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!

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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


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...

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

  • 50Watt to 70Watt Upgrade

    michael_sheaffer10/06/2022 at 23:28 0 comments

    Hi All,

    It's been quite a while since I checked in on this project, but realized there was a super cheap upgrade that is almost a 'why not' for anyone with decent soldering tools!

    So the TPA3116D2 is rated at 50W into 4ohms, and in that same family of amp chips is the TPA3156D2, which is 70W into 4 ohm.... it's a drop-in replacement, just has 20W more power with the same exact specs. 
    (highest upgrade that seems available as a drop-in replacement)

    You do need a decent hot air station (or something similar) in order to heat the chip up enough to remove it, and because there's a good amount of GND connections to the chip and gnd planes under it, you really need to heat it up high.... I'd recommend 350C or higher... I was at about 325C, and it wasn't quite enough, I ended up damaging a small trace being a bit too aggressive and i didn't get enough solder good and melted...

    You can get the TPA3156D2 for about $4-5 or so, I just bought a pack of 5 from mouser...

    I did a quick test with a DB meter on my phone, about 6 inches away from the speakers, running a few acoustic songs, and then did the same test with the upgrade, looks like at least a 5db increase at least at full volume, seems good to me!

    ** note:  the increase may even be much more than that, I realized I didn't even have my bluetooth source volume pushed up... so it gets super loud now :)


    you definitely want to use a good amount of flux to clean up the pads after the chip removal (ie flux and copper braid)... and then use a good bit of flux when soldering, to help prevent bridges!

    Pic of the original TPA3116D2 (heat sink removed)

    Pic of the board with the chip removed (notice the small damaged trace from not enough heat and me being too aggressive..

    Final pic with the TPA3156D2 installed (before applying new heatsink compound along with heatsink)

  • Speaker Replacment

    michael_sheaffer09/12/2020 at 02:21 3 comments


    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.

    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 1 comment

    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 :)


    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!


    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...



    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.


    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.....


    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.


    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 8 project logs

Enjoy this project?



mr.johanlindstrom wrote 02/10/2024 at 15:29 point

Hi, i have just recived a Spark 40 that i bought used. Unfortunatelyit is not working. It just  makes a high buzzing sound. I have opened it up and checked for bad wirering or bad connections. But i cant find anything that looks unnormal. 

Any tips on what can couse this, seams to be a common problem with many reports on Positive Grids forum. 

Here is a video of mine. Warning for bad sound:

Would be very thankful for any tips or ideas. 

  Are you sure? yes | no

oskar.sjogren wrote 10/06/2023 at 10:27 point

Hi, I have bought a Spark 40 amp and would like to add a line out. I have seen the posts about connecting capacitors to TP56 & TP57 to a line out. But my PCB does not look like the one in the posts, and I'm afraid I will screw something up by starting to solder on this. Do you know if the PCB has changed since 2020? Or how would I go about finding that information?

Thanks in advance!

  Are you sure? yes | no

lennykmusic wrote 08/09/2023 at 04:45 point

I have a question regarding the headphone/line out jack. It has a terminator switch so as soon as you plug something in, it shuts off the speakers. Can anything be done to keep the speakers on while you plug in the line out cable so you get both at the same time? 

Thanks in advance (I have the Spark Mini but I assume the use the same headphone jack) 

  Are you sure? yes | no

manningcustom wrote 03/22/2023 at 03:08 point

did you finish the upgraded amp

  Are you sure? yes | no

michael_sheaffer wrote 10/06/2022 at 23:33 point

Hi All,

sorry haven't check this in quite some time, I haven't been using this amp much lately, just been so sidetracked!

But I did post a new project log, as I realized there was a super cheap upgrade to push the amp to 70W from the stock 50W, drop-in replacement from the TPA3116 to the TPA3156...

  Are you sure? yes | no

sav.radioelec wrote 09/01/2022 at 12:22 point

Hello, can anyone tell me what is the reference of U17 ? It's a chip near headphone output that burn on my card. I think it may be an AOP but can't said. Thanks !

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donm1000 wrote 03/18/2022 at 21:10 point

I've 3D printed some speaker brackets that angle the stock speakers out. To my ear this really improved the sound of the amp and makes it feel like an amp with bigger speakers.

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adam.copp82 wrote 11/30/2023 at 20:46 point

Hey there, any chance you can share that 3d model for us to print and use as well? I sent you a private chat message as well. Thanks!

  Are you sure? yes | no

Laurentb31 wrote 02/11/2022 at 09:56 point

hello everybody… do you think is it possible to had effect loop in this  amp. 

Is it a test point between preamp and power amp? Is it possible to connect a looper ? 
thanks a lot

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soulmaster27 wrote 12/13/2021 at 12:39 point

Got my line outputs working:

LINE OUTPUT for Spark Amp 40 | soulmaster27 |

By the way: 

"U23   A3JG   It has 10 pins (3x2x3x2); Unknown chip and function"

This is most likely a dual-analog-switch, like MP2735. MP2735 | Low-Voltage 0.45O Dual SPDT Analog Switches with a Channel Select Pin | MPS (

Plugging in to "AUX IN", digital audio from USB and BT is switched off. :-( 

I´m searching for a point to inject (i.e. MIX in) an external MIC or LINE signal. Any suggestion? Thanks for all the reverse-engineering that had been done here before. It saved me a lot of time getting started.

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kirk.fabbri wrote 11/23/2021 at 03:26 point

Quote "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."

You could be right on this. But the speakers are only rated for 40W, so it's possible they grounded PLIMIT, but control the overall power to speaker by limiting the input signal levels. 

The TPA3116D2 IC has selectable input gain as well. It is set by a resistor divider combination.  So it's possible they have limited the input signal levels, and fixed the gain on the front of the power amp IC. Maybe there is more to get out of this amp by changing the gain settings / adjusting the input levels.

I would be nervous to increase the input gain without knowing how much the current input signal yields in output power to the speaker. 

  Are you sure? yes | no

rloschiavo wrote 03/24/2021 at 12:08 point

Are the morel speakers as efficient as the originals. That could cause the amp to bel less powerful/loud.

  Are you sure? yes | no

rloschiavo wrote 03/24/2021 at 12:07 point

For those that replaced the speakers with The Morels and then commented that the amp was not very loud. Could that be because the Morel speakers are not as efficient as the original speakers.  I, too, am frustrated by the lack of Treble but do not want to sacrifice power/volume. Please advise....  Thanks alll!

  Are you sure? yes | no

rloschiavo wrote 03/24/2021 at 12:06 point

For those that replaced the speakers with The Morels and then commented that the amp was not very loud. Could that be because the Morel speakers are not as efficient as the original speakers.  I, too, am frustrated by the lack of Treble but do not want to sacrifice power/volume. Please advise....  Thanks alll!

  Are you sure? yes | no

bpmitchell101 wrote 03/05/2021 at 02:54 point

Anyone know what the minimum ohms this thing can handle is?

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kirk.fabbri wrote 11/23/2021 at 14:43 point

The TPA3116D2 Class D amp they use in this design shows the following:

2 × 50 W Into a 4-Ω BTL Load at 21 V
2 × 30 W Into a 8-Ω BTL Load at 24 V
2 × 15 W Into a 8-Ω BTL Load at 15 V 

They also say you can run 100W into a 2 ohm load in a mono application

So I would say 4 Ohms is the lowest you can run in a stereo application.

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Ben wrote 12/29/2020 at 18:44 point

Newbie here, so sorry in advance for my lack of technical understanding. Any way that a 6" speaker could be installed for better sound? It would require a larger hole to be cut, but is there room with the amp head? Thinking eiher a 6" guitar speaker or a a larger 2 way car speaker like what was done by michael_sheaffer? I'll be using this mainly as a guitar amp and not a bluetooth speaker so not sure if the 2 way would be needed? Any feedback on if a 6" speaker would fit though would be helpful, along with suggestions for or against a larger guitar vs 2 way speaker.

Also, the reviews online all mention too much bass. What can I put in the cab to dampen the bass reflection without deadening the sound? There was a post by jasper56 mentioning adding neoprene sheeting, but not sure what that is since normally I've seen speakers with insulation type badding inside for bass control. Any suggestions on what can be done (by a NON technical person who can't solder or read schematics)?

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michael_sheaffer wrote 12/22/2020 at 00:12 point

Hi All,

Nice job keeping all the discussions going, I wasn't doing much on this thing for the last few months, got busy with work and kids!   I'll play some more over the next couple weeks while I have some time off :)

  Are you sure? yes | no

jasper56 wrote 11/20/2020 at 20:57 point

I had some neoprene sheet left over hanging around. I fed it in and lined the inside back of the speaker cab with it in a c shape sheet  If you want to do this you'll need 25cm x 31cm .

(don't seem to be able to post images in comments or I could make it clearer)

anyhoo the boominess is instantly totally under control without any further mods, didn't even need to plug the breather. It's now at least tolerable to listen to (I'm a bit of an audiophile tho').
The stock speakers on mine are ALL low mids. so if I adjust the treble, nothing happens as it's outside the response range of the speaker cone. Same with adjusting the bass. Adjusting the mid just makes the whole thing louder & quieter. That confirms a really narrow frequency response.

My spontaneous foam mod today stopped the massive re-enforcement of low mids, and now bass and treb'  controls at least make a minor difference.

next step is to get replacement speakers on order and grumble a bit about how immediate mandatory mods are not the mark of an excellent product.

  Are you sure? yes | no

kim.rusch wrote 11/17/2020 at 18:38 point

Can you please measure the latency from input to speakers?  I think the da converters and processing makes a latency that i noticable. Maybe like 12ms or even more. 

  Are you sure? yes | no

Justin wrote 10/19/2020 at 16:01 point

Effects Loop.

Anyone look into where to place a passive effects loop in the Spark yet?

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kirk.fabbri wrote 11/23/2021 at 17:58 point

No, but a good idea. 

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Mark Williams wrote 09/30/2020 at 19:26 point

Line Output.

          The Combined Guitar and Computer Audio Line outputs are available on Test Points 56 and 57 (TP56, TP57).  The guitar line output alone is available on TP58.  The Computer Line outputs alone are available on TP60 and TP61.  Thus TP56 and TP57 could be used (through a capacitor) to a line output jack.  The DC voltage on TP 56 and TP57 is +2.72 volts.  Tp58 has +2.42 volts and TP 60 and 61 have 0 volts DC.  I used a simple oscilloscope to fine the signals on the test points.  I have not hooked these up yet myself.


Update Spark Amp Chips

U901 5 pin chip near CPU on top of board.  S2SJ  Unknown

U902?  Not Labeled on board; CPU: STM32F427

U903  SRAM: IS66WVE1M16EBLL - 16Mb (2MB) Async /Page PSRAM; under CPU board.

U1 54335    Voltage Regulator 4.5-28 Volt input; 3 Amps

      T1 03A

      POGZ G3


U2 only has 5 pins.  S2SJ.  Left of USB Chip U21


U3 only has 5 pins.  M7TC. Unknown.


U4 only has 5 pins S2SJ.  Unknown

U5, U6, U8 Op-Amps:  NJM2740 - dual low saturation output operational amplifier featuring low noise of 6.5nV/√Hz.  U5 and U6 probably audio outputs from U26; U8 probably output from U25.

U7  Not labeled on board

U9     2582    Guitar input dual op amp.  High voltage.

U10 Flash Memory:  FM25Q08A - 8M-BIT (1MB) Serial Flash Memory

U11, U12  Not labeled on board.

U13   H25S32    Near Bluetooth Module (Serial Flash Memory?) 8 pins




U15, U16  Not labeled on board.


U17 A1W1     Unknown chip.  16 pins, 4x4 pin square chip

        T1 038


U18 Power Amp: TPA3116D2 - 2x50W Class-D Stereo Amp Pin4 +R In; pin5 –R in; Pin 10 +L in; Pin 11 –L In; 32 pins.  Check TP 67 and 68 for possible line outs.  Heat sink may be inadequate.

U19 Missing but label present. 32 pins. Was to be another TPA3116D2 probably.  Output says “To Sub”; Probably a dropped Sub-Woofer Amplifier project.


U20 TKTD only 3 pins     Unknown Regulator??

U21 USB:  GL850G - USB 2 Hub Controller IC

U22 DSP:  AK7755 - DSP with Mono ADC Stereo CODEC + Mic/Lineout Amp. Probably drives U26.

U23   A3JG   It has 10 pins (3x2x3x2); Unknown chip and function


U24 Labeled on board but not mounted.   Would have likely been another NJM2740 Op Amp by symmetry, perhaps for the uninstalled Sub-Woofer circuit.

U25, U26 DAC: ES9023 - 24-bit stereo audio DAC with an integrated 2V RMS op-amp driver.  U26 probably for Computer generated audio; U25 perhaps a 3rd computer generated line.

No U Number. Bluetooth module:  ATS2825 v1.2 Bluetooth Module

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

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michael_sheaffer wrote 12/22/2020 at 00:11 point

Nice job on this BTW, I was busy with work and other fun things and completely forgot about playing more with this thing!   I plan to take another look over christmas break and check out these points...

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Gary Koski wrote 12/07/2021 at 23:27 point

Could you show a wiring diagram? What size capacitor for the Line Output. Just bought the unit a couple of months ago, tried connecting headphone jack to a digital mixing console (audio not so good).

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