How do you evaluate the performance of a project through pictures? - Page 1
Forum section: electronics / projects

author: iampoor
author_rank: Frequent Contributor
timestamp: May 01, 2014, 06:14:39 am
content: Has anyone ever come across a prebuilt, or premade pcb project on Ebay that they are (not very optimistically) curious about? What are the telltale warning signs of a piece of junk? Ive seen many a power amp without distortion ratings on the "rms output"I dont think I would trust this ap at 2500w into 2 ohms.http://www.ebay.com/itm/Mono-850-Watts-8-Ohm-Module-Class-D-Audio-Power-Amplifier-Board-Assembled-/111310062228?pt=US_Amplifier_Parts_Components&hash=item19ea98c294Stories welcome!

author: peter.mitchell
author_rank: Super Contributor
timestamp: May 01, 2014, 11:47:24 am
content: On this kind of thing, a dead giveaway is skimping on the PCB itself, the cost of a 2 layer board with double silk, double soldermask is almost nothing to a vendor like that.Mind you, that probably can do 2500w peak, into 2 ohm for a moment or two - it'll sound like shit though...There are a few "name brands" amongst chinese stuff, and in this specific category, audio, my first preference would be yuan-jing audio(often identified by their red pcbs), and my secondary would be sure-hifi/sure electronics (not to be confused with shure, the headphone company). Build quality on the sure units are higher, but the output quality of the yuan jing units is higher.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 01, 2014, 09:12:19 pm
content: Odd, the blue core suggests... uhh MPP I think? which is a relatively expensive grade of powder core. Doesn't mean there's enough (or fast enough) MOSFET to handle it of course, or caps for the ripple, let alone EMC conditions (even with a good coil, it probably radiates like a motherfucker?), etc.Tim

author: SL4P
author_rank: Super Contributor
timestamp: May 02, 2014, 07:49:34 am
content: Visible smoke, or scorch marks are a strong warning for future disappointment.

author: iampoor
author_rank: Frequent Contributor
timestamp: May 03, 2014, 12:45:54 am
content: Quote from: peter.mitchell on May 01, 2014, 11:47:24 amRight. Going single sided with a device like this is just asking for trouble? right? I cant iagine the traces being large enough, or the routing being ideal...Oh I sure it will do, Im sure it would be at some outlandish THD value.Yeah Yuangjing kit looks great. Good prices, good documentation, all over ebay. They seem to be fairly honest with the power ratings too. Im noticed alot of These cheapie amps dont specificy bandwidth, test conditions, distortion, efficency, etc.The sure designs look really slick, but the whole system of rating their power into loads with very high distortion made e fairly suspicious of the claims. But I havent heard much bad about em. Im looking for high powered class D modules for bass amps.Quote from: T3sl4co1l on May 01, 2014, 09:12:19 pmInteresting, I would never catch that. It might just be painted blue? Or madybe its the cheapest part they could get at the local surplus market?Id rather not think aboiut its EMC 'complience"Quote from: SL4P on May 02, 2014, 07:49:34 amMaybe they were designed in hell and assembled in china?

author: SArepairman
author_rank: Frequent Contributor
timestamp: May 03, 2014, 02:45:33 am
content: now all the chinese sellers will be painting the inductors blue.honestly its probably wound around a gumball machine ring, or maybe a washer if you are lucky

author: Rerouter
author_rank: Super Contributor
timestamp: May 03, 2014, 03:04:08 am
content: Next immediate thing is the trace thickness, for 2550W at 2 ohm, that comes to 20.4 Amp!, which with a handy trace thickness calculator says that for the 1cm thick traces they are using there would result in the traces alone being about 45 degrees above ambient if constantly run at this power level....Not to mention those PCB mounted space terminals, with only ~2mm^2 of conductor into the board would be running hot on top of that...I'll commend them on at-least choosing capacitors at twice the voltage rating, even if it makes the ESR worse...All in all it will make a lovely wide-band RF jammer

author: iampoor
author_rank: Frequent Contributor
timestamp: May 03, 2014, 03:29:25 am
content: Quote from: SArepairman on May 03, 2014, 02:45:33 amOr maybe a stack of washers if they are feeling really generous.Quote from: Rerouter on May 03, 2014, 03:04:08 amThats also under the assumption that they havent skiped on the amount of copper on the PCB too right?How does it make the esr worse? I wonder if those capacitors could handle that much current....

author: peter.mitchell
author_rank: Super Contributor
timestamp: May 03, 2014, 04:28:13 am
content: Quote from: iampoor on May 03, 2014, 12:45:54 amFor the sure products, they provide pretty good documentation for a bit of chinese kit, check this out;http://www.sure-electronics.net/download/AA-AB32191_Ver1.0_EN.pdfhttp://www.sure-electronics.net/download/AA-AB32191_Schematic.pdfFor the yuan jing stuff, there isn't much documentation, but there are amazing threads like this(i think it has some posts from the ti apps engineer in it too);http://www.diyaudio.com/forums/class-d/237086-tpa3116d2-amp.html

author: iampoor
author_rank: Frequent Contributor
timestamp: May 03, 2014, 05:43:26 pm
content: Quote from: peter.mitchell on May 03, 2014, 04:28:13 amWow not bad! I should have looked deeper. The Parts Express ads for them were always very misleading. Are there any other companies like yuangjiang? I really like that you dont have to pay for rca inputs, or attenuaters etc. Im looking for the most basic of basic amps. The preamplifier im working with would easily drive the sure amps very very hard (1-2v rms out), I wonder how it will perform with some others... Im using it for a bass guitar amp. :-)Quote from: 3roomlab on May 03, 2014, 04:33:42 amIts tough enough to get the good companies to confirm that!I look the look of those designs, but holllllyyyyy cooowwww-a-buunnngggooo, way too flippin expensive!

author: iampoor
author_rank: Frequent Contributor
timestamp: May 03, 2014, 06:57:41 pm
content: Quote from: 3roomlab on May 03, 2014, 06:30:38 pmProbably just a matter of time!