[PA Audio] Class-D Amp replacement for efficient mobile PA setup - Page 1
Forum section: electronics / projects

author: Philipp F.
author_rank: Contributor
timestamp: May 07, 2018, 04:27:30 pm
content: Hey Forum,festival season is approaching rapidly and I was thinking about changing my PA setup a bit. I have this homemade 2.1 mobile PA setup I run for my friends.https://imgur.com/a/uQQY3The sub-woofer unit has a 4 channel car amplifier in the top that I use in a 2.1 configuration to drive the sub and 2 satellite speakers. The things is, carrying lead acid batteries is a chore and I don't always have my PV setup or a generator to accompany it.I think the car amp is really inefficient as it heats up A LOT, that's why I was thinking about using some setup of those Class-D amp boards everybody is talking about that you can get dirt cheap on aliexpress and ebay instead of the clunky car stereo amp.Now there seems to be a lot of different opinions and IC's to choose from and I am a little lost on what I should get and what kind of power rating the ACTUALLY have, I probably need to parallel some up and have a crossover filter of some kind for the subwoofer ones.Here is what it needs to run:Tapped-Horn Subwoofer with260W RMS 12'' 8Ohm Driver2x 150W RMS, 600W Peak 8" + 1" 4Ohm Fullrange TopsCan someone help me choose the right thing for the job?Can I just parallel those up, and how does the volume control work when they are parallel?What is an appropriate way of line level crossover filtering for the subwoofer amps?

author: Jr460
author_rank: Regular Contributor
timestamp: May 08, 2018, 12:01:42 am
content: Not to be rude, but you may be better off just picking up a used already built amp designed for PA use. Even something from Mackie or Behringer.Or do what both of those companies do, steal an existing design from them. The service manuals with complete schematics are available for free. You can see what audio power IC they use and how they are driving it.It can be very enlightening.I was doing some small PA work for a guy that insisted we use his Mackie powered speakers. They just didn't have the power I was expecting for the size. A look at the schematic and the specs pointed out the problem. The listed specs said the sub was rated at 600W. And it was a 600W EV speaker. However they never told you what the size of the amp for sub was rated at. I forget the numbers, but just seeing the rail voltages and knowing it was an 8 Ohm sub, you could figure out the peak power, and was maybe 150 watts. They didn't lie on the specs, they just didn't tell you what you wanted to know.

author: Audioguru
author_rank: Super Contributor
timestamp: May 08, 2018, 01:40:15 am
content: Aliexpress has a class-D amplifier with 2 x 300W into 4 ohms with horrible distortion. Into 8 ohm speakers with less distortion the power is only 125W per channel. It needs a 50V power supply that is a lot of 12V lead-acid batteries. A car amplifier has a voltage-boosting power supply.Guess what? Texas Instruments does not recommend its TAS5630 IC for new designs.Texas Instruments says the two channels can be paralleled for higher power into a lower impedance that you do not have. Aliexpress does not say their channels can be paralleled.

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 08, 2018, 02:26:51 am
content: The TAS5630 was replaced with the TAS5630B.

author: ogden
author_rank: Super Contributor
timestamp: May 08, 2018, 06:15:02 am
content: Quote from: Jr460 on May 08, 2018, 12:01:42 amRight. Other option would be to use Class-D car amp which is efficient and does not heat-up A LOT.First google hit.

author: Philipp F.
author_rank: Contributor
timestamp: May 08, 2018, 06:28:42 am
content: Quote from: Jr460 on May 08, 2018, 12:01:42 amNo doubt this is the proper way to do it. And I have the proper gear, however this is not about this. Im looking to drive my setup with no access to the power grid on music festivals while camping with friends.And I have done this successfully for some years now. I run a single 12V lead acid battery with a rather large solar setup with mppt (no gas generators allowed on some festivals here in germany). I usually get a lot of guys coming over chilling and looking at my setup because we are the only ones blasting at full volume for 4 or 5 days. Usually the music stops around das 2 or 3 when they run out of batteries haha.

author: ogden
author_rank: Super Contributor
timestamp: May 08, 2018, 02:52:11 pm
content: Quote from: Philipp F. on May 08, 2018, 06:28:42 amWow, now we are talkingI would never rely on aliexpress or alike amplifiers in such application, ever. Better use reliable, heavy duty stage amplifiers and just address DC part of your system. All you need - go higher DC voltage to get better DC->AC conversion efficiency. Consider 48VDC (deep cycle) battery pack and according solar system with MPPT charger and inverter.  Higher voltages shall not be used in "portable" applications due to safety considerations.Other crazy option would be to hack your electric car, if anyBetter two so you can rotate them to get continuous off-grid power for as long as needed. www youtube com/watch?v=kcqUhbsP3FE

author: b_force
author_rank: Super Contributor
timestamp: May 08, 2018, 03:14:40 pm
content: The problem with these Chinese Amps is that are not very reliable, which is a shame since they have a lot of potential for a fair price.How much power you need really depends on the whole design.Since you build a horn I assume you used Hornresp or something similar to simulate and calculate the horn?That way you can also calculate the needed amount of powerWhich is a combination of the complex impedance, max power woofer, max excursion woofer, sensitivity and needed SPL.I can already give an hint, it's gonna be NO WAY 280W rms and or those 150WOne good thing though, the tops are 4ohm, so you can probably get away with some TI Class-D chip.For the subwoofer it's gonna be a bit more tricky to find any affordable designs.(amount of good mid-low power amplifiers on the market is pretty slim).My suggestion would be a 230V inverter and just buy a dedicated amplifier (maybe with a DSP on board)

author: Philipp F.
author_rank: Contributor
timestamp: May 08, 2018, 03:42:11 pm
content: Well, I should mention that in most cases we can’t camp near the car. It’s because often the camping areas are in "water protection areas" where no cars or generators are allowed, and we have to carry everything from the parking area to the camping grounds by hand and on carts (yeah, I know it sucks). There are festivals where everything is allowed, that's where I take the big setup with diesel generator and proper PA amps and we can camp right by our cars. On these kinds of festivals there are seriously people that build whole stages and huge DJ setups with stage lighting, line arrays and everything and that is just the camping part of an ACTUAL music festival that’s in the evening.Until now I had the incredible luck that we had amazing weather every time and I had plenty power on the panels, so the battery could charge all morning and during the day when the setup is running. I noticed a couple of times when the sky was overcast for too long the battery got quite low and I want to reduce that risk by making the mobile setup more efficient (and maybe even a bit more powerful).The crappy class AB car stereo amp worked flawlessly every time but gets extremely hot and we have to "water cool" it with moist paper towels and that’s just wasted power that could go into more music blasting.The horn is build after the “mth-30” design found online.I want to stay away from AC and proper amps for the portable setup as this would throw in more factors that I want to avoid, some of which are cost and weight because we already carry big PV panels, the battery, the speaker setup, all camping gear including pallets of beer and food and things break when people get drunk.Like I said, this is only for the weight reduced configuration of my setup, by no means is this a “critical” application, this is just my friends and me dicking around with some beers and music.I was wondering how efficient it would be to just use a mono and a stereo TAS5630 module or something like that in combination with a couple of those DC voltage booster modules. Surely it cant be less efficient that that car amp...EDIT: I ordered a couple of big fat resistors so I can actually measure power and efficiency.