EEVblog #354 - CityRail PA Amp Teardown - Page 1
Forum section: electronics / general

author: mariush
author_rank: Super Contributor
timestamp: September 18, 2012, 08:35:43 pm
content: Just fascinating how many things had to be considered when designing such hardware.Our old trains here from the communist era didn't even have intercom or speakers, some didn't even have heatingThe new trains are relatively modern but I have no clue what they use.

author: rollatorwieltje
author_rank: Unknown
timestamp: September 18, 2012, 09:10:54 pm
content: The PA on some of our new trains is also crap. Well, it's not crap really, but the implementation is a bit funny.It basically has a lower and upper volume limit on the microphone. The lower limit basically works like any telephone does, if there's not enough sound it'll mute (instead of infinite amplification).The upper volume limit kicks in when too much sound is detected, and it also mutes the sound... The old trains were quite loud inside, so the staff was used to speak quite loudly into the microphone. On the new trains this triggers the upper volume level mute... The natural reaction of most people is to speak even louder, causing the limiter to mute even moreThe system is perfectly capable of picking up voice even if there's lots of ambient noise, no need to shout at all. Even a Monday morning voice is picked up quite well

author: krivx
author_rank: Frequent Contributor
timestamp: September 19, 2012, 02:16:24 am
content: I really enjoyed this episode, I think I got quite a lot out of it. It's one of those interesting cases where a few different areas of electronics intersect.

author: johnwa
author_rank: Frequent Contributor
timestamp: September 19, 2012, 06:04:38 am
content: It is nice to see that stuff like this is still made in Australia. It is a little bit surprising that they went with a custom solution, but I guess there can't have been anything suitable on the market.It would be interesting to know a bit more about what went into the design process - how the spec was worked out, how long it took to design, what the budgets were for prototypes and production, etc.I liked the choo-choo trains on the silk screen too!

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: September 19, 2012, 12:29:20 pm
content: I cringed when I saw the title of this episode, and sighed when I saw the orange fascia of that amp.It brought back a lot bad memories, memories of getting multitudes of those amps landing on my service desk( my second ever technical job), smelling of burnt components. Normally once a week and some days 6 at a time.The story about the lack of coupling capacitors is true, and it resulted in a lot a burnt amps.For some reason my company was the middleman between the Railways and the manufacturers (Jands?). Each burnt amp would come back with a huge repair bill from Jands and my boss then told me to double the price, before passing it back to the Railways. I actually was told not to fix anything as it was all paid by the Railways.Then all the amps that went out initially had to be recalled thankfully, to have coupling caps put in, at the same huge markups. Something like 4 inline caps wired into the loom costing hundreds of dollars in 1990s prices and then x 2.I guess the things that really irked were the waste created by this fuck up, because that's what it was, and the obvious price gouging of the government and the fact that I was part of it.Eventually I think it came good, and the dreaded orange amps became less numerous in my workshop.I guess there were a few lessons in this to those who are interested and to those who got burnt.Test before you make and install hundreds of these things. Things rarely work first time.Dont rely on the spec, you have to look into what the customer really needs as well as what they have specified, they are human and not normally experts, sometimes just cut and paste merchants.If the spec looks stupid ie. 1 pair of wires with 50 different jobs, the result will be stupid, they should have run more cables. (Ok I will admit that they were never going to do that, but running more cables would have been the real solution.)

author: bullet308
author_rank: Frequent Contributor
timestamp: September 20, 2012, 01:36:20 am
content: Doug is an *excelent* guest to have on the blog. Very entertaining and a real whiz at what he does.This sort of soup-to-nuts overview of the design and engineering process for a product is absolute gold.

author: Christe4nM
author_rank: Unknown
timestamp: September 20, 2012, 09:22:10 am
content: I really enjoyed this one very much. To me this kind of episodes is why I follow the EEVBlog in the first place. Thanks Dave!

author: EEVblog
author_rank: Unknown
timestamp: September 20, 2012, 10:15:23 am
content: We shot more footage on that day, so more Doug to come!Dave.

author: Bored@Work
author_rank: Super Contributor
timestamp: September 20, 2012, 05:24:13 pm
content: There should be a law that equipment should not come with schematics, but with the original designer.

author: firewalker
author_rank: Super Contributor
timestamp: September 20, 2012, 09:21:49 pm
content: Quote from: EEVblog on September 20, 2012, 10:15:23 amWhat did you blow up?Alexander.

author: SeanB
author_rank: Super Contributor
timestamp: September 20, 2012, 09:31:02 pm
content: How did you get the train into the lab without anybody noticing? The cleaners will moan about the track in the corridor, and the mess from the toilets.

author: baljemmett
author_rank: Unknown
timestamp: September 20, 2012, 11:39:49 pm
content: Quote from: SeanB on September 20, 2012, 09:31:02 pmDO NOT FLUSH TOILET WHILST TRAIN IS IN LAB.

author: EEVblog
author_rank: Unknown
timestamp: September 21, 2012, 02:35:45 am
content: Quote from: firewalker on September 20, 2012, 09:21:49 pmThe product we were installing as a matter of fact!Shame we didn't get the bang on tape though, and the stupid wireless mic died during some of the live commentary I only found out later.Dave.

author: JoannaK
author_rank: Frequent Contributor
timestamp: September 21, 2012, 02:59:19 am
content: Quote from: EEVblog on September 21, 2012, 02:35:45 amMan.. you'll need couple of those continuous recording cameras that's used for trafic recording and connect them to some kind of IR-motien detection system so that there's allways cameras rolling when you are at the lab..

author: SeanB
author_rank: Super Contributor
timestamp: September 21, 2012, 04:49:52 am
content: Call Mike and get a few crash recorders and keep them permanently powered to a room microphone............

author: PeteInTexas
author_rank: Frequent Contributor
timestamp: September 25, 2012, 05:15:55 am
content: This video had it all- digestible amount of technical substance balanced with amusing anecdotes by watchable personalities. Thank you both for taking the time (all 70 minutes of it)