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Poor Man's version of the Monster GO DJ (Read 18610 times)

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Re: Poor Man's version of the Monster GO DJ
Reply #15 - Sep 11^th, 2020, 9:06am

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.

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Re: Poor Man's version of the Monster GO DJ
Reply #16 - Sep 14^th, 2020, 1:59pm

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.

« Last Edit: Sep 14^th, 2020, 3:08pm by Administrator »

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Re: Poor Man's version of the Monster GO DJ
Reply #17 - Oct 24^th, 2020, 9:34am

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.

« Last Edit: Jan 17^th, 2021, 12:38pm by Administrator »

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Re: Poor Man's version of the Monster GO DJ
Reply #19 - Jan 17^th, 2021, 1:57pm

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: ~~The PM GO DJ players will play FLAC files,~~ 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. ~~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.~~
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.
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.

« Last Edit: Feb 18^th, 2021, 8:00pm by Administrator »

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Re: Poor Man's version of the Monster GO DJ
Reply #20 - Jul 3^rd, 2021, 7:44pm

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.

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Re: Poor Man's version of the Monster GO DJ
Reply #21 - Jul 3^rd, 2021, 8:01pm

This post continues a mini-review of 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" and it's applicability to the "Poor Man's Go DJ" project, and other uses.

Other features and improvements over the more primitive player modules:

They support Cryllic characters in filenames. (Yes, I’m publicly admitting that I listen to Soviet Wave, and maybe even a little Russian Hardbass). Interestingly, they do not seem to support European accented characters (Like Ü, for example).

The CD-028 Media players support Cryllic characters in filenames.
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.

One of the repeat options is “random”, although it is random throughout the entire media. There does not seem to be a way to play the tracks in a single folder, for example.
They display the track playing in a list on the left, and the full file name at the bottom right. (See bugs later.) You can go to the next or previous track without leaving the “Music” function. In other words, the same functionality of the JL players, however, navigating via the “Folder” function is also available.
Quality -- They play 32 bit/sample FLAC files that the JL medial players would not recognize. Over all, the sound quality of both players is very good. I have not noticed any pauses or stuttering.
The display is crisp and clear. The top-to-bottom viewing angle is good, but if the unit is observed from the side, the user quickly gets out of the optimal viewing angle. I have not tried it in bright sunlight, but user expectations should be low in this regard. Having color displays also improves the appearance of the "Poor Man's Go DJ".

In general, the “CD-028” Media Player modules are stable, and navigation speed and robustness is adequate, but like all devices in this class, they have their bugs and issues.

Bugs and issues:

They feature a front panel power button, but it continues to draw almost 250mA while “off”. Current when on is about 350mA. With 2 players, and the analog circuitry, total current draw of the “Poor Man’s Go DJ will rise to nearly an amp, (almost 4 times what it is now.) External control of the power will be necessary for any battery powered or mobile application.
There is an attempt at a spectrum display on the “Music” page. It may look cool to the casual observer, but it is so slow that it serves no function. The spectrum feature cannot be turned off.

The Music display features an attempt at a spectrum display. This is so slow as to be meaningless.
It would have been better to use available processing power to improve the overall user interface.
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.

Like the JL players, the CD-028 board features software (DSP) equalizer presets. While the better processor in the CD-028 allows for a little better equalizer effect, I still recommend leaving this feature off (“standard”), and using external analog tone control/equalization if desired. There is no “custom” equalizer setting.
They do not seem to recognize ID3 tags; only the filename and directory (folder) names. While I did not specifically try including a playlist file, I am pretty sure that there is no playlist functionality. The player does not seem to use album art, but if cover art is included as a separate file, it can be displayed by opening it separately. Music continues to play while a picture is selected and displayed in the “Folder” function.
There are display/graphical bugs including filenames displayed partially off the screen, and areas of the screen not being drawn, resulting in black rectangles (or as black as the display is capable of).
The CD-028 will display picture files if selected from the “Folders” display. Doing so enables several possible slide show functions, but if this menu is opened, it seems to get “stuck” to the bottom of the display, and overlays other functions. The only way I could get rid of it was via a hard power cycle.
The user interface is inconsistent. For example, the functionality of the >>, <<, and >| buttons are not consistent between navigating files and folders, and navigating the settings page.

The CD-028 modules are slightly larger than the monochrome JL based players, but they should fit in the Poor Man’s Go DJ with minimal physical and electrical modifications. Of course since the cut-outs must be enlarged, there’s no going back. Once I do a little work to ensure that the increased current draw will not cause any problems, I will probably modify my project with these players in the coming days. Check back for updates and pictures.

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Re: Poor Man's version of the Monster GO DJ
Reply #22 - Jul 8^th, 2021, 8:35pm

New Player Modules Installed.

I have installed the new player modules in the "Poor Man's Go DJ".

Here are a few notes on other functions of these players:

Bluetooth does not work at all. Both Players have the same Bluetooth Name (CD-028), and they respond to a Bluetooth Pairing request even when not in Bluetooth mode, and even when not powered on. There is no way to disable Bluetooth, and no way to change the name. So if there are 2 of these players any where near each other (not just in the same box) they continuously attempt to pair and then disconnect. See below for possible work arounds.
The Microphone jacks on the PM Go DJ are no longer functional. These modules do not support recording or an external microphone. The internal mics (seen at the top of each player) are for a Bluetooth phone call only.
Line-In does not seem to work either. I connected the RCA Input jacks to the line input of player 1, but all I get is that same Bluetooth connecting sound. More research into this issue is needed, but the result of this is that I currently have no way to play my phone through the PM Go DJ. Connecting the phone to a separate mixer is the only option.
As mentioned, the high power consumption of these modules is a significant problem. In addition to the problem of reducing battery life, this causes two other issues: 1.) The 5VDC power supply (Boost module) currently installed in the PM Go DJ is only rated for 1A continuous, 2A surge. 2 modules, plus the other hardware in the PM Go DJ now add up to nearly an amp @5VDC, and thus well over 1A draw from the battery. In addition, the built-in charger only charges at 1A, in other words, I am am likely discharging the battery even when powered from external USB power -- no matter the rating of the USB power source. With both modules "off", draw is still over 600mA, so I am charging the battery only very slowly.

A Little Good News:

As long as the batteries and the boost module hold out, it works very well as a basic, improvised DJ player/mixer. As I mention in both the YouTube video and post #20, Having at least some indication of time remaining, as well as stopping at the end of the track improve the usability of the PM Go DJ enormously.
The Color Screens make the PM Go DJ look more like a contemporary product.
Battery life should still be somewhere around 4 hours (assuming the battery can be fully charged). Battery life would be significantly extended beyond that by using an external USB power source.
It's even more fun to use and play music on, although due to the issues mentioned above, I would not rely on it to actually DJ an event right now.
It still sounds great, and seems to have a little stronger output level if the media player volumes are turned up.

Solutions:

The obvious solution to the additional load on the 5VDC boost module is to use a boost module rated for the observed current. This is not a problem from a cost or space point of view. I will order a 4A/5A rated module in the next few days and install it when it arrives.
The charging problem can be solved by simply rearranging the power as it is in "normal" devices. In other words connecting the power switch downstream of the charger circuit. I like having a true battery disconnect from the point of view of both safety and shelf life.
Another solution would be to install a separate power switch for one or both of the modules. This would have several benefits:
   1.) It would likely solve the Bluetooth issue since one module could be completely shut down during Bluetooth pairing and/or operation.
   2.) It would allow faster charging by eliminating draw during charging.
   3.) A single player could be used when not actively mixing tracks, allowing much longer battery life.
It may be possible to change the Bluetooth name of one (or both) of the player modules. Note that the Bluetooth chip is made by JieLi -- the same company that makes the main chip in the previous (monochrome) players. While it seems this is at least plausible, it is unlikely it is worth the effort.
Another solution to the Bluetooth issue would be to disable Bluetooth on one module by simply destroying the JieLi Bluetooth chip. Of course if this affects other functionality, it would probably be necessary to replace the entire player module.

Sadly, this is a classic case of an engineering trade off -- trading improved functionality in one area for less in another.

The "Poor Man's Go DJ" is still a very cool and nice looking (IMHO) project. It is now more usable as a fun personal media player with analog controls, and a useable backup media player/mixer for casual events.

The ultimate project would be to combine 2 Raspberry Pi's with quality DAC's, and quality touchscreens with the analog hardware from this project. It would also need some good artwork, and lots of programming. This would result in a consumer -- or possibly even professional -- grade product that could represent not just a replacement for the Monster Go DJ, but a significant improvement over it.

« Last Edit: Jul 30^th, 2021, 1:49pm by Administrator »

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Re: Poor Man's version of the Monster GO DJ
Reply #23 - Jul 17^th, 2021, 8:30pm

The new incarnation of the "Poor Man's version of the Monster GO DJ" had it's first real job today -- again, a local Saturday morning car show.

It was a pretty good stress test. It was a very hot Summer day here in central Florida. There was no breeze for the first hour or so of the event, and the sun was low enough to come in under my canopy tent. Between still having the Boost converter rated for 1A max, and the direct sun on a black case, the unit got very warm.

The sunlight coming under the canopy also provided a test for the displays that are part of the CD-028 Media Player Modules. They actually performed better than expected. Using the high-contrast white-on-blue really helps. It was definitely easier to see the displays on the PM GO DJ than the display on the Stanton SCS.4DJ.

So it didn't burst into flames, and I could see the displays, but did it actually play any music?

It did. While the Stanton was there as a back up, I never even cued up a single track on it.

With the track progress indication, my mixes (simple fades) were much better, and there was only once -- for a few seconds -- that I inadvertently had an incorrect track playing in the background.

Pictures always make a post more interesting, so I'll finish this off with a simple graphic I made for this unit:

« Last Edit: Jul 18^th, 2021, 3:13pm by Administrator »

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Re: Poor Man's version of the Monster GO DJ
Reply #24 - Dec 2^nd, 2021, 2:58pm

Previously in this thread, I have mentioned other products similar to the "Poor Man's Go DJ".

I have since come across 2 additional products that are even more similar -- Both bearing the "Technical Pro" brand name. These units are particularly pertinent to this thread, because these units seem to share the idea of using simple, generic music player modules.

Technical Pro DJ2USB. Photo from Manufacture's website

An even more basic unit seems to exist, or have existed:

Technical Pro DJ4PB. Photo from eBay vendor

Given how basic the players look in both of these units, I'm going to say that they probably have similar or more limitations than either the original players used in the "Poor Man's Go DJ", or the new, color screen media players currently installed.

I want to be clear that I have never seen either of these Technical Pro units in person, and of course never used them, but I am confident that as with the project described in this thread, the Technical Pro offerings also lack features such as:

Beat detection
Speed Control, or Pitch Bend, Brake, etc.
Scratching
A-B looping
Waveform Display

Note also that they do not seem to share the USB or SD card slots. Like the "Poor Man's Go DJ", separate media for each player appears to be required.

I would hope that at the vary least, the media players display time remaining, but unless Technical Pro developed or modified the players, these decks (and it's quite a compliment to call them "Decks") may suffer from the same awkwardness as the players originally used in the "Poor Man's Go DJ".

I'd like to point out the fact that the DJ4PB has 2 microphone inputs with separate level controls, and Bluetooth on one of the players. The DJ2USB has analog tone controls (although "High" and "Low" only, no Mid Range).

They appear to support only MP3 and WAV file formats.

There is no indication that either of these units will run from Batteries.

Am I publicly bragging or dissing Technical Pro here? Well -- Yeah -- Maybe a little. The "Poor Man's Go DJ" has been a very successful project. It has more features, and likely better sound (when playing a better quality FLAC file) than the Technical Pro offerings. It also has the 8 sound effect/beat/sample player.

The Technical Pro units win in terms of a mountable metal chassis, and microphone inputs. I should also mention that Technical Pro also make players other than the ones shown here, and some of those do have more elaborate player mixers, and some support scratching/etc.

However, while Technical Pro has some very compelling and desirable Karaoke mixers/amplifiers, for casual events, they are not really known for living up to the "Pro" in their name.

« Last Edit: Feb 4^th, 2022, 12:30am by Administrator »

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Re: Poor Man's version of the Monster GO DJ
Reply #25 - Feb 9^th, 2022, 11:49am

Who saw this one coming?:

Given the Stanton SCS.4DJ "Purchasing Incident", and the fact that I am obviously more than a little "Go DJ obsessed", perceptive readers may have foreseen a photo like the above eventually popping up here.

I regularly search eBay for a number of things, and after passing up a very reasonably priced Go DJ plus, I got the "Should've's". So when this Original Go DJ came along at well under half what they normally sell for, I went for it.

...and I have to say that it is incredible. Completely open, public admission:

It puts my "Poor Man's Go DJ" absolutely to shame!

Going all the way back to my Gemini Dual CD player with remote control head, I wish I had just bought a brand new, full price Go DJ, and never bought any other DJ player/mixer. The elegance and functionality of the Go DJ is amazing.

So... With all that said, I still also stand by everything I previously said about the Go DJ and Go DJ Plus.

In the first post of this thread, I wrote: "The Monster Go DJ, cool as it may be, is also totally useless." Maybe a bit harsh for such a cool product, but I stand by that statement for the reasons I gave at the time.

I also agree with the statement under "Reception" on the relevant Wikipedia page: "It has been criticized for its small size, which belies its feature set and likens it to a toy or game, and for its lack of dedicated hardware equalization knobs."

Lastly, I'll point out that even though I paid less than 1/4 of what it costs new, paying that much for a 2G MP3 player in 2022 -- no mater how cool looking -- is also complete lunacy. (Although apparently people are paying far more ludicrous amounts for original iPods)

With all of the above said, I still like the "Poor Man's Go DJ", and here again are some points:

I'd like to note that the PM GO DJ addresses both of the points of the Wikipedia criticism. My PM Go DJ is a very good size for actual DJ'ing. The analog controls are better for professional use due to their size, single functions, and layout.
In addition to physical (and analog) tone controls, it has a dedicated physical master volume at the top right corner. Master volume should not be 7th function of an encoder wheel.
Ability to play FLAC and other high quality file formats.
Storage capability -- The internal 2G storage of the Go DJ is wholly inadequate by modern standards. I do not know the size limitation of the SD card slot. My PM Go DJ has (2) 64G drives in it right now -- I use them redundantly since the players can't share storage, but it could be used as 128G total. I'll also note that the PM Go DJ players can take larger drives, and can use USB drives and SD cards simultaneously.
Physical Pads for effects instead of on a separate screen. (Yes, the Go DJ Plus has this)
The VU meters on my version are far better.

The Poor Man's Go DJ project was certainly not a waste of time. Despite lacking features like beat detection/matching and scratching (does anybody even do that anymore?) it is still a very functional digital music player. I will be DJ'ing a car show tomorrow evening, and I still plan to use my "Poor Man's" version. I'll take the real Go DJ as a back up.

« Last Edit: Feb 11^th, 2022, 12:22pm by Administrator »

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Re: Poor Man's version of the Monster GO DJ
Reply #26 - May 21^st, 2022, 1:59pm

So this project is finished (or is it?), but I still have a few updates:

1. I continue to use the Poor Man's GO DJ to DJ local car shows and other events. I prefer it over the Real Go DJ for the reasons mentioned. Most importantly it stays on the table. The Real Go DJ has no rubber feet, and very little weight. It tends to move around on the table when used, or pulled by the cables.
2. I use the Real Go DJ as a bedroom audio player, and a compact back up for events.
3. I have made a simple modification to the power system in my Poor Man's GO DJ so that the batteries remain connected to the charger module. The main power switch isolates the rest of the circuit. Some may say this is how it should have been in the first place -- and I'll take that. The load of the 2 media players was never allowing the battery to charge. I ran the unit on batteries last evening for almost an hour. I have a major event coming up in a few hours, (supposedly televised on 3 local TV stations), so perhaps making a change like this wasn't smart either, but we'll see how it works. It sure wasn't working acceptably the other way.

More updates if/as needed.

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Re: Poor Man's version of the Monster GO DJ
Reply #27 - Oct 11^th, 2022, 2:34pm

Power System Upgrade

As mentioned in previous posts, the power system if the Poor Man's GO DJ was never really designed correctly.

The charger module (salvaged from a portable "power bank") was not connected as intended. This was mainly for 2 reasons:
1. The module only supplied around 4.5VDC to a connected load, while it was charging the batteries.
2. I wanted to implement a full battery disconnect switch.

5VDC was produced by a separate Boost converter. I later re-arranged the power so that the unit could be charged while powered off, but I was still having issues.

The Boost supply wasn't designed for powering a device from a Lithium Polymer battery. It did not feature (for example) low voltage cut-off. It would stall at low voltage, but still present a load to the batteries. Most significantly, It was only rated for 1A max, and with the new color media players, I was pulling much more than 1A on the 3.7 (Batter) side of the Boost module. The boost module was also running (even with a charged battery) very close to it's minimum input voltage. It was operating in a region well below it's best efficiency. This made it get hot enough to warm up that entire end of the unit. Even the USB drive in the left media player was getting quite warm. I'm quite surprised that the Boost Module withstood the abuse.

While the Poor Man's GO DJ always got me through an event, and I never had to resort to the real Monster Go DJ or any other player/mixer, I knew I did not have a proper power supply or proper battery management.

I finally ordered one of these from a US eBay vendor:

This module is rated for 2A load, and 2A charging. It produces 5.1V out during charging ~~or discharging~~. CORRECTION: See Next Post. It also features automatic power on and off, so the large power switch at the top left of the PM GO DJ retains it's functionality as master power. The batteries can be charged with the unit (load) on or off.

I have been running the PM GO DJ for over 2 hours, and nothing is getting hot or even warm.

The original charger board remains in place. but the incoming USB power traces have been cut so that the only thing it is doing is acting as a mount for the USB connector.

The pictured module is currently installed inside the unit, and the 4 LED's are not visible. I have ordered a small Digital Panel Meter (DPM) that I will connect to show battery voltage. This will give me more insight into the condition of the battery than the 4 LED's or a 0-100% indication. I will mount it in place of the 0-100% indication on the original battery board -- again using that original board only as a mounting support.

« Last Edit: Nov 22^nd, 2022, 11:54am by Administrator »

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Re: Poor Man's version of the Monster GO DJ
Reply #28 - Nov 22^nd, 2022, 2:03pm

The Poor Man's GO DJ let me down during an all - day Car Show earlier this month. For part of the show, I had to switch over to the real Monster GO DJ, which also presented a problem -- I was set up in direct sunlight, and I couldn't see the displays of the real GO DJ.

I finally had to go sound off, unplug the real GO DJ, take it over to some shade, find the backlight brightness setting burried in the various settings tabs and pages, and turn it all of the way up. I'll note that there is no contrast setting. Even with this done, I still struggled to see the screen of the real GO DJ. I was not having any problem seeing the screens of the Poor Man's GO DJ under the same conditions.

As it turned out, once the Poor Man's GO DJ charged for a while, I was able to go back to using it to finish out the day. It ended up only being 2 breif periods without music. I still got paid, and I got several compliments on the song choices and sound quality.

So why did my Poor Man's GO DJ let me down? As mentioned previously, the new, color LCD player modules draw a lot more power than the B&W screeen modules used in the original design.

While the charge/discharge module mentioned in the pevious post seems to power the PM GO DJ fine from the internal battery, it does not -- unfortunately -- maintain 5VDC output during charging.

When charging, the output voltage (to the load, not to the battery) drops to several tenths of a volt lower than the input voltage.

Given the length of wire from a 5 V USB charger, and the load of both charging the batteries and running the device, I end up with about 4.7 V at the USB connector, and less than 4.6V for what is suppose to be a 5V supply.

Typically, devices designed to run from a regulated 5 VDC power source have a tolerance of 5VDC +/- .25V. So a voltage down around 4.6 won't cut it. The player modules glitch or spontaneously re-boot.

I should also mention that the +/- boost converter that supplies the dual rail voltage for the analog sections seemed perfectly happy with this input voltage. The failure is silent -- the music simply stops -- there are no pops, clicks, etc. when this happens.

So I still have the original problem -- I need a steady source of +5VDC at about 1 amp under all conditions. This should be easy, but I have not found a module that will do this reliably.

Solution space:

1. Forgo battery power --- After all, I am never going to do a DJ job on battery power. All of the other equipment (except wireless mics) need external power available, so why shouldn't the player have the same requirement? I designed the player to run from a battery only because the real Monster GO DJ has a built-in battery.

1a. Power the PM GO DJ from an internal 5VDC SMPS. SMPS's with more than enough current capability are redily available, inexpensive, and would easily fit in the current player.

1b. Simply remove the battery, and rely on the power directly from an external USB source. A quality USB charger and cable should provide the needed voltage without a problem.

2. Down - then up again solution -- use a buck converter to drop the output of the charger module to about 4 V then boost it again to a stable 5.1 V. The chager module would always provide enough voltage to operate the buck, and I have bucks on hand that are rated for the full load current even at 4V.

3. Up - then down again solution -- take the output of the charger module and boost it to ~8 V, then use a buck to make a regulated 5V. Again, the charger module should provide sufficient voltage for the boost converter under all circumstances. With a minimum of 4.6 V input, and ~8V output, the boost converter is working at lower currents than it was in the original design (when it was boosting the battery voltage), so it should be running in a more efficient range, and thus it should remain cool.

4. One additonal Conversion -- Find a buck/boost converter that will reliably provide 5VDC output from inputs very close to that same value. So far, I have not found this. Most boost converters want the output to be at least 1V more than the input, and similarly, most buck converters need the imput to be at least 1V more than the desired output.

5. By using a very short USB cable, the charger module may provide enough voltage as-is. I would then power the GO DJ from a USB power source very close to the unit. If I can eliminate voltage drop in a long USB cable, I may be able to tolerate the drop through the charger chip. As long as I can reliably stay over 4.8V, I should be good.

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Re: Poor Man's version of the Monster GO DJ
Reply #29 - Nov 30^th, 2022, 2:22pm

I am basically applying the Infinite Monkeys Theroem to power supply design.

I agree that providing +/9 Volts and + 5 Volts from a Lithium Ion battery source is not complex these days; However, I have a few constraints:

1. I am not using a microprocessor to do the battery management, as is done in most devices such as the Real Monster GO DJ, a mobile phone, or this tablet I am using right now.
2. I am not making custom PC boards, or purchasing individual components. I am limited to available modules/circuit boards.
3. The high power requirements of the 2 player modules.

I have basically returned to the original design with the following changes:

1. I am using the 2A battery management board instead of the original Portable Battery Pack board.
2. I am using a Digital Panel Meter (DPM) for battery monitoring instead of a 0-100% meter, or the LED's on the battery management board.
3. I have added a small heat sink to the same adjustable boost module that I was using before.

Here is a current schematic of the Poor Man's GO DJ power system:

Note that +5 VDC for the DPM is provided by the Battery Management Board. This allows me to check the battery voltage while the rest of the unit is fully off -- In other words, I can check both the no-load voltage and the loaded voltage of the battery pack. I can also monitor the voltage during charging with the unit off.

Another big improvement was basically to make a low-resistance USB A - to - micro charge cable. I cut a 10' cable, which used slightly heavier guage wire, down to about 4 ft. With this cable, the PM GO DJ will now charge at 1.2A (up from 900mA using a regular USB cable.)

This arrangement seems to work adequately. I have run the PM GO DJ for several hours without drain on the batteries. The boost board still gets warm, but the heat sink is definitely helping.

Why not run the +/-9 VDC Boost either directly from the Battery Management board, or from the battery -- thus reducing load on the 5V board? As mentioned in a previous post, when the Battery Management board is simultaneously charging and supplying power, the output drops below 4.75VDC, but it also seems unstable. To prevent any noise, I did not want to chance running anything from this output. Also, the +/-9 VDC Boost will not function when the input drops much below 5V.

Remaining problems -- There is still no real under volt protection. If the unit is left on, the boost converter will stall someplace around 3.3V. At first that sounds good, but when it stalls, it does not present an open or high resistance. Boost modules of this design present a straight-through path when they stall. This could continue to discharge the battery to a level where damage will occur. The mitigation is the user's ability to monitor the battery voltage, and turn the unit off when the battery voltage is too low, or the players start to behave erratically.

I'm confident the PM GO DJ will make it through my next DJ Job, which is important, as I have a full-paying gig on December 3rd.

« Last Edit: Nov 30^th, 2022, 7:58pm by Administrator »

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