[DIY Build Log] Mobile PA 12V/230V 2.1 Class D Amp Build (and fitting sub)
Hello everyone,
for the last few years I've been taking my little homemade mobile 12V PA system to music festivals where we only have 12V car batteries charged by solar panels.
It's been working out pretty okay but the AB car amp that we use is a little weak and gets very hot very quickly.
Since I really enjoy building stuff and stumbled upon the wonderful world of class-d modules I decided to build a dedicated "amplifier box thingy".
The amp is meant to be power efficient and somewhat universal and upgradable, here are some specs on what I'm planing to accomplish:
From reading around TPA3255 seemed like the way to go so here are those and some other things I already ordered:
I'm also planing to have the whole thing microprocessor controlled (either Arduino or STM32). People have done some work on controlling the ADAU1701 via Arduino, my plan would be to have a LCD with rotary encoder on the amp which lets me adjust the DSP parameters. Much simpler things would include thermal management (display and warning, since TPA3255 have a cutout built-in).
I've just began planing and ordering parts. I will update and post pictures as things arrive and the build progresses. In the meantime I will surely have lots of questions.
->Spreadsheet<-
Please tell me what you think and/or if I'm totally on the wrong path.
DISCLAIMER: I'm not at all experienced with audio electronics. I'm just having fun putting things together hoping it will work out
please scold me when I do things wrong
Hello everyone,
for the last few years I've been taking my little homemade mobile 12V PA system to music festivals where we only have 12V car batteries charged by solar panels.
It's been working out pretty okay but the AB car amp that we use is a little weak and gets very hot very quickly.
Since I really enjoy building stuff and stumbled upon the wonderful world of class-d modules I decided to build a dedicated "amplifier box thingy".
The amp is meant to be power efficient and somewhat universal and upgradable, here are some specs on what I'm planing to accomplish:
- 12VDC and 230VAC operation
- 2.1 channels (2x 150Wrms @ 4ohm + 1x 280Wrms @ 8ohm)
- 19-inch rack housing (most likely 3U)
- DSP shenanigans (mainly X-Over)
- RCA DSP input and XLR direct input
- SpeakOn/Screw Terminal output
- Budget <400€
From reading around TPA3255 seemed like the way to go so here are those and some other things I already ordered:
- TPA3255-2ch-260w 3e-audio module
- TPA3255-1CH-480W 3e-audio module
- ADAU1701-2In4Out 3e-audio module
- DC-DC (12 to 48V) boost converter
I'm also planing to have the whole thing microprocessor controlled (either Arduino or STM32). People have done some work on controlling the ADAU1701 via Arduino, my plan would be to have a LCD with rotary encoder on the amp which lets me adjust the DSP parameters. Much simpler things would include thermal management (display and warning, since TPA3255 have a cutout built-in).
I've just began planing and ordering parts. I will update and post pictures as things arrive and the build progresses. In the meantime I will surely have lots of questions.
->Spreadsheet<-
Please tell me what you think and/or if I'm totally on the wrong path.
DISCLAIMER: I'm not at all experienced with audio electronics. I'm just having fun putting things together hoping it will work out
please scold me when I do things wrong
Last edited:
Does anyone have suggestions on a 230V power supply? I've been looking at some inexpensive meanwell units, however I find it hard to judge how "low noise" the output needs to be and what kind of power I actually need because of all the crest factor/peak and RMS stuff I have to little experience with.
I have 2x 3e Audio TPA3255 boards with auda1701 as well and ordered a LRS-350 power supply today. It should do max 150% for 1 second, so should be enough to power 1 board at max output@1%THD. It has a fan that only goes on if needed and idle power is low. (<0.75W) not big or heavy and €36+vat @Mouser.
The booster reads: " New 1800W 35-40A 30A DC-DC"
So it does 30A?; 12V x 30A = 360W peak? or 40A peak? makes 480W
They seems to have mixed up the 1800W and 1200W specs or might be the same boards.... be very careful with these Chinese watts. I would not power more then 1 board with it from 12V.
I burnt the TPA3255 chip on my EVM board with a voltage booster and am not sure why but the mosfet on the booster is stuck in closed position. Maybe just bad luck.
So I ordered a new TPA3255 chip as well.
For portable use I'm thinking of using 2x 24V 6S li-ion packs which I can switch from parallel 24V to serial 48V to safe on idle power and heat if I don't need full power. The 2 3eboards and dsp use 7.2W @24V at idle and 12.5W @40v and about 15W at 48V, so I can get double run time at low power/volume with a simple DPST switch. Other thing is that I can use these 24V packs for TPA3116 and others.
// you wont get much power into the 8ohm subwoofer speaker, about 150W why did you make this choice?
The booster reads: " New 1800W 35-40A 30A DC-DC"
So it does 30A?; 12V x 30A = 360W peak? or 40A peak? makes 480W
They seems to have mixed up the 1800W and 1200W specs or might be the same boards.... be very careful with these Chinese watts. I would not power more then 1 board with it from 12V.
I burnt the TPA3255 chip on my EVM board with a voltage booster and am not sure why but the mosfet on the booster is stuck in closed position. Maybe just bad luck.
So I ordered a new TPA3255 chip as well.
For portable use I'm thinking of using 2x 24V 6S li-ion packs which I can switch from parallel 24V to serial 48V to safe on idle power and heat if I don't need full power. The 2 3eboards and dsp use 7.2W @24V at idle and 12.5W @40v and about 15W at 48V, so I can get double run time at low power/volume with a simple DPST switch. Other thing is that I can use these 24V packs for TPA3116 and others.
// you wont get much power into the 8ohm subwoofer speaker, about 150W why did you make this choice?
Last edited:
Philipp, you miss understood the power output claims of the TPA3255 amps, there is no way to get soemthing like 280 W rms / 8ohm out of them.
The booster is not for 12v-48, but for 48v to xx. Wrong product.
Anyway, you need 480W/12V = wires for 40 ampere. 40 A is a quite conservative estimate. Quite fat cables...
With your momentary knowledge, it would be best to buy a 4 channel, bridgable car amp in class D and follow the instructions that are included. You save your self a lot of money for secondary stuff you don´t think about by now and have reliable gear with a manufacturer warantee. Buy, connect, play.
Getting allong with the DSP will be enough trouble for you, trust me.
If you realize I´m right, the usual active x-over of such an amp is perfectly fitted for a PA system like yours and get´s you started in 30 seconds.
You can use any laptop/ Netbook or even smart phone to run an equalizer app that can bend the sound to your liking.
So, have a look in a car audio publication like "CarHIFI" or "autohifi", the power figures can be trusted. In general, 4 ohms output is 2x 8 ohms output. For your system a solid, medium/low priced 2x150 + 400W/4 ohms D-amp should be all you need for a start. More power with 12V feed is unrealistic.
If you know how to build a box, consider to use 4 ohm speakers with your system instead of 8ohm . A hot tipp: Mivoc MPA chassis (look: mivoc WS 1565 C-4 15" Subwoofer) in 15"+18" are sold at eBay for ridiculos prices, exactly what you need for a battery powered system, where 1500W 8 ohm Pro-chassis are the wrong decission. 4 Ohm speaker give you twice the power at the voicecoil! Look how much you have to pay for 2x amp power!
The booster is not for 12v-48, but for 48v to xx. Wrong product.
Anyway, you need 480W/12V = wires for 40 ampere. 40 A is a quite conservative estimate. Quite fat cables...
With your momentary knowledge, it would be best to buy a 4 channel, bridgable car amp in class D and follow the instructions that are included. You save your self a lot of money for secondary stuff you don´t think about by now and have reliable gear with a manufacturer warantee. Buy, connect, play.
Getting allong with the DSP will be enough trouble for you, trust me.
If you realize I´m right, the usual active x-over of such an amp is perfectly fitted for a PA system like yours and get´s you started in 30 seconds.
You can use any laptop/ Netbook or even smart phone to run an equalizer app that can bend the sound to your liking.
So, have a look in a car audio publication like "CarHIFI" or "autohifi", the power figures can be trusted. In general, 4 ohms output is 2x 8 ohms output. For your system a solid, medium/low priced 2x150 + 400W/4 ohms D-amp should be all you need for a start. More power with 12V feed is unrealistic.
If you know how to build a box, consider to use 4 ohm speakers with your system instead of 8ohm . A hot tipp: Mivoc MPA chassis (look: mivoc WS 1565 C-4 15" Subwoofer) in 15"+18" are sold at eBay for ridiculos prices, exactly what you need for a battery powered system, where 1500W 8 ohm Pro-chassis are the wrong decission. 4 Ohm speaker give you twice the power at the voicecoil! Look how much you have to pay for 2x amp power!
Last edited:
The Aliexpress page has a data sheet at the bottom, where the max. amp´s are stated. So, with 40 amp´s and 12 volt, you will not come near 1800 watt.
Sure, 420W continous or peak 480 watt´s are still some power, but it is not a typical high amp 12 volt device. Include the Chinese "sales talk multiplyer" of real performance data and it might not be what Phillip hopes for. Maybe with some active cooling... fine it works for you, but how hard do you really push it? Depends on music compression and level. Worst case would be high compressed music with the amp driven into clipping. He wanted 580 watt rms output at the speakers.
Doc, you are a professionel with this stuff. Don´t always expect your experience, knowledge and resources from any one else. You know how easy such a "battery powered outdoor PA system" is configured on paper and in theory, but how hard it is to put it together without even one mistake. Because this one mistake might blow up the whole construction in a 1 second if you handle 12V from batteries putting out hundreds of amps with ease.
Sometimes it is better to go to ready made components. Fitting the whole stuff into a case and wiring it up is even with a few parts quite some work and money. I have seen to many ambitious, expensive projects go down the drain. You open up a drawer and just take out any neccesary connector, plug, fuse wire or what else, consider someone buying all this stuff in small amounts. 400€?
Sure, 8 to 4 ohms is 3 dB. That is quite some extra headroom. 2 ohm would be even better, with a second driver in parallel, 9dB in theory compared to 8 ohm or am I wrong?
Sure, 420W continous or peak 480 watt´s are still some power, but it is not a typical high amp 12 volt device. Include the Chinese "sales talk multiplyer" of real performance data and it might not be what Phillip hopes for. Maybe with some active cooling... fine it works for you, but how hard do you really push it? Depends on music compression and level. Worst case would be high compressed music with the amp driven into clipping. He wanted 580 watt rms output at the speakers.
Doc, you are a professionel with this stuff. Don´t always expect your experience, knowledge and resources from any one else. You know how easy such a "battery powered outdoor PA system" is configured on paper and in theory, but how hard it is to put it together without even one mistake. Because this one mistake might blow up the whole construction in a 1 second if you handle 12V from batteries putting out hundreds of amps with ease.
Sometimes it is better to go to ready made components. Fitting the whole stuff into a case and wiring it up is even with a few parts quite some work and money. I have seen to many ambitious, expensive projects go down the drain. You open up a drawer and just take out any neccesary connector, plug, fuse wire or what else, consider someone buying all this stuff in small amounts. 400€?
Sure, 8 to 4 ohms is 3 dB. That is quite some extra headroom. 2 ohm would be even better, with a second driver in parallel, 9dB in theory compared to 8 ohm or am I wrong?
Last edited:
Hmm yeah the "datasheet" definitely makes it seem that was and that sounds a bit low. Maybe I should order another one and just use one per TPA3255...
Definitely! I built that subwoofer years ago when I just wanted something that works, I didn't think about impedance and such things back then.
I've been planing to upgrade or replace that sub.
The design is called MTH-30 and the chassis I put in there is recommended on a German forum where the MTH-30 has somewhat of a following.
I am currently investigating if I can just put a 4 ohm chassis like the Delta 12LFC in there of it will mismatch that design in which case I'm just gonna look for new plans for a 4 ohm chassis or parallel 8 ohm (any recommendations?).
As far as I understand I will never have continuous 40 amps? I will be using 4 core 2,5mm² and bundle ground and voltage for power handling, I'm "hope-guessing" that will be enough.
That would be the right course of action for most people and is of course true, if what I wanted is something that just works out of the box and that is how the system has been working for the last few years.
However, I'm doing this because its fun to me. I'm not totally inept when it comes to electronics, just inexperienced. I'm hoping I know how to fuse things in a way so things will not totally explode when I make a mistake, and if they do so be it its all a learning experience.
The DSP is definitely something I want. I'm a software developer and do lots of digital electronics stuff but never got the chance to play around with DSPs. SigmaStudio was already enough fun to play around even without even a DSP connected so I'm definitely looking forward to that.
I've been planing out most parts of the amp already including a full set of Neutrik connectors, switches, case, hardware, fan, LCD, MC, etc. I will make a full spreadsheet to see where I actually land budget wise...
I've been planing out most parts of the amp already including a full set of Neutrik connectors, switches, case, hardware, fan, LCD, MC, etc. I will make a full spreadsheet to see where I actually land budget wise...
I'm sure I've forgotten many things but here is a first overview, I will be updating the spreadsheet as I go.
I've left out most of the micro-controller stuff since I have that laying around.
->Spreadsheet<-
The MTH30 is something like a transmission line horn. If you use a driver with compareable excursion (at least 7mm) , Vas, Qts and Fs, you will get about the same result. Simulations give a good estimate what will happen and you can exclude drivers with unappropriate parameters. Don´t give to much for the simulated frequency response, the position of box and the audience will show something really different.
To replace the original driver 1:1 this one fit´s: Precision Devices PD.123C01
To replace the original driver 1:1 this one fit´s: Precision Devices PD.123C01
There is a fact that often is overlooked: The larger the cone area of a speaker, the louder it get´s. So if this an option, better use a 18" than 12".
12" are typical middrange drivers, no subwoofers, if we talk PA and outside.
There are many tapped horn plans out there, if you need to use this principle.
In a fair comparison the TH has no advantage over a well planed reflex construction. There is a whole lot of mystification over the TH principle.
12" are typical middrange drivers, no subwoofers, if we talk PA and outside.
There are many tapped horn plans out there, if you need to use this principle.
In a fair comparison the TH has no advantage over a well planed reflex construction. There is a whole lot of mystification over the TH principle.
Considering the DSP and Sigma Studio. Have you ever used it in practice? The programming procedure is very uncomfortable, using it as an field adjustable controller is not recommended. It is more something you adjust measure and programm in a lab and fit inside of an active speaker or the like. So no user programming.
There are other DSP solutions around, that are not more expensive, if you look as a finished DSP with programmer, plugs and power supply.
No, not Mini DSP, maybe look at OMNITRONIC SMARD-24RCA Digitaler DSP-Controller.
Plug it in, start the software and you are there.
It does not matter that you are comfortable with programming, if the hardware is the problem.
There are other DSP solutions around, that are not more expensive, if you look as a finished DSP with programmer, plugs and power supply.
No, not Mini DSP, maybe look at OMNITRONIC SMARD-24RCA Digitaler DSP-Controller.
Plug it in, start the software and you are there.
It does not matter that you are comfortable with programming, if the hardware is the problem.
My idea was to try and fit a 4 ohm chassis in that box hence the Eminence Delta-12LFC. However I have have no clue what would classify as "comparable" for all these specs. I never used simulation, I can try but I'm not sure if it will help me judge at all if this chassis will work.
Yes, the sheer amount of plans overwhelmed me, I'm still looking for anything (BR, TH, whatever) that has similar dimensions and will give me more output at 12" or 15", I think 18" will get to big. For festival use the MTH-30 has pretty much the ideal size. Any recommendations?
No, I've not had the chance to work with it in practice yet, however I've played around with the SigmaDSP Arduino Library and the Header File Parameter Generator this works surprisingly well, although the way this computes the export files is kind jank, it works and the usage is also surprisingly easy. The Idea is to have a pretty "simple" dsp chain and control the most important parameters via the microcontroller (EQ, X-Over, etc.). I'm not planing to "program" it on site per se, the dsp program is stored on its own EEPROM (or the Arduino, if so desired) and loaded by the startup routine (either automatically or via i2c). The i2c parameter control is injected into the header file by the script. And yeah, the programming procedure is kinda annoying, but I've dealt with worse (like manual fuse bit, low pin count MC programming procedures, eugh
).And if that doesn't work, I can always switch to something different. I've already bought it, might aswell try ¯\_(ツ)_/¯
The trouble with Sigma Studio starts, when you begin to use real hardware, like a DSP, programmer, jumpers, power supply and wire connections...
The programm itself is straight forward if you know what you want to do with it.
Did SS recognize your progrmmer?
With PA, first, find out what the largest box dimensions are you can handle. Then, do the same with weight. Now you take a look what kind of plan fit´s your possibilities.
The largest driver is always the best, no discussion needed.
If you can handle 300 litres, go for 18", it sounds like 2x15". As I told you before, there is some kind of hype about the TH, but fair comparisons did not show clear advantages over a well tuned reflex system. A reflex cabinet can be predicted by a simulation closer than 90%. It can be build out of "Baumarkt" cut wood panels and with a box of screws and some Wood glue finished in an afternoon. Today there are many unexpensive speaker chassis in good quality around, so even with a low budget you can have fine results (if you do not insist in putting 1200W into a single 15" speaker). Thomann?
I will not give you any recommendations for a 4 ohm speaker, because I don´t like wasting other peoples money. Maybe ask in some speaker builder forum. I feel uncomfortable with TH, because it seems some kind of try and error design. Even as there is some software for simulations.
PS the hard part seems to find well priced speaker that fit and have 4 ohm. So maybe 2x 15" in 8 ohm will do better than one 18".
The programm itself is straight forward if you know what you want to do with it.
Did SS recognize your progrmmer?
With PA, first, find out what the largest box dimensions are you can handle. Then, do the same with weight. Now you take a look what kind of plan fit´s your possibilities.
The largest driver is always the best, no discussion needed.
If you can handle 300 litres, go for 18", it sounds like 2x15". As I told you before, there is some kind of hype about the TH, but fair comparisons did not show clear advantages over a well tuned reflex system. A reflex cabinet can be predicted by a simulation closer than 90%. It can be build out of "Baumarkt" cut wood panels and with a box of screws and some Wood glue finished in an afternoon. Today there are many unexpensive speaker chassis in good quality around, so even with a low budget you can have fine results (if you do not insist in putting 1200W into a single 15" speaker). Thomann?
I will not give you any recommendations for a 4 ohm speaker, because I don´t like wasting other peoples money. Maybe ask in some speaker builder forum. I feel uncomfortable with TH, because it seems some kind of try and error design. Even as there is some software for simulations.
PS the hard part seems to find well priced speaker that fit and have 4 ohm. So maybe 2x 15" in 8 ohm will do better than one 18".
Last edited:
I'd go for 1-2x 15LB075-UW4, available at Thomann:
the box 15LB075-UW4 Speaker 15" – Musikhaus Thomann
I use this in my bike PA in 90L at 17kg per speaker.
Not a beauty, but a workhorse.
the box 15LB075-UW4 Speaker 15" – Musikhaus Thomann
I use this in my bike PA in 90L at 17kg per speaker.
Not a beauty, but a workhorse.
Attachments
That's for sure, maximum output is limited by input current.
The device has some reserve for peaks, thanks to crest factor in natural music it will "ompf" quite alot.
Well, isn't it more realistic that this combined 580Wrms isn't needed at the exact
time? I mean what music program has an energy density with this profile over the full frequency range?
I drove this module up to the limits, unfortunately with 3x12V SLA in series - unvented at 35°C+ ambient in an enclosure stuffed with batteries and amp modules.
But that's what fuses are made for.. And some thinking and drawings before putting anything together into blocks.
Correct, but that way it most likely doesn't end up in the budged.
Sure, 8 to 4 ohms is 3 dB. That is quite some extra headroom. 2 ohm would be even better, with a second driver in parallel, 9dB in theory compared to 8 ohm or am I wrong?[/QUOTE]
Would sign this.
At that price I might just go for that chassis, just have to find a box for it.
I neither have the DSP nor the programmer, I will report back when they arrive. If it doesn't work then I will try the one you suggested.
Like I said, I'm not set on using a TH. I will use whatever gives me the most output power.
I am currently looking for something somewhat similar to the dimensions of the MTH-30, a bit bigger might be okay and probably wont be avoidable if I want to go for that 4ohm 15" thomann chassis.
I've stumbled across this German thread: hilfe bei 15" hybrid-horn, Subwoofer - HIFI-FORUM
The 15" hybrid horn and the jm-sub212 2x12" BR discussed there both look really good.
The OP went for the horn but I think I might go for the jm-sub212 since I ready have one of the the box Speaker 12-280/8-W that are supposed to fit that box, in parallel that will give me the 4 ohm that I want, right? Furthermore its almost exactly the same size as the MTH-30.
What do you guys think about those?
EDIT: I've found this video https://www.youtube.com/watch?v=ymC8ZfMVAbU comparing exactly those two, they seem to be somewhat similar. Wont I get more power out of the jm-sub212?
The 15" hybrid horn and the jm-sub212 2x12" BR discussed there both look really good.
The OP went for the horn but I think I might go for the jm-sub212 since I ready have one of the the box Speaker 12-280/8-W that are supposed to fit that box, in parallel that will give me the 4 ohm that I want, right? Furthermore its almost exactly the same size as the MTH-30.
What do you guys think about those?
EDIT: I've found this video https://www.youtube.com/watch?v=ymC8ZfMVAbU comparing exactly those two, they seem to be somewhat similar. Wont I get more power out of the jm-sub212?
Last edited:
This "Hybrid Horn" is a combination of reflex with a very short/small horn throat. I do not expect it to work as a sub woofer. I have not seen any reliable measurements so far, which is somehow curious, as anyone can afford a microphone and free software today.
Please be careful with the praise of these constructions by people who build them by them selves. "The last gadget I build is always the best, until I start with the next one." Keep that in mind... so no one will really admit he build something disappointing.
German forums are know to be notorious for this hyping of cheap, simple constructions, if you criticise any high praised construction, you get attacked from all sides, even if you are right. Every single 4" loudspeaker in some wood panel is lifted to high end spheres by these simple minds.
The JM 2x12" will work down to 45Hz open air I suppose, you can tune it (in a limited region) a little deeper or higher. A clean, simple construction. 45 Hz is really low for outdoor PA on a budget, as for example 30 Hz need extreme power and cone area.
The Thomann chassis are very good, compared to the same quality from Brands like Visaton, they cost not even a quarter. They find their limits in excursion and max. input power, but in a region you will not drive by any battery.
Instead of 2x12" in one box, you will get exactly the same result with two 1x12" boxes, just before you ask. Before building, running a simulation will tell you how long the ports have to be and what to expect. I think you understand that you can trade some low bass for SPL and vice versa with the tune of your construction.
The Thomann 15LB075-UW4 mentioned by “doctormord” is on my list for low frequency cheap PA chassis, other 15” are more often made for mid bass. It´s price is ridiculous low and 4 ohm make it ideal for battery use (two in 2 ohm configuration get the most out of typical PBTL amps.
Please be careful with the praise of these constructions by people who build them by them selves. "The last gadget I build is always the best, until I start with the next one." Keep that in mind... so no one will really admit he build something disappointing.
German forums are know to be notorious for this hyping of cheap, simple constructions, if you criticise any high praised construction, you get attacked from all sides, even if you are right. Every single 4" loudspeaker in some wood panel is lifted to high end spheres by these simple minds.
The JM 2x12" will work down to 45Hz open air I suppose, you can tune it (in a limited region) a little deeper or higher. A clean, simple construction. 45 Hz is really low for outdoor PA on a budget, as for example 30 Hz need extreme power and cone area.
The Thomann chassis are very good, compared to the same quality from Brands like Visaton, they cost not even a quarter. They find their limits in excursion and max. input power, but in a region you will not drive by any battery.
Instead of 2x12" in one box, you will get exactly the same result with two 1x12" boxes, just before you ask. Before building, running a simulation will tell you how long the ports have to be and what to expect. I think you understand that you can trade some low bass for SPL and vice versa with the tune of your construction.
The Thomann 15LB075-UW4 mentioned by “doctormord” is on my list for low frequency cheap PA chassis, other 15” are more often made for mid bass. It´s price is ridiculous low and 4 ohm make it ideal for battery use (two in 2 ohm configuration get the most out of typical PBTL amps.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.