Poor Man's version of the Monster GO DJ

[admin]

Originally Posted: Tue Aug 11 2020 14:02:33 GMT-0400 (Eastern Daylight Time)


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)
• [s]Op Amp boards[/s] (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.

[admin]

Originally Posted: Tue Aug 11 2020 14:02:33 GMT-0400 (Eastern Daylight Time)


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.

[admin]

Originally Posted: Sat Aug 22 2020 21:30:59 GMT-0400 (Eastern Daylight Time)


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.

[admin]

Originally Posted: Tue Aug 25 2020 08:56:10 GMT-0400 (Eastern Daylight Time)


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.

[admin]

Originally Posted: Fri Sep 11 2020 10:06:12 GMT-0400 (Eastern Daylight Time)


First Power Up!

It Works!



A few things to note:

1.  Note wires on left side.  It is currently powered from +5VDC from my bench supply. The battery is not installed, and as you can see, the battery meter board is not in the circuit.
2.  Film is still on, knobs not installed.
3.  It basically works/sounds pretty good, but it does have a few issues.
4.  The sound effects board was not working at all.  After hours of troubleshooting, I finally discovered that the problem was due to my bench power supply.  I was very conservative in setting the PS current limit -- Just in case.  With each of the tone/op amp boards having lots of filtering, it was presenting a large initial load on the PS.  The current limiting was apparently causing the voltage to come up in a way that hung the sound effects board.  Nominal (steady state) current is almost exactly 0.25A, but in rush is over 0.5A.  With the PS current limit set higher, everything powers up OK, and it does play the sound effects.
5.  There was an issue with the Cue/Live switches due to a short resulting from the close soldering on the tiny toggle switch contacts.  This was fixed, but I'm still not sure if something is wrong with the Cue switches/cue bus wiring or not.  More testing will be done to determine if there is still a wiring problem or not.
6.  Generally, control ranges are pretty good.  One significant problem is that the fader does not fully fade out the opposite player when fully faded to the other side.  I don't have a solution for this at the moment.  It is fundamental to the way the fader pot is made, and a relatively high impedance downstream of the fader.  It's more of a problem because the player modules do not stop at the end of a track -- they go on to the next track, so unless the gain for that side is turned down, or the player is stopped, the next track will be heard faintly in the background.  More thought is necessary on this issue.
7.  I will experiment with different options for power/battery/battery board configurations.  Hopefully I'll make a decision on the configuration today.
8.  It seems at least acceptable from a noise/interference point of view.  I may line the bottom panel with grounded aluminum tape just for shielding "best practices".
9.  The effects keyboards are not sticking to the chassis.  I will remove them, add 3M outdoor permanent double sided tape, and re-attach them.

Once I get the power system configured as it will be, and I have installed knobs and removed the protective film, I plan to do a video showing how it works.

[admin]

Originally Posted: Mon Sep 14 2020 14:59:10 GMT-0400 (Eastern Daylight Time)


Here's a pretty much final picture:




Current Status/Notes:

• It runs from the internal LiPo battery.  I went with the separate boost converter to go from battery voltage to the +5V.  The charger/display board handles charging and battery level only. Battery life seems to be pretty good.  As mentioned, it draws less than 0.25A.  With a 5000mah battery, it will last longer than any party I will ever get invited to.
• The issues with the cue switches was due to a short from soldering in very tight spaces.  2 soldering/wiring issues have been corrected.
• I have not fixed the issue of the fader not completely silencing the opposite channel. Since the fader (and the headphone cue/live mixer) are just wired as resistors in the line-level audio instead of actual stage gain controls, they are not going to fully cut off the audio.   More engineering is needed.  I am not sure how much more effort I want to put into this project.
• I turns out that the fader (linear potentiometer) board was not wired like I though it was.  Basically, both sides are wired in parallel on that board. The result of this was that it was not actually playing in stereo. I had to de-solder and re-work the board to make it 2 electrically independent pots.
• If you look closely, you can see that I re-taped one of the membrane keyboards, and that the other is sill coming up near the center.  I'll re-glue this when I have the time and patience to do so.
• Labels are not installed.  I have made some labels with Libre Office.  Again, I'll print, cut, and apply them when I have the time and patience to do so.

[admin]

Originally Posted: Sat Oct 24 2020 10:34:33 GMT-0400 (Eastern Daylight Time)


I used my Poor Man's GO DJ for an actual gig last night.

I was hired to DJ for a small car show in my local area, so I decided to take my PM GO DJ along as a back up.  The Stanton SCS.4DJ was my primary Player/Mixer.  Early in the evening, I got a request from the wife of the venue owner for Thriller by Michael Jackson.  I was certain I had loaded up Thriller, as well as a hand full of other Halloween classics on both the thumb drive I use with the Stanton, and the SD cards in the PM GO DJ .  However, I was unable to find Thriller on the USB drive I had in the Stanton.  I verified that Thriller was on the SD cards in the PM GO DJ.  Since the Stanton does not have an SD card slot (add that to my list of complaints), I couldn't simply swap or add media.

I figured this was a good enough excuse to actually try live DJ'ing on the PM GO DJ in front of a real audience.  It took a moment of down time to switch over, but the PM GO DJ connected to the amp I was using, and Played the request flawlessly.  I stayed with the PM GO DJ for several tracks before switching back to the Stanton SCS.4DJ.

Despite the previously mentioned limitations in the Media Players used in my PM GO DJ, it was actually quite usable.  Here are some more observations.

• The font on the PM GO DJ Media players is much larger than the tiny font on the small Stanton display.
• The Stanton Browse list does not retain the directory structure of the media, so you cannot use the media's directory structure to organize your tracks.  The media players in the PM GO DJ do retain the directory structure.  While I generally just have folders for artists, one could also use folders basically as crates, or any other structure you would like (such as a directory for "Halloween Songs").  Of course you can create playlists on the Stanton, but that would be tedious using the Stanton interface itself, or would require using other software on a PC.  Simply using the directory structure for crates or playlists may not be sophisticated, but it is simple and easy.
• Quickly moving through large numbers of tracks is actually just as easy or easier than on the Stanton. Quickly browsing the browse list on the Stanton using the jog wheel is not smooth, and suffers from lag.  You either have to scroll slowly enough for it to keep up, or risk significant overshoot.  As mentioned, the Media Players used for the PM GO DJ are fast and direct if you just keep mashing the >> or << buttons.
• The combination of the Media Players not stopping at the end of the track, and the Fader not totally silencing the opposite (faded away from) player leads to the next track playing in the background if you forget to stop it.  I think I did this for over half the tracks I played using the PM GO DJ.  I should state that the level of the undesired track is very low, and I don't know if it was noticeable to the audience or not when it happened.
• While the PM GO DJ has 2 mic inputs (as opposed the the Stanton's single mic input), they do not pass through, so they can only be used for recording.  A live mic input is really needed, and it would be nice if it had equalization.

I'm still planning on doing a video demonstration. Check back for a link soon.

[admin]

Originally Posted: Fri Nov 20 2020 19:04:27 GMT-0500 (Eastern Standard Time)

Finally -- As promised -- The demonstration video:

https://www.youtube.com/embed/SOv9ZFt-Qzg

[admin]

Originally Posted: Sun Jan 17 2021 13:57:46 GMT-0500 (Eastern Standard Time)


The folks that run the local True Value Hardware Car Shows continue to hire me to DJ, and I continue to bring my PM GO DJ as a "Back UP".

I am also bringing a Samson L1200 Professional Mixing Console.  Yeah, that's overkill for a neighborhood Car Show, but in addition to being able to use more than one microphone, I can also have the PM GO DJ and the Stanton SCS.4DJ connected simultaneously. This gives me 4 player decks, as well as the other features (such as Bluetooth) of the PM GO DJ without switching or downtime.

In fact I find myself using my PM GO DJ more than the Stanton SCS.4DJ.  This isn't a conscious decision just so I can use the device I designed and built.  I really find myself naturally or subconsciously gravitating back to the PM GO DJ.  There are a few reasons for this:

-- The larger text on the player modules that comprise the PM GO DJ.  I'm not a young DJ.  I can read the small text on the Stanton, but having the larger text on 2 separate screens is much easier for me.
-- I don't have to continuously switch between the "Waveform" display and the "Browse" screen like I do on the Stanton.  I actually think it is about the same number of button presses to cue up the next track, but on the PM GO DJ it's all on the same screen.  That makes it ergonomically easier.
-- As previously mentioned, the Chinese media players are very quick at moving through the tracks.  The Stanton skips, and does not scroll smoothly.

Lastly, I'm beginning to think that my PM GO DJ actually sounds better than the Stanton SCS.4DJ.  Yeah, OK -- I know the response to that.  I'm not an un-biased, or objective observer here.  It could be totally opposite.  Also, I generally connect the the PM GO DJ to 2 channels of the Samson mixer, and the Stanton to the "CD/Tape" input.  All of the EQ controls for the 2 channels are set to null, and the pans are set so that each channel is properly mixed by the Samson, but it's possible that the Samson just does not have as good a quality components on the CD/Tape input as it does on the actual mixer channels.  Obviously more objective testing (and a far more objective tester) would be needed to determine if there really is a perceptible difference one way or the other.

A few more notes on this:  [s]The PM GO DJ players will play FLAC files,[/s] which the Stanton will not.  Using High quality FLAC files *will* make a
difference in the sound as compared to an MP3.  Objective or otherwise that is an objective fact.  [s]However, very few of the files loaded onto the PM GO DJ's SD cards are FLAC.  90+ percent of them are the identical MP3 files loaded onto the Stanton.[/s]
[s]Actually none of them are FLAC.  I attempted to load some FLAC files, and they would not show up in the Media Players.  As of right now, I don't think this actually will play FLAC files.  It may still play other lossless formats such as WAV.[/s]
Another Edit:  Sorry to keep changing the story on this, but here is the issue:  The Chinese Media Players will play FLAC files.  However, the players are limited to 24 bit samples.  The FLAC files I was attempting to play were 32 bits/sample. They would probably work fine if I used ffmpeg to reduce the depth to 24 bits/sample, but of course that would probably "hurt" the file (reduce fidelity) almost as much as just re-encoding it as a high bit rate MP3.

It's also an objective fact that there is a *lot* more digital circuitry on the Stanton between the digital source files, and the output jacks.  I'm not sure if the Stanton implements it's tone control in a DSP environment, or with analog components.  I can tell you that I don't remember seeing groups on OP amps and analog circuitry.  I also know that the Stanton is very slow at scrolling, scanning media, etc.  It seems very limited on computing power for the job at hand.  If the Stanton is trying to do a lot of real time signal processing on a system that seems to be somewhat limited, then it is very likely that my PM GO DJ really does sound better.

[admin]

Originally Posted: Sat Jul 03 2021 20:44:12 GMT-0400 (Eastern Daylight Time)


How do you fix software bugs?  Change the hardware!

As mentioned previously, I’ve been using my “Poor Man’s Go DJ” to actually DJ public (although very casual) events.  I like using it and for some smaller local gigs, this home made player/mixer is the only player I take with me.  The features I like about the “Poor Man’s Go DJ” are outlined in the previous 2 posts, and I stand by those comments.

That said, I have also pointed out some of the deficiencies of the “Poor Man’s Go DJ”, and that most of those deficiencies are due to the lack of functionality of the very basic JeiLi 690X based Media Players used in this project.

I have actually looked into what it would take to do software development for the JeiLi based players in order to fix bugs and add functionality.  It turns out that there is a development board available (Search “JeiLi Development” on sites like AliExpress), but buying the development board would put the cost of this project over what it would cost to buy a real Monster Go DJ and it looks like the tools are Windows only.  While the source code is provided, I’m not going to jump into something like that for a media player with such basic functionality.


JeiLi (JL) 690X Development board.  Picture from vendor site on AliExpress.  Linuxslate.com is not affiliated with, and does not recommend any particular AliExpress vendor.


Enter to the story the “CD-028 Wireless Bluetooth 5.0 Decoder Board Stereo Audio HD Video Player MP3 FLAC WAV APE Decoding FM Radio USB TF Music player”.

These are similar player modules to the JL modules, but with a color screen, and more functionality.


The "CD-028 Wireless Bluetooth 5.0 Decoder Board Stereo Audio HD Video Player MP3 FLAC WAV APE Decoding FM Radio USB TF Music player"
is similar to the JeiLi Media Players, but with a color screen and more functionality.
Picture from vendor site on AliExpress.  Linuxslate.com is not affiliated with, and does not recommend any particular AliExpress vendor.

While these are improvements, these players are still fairly primitive, and of course they still don’t have features that would be expected on a “real” DJ deck. They don’t have anything like jog, scratching, pitch, etc. In fact, there does not seem to be any way to position playback within a track at all without using the remote control.  Obviously, they also don’t have features such as beat detection, or beat synchronization. There is also no A-B looping.

I have purchased 2 of these players, and I would like to describe them here, with particular attention to features relevant to the “Poor Man’s Go DJ”.

Here is a list of the most significant improvements over the JL-based player modules:

• While there is still no way to display track remaining time, they do display track total time in addition to time in track, and they provide a very basic display of position in track.  For doing simple mixing between 2 players, this is a huge improvement.
• They have several options for repeat, including “once”. If this option is selected, it causes the players to stop at the end of each track, which is the expected behavior for a DJ deck.

Note the right curving arrow symbol at the top center of the display.
This shows that the unit is in "once" play mode.  In this mode, playback will stop at the end of each track
which is the expected operation of a DJ player deck.
One can also select the preset equalizer functionality from this screen. (Small white icon, center right of screen)
NOTE: The light color of the right side of the screen is an artifact of the camera only.
This is not a deficiency of the screen.

• They have a “Folder” function, which preserves the Directory Structure of the USB or SD media.  It also displays several files at a time, and allows the user to navigate the structure while a track is playing in the “Music” function.

In the next post, I’ll continue with some other information about the functionality of these players -- both from the point of view of using them in the “Poor Man’s Go DJ”, as well as information applicable to other uses of the “CD-028” Media Player modules.