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Class D Switching Power Amplifiers and Power D/A conversion

[DIY Build Log] Mobile PA 12V/230V 2.1 Class D Amp Build
[DIY Build Log] Mobile PA 12V/230V 2.1 Class D Amp Build
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Old 8th July 2019, 03:14 PM   #1
Philipp F is offline Philipp F  Germany
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Join Date: Oct 2014
Default [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:
  • 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:
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 by Philipp F; 10th August 2019 at 03:50 PM.
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Old 8th July 2019, 03:20 PM   #2
Philipp F is offline Philipp F  Germany
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Join Date: Oct 2014
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.
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Old 8th July 2019, 10:15 PM   #3
Think is offline Think  Netherlands
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Join Date: Nov 2017
Location: Den Haag, Holland
[DIY Build Log] Mobile PA 12V/230V 2.1 Class D Amp Build
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?

Last edited by Think; 8th July 2019 at 10:33 PM.
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Old 9th July 2019, 03:09 AM   #4
Turbowatch2 is offline Turbowatch2  Germany
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Location: Northern germany
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 donīt 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 Iīm right, the usual active x-over of such an amp is perfectly fitted for a PA system like yours and getīs 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 by Turbowatch2; 9th July 2019 at 03:14 AM.
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Old 9th July 2019, 06:23 AM   #5
doctormord is offline doctormord  Germany
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@Think, the boost converter does okay, i use the 20A on a 36V battery stack to power a 3255 at 52V and i really push it hard and hot with Neurofunk.

Quote:
The booster is not for 12v-48, but for 48v to xx. Wrong product.
The description is misleading, it work fine from 10V up, current is limited to 40A cont., as stated..

Btw. 8R vs 4R,it’s just 3dB.

Last edited by doctormord; 9th July 2019 at 06:29 AM.
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Old 9th July 2019, 08:12 AM   #6
Turbowatch2 is offline Turbowatch2  Germany
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The Aliexpress page has a data sheet at the bottom, where the max. ampīs are stated. So, with 40 ampīs and 12 volt, you will not come near 1800 watt.
Sure, 420W continous or peak 480 wattīs 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. Donīt 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 by Turbowatch2; 9th July 2019 at 08:16 AM.
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Old 9th July 2019, 09:37 AM   #7
Philipp F is offline Philipp F  Germany
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Quote:
Originally Posted by Think View Post
So it does 30A?; 12V x 30A = 360W peak? or 40A peak? makes 480W
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...

Quote:
Originally Posted by Think View Post
// you wont get much power into the 8ohm subwoofer speaker, about 150W why did you make this choice?
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?).

Quote:
Originally Posted by Turbowatch2 View Post
Anyway, you need 480W/12V = wires for 40 ampere. 40 A is a quite conservative estimate. Quite fat cables...
As far as I understand I will never have continuous 40 amps? I will be using 4 core 2,5mmē and bundle ground and voltage for power handling, I'm "hope-guessing" that will be enough.

Quote:
Originally Posted by Turbowatch2 View Post
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 donīt 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.
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...
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Old 9th July 2019, 10:19 AM   #8
Philipp F is offline Philipp F  Germany
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Join Date: Oct 2014
Quote:
Originally Posted by Philipp F View Post
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<-
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Old 9th July 2019, 06:56 PM   #9
Turbowatch2 is offline Turbowatch2  Germany
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Location: Northern germany
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. Donīt 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 fitīs: Precision Devices PD.123C01
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Old 9th July 2019, 07:02 PM   #10
Turbowatch2 is offline Turbowatch2  Germany
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There is a fact that often is overlooked: The larger the cone area of a speaker, the louder it getīs. 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.
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