Vintage mixer - Page 1
Forum section: electronics / repair

author: nuno
author_rank: Frequent Contributor
timestamp: November 03, 2019, 07:57:51 pm
content: Not exactly a repair, but...I have this vintage audio mixer that was given to me years ago stored in a box, and decided to give it some use. I've opened it to clean, fix minor issues, clean pots and so on. Being an "old" piece of equipment, this is an all metal chassis and panels, mains plug without earth (original); the mains wiring inside had some worrying bits which I fixed (the most worrying thing being what you can see in attach) by adding double insulation, securing flying cables, applying thermal shrink sleeve, etc.My question: would you change the equipment to have the box grounded? That implies new cable, opening a bigger hole in the chassis/box for it and a screw ground connection somewhere in the chassis.

author: Whales
author_rank: Super Contributor
timestamp: November 03, 2019, 10:39:01 pm
content: It depends.Big wound transformer as the power supply? If so then I would keep everything doublish insulated until the transformer and then leave the chassis ungrounded so that ground loops are harder to make; albeit for other people I would recommend grounding the unit instead for safety reasons.Context: experienced horrid ground potential differences in a venue once before, friend shocked his hand when it bridged between the audio mixer & the lighting desk. One point of view is to ground everything to force breaker trips, RCD trips (not in these venues) or set fire to your cables. The other point of view is that the "show must go on", esp if it's a nonprofit school event.Disclaimer: Whales is not a good source of safety advice, he will (where possible) attempt to cause the maximum harm possible and bromeliad cuts his cable ties.

author: nuno
author_rank: Frequent Contributor
timestamp: November 03, 2019, 11:09:39 pm
content: It has a transformer inside, it's all metal closed with just some squares for the wires to pass through.

author: rsjsouza
author_rank: Super Contributor
timestamp: November 04, 2019, 12:00:56 am
content: I don't know about this particular mixer, but lots of vintage equipment that I used and repaired had a thread sticking to the back that was specifically designed to ground the chassis.However, as others have said, grounding is something to be taken with quite the consideration if the equipment will be immersed in a larger venue.

author: nuno
author_rank: Frequent Contributor
timestamp: November 05, 2019, 03:26:50 pm
content: No thread for grounding anywhere on the box.

author: PKTKS
author_rank: Super Contributor
timestamp: November 06, 2019, 10:47:03 am
content: Several good comments... I will just add thatFor AUDIO gear you really want SHIELDING not GROUNDING.If the manufc. already provided a GND - there should be reasonsOtherwise your audio requires shielding and this is not relatedto ground - by no means the EARTH ground which may causeground loops or induce classic hums...Usually your shields refers to the "common" of the devicePaul

author: Marck
author_rank: Regular Contributor
timestamp: November 07, 2019, 10:59:10 am
content: I am very much a beginner and live in a country where protective earth is just the way it isThe issue of ground loops will also depend on what you have it connected to. If the devices connected are grounded to the protective earth also this is where you might run into problems if your interconnects are not floating. You could just use a ground lift switch so that you can isolate the protective earth from the signal ground if you get the dreaded mains hum. This could be a bit of a task isolating everything from the chassis.The other option might be to move the transformer or entire power supply out of the mixer into its own insulated enclosure and just pass the safer voltages to the mixer. This is what I have just done on a valve preamp I only pass 24v to the Amp and the mains potential is kept safe and sound tucked away.M