Cheap Chinese T Class Amplifiers - Grounding issues - Page 1
Forum section: electronics / general

author: Marlon
author_rank: Newbie
timestamp: April 14, 2015, 11:15:06 pm
content: Hi People,Firstly, apologies for being that guy who signs up and immediately asks for advice, you probably get millions. None the less, I have a strange(ish) issue.Bit of background first, I have had an old Sony RDX9 amp + speaker setup for my computer for the past 15 or so years - unfortunately the main unit gave up the ghost a few weeks ago so I set about finding a cheapish alternative.Over the past few years the case of the sony amp was giving me that electrically current tingly feeling, but it was intermittant so I didn't really think much of it - and yes I realise that was probably a bit dangerous of me to just leave it.I saw you could get these T Class ampliferis which I gather is just a term for D class amps with the tripath chip in them. So I gave it a shot and got a SMSL SA-50 off of amazon. It arrived and it sounded amazing for what I paid for it, but then I ran my fingers across the case and I feel the same sensation I did with the old amp.Having investigated further, it only happened if I had my feet on the peddles of my G25 racing wheel I use for games, or I hold the metal of the wheel itself. So I thought I had got a faulty product which wasn't grounding properly and returned it for a replacement. I got the SA-60 instead this time as its the newer model but this one does exactly the same. Thinking about it, this was what the old Sony amp must of been doing as well, I just didn't put the two together.This leaves me with 3 different amps all exibiting the same issue, and I am wondering if it isn't the amps but its the wheel that is passing current over its metal parts - but given the way the wheel is built I find this unlikely.I tried using a multimeter to see what the current is but I must be using it incorrectly as it's not reading anything, but it definitely feels like current is flowing and I assume if its strong enough to feel it should be readable.Has anyone got any advice please, I could just leave it as it is, but it just feels wrong to do so.

author: ivan747
author_rank: Super Contributor
timestamp: April 15, 2015, 03:00:34 am
content: Do you know about mains earth and appliance grounding? It could be a problem related to that and your computer's power supply and/or speakers. Try touching the speakers and a metal piece (like the usb shield) on the PC.

author: nfmax
author_rank: Super Contributor
timestamp: April 15, 2015, 02:00:47 pm
content: Many years ago, I had a similar problem. It turned out that the socket into which the 'tingly' item was plugged in had an open-circuit safety earth connection. Since most power supplies (in equipment requiring a safety earth) include a filter capacitor between the live connector and safety ground, current was flowing through this capacitor, to the ungrounded equipment case, and via me, to ground via whatever I was touching that was adequately grounded. Since I was working in a damp basement at the time (it flooded later) I would get a tingle if I was stood on the crack between two of the plastic floor tiles, but not if I stood on the middle of a tile!Check the earth wiring to the socket you are using - or get it checked professionally!Max

author: G7PSK
author_rank: Super Contributor
timestamp: April 15, 2015, 02:20:10 pm
content: I don't know if others do but I can feel a current that is too small to measure with a DMM, the body feels voltage rather than current so it is better to set your meter to volts rather than amps for running down leakage voltage.

author: amyk
author_rank: Super Contributor
timestamp: April 15, 2015, 02:43:30 pm
content: Quote from: Marlon on April 14, 2015, 11:15:06 pmIt might not register if you're not using a low enough range (uA). As long as it can't source a significant amount of current it's not dangerous.

author: TimFox
author_rank: Super Contributor
timestamp: April 15, 2015, 02:48:14 pm
content: Have you set the meter on AC volts and measured the voltage from the various metal parts (chassis, wheel, etc.) to an independent ground (screw on outlet plate, conduit, water pipe, etc.)? Typically, if the problem is with an EMI filter on the power connector, or similar line-to-ground capacitor network, you will measure up to 1/2 the nominal line voltage into the high-impedance (10 Meg) load.