck Express, it has way better features, including true waveform display on an internal 4.3 inch color display.  It also dispenses with the legacy CD drives, which I think is a good thing.
Stanton may not have the name recognition of Denon or Yamaha, but the company has deep roots.  It's not too far off to say that Stanton invented the modern style phono cartridge.
Again, Stanton SCS.4DJ's can be found used on eBay for less than I'll have in this project if I don't get my money back.
 
Tracking information shows I should be getting the media player modules sometime in the next week or so.  The fate of this project will lie in the arrival and acceptability of those media players.
 
More news once I've powered up the media players on the bench.
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Re: Poor Man's version of the Monster GO DJ
Reply #7 - Jul 6th, 2020, 9:15pm
 
Update -- The Media Players are here!
 

 
Here is a Mini Review of these modules that seem to be referred to as  
"4.2Dc Bluetooth Mp3 Decoder Board" or "MP3 Decoder Board BT 4.2" on eBay and Aliexpress
 
Setup and Initial Impressions:
To check them out, I simply connected mine to my bench supply set to 5 VDC, and I made a quick adapter from the small 3 pin output connector to RCA jacks.
 
They can also be powered from a battery, and I believe that doing so gives some sort of battery health/voltage indication.
 
The simple blue LCD dot matrix display is pretty good for what it is. The backlight is uniform and it frankly looks better than it does in the vendor listings.  While it's small and very basic, it actually looks crisper than the displays on my Numark Mixdeck Express.
 
The displays for each mode are pretty simple. There's a cool phone plug icon for Line-in. A very minimal frequency display for FM, and a icon for each of Bluetooth unconnected  (pairing mode), and connected.
 
Adding an SD card with music on it enables the playback display, which is also very minimal.  There are no additional pages for settings, or the equalizer.  Yeah, it's wholly inadequate for any "real" DJ media player or mixer, but it is functional as a (very) basic player.
 
Details of the recording function will be presented later.
 
Sound Quality:
For a quick test, I simply dumped about a Gig of songs on a full-size SD card, and put the card in the Media Player.  So far, I have only tried MP3's.  I haven't noticed any distortion or hesitation.  It seems to be pretty "hot" on the line level out, with even fairly low volume settings driving my straight power amp to a pretty high volume.  Large steps between each volume level are a "feature" that seem to plague a lot of consumer products. While certainly not "audiophile" or "analog", it's not bad in these players. I suspect the steps are smoother than the default settings/player in a $1000 iPhone 11.
 
As with most inexpensive players, the built in equalizer function is pretty useless.  Any of the 6 settings other than "Norm" substantially reduce both volume and fidelity.  In this case, this isn't a problem, as the project will have actual analog hardware tone controls.
 
Issues for use as a DJ Player:
Here are some of the major issues for use in this project:
  • It begins playing a track immediately on power up, selecting a track, or changing modes to the media player.  -- Workarounds for my project. -- Be quick on the Play/Pause button.  Check your levels/fader. Use the Cue switches.
  • There is no way to navigate folders from the device itself.  (You can move through the folders from the remote).  You can only scroll through every song on the media.  That said, navigating is fairly fast, and track names are displayed without hesitation.  Again, it's actually better in this respect than the players in my Numark Mixdeck Express.  Navigating a massive library would be impossible, but if you load an SD card with a few hours' worth of songs for a particular Gig, finding the track you want isn't too bad.   EDIT:  Pressing the large button, which is strangely marked with what I interpret as a "Mute" symbol, takes you to a certain file, in multiples of 10.  Files can be directly accessed by number using the remote.
  • It does not display time remaining.
  • Obviously it has no scratch or jog functionality, but for a while I thought there was no way at all to position playback with in a track at all -- at least without the remote.  It turns out that you can in fact go to any position within a song from the player itself, but it is actually a bit of a "hack", and even then very awkward.  Yeah, a DJ could probably mix a set with it, but it would have to be a very good, and extremely patient DJ.  The workaround is to hold the EQ key while pressing the track forward or track back button.  As mentioned, however, this is a hack, not intended functionality.  This means that the buttons are marked backwards.  Pressing [EQ]+[>>|]  Rewinds through the track, and [EQ]+[|<<] Fast Forwards through the track.  The track plays during positioning, even if it was paused.  More on this later, but this post is already too long.  Again, for this project, the level controls, crossfader, and Cue switches will mitigate this problem.
  • It has no A-B repeat or looping functionality short of repeating a whole track.  It can also repeat a whole folder, or the whole disk.
  • There is no random play, and I don't have any reason to suspect it supports playlists.  In other words, the DJ can't take a break unless he just let's it play through the current folder.

 
Using these players would make any "Real" DJ throw my "Poor Mans GO-DJ" project across the venue within seconds of attempting to use it.  None the less, I still plan to use them.  Two of them side by side with a bunch of real, analog knobs and blinky LED's is going to look pretty cool, and be functional as a media player with some DJ functionality.
 
For now I'm going to leave you with an updated drawing.  Note that I have settled on the smaller 12 segment VU meters, and thus reduced the height (depth) of the whole unit by 5mm.
 
If you make the whole image the size of a US legal page, it is very close to actual size.
 

 
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Re: Poor Man's version of the Monster GO DJ
Reply #8 - Jul 7th, 2020, 3:41pm
 
More on the specific media player modules that I am using in this project:
There is a thread about these modules on the Parts Express Tech Talk Forums.
 
Specifically, the Original Poster is asking about adding a rotary volume control.  He noticed that there appear to be pads for exactly this purpose.  I'm not sure if he ever was successful or not.  I have a number of rotary encoders left from the repair of a damaged Yamaha 02R96, but since I plan to have analog volume control downstream of the player, I don't really need this.
 
What was interesting however is the other information about this module that was compiled in that thread.
 
The modules are based on an SoC (System on Chip) marked AC19AP1R339-1A8, and a company logo -- "JL" ("JieLi"). According to that thread, an AC19AP1R339-1A8 is a custom programmed AC4602.
 
Not only that, but it seems that most similar players are based on the same or similar SoC's. If it has Bluetooth, and doesn't have a color screen and video capability, it's probably a AC4602 or AC4601.
 
EDIT: More information, including a schematic:  http://sxemy-podnial.net/aiyima-bluetooth-4-2-dekoder-s-zapisyu/ (Also linked from the Parts Express Tech Talk Forums post).
 
Buttons Implemented as a Voltage Divider:
One thing that is interesting is that most of the function buttons are implemented as a voltage divider connected to a single analog (ADC) input.  So basically, 3.3V is "Do Nothing", and ground is "Play/Pause" with all of the other button functions implemented as some voltage in between.  Each button is connected to a resistor that, along with the common pull-up, results in a pre-set voltage.  This ADC pin is even brought out to the "Key" connection on one of the connectors.
 
Fast Forward and Rewind could be implemented by simply adding buttons and the correct value resistors. There is a table from a vendor site that shows the values, but it's not really readable, and I have not been able to find a better version:
 

 
See above link to Russian site, which has full schematic, including resistor values.
 
When I press  [EQ] and [>>|] simultaneously, or  [EQ] and [|<<] simultaneously, I am simply adding resistors in parallel that happen to add up to the correct values to get Fast Forward and Rewind.  This is why the button labeling is incorrect when [>>|] or [|<<] are used this way.
 
If I wanted to add specific keys, it would be fairly easy to measure the values for the resistors associated with [EQ] and [>>|] and calculate resistors in parallel.  I'd then wire a separate button to a resistor of that value, and I should have a dedicated FF button.
 
This also could allow for more "DJ-like" controls. By changing the SMD resistors, buttons could be moved or re-defined.
The provided access to the "Key" line opens the possibility of using the modules and displays, but not the front panel or buttons.
 
Development Tools:
So the intent of this project is to be a zero software effort.  That said, there is development information out there (mostly in Chinese), and also also lots of development boards for systems based on these and similar chips (AC690X -- AC6901AC6901A -- AC6901258A, etc.)
 
For now, I'm sticking with the modules as they are.  The FF/RW situation is a little awkward, but functional.
 
If I were going to do software development, I'd probably start with a ESP32, a couple of audio CODEC chips, and a couple of color OLED displays:
https://docs.espressif.com/projects/esp-adf/en/latest/index.html
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Re: Poor Man's version of the Monster GO DJ
Reply #9 - Jul 8th, 2020, 4:00pm
 
Knowledge is not power unless it is used.
 
With the information from the sites mentioned in the previous post, I decided that I would swap the x10 track selection key (strangely marked with a "Microphone Mute" symbol), and the "Play/Pause" button.
 
It made no sense to me, especially in what is supposed to be a "DJ environment", not to have the physically larger button serve as Play/Pause.  Even if the button originally marked "Mute" actually has some sort of Recording Mute function, having it on the smaller key still makes more sense.
 
Because of the ADC button implementation, changing the function of a button is as simple as changing it's corresponding resistor.
 
In this case, we just need to swap the smaller value resistor (22 ohms -- R8), with the 2.2K resistor (R10), as shown below:
 

 
Some basic SMD tools and experience are needed. The tiny SMD resistors were easily lifted with hotweezers, and then simply soldered in the opposite positions.  No development environment or software changes needed, no need to cut traces or rewire, and the unit generally appears exactly as it did before.  This ADC keyboard thing is starting to grow on me.
 
Of course we also need to change the markings on the buttons.  A fine wire brush in a Dremel tool makes short work of the original markings, and the new functions were simply drawn with a Sharpe.  I marked the small button as "T" for "Track" or "Ten". Yeah, some sort of stencil would be more professional.  Another alternative is to remove all of the button markings, and apply labels to the panel that the device is installed into.
 
Having the larger button for play/pause makes using these modules more enjoyable no matter what the application or environment.
 
I also verified that a 9.1K  (9K1) resistor connected between the "Key" pin and ground causes the unit to rewind.  The value for Fast forward should be around 12K.  For now I still plan to stick the the rather awkward [EQ] and opposite search button for FF / RW functionality.
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Re: Poor Man's version of the Monster GO DJ
Reply #10 - Jul 19th, 2020, 10:05pm
 
Sometimes I Hate the Internet.
 
I'm still waiting on parts for my "Poor Man's version of the Monster GO DJ" project, but I have a few minor updates...
 
As mentioned a couple of posts ago, I just recently learned about the Stanton SCS.4DJ Controller/Mixer/Player while researching devices similar to the Monster GO DJ.  Yeah, I (now) know the Stanton SCS.4DJ been out for several years, but it had never "popped up on my radar" before I began researching this project.
 
What I did know is that you can find anything you want to -- good or bad on the internet, but knowledge is only power if you do, or in this case don't do something based on that knowledge.
 
My failure was a failure to avoid searching for cheap "for parts or repair" Stanton SCS.4DJ's on eBay.  So you already know how this is going to end -- I ended up with an interim project while continuing to wait for parts for my "Poor Man's Monster GO DJ".
 
A couple of clicks, and only a couple of days later, I am the owner of an very used, abused, and smelly Stanton SCS.4DJ:
 

 
This unit was listed as for "parts only" mainly due to a failed player "A" pitch slider.  By the time it got to me, it had not only a bad "A" pitch slider, but it was also missing a headphone mix knob, and it had damaged pots for the Master Volume, and the Headphones Volume. The additional damage being due to poor packaging by the seller, and compromises in the handling of packages by the shipper due to the volume of packages going through the mail in the current epidemic.
 
Add to that a strange smell that seems to be a combination of old electronics, and whatever other odors may be floating around the previous owner's abode.
 
In addition to several failed pots the "Playlists" button must be pushed very hard in order to work.
 
I de-soldered the "A" pitch linear slide pot, opened the part itself, and was actually able to make it work, although as one might expect after attempting such an "improvised" repair, It feels absolutely terrible now.  The volume controls were made temporarily functional by basically just squeezing them back together with a pair of pliers, but again, they will never work as they should, and will be replaced.
 
Apart from the physical damage, I am impressed with the Stanton SCS.4DJ -- although like knowledge itself, "impressed" can be either good or bad.  Here are a number of observations:

  • I'm very happy that I did not pay more for this device.  It's build quality is just not up to my expectations for even "Party grade" DJ equipment.  It certainly is no where near "Pro Audio" in quality or construction.  I don't consider my Numark Mixdeck Express to be "Pro Audio", but the SCS.4DJ is a big step down from that in terms of weight, durability, or ruggedness.
  • Even the "good" (non broken) sliders and other controls (especially the buttons) feel very cheap.  I wouldn't consider them adequate for even home entertainment equipment.
  • They've really made the most out of a wholly inadequate processor.  It took several hours to build a database of BPM, and waveforms for a thumb drive with about 250 songs on it.  The processor is a tiny chip with no heat sink. IMHO, they should have just put some more CPU power in it -- especially for the retail price.
  • Based on GPL and LGPL references on in the manual, and other similar products, I'm pretty sure it's running Linux which is appropriate since we are discussing it on a Linux website.

The parts for the Stanton will probably be here before the rest of the parts for the main project of this thread.
 
Speaking of parts arriving, the small VU Meter board has arrived.  I connected it directly to one of the Media Player modules, and it seems to work well.  It is nice and bright just like the other one.  The only potential problem is that it seems to be set for a pretty high line level even with the trimmers all the way up.  The 1st orange LED (or "0") is set for 0.775Vrms signal.  I suppose this is "accurate", but that means that when I go directly into a straight (tube) power amp, only a few green LEDs light for normal listening levels.  We'll have to see what kinda of overall gain the tone boards have.
 
I noticed that the Stanton takes the VU levels before the Master Volume.  Most professional mixers give you a choice of pre-fader, or post fader for the VU meters.  I plan to set up the Numark to refresh my memory as to what it does.  I thought it displayed the actual output levels on the VU meters (i.e. after the Master Gain).
 
UPDATE:  The Numark works as I remembered.  The 2 units are different in how they implement the VU meters.
 
I think the Mixxx DJ software displays the VU graph pre-Master.
 
If I go with Pre-master, that will result in a minor schematic change.
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Re: Poor Man's version of the Monster GO DJ
Reply #11 - Aug 11th, 2020, 1:02pm
 
It's been a while since I posted an update, and while I am still waiting on parts, I do have some relevant news.
 
Right now, I still need the following before I can begin construction:

  • Crossfader board
  • Tone boards (2)
  • Op Amp boards (4)

These packages have been with Pitney Bowes for a month.
 
Minor Update:  The Op Amp Boards have been received.  I have opened a "case" with Pitney Bowes on the package that has apparently been in their possession for well over a month.  That package should contain both the fader, and the tone boards, which would allow me to finalize hole locations, and start construction.
 
In other shipping news, Banggood finally refunded my money from the order that got sent back.  At least that takes $90 off the cost of this project.
 
One of the things that I never got from BG was the battery charger/monitor board.  Rather than order a different one in the current environment, I pried open a mobile phone portable charger pack, and got a battery manager board with a nice, blue LED display, and a 5000mah rated 1 cell (1S) LiPo battery.  Interestingly, the output of this unit drops to about 4.25V output if used while it is being charged.  Since it is desirable to be able to use the device while it is being charged, this is somewhat of a concern.  The MP3 modules seem perfectly content at 4.25V.  The 12V boost converter also has no problem providing +12V from down to almost 3V.  I haven't tested the ADA Fruit sound effects board yet, but as far as I know, it should also be fine down to around 4V.  I can always add another boost converter (set to +5V), and run it directly from the LiPo battery -- thus letting the battery manager board deal with charging and charge level only.  I plan to leave one of the standard sized USB ports available for e.g. an LED nightlight, phone or MP3 power.
 

 
The mic input on the MP3 player modules does not pass thru to the output.  In other words, there won't be any live mic capability without a design change.  I can either add a parallel Mic path, or just leave the mic inputs for recording only.  I haven't made a decision on this yet.
 
In other (but related) news, I have completed repairs on the Stanton SCS.4DJ Controller/Mixer/Player.  This is relevant to this project not only by it being essentially a similar device, but also because I can use some of the same parts that I ordered for the repair.  To get the proper replacement part for the Master Volume, and Headphone Volume pots, I would have had to order 1000 of them.  Instead, I purchased 10 (qty) 10K pots, and hard-wired them into the Stanton.  It's not perfect, but 100% functional, and I now have a choice of what pots I use in this project for the same functions, as well as the EFX volume.  I also have one removed, and functional (but very used) fader (linear pot) that I can use for the fader in this project if I have to.
 
Working with the Stanton also pointed out the importance of a Master (or Live) to Cue (Headphone) mix capability.  Especially with the limitations of the MP3 modules in this project, mixing the Live and Cue'd tracks in the headphones is essential for beat matching, or really anything beyond a simple fade. I plan to add a Master/Headphones mix pot and associated circuitry.  I just have to figure out how to do this without crowding the knobs, or increasing the overall size of the device.  Physical and electrical drawings will continue to be updated and shared.
 
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Re: Poor Man's version of the Monster GO DJ
Reply #12 - Aug 18th, 2020, 7:12pm
 
Finally -- Major Update!
 
All of the major components of my "Poor Man's GO DJ" have finally arrived!
 

 
I had no idea that it would take me over 4 months before I was able to post that picture.
 
If you have been following this project, you should be able to find most of the parts and components mentioned in previous posts, or shown on the drawings. (It's kinda like one of those books for children)
 
A few of the major components/highlights:

  • Obviously, the 2 media players detailed previously.
  • The Tone Boards (To the upper left of the remote controls)
  • The Fader Board (Left of the remote controls)
  • The Op amps (Near center, still in packaging)
  • Bags of both types of pots, although only 1 type is planned to be used.
  • Obviously I will not use all of those JST connectors (Right)
  • 2 Sheets of Lexan (Underneath other components)

What is NOT in the picture:

  • Hardware (Screws, Standoffs, Feet, etc.)
  • Wire
  • Perfboard (if/as needed)
  • Additional Metal Knobs (More Knobs are on the way and can be changed at a later date.)

There are a few things I still need to do before I can actually begin cutting/drilling Lexan:

  • Measure the spacing of the holes for the tone boards, and change drawings if needed.
  • Address the issue of a Main/Headphones Mix (Circuit Design point of view)
  • Address the issue of a Main/Headphones Mix (Panel Layout point of view)
  • Determine Mounting of Op Amp boards and misc discrete parts.
  • Determine gains of tone and buffer stages, and change components if necessary.

 
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Re: Poor Man's version of the Monster GO DJ
Reply #13 - Aug 22nd, 2020, 8:30pm
 
I started this thread 104 days ago, and I finally have actual progress to show you:
 

 
In this picture, the front panel is cut and drilled, and I have test-fitted a few components.
 
In actuality, I am a little farther along than this.  The case is generally assembled, and it will be ready for painting in the morning.
 
I have also revised the schematic to show the Live/Cue headphone mix, and a few other updates.
 
One of these updates includes going back to using a dual-rail boost module to power all of the analog circuitry, as I was having significant noise problems when trying to use the tone boards in a single-ended configuration.
 
I am also reconsidering my power supply philosophy.  Early on, I mentioned having the master power switch isolate the Lithium Polymer battery to allow it to not drain when the unit is not used for an extended period of time.  However, the mobile phone charger that provided the battery manager board was really good about not draining the battery.  I don't really think isolating the battery has any real advantage.  It also seems to me that the large power switch should actually power on the unit without a 2-step process being needed.  There is also the previously mentioned issue of the phone charger providing only 4.5 volts when being charged.  It seems that a separate boost module, powered by the large switch would make a more "normal" configuration, and would be totally independent of whether the battery was being charged or not.
 
Since I am nearly ready to start mounting components in the case, I am going to do that, including most of the wiring.  The power supply considerations will not affect component mounting or layout, so I can wait until I can actually power it up to experiment, and then I will make a decision.
 
With a little luck, I'll be able to post a picture that is much closer to a finished product in a few days.
 
One final small note:  The additional metal knobs I ordered from Banggood on May 13, 2020 have finally arrived, however, the knobs I got with the tone boards are different that the knobs that would have been included with the tone boards in the shipment that got returned.  This means that I still won't have a full set of matching knobs unless I wait another 3 months for another shipment from BG.
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Re: Poor Man's version of the Monster GO DJ
Reply #14 - Aug 25th, 2020, 7:56am
 
As promised... A picture that looks much more like it will look when finished...
 

 
Note that in this picture, the plastic covering is still on most of the plexiglass.  I am trying to prevent scratches during the handling that is necessary during construction.  Also, and again for obvious reasons, the knobs are not yet installed.
 
Inside, it is still mostly empty.  I have a *lot* of wiring ahead of me.  While the modules are, of course, printed circuit boards, the rest will be built with old fashion style point-to-point wiring.  Soldering small coax to very small PC mount potentiometers is not something that I am looking forward to.
 
So far, the only wiring done is the Headphone jack, and the harnesses to connect the keyboards to the sound effects module.
 
I am not rushing to get this thing working.  I'll work on it at my leisure, and stop when I get frustrated with the soldering.  Until it gets to the point were I can power it up, it won't look much different, so don't expect more pictures for a while.
 
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