AudioFool Rant - Page 1
Forum section: electronics / general

author: _Andrew_
author_rank: Regular Contributor
timestamp: January 03, 2016, 02:25:05 am
content: No No I'm cutting the wires off and putting it in the scrap metal pile.Encountered some AudioFool tranfoolery. "Balanced output mains isolating transformer" The transformer is intended to provide a balanced mains supply being a 3000va 240v 1:1 transformer with a center tapped output connected to earth. So the earth output on this transformer being at 120v mid point with reference to the L and N output terminals. Is that such a good idea. For example if the fuse blew with in the equipment there would still be the potential of 120v to still be present on the neutral. Or a fault between E and N with no fuse in line....Any way the transformer ended up with a red "Failed. Do not use" sticker on it and the connectors removed from the input and output wires. Oh yes the wiring trailing out of the bottom of casing of the potted transformer was individual single core wires with basic insulation, this was also reason enough for me to condemn it.I did do some research about these transformers but the manufactures do not seem to be too forthcoming about

author: langwadt
author_rank: Super Contributor
timestamp: January 03, 2016, 02:48:52 am
content: Quote from: _Andrew_ on January 03, 2016, 02:25:05 ambalanced supply is common on ships so they can measure impedance to "ground" and quickly see leakageI guess ti similar to the main in the US, two 120V phases and a neutral

author: helius
author_rank: Super Contributor
timestamp: January 03, 2016, 04:16:06 am
content: You will find many dozen threads on this site about isolation transformers and their uses and hazards. This is definitely the first one to associate them with "audiophools".

author: _Andrew_
author_rank: Regular Contributor
timestamp: January 03, 2016, 07:25:32 am
content: This was with a transformer that was intended for domestic use. The combination of the voltage between the the center tapped earth and the L and N being 120v-0v-120v. No double pole breaker to isolate both the L and N on the secondary in the event fault conditions, the single core switch gear wire hanging out the bottom unprotected (in the UK mains appliance cords have to be double insulated). The person using it had no idea of the risks.Just a hole can of worms.In pro audio installs where incredibly low noise levels are required, and after exhausting all the common causes of ground loops issues. Then The use of balanced supplies may be considered. The supply in these situations is professionally designed and installed by an electrician with specialist knowledge. With consideration all of the risks and determining in all the necessary safety precautions to mitigate them.

author: G7PSK
author_rank: Super Contributor
timestamp: January 03, 2016, 04:47:43 pm
content: Site transformers have a centre tap earth, Reduces likelihood of shock, only 55 volts to ground, I guess that might be a reason for your transformer,120 volts to ground instead of 240. But if you snip the centre tap you have yourself an isolation transformer.

author: Zero999
author_rank: Super Contributor
timestamp: January 03, 2016, 05:15:52 pm
content: Unfortunately, the Internet is full of audiophool articles about balanced transformers.A balanced transformer is supposed to reduce EMI problems. Here's a link:http://www.avalonglass.co.uk/power-supplies/I doubt if it helps much for audio because, in most amplifiers the first thing in the path of the mains is a big transformer which totally isolates everything from earth.There's no need to scrap it, as it's quite likely perfectly fine, just badly miswired. Replace the wiring to the primary with proper flexible cable, remove the centre tap to earth connection and sell it on ebay as an isolating transformer. You'll find it's quickly snapped up and you make a nice profit.

author: gadget73
author_rank: Regular Contributor
timestamp: January 03, 2016, 05:21:35 pm
content: Isolation transformers are indeed quite useful. I'd also be real tempted to re-purpose that without the grounded center tap. That actually makes the isolation part of it not work anyway. SWPS repair work usually needs one since they rectify the mains to get the HV DC. Also useful if you're into cheap 1950s "hot chassis" radios that rectify straight across the line for the plate voltage supply. One side of the power line is usually tied to the chassis of the radio.That said, there is indeed a lot of marketing wank that goes with audio nonsense.

author: dannyf
author_rank: Super Contributor
timestamp: January 03, 2016, 06:07:53 pm
content: QuoteMany of the anti-audio gimmick rant here has been "fools rant" involving people who rant to show off their supposedly technical superiority, rather than the idiocracy of the said audio gimmick.Both are equally foolish in my view.

author: madires
author_rank: Super Contributor
timestamp: January 03, 2016, 06:44:39 pm
content: An isolation transformer would defeat any mains protection like a breaker or RCD. The earthed middle tap wins the Darwin award. The transformer filters mains to some extend but it won't help with noise. It's still 50Hz AC. Good PSUs and suppressing ground loops are the things to look into.

author: SeanB
author_rank: Super Contributor
timestamp: January 03, 2016, 07:43:05 pm
content: Nothing stopping you putting a RCD device after an isolation transformer, you just need a medical isolated device trip, which uses 2 high value resistors to reference the transformer secondary to a ground connection, then looks for as voltage imbalance across them. No high current for a dead short of any line to ground, but a low current which first flags a low impedance then with higher current it trips out.

author: Electro Detective
author_rank: Super Contributor
timestamp: April 23, 2017, 09:44:48 am
content: Yes I know this post is a bit vintage, but the circuit option described above by SeanB would solve most isolation transformer issues raised at many posts for those gambling on the floating game.Anyone got some links or parts to source or build this add on, without selling their car or Rigol, Fluke and Hakko rigs to buy a used purpose built medical device?