Hi folks,
First post here. Hello everyone. I have a little background in DIY audio, but I am still very much a newbie to this. I'm hoping to get some advice from y'all, and to share what I learn with others.
Positive Grid are selling a small guitar and bass amplified called the Spark. It has been in pre-order for a while with only a few being shipped. Recently, more and more folks are receiving delivery. It could be a very popular device.
It is 40 watts, and has two (supposedly frfr) 4 inch speakers. It is not great for bass, but sounds okay for guitar. The main selling point of the amp is that it is a practice amp that can analyze songs to show you the chords, create a backing track to play against, and has a tone library. It is okay. Like I said, not great for bass.
There is a pretty good group on facebook called Spark Amp mods where a couple of folks are pulling it apart. My focus is on measuring the speakers, and seeing if we can just drop in some other speakers.
I have a UMIK 1 and REW (from an old mini dsp hi-fi setup). Can anyone here help me interpret the REW results?
The following is from another person on the Spark Amp Mods group. I have not had a chance to tear into mine yet to get the exact cabinet measurements.
The cabinet the speakers are in is....
The speakers have identical ink-printed markings on the back of the approx. 2.5” OD magnets: PSP00471001, above G(or 6)3 120144.
I seem to remember some loudspeaker design software where you could put in the cabinet dimensions, but for the life of me I can't remember the name of that software.
My hope is that with the REW graphs, and those dimensions then together we could identify a better set of drivers.
This could be a really popular practice amp as it is selling for about $250 US at the moment.
Thanks for reading. I'll get the UMIK 1 out and take some measurements asap.
cheers,
John
First post here. Hello everyone. I have a little background in DIY audio, but I am still very much a newbie to this. I'm hoping to get some advice from y'all, and to share what I learn with others.
Positive Grid are selling a small guitar and bass amplified called the Spark. It has been in pre-order for a while with only a few being shipped. Recently, more and more folks are receiving delivery. It could be a very popular device.
It is 40 watts, and has two (supposedly frfr) 4 inch speakers. It is not great for bass, but sounds okay for guitar. The main selling point of the amp is that it is a practice amp that can analyze songs to show you the chords, create a backing track to play against, and has a tone library. It is okay. Like I said, not great for bass.
There is a pretty good group on facebook called Spark Amp mods where a couple of folks are pulling it apart. My focus is on measuring the speakers, and seeing if we can just drop in some other speakers.
I have a UMIK 1 and REW (from an old mini dsp hi-fi setup). Can anyone here help me interpret the REW results?
The following is from another person on the Spark Amp Mods group. I have not had a chance to tear into mine yet to get the exact cabinet measurements.
The cabinet the speakers are in is....
- Glued 1/2” thick MDF.
- The speaker baffle, also 1/2” thick MDF, has been routed down 1/8” to inset fit the 4” speaker frames
- The bass reflex port appears to be a 6” long, 1/8” thick, 1-1/2” ID plastic tube, offset from the flat back wall of the enclosure about 0.5”, and flush mounted to the front speaker baffle.
- There are no other internal ports or baffles.
- The back reflections from the 4” speakers appear to just rattle around inside the box, and whatever gets reflected into the bass tube determines bass response.
The speakers have identical ink-printed markings on the back of the approx. 2.5” OD magnets: PSP00471001, above G(or 6)3 120144.
I seem to remember some loudspeaker design software where you could put in the cabinet dimensions, but for the life of me I can't remember the name of that software.
My hope is that with the REW graphs, and those dimensions then together we could identify a better set of drivers.
This could be a really popular practice amp as it is selling for about $250 US at the moment.
Thanks for reading. I'll get the UMIK 1 out and take some measurements asap.
cheers,
John
Pictures?
Front, side and back.
Impedance? DC resistance?
TS parameters? (measure them yourself, I think REW and maybe a couple resistors can help you there)
Cabinet in/out pictures? Dimensions?
Those are cone Tweeter sized magnets, 63 mm; tiny to begin with and even worse if supposed to help reproduce a Bass Guitar.
You can easily fit 73mm and even 86 mm magnets in a 4" frame, leaps and bounds more magnetic "power" available, not sure why they chose the tiny ones.
But always your best option is to install external speaker jacks and drive "real" speakers with it.
Front, side and back.
Impedance? DC resistance?
TS parameters? (measure them yourself, I think REW and maybe a couple resistors can help you there)
Cabinet in/out pictures? Dimensions?
Those are cone Tweeter sized magnets, 63 mm; tiny to begin with and even worse if supposed to help reproduce a Bass Guitar.
You can easily fit 73mm and even 86 mm magnets in a 4" frame, leaps and bounds more magnetic "power" available, not sure why they chose the tiny ones.
But always your best option is to install external speaker jacks and drive "real" speakers with it.
> ...pictures?
Guitar Amp | Smart Practice Guitar Amp | Spark Amp and App
Spark – Help Center
I think Johnny said several times "not great for bass".
I can't even think 2 Fours is a "real guitar speaker". But it is quite affordable, and more than ample for the bedroom, which is surely the intended market.
And they need to shave those pennies because the truly unique features are leading edge algorithms, meaning (we hope) lots of time from clever programmers who now need to pay the rent.
Guitar Amp | Smart Practice Guitar Amp | Spark Amp and App
Spark – Help Center
I think Johnny said several times "not great for bass".
I can't even think 2 Fours is a "real guitar speaker". But it is quite affordable, and more than ample for the bedroom, which is surely the intended market.
And they need to shave those pennies because the truly unique features are leading edge algorithms, meaning (we hope) lots of time from clever programmers who now need to pay the rent.
Thanks for the responses!
I am working on getting some pictures, and exact measurements of the cabinet. What is the best way to share pictures? An imgur album link, or share them all on here? I don't want to spam this thread with pictures, but maybe that is the best way. I also have found lots of pictures of the circuit boards should anyone be interested in those as well.
I'm getting the exact inside & outside measurements of the cabinet. Should have those very soon.
The speakers are listed as 4 ohm. I don't know what their DC resistance is, or how to measure that. Also, I don't know what TS parameters means. I'm not an electrical engineer. Sorry.
Several folks in the group are working on an external speaker jack solution. The amp is 40watts (apparently) so I am not sure how it could ever really function as a modelling amp that will cover bass guitar ... beyond very quiet practice. Perhaps you folks know some great frfr speakers this thing could push? For bass though I am guessing you'd need some more amplification, so that would probably mean the headphone out into a powered frfr (headrush 12 is cheap)?
Really interesting to read the initial thoughts that the 63mm magnets are undersized, and that suggests that maybe there is room for significant improvement "inside the box".
As PRR said, they have almost certainly spent all their money on the modelling. I'm curious to see how good it could be.
I am working on getting some pictures, and exact measurements of the cabinet. What is the best way to share pictures? An imgur album link, or share them all on here? I don't want to spam this thread with pictures, but maybe that is the best way. I also have found lots of pictures of the circuit boards should anyone be interested in those as well.
I'm getting the exact inside & outside measurements of the cabinet. Should have those very soon.
The speakers are listed as 4 ohm. I don't know what their DC resistance is, or how to measure that. Also, I don't know what TS parameters means. I'm not an electrical engineer. Sorry.
Several folks in the group are working on an external speaker jack solution. The amp is 40watts (apparently) so I am not sure how it could ever really function as a modelling amp that will cover bass guitar ... beyond very quiet practice. Perhaps you folks know some great frfr speakers this thing could push? For bass though I am guessing you'd need some more amplification, so that would probably mean the headphone out into a powered frfr (headrush 12 is cheap)?
Really interesting to read the initial thoughts that the 63mm magnets are undersized, and that suggests that maybe there is room for significant improvement "inside the box".
As PRR said, they have almost certainly spent all their money on the modelling. I'm curious to see how good it could be.
The specs say 40 W class D into 4 ohms..I agree with JM for putting an external speaker jack in there. That is plenty of power to drive a stack of twelves ;-)
Even the enclosure looks like a guitar amp head, to me anyway.
Even the enclosure looks like a guitar amp head, to me anyway.
Please double check speaker connections, it´s highly possible that Class D amp has BTL/floating speaker out.
Speaker out jacks are still possible, of course, but "-" out is NOT ground.
Use plastic jacks or insulate them.
As of considering magnet size small, specially in a full range Guitar speaker or even more, a Bass Guitar one (even if intended for desktop practice), my comment came because I use a 73mm magnet in my own *Tweeters*, go figure.
Admittedly a beefy one, a 4" cone unit, intended for biamped Bass, Acoustic Guitar, Keyboard or mini PA systems.
Speaker out jacks are still possible, of course, but "-" out is NOT ground.
Use plastic jacks or insulate them.
As of considering magnet size small, specially in a full range Guitar speaker or even more, a Bass Guitar one (even if intended for desktop practice), my comment came because I use a 73mm magnet in my own *Tweeters*, go figure.
Admittedly a beefy one, a 4" cone unit, intended for biamped Bass, Acoustic Guitar, Keyboard or mini PA systems.
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Hi Guys,
I started a teardown of this amp, still in progress, but I have pics up for mose of the sections of the PCB, and the amp section
... took the heatsink off so you can see a nice closeup of the TPA3116D2 amp IC and it's connections...
Also, the speakers are 4ohm...
https://hackaday.io/project/174163-positive-grid-spark-40-teardownmods
Also, the facebook group:
Spark Amp Mods Public Group | Facebook
I started a teardown of this amp, still in progress, but I have pics up for mose of the sections of the PCB, and the amp section
... took the heatsink off so you can see a nice closeup of the TPA3116D2 amp IC and it's connections...
Also, the speakers are 4ohm...
https://hackaday.io/project/174163-positive-grid-spark-40-teardownmods
Also, the facebook group:
Spark Amp Mods Public Group | Facebook
For what it is, those drivers look fine. Chances are there's some pretty specific DSP going on in there, so it's not particularly likely that simply swapping drivers will make it any better.
What is it you're hoping to achieve?
Chris
What is it you're hoping to achieve?
Chris
Well, even if they are always doing some DSP on the incoming signal, I don't think anyone has verified for sure yet what the in/out freq response is of the entire amp?
So, for a typical 'guitar amp', yes, these drivers are probably adequate for the price, and for the box size... and you usually don't see any mids or tweeters in guitar amps!
But this is also a nice/portable bluetooth speaker... (I haven't had a chance to really do some audio testing yet to get a better feel for it's range)
But if they do pass the full spectrum on to the amp in certain modes, than those drivers are not going to sound anywhere near as good as at least 2-way coax speakers in this size... you will have much crisper mids and highs because of the separate tweeter...
So if there is a full pass of the audio spectrum through, then it would be pretty sweet to put some better full-range setups in there and get a much fuller sound...
That's what my goal is anyhow, I just need to get back to this thing test with some music!
So I took the plunge and changed out the drivers on my Spark this evening following MikeS1974's very helpful teardown guidance. I fitted drivers of the same form factor and power handling, but purporting to have a frequency response to 20kHz. That definitely helped to neutralize the high frequency rolloff with the standard drivers, but the bass was still somewhat dominant. So I fitted a foam plug to the bass reflex port, and the combination made all the difference - balanced, nicely tight on bass lines (but still plenty of low end) and nice high frequencies too now provided that the amp isn't pointing at the floor or your feet.
So I would suggest it is worth experimenting with new drivers.
So I would suggest it is worth experimenting with new drivers.