Close
0%
0%

Positive Grid - Spark 40 Teardown/Mods

This project is to document the teardown of the Positive Grid Spark 40 Amp, the internal components, and any cool mods!

Similar projects worth following
The Positive Grid Spark 40 is a hot-new guitar 'practice amp' out for 2020! It has been selling like crazy, and many buyers are just starting to get their hands on them now (including me).

The amp is catching on because of it's small footprint, even for a practice amp, it's lightweight with a built-in carry strap. It can really be considered a 'hybrid' bluetooth speaker and guitar amp. PostiveGrid developed an App that pairs along with the Amp to provide all sorts of features like playing backtracks, smart jam, auto chords, voice command, tone engine, home recording, etc, etc...

Amp supports bluetooth and usb for external interface...and has aux input jack and of course the main guitar in jack.

THIS page will be dedicated to the teardown of the amp, and showing pictures and describing individual components of the amp, as much as can be identified.

THIS page will ALSO be used to tracking and discussing any mods we/the community can come up with to make this amp better or just add more features!


Construction:  The amp is main built using MDF (medium-density fibre board), which is epoxied together to create the main housing.  The front grille is also formed with MDF, with the fabric covering stapled on, and velcro straps used to make it removable from the main housing.

Main Components:

--------------------------------

Processor:  STM32F427

Flash:  FM25Q08A - 8M-BIT (1MB) SERIAL FLASH MEMORY

SRAM: IS66WVE1M16EBLL - 16Mb (2MB) Async/Page PSRAM

Amp: TPA3116D2  - 2x50W Class-D Stereo Amp

DSP:  AK7755 - DSP with Mono ADC Stereo CODEC + Mic/Lineout Amp

DAC: ES9023 - 24-bit stereo audio DAC with an integrated 2Vrms op-amp driver

Bluetooth:  ATS2825 v1.2 Bluetooh Module

Op-Amps:  NJM2740 - dual low saturation output operational amplifier featuring low noise of 6.5nV/√Hz

USB:  GL850G - USB 2. Hub Controller IC

Speakers:  PSP00471001  G3  120231 - Custom made speaker for PG????

** FYI:  **


There is a thread started on "DIY AUDIO" that is referencing a possible speaker mod, may be a great place to join the discussion...

https://www.diyaudio.com/forums/instruments-and-amps/358004-hacking-positive-grid-spark.html

Also facebook groups for the 'spark owners' as well as 'spark mod group' for actual mod discussions:

https://www.facebook.com/groups/241616417119881

  • Speaker Replacment

    michael_sheaffer09/12/2020 at 02:21 3 comments

    Well,

    I decided to try out these Morel 2-way car audio 4" speakers, as they looked to be the right dimensions.  And voila, they fit perfect, even the mounting holes lined up just enough to use the already existing screw holes.

    https://www.crutchfield.com/p_210MAXIM4/Morel-Maximo-Coax-4.html

    Even the crimp connectors are the standard for these car audio speakers, so it was a quick removal of the old ones, and install the new ones, 30 secs to replace each. 

    So, adding these speakers definitely added much more high range, the treble is much clearer and streaming music sounds so much better...

    BUT, I do feel the amp in this unit is really underpowered for the design.  You really can't get it that loud, if it just had at least another 25W per channel I think it would be so much better.  Anyhow, even though it doesn't get real loud, it did really clear up the sound spectrum...

  • STM32F4 - Processor Module

    michael_sheaffer09/02/2020 at 17:54 0 comments

    The Spark 40 uses the STM32F427 as the main CPU of this amp.  The processor is mounted on a 'removable' pcb module, using standard .050" (1.27mm) M/F headers for the ease of removing the module from the main PCB.

    On the underside of the processor module is the ISSI 16Mbit (2MB) SRAM, added on for extra external SRAM to the CPU, since the STM32F4 really doesn't have much internal SRAM.

    Underneath the processor module on the main board is not much at all, some passive components, and one IC, the FM25Q08A 'Serial 8Mbit (1MB) Flash'.   Not sure what exactly they are storing in here... maybe the 4 profiles on the amp, not entirely sure....


    You can actually use the processor's 'flash program area' to also store things that the program can use (ie like the profiles), but you also have to be careful to not overwrite this when updating the firmware itself.

    So they may have found it easier to just hang a serial flash off of one of the SPI/I2c interfaces on this chip, as the STM32 family has plenty of these.


    The processor module also has an interesting piece of copper strip, looks like they wanted to use it as some extra grounding between the processor module and the main PCB?  But I'm sure they added GND pins through the headers, so not sure why they added this... Also it wasn't really connected to the GND pad that it was touching, only through some contact glue..


    But I added some actual solder between them to make a real connection :)

  • SPEAKERS - 4 OHM

    michael_sheaffer08/05/2020 at 18:02 1 comment

    The two woofer/driver speakers are one-way speakers (ie no mids or tweets), which is pretty much the usual with a guitar amp anyhow, since the lows to mids are the usual frequences we worry about in the guitar amp world.   

    But... considering this IS also a 'bluetooth' speaker you can play your own music on, would be nice to add a couple two-way coaxial speakers, commonly found in the car-audio realm.... I honestly don't know if they are passing the full freq. spectrum to the AMP section anyhow, they may have a low-pass filter setup somewhere along the circuit to cut all mids and highs out...

    The amp is stereo (2x 50W), so each 4 Ohm speaker is connected to one channel of the 2 channel amp.   My guess is that these speakers are rated at 40W, which is why it appears the TPA31162 amp chip (PLIMIT pin 6) is setup with a value, to limit the max output power.  (ie 40W max versus 50W full power of this chip).

    *** UPDATE:  ****

    I did check out the PLIMIT SETUP, there is NO resistor divider setup, they had the footprints there if they wanted to drop the output power, but currently PLIMIT is tied directly to GVDD, so indeed this AMP is setup as full power, 50W x 2.

    *******************

    So really we will just have to test it out unless we can identify filters on the PCB....

    The 'cutout' holes are 3.75" diameter, and the mounting area for the speaker 'flange' is around 4 1/8", a little more in the areas where the corners/screw holes are because of the odd shaped mounting flange.

    Shouldn't be too hard to find some car audio 2-way coaxials that have a 3.75" (or smaller) cutout size, as long as the mounting area is larger than the 3.75" hole so we can mount them!

  • USB 2.0 SECTION

    michael_sheaffer08/05/2020 at 16:46 0 comments

    The picture below shows the USB section of the pcb, nothing too exciting, a standard USB interface IC...


    (GL805G)

  • CLASS-D AMP SECTION

    michael_sheaffer08/05/2020 at 16:40 0 comments

    Below is a close up of the Class-D amplifier section, which uses the TPA3116D2  50W x 2 (Stereo) amplifier IC.  The heatsink and heatsink compound has been cleaned off to show the pinout and associated components.

    (https://www.ti.com/product/TPA3116D2)

    I've been looking at the input audio signals on my scope, and I'm starting to get suspicious that the input gain range is too low, which would explain why the volume doesn't get very loud.   Normally a 2x50W system at full volume can get really loud.  This thing at full volume almost sounds like a 2x20W radio.

    I'll probably at some point post up a partial schematic of the DSP, OpAmps, to TPA3116 connectivity, to show how the DSP outputs through the op-amps and out to AMP.....

  • DSP SECTION

    michael_sheaffer08/05/2020 at 16:33 0 comments

    Below is the close-up of the DSP and related section, showing the three NJM2740 op-amps, around the ES9023 Stereo DAC, and the AK7755 DSP.

  • JTAG HEADER

    michael_sheaffer08/05/2020 at 16:30 0 comments

    The main PCB has a populated JTAG header, for standard 5-pin JTAG debug and flashing of the firmware.

    I did not test out the header to see if the STM32F4 has the 'ROP' (read-out protection) enabled or not.  This is a feature on most of the STM32 family.  You can set 'level's of the ROP protection, protecting the flash contents of the chip from being read from the debug interface.

View all 7 project logs

Enjoy this project?

Share

Discussions

David wrote 6 days ago point

Hi. Cool project - How do I remove the back - I already took the 6 screws out.

Thanks

  Are you sure? yes | no

Jonathan Tarbay wrote 09/06/2020 at 12:44 point

I am looking into replacing the speakers and was wondering if putting a 2 way crossover speaker set would make the audio sound less muddy and clearer when using it as a Bluetooth speaker. If so, would this have a negative impact on the sound of the amp while playing guitar?

  Are you sure? yes | no

michael_sheaffer wrote 09/08/2020 at 21:41 point

Yeah, that's what I've been wondering as well, I've been so busy with other things I really haven't even played with my amp at all as a BT speaker, and it's still apart on my workbench.. lol..

But it's certainly worth a shot, can't hurt anything, I was going to look into a pair of 'coax' car audio speakers if I could find a set that would fit


ie something like this:

https://www.crutchfield.com/p_210MAXIM4/Morel-Maximo-Coax-4.html


(not sure if these would actually fit, but a coax set like these)

As I'm not surprised at all these are muddy when playing regular music... if you've ever done car audio, it would be like putting 1-way drivers in your car doors, and having no tweeters anywhere in the car... it would sound just as muddy...

or even home speakers, if you took everything but the biggest drivers/woofers, and played music, it would be awful.

  Are you sure? yes | no

Jonathan Tarbay wrote 09/13/2020 at 14:40 point

Let me know how it sounds if you end up putting the Maximo speaker. These were the ones I was looking at:

DS18 PRO-X4.4BM LoudspeakerSize - 4"
RMS Power - 100W
Max Power - 200W
Impedance - 4 ohm
Voice Coil Size - 1"
Sensitivity - 92.7dB
Mounting Depth - 2.2"
Cut-Out Dimension - 3.66"
4.5 x 2.5 x 4.5 inches

Kicker 43DSC44 D-Series 4" 120 Watt 4-Ohm 2-Way Car Audio Coaxial SpeakersPeak: 120 watts per pair
RMS: 30 watts per pair
Thin-Profile
Zero-to-Minimal Tweeter Protrusion
Cutout 3.75"

JBL GX402 4" 210W Peak Power 2-Way GX Series Coaxial
Description4" 2-Way GX Series Coaxial Car Loudspeakers Power Handling: Peak: 210 watts per pair / 105 watts each RMS: 70 watts per pair / 35 watts each Plus One polypropylene cone Rubber speaker surround Balanced dome tweeter 2.3 ohms Nominal impedance Frequency Response: 75 - 21,000 Hz Top-mount Depth: 1.88" External Diameter: 4.125" Cutout Diameter: 3.75" Total Depth: 2.60" (top of tweeter) Sensitivity (2.8V/m) : 90 dBFeatures & detailsPeak: 210 watts per pair / RMS: 70 watts per pair
Plus One polypropylene cone Rubber speaker surround
Balanced dome tweeter 2.3 ohms Nominal impedance
External Diameter: 4.125" Cutout Diameter: 3.75" Total Depth: 2.60" (top of tweeter)
Frequency Response: 75 - 21,000 Hz Sensitivity (2.8V/m) : 90 dB
1.65 x 3.94 x 3.94 inches

PRV Audio 4MR60-4 Mid Range Loud Speaker 4 Ohm 120W Pro Car Audio Speaker
Description2 - 4" Mid-Range Loud Speaker Impedance: 4Ω RMS Power: 30 Watts Each Speaker Program Power: 60 Watts Each Speaker Sensitivity 2.00V at 1m: 90 dB Frequency Response at -10 dB: 90 - 15,000 Hz Recommended Hi Pass X-Over: 190 Hz (12 dB/Octave) Voice Coil Diameter: 0.78" Frame Material: Stamped Steel Overall Diameter: 4.96” Hole-To-Hole (Diagonal): 4.5" Front Mount Baffle Cutout: 4.02” Mounting Depth: 2.20” Overall Depth: 2.36” Net Weight: 1.15 Lbs Shipping Weight: 1.24 Lbs

Pioneer TS-G1020S 420 Watts Max Power 4" 2-Way G-Series Coaxial Full Range Car Audio Stereo Speakers 

Description4" G-Series 2-Way Car Speakers Power Handling: Peak: 420 watts per pair / 210 watts each RMS: 60 watts per pair / 30 watts each Injection molded polypropylene with mica cone Rubber coated cloth surround 1-3/16 Balanced dome tweeter Progressive Flex Suspension System spider gives extra support to the voice coil Ferrite magnet motor structure Top-mount Depth: 1-3/4" Cutout Dimensions: 4-1/4" 4 ohms impedance Frequency Response: 35 - 27000 Hz Sensitivity: 87dBPower Handling: Peak: 420 watts per pair / RMS: 60 watts per pair
Injection molded polypropylene with mica cone
Rubber coated cloth surround / 1-3/16 Balanced dome tweeter
Top-mount Depth: 1-3/4" / 4 ohms impedance
Frequency Response: 35 - 27000 Hz / Sensitivity: 87dB
5.11 x 2.16 x 5.11 inches

I will also report back if I end up installing any of these. I will probably want to try the PRV which I think is not a 2-way speaker as well as a 2-way speaker to see if there is a difference while using it as an amp as well as a bluetooth speaker.

  Are you sure? yes | no

michael_sheaffer wrote 09/13/2020 at 16:58 point

Hi,

Yep, I put the Maximos in.. sorry Hackaday can be messy when trying to discuss things, it only let's you go like 2 replies deep and then you can't reply anymore...


So I had to reply here, I added another project log yesterday, about adding these speakers, they do sound much better!

https://hackaday.io/project/174163-positive-grid-spark-40-teardownmods/log/183474-speaker-replacment

But still there is just not enough power in this amp, can't get it very loud, for 2x50W it should get much louder, I still think their gain is too low, I'm looking at trying to improve the circuit and get more gain....

  Are you sure? yes | no

michael_sheaffer wrote 09/02/2020 at 18:06 point

** Update **:

I finally got back to taking this apart again, and removed the processor module and took the underside photos of the module and PCB, so we could know all that is under them, nothing too special, just SRAM and external flash chip.

I plan to buzz out some connections this week to see if we can find a nice easy place for LINE OUT connections we can put onto the back of our amps.... hopefully will get to it this week or weekend...

  Are you sure? yes | no

michael_sheaffer wrote 08/19/2020 at 16:17 point

Awesome!  Glad to hear!  One more thing I need to do for the teardown pics is remove the STM32 processor module to take another board pic of the module itself, and the PCB underneath... from a quick look I didn't see anything interesting underneath, so I have a feeling this 'module' for the processor may be because they use this processor in some of their other products, and made it cheaper in production to use a stand-alone plug-in module..


that's just my guess anyhow... but I"ll get some more pics soon for that...

  Are you sure? yes | no

jstenlake wrote 08/14/2020 at 21:34 point

Many thanks for doing this teardown.  As a result I was able to change out the speaker drivers on my Spark and am now much happier with the sound - treble response is greatly increased and I also fitted a foam plug to the bass reflex port which tightened up the bass - bass lines now sound superb!   I really appreciate the guidance you supplied.  i'm not changing anything else yet but it's good to know that the path is laid out if needed... thanks again!

  Are you sure? yes | no

seanrstone88 wrote 09/03/2020 at 11:03 point

Out of interest, what drivers did you replace it with?

  Are you sure? yes | no

michael_sheaffer wrote 09/12/2020 at 02:22 point

I ended up using these, which sound so much better..

https://www.crutchfield.com/p_210MAXIM4/Morel-Maximo-Coax-4.html

curious which ones jstenlake above replaced the stock with?

  Are you sure? yes | no

Similar Projects

Does this project spark your interest?

Become a member to follow this project and never miss any updates