Relay Controlled Power on/off Switch for Drip build

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corgan4321

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Hello,

I've got a couple of Drip EQ1s that I'm finishing putting together. I've got the noise floor down to -88DbFS when I short the power switch terminals on the board which I think I'm pretty happy with. However, with the power switch connected and the wires running all the way over to the other side of the chassis, the noise floor goes up to -77dBFS.
I don't think I can use the regulated 6.3V heater supply unfortunately since I'm using 1.35A of the 1.5 amp regulator already, but since I've got an extra 5VAC on this Hammond X-former, I'm thinking of adding relay control instead of running AC Mains across the whole chassis. I've not worked with relays before so I'm hoping for some input from you guys. Is this sensible? Any specific component suggestions?

Thank you
 

abbey road d enfer

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You need some kind of power to activate the realay. You can't get it from an unpowered transformer. That means you would need to add a non-interrupted source, such as an ancillary xfmr or a battery..
I think you should try to trace where the interference occurs, probably have to move the wires, or use high-voltage shielded cable.
 

corgan4321

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:-X

Duh...

Okay thank you. The interference seems to come from the power switch and wires being near the pots.
I'll look into finding some shielded mains wire.
 

elskardio

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A quick fix you could try.

Take a long piece of hookup wire and tightly wrap it around the full length of your power switch wires.
Then connect one end to the chassis.
 

corgan4321

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Wow that's a great idea. Just did a test and it seems to help a lot!!!
Is it normal for the input transformer/phase splitter to pick up so much EMF from the power line? I'm using a https://www.sowter.co.uk/specs/1475.php for this and the case of it isn't grounded - could this be part of my issue?

elskardio said:
A quick fix you could try.

Take a long piece of hookup wire and tightly wrap it around the full length of your power switch wires.
Then connect one end to the chassis.
 

corgan4321

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I'm down to -89/-90dBFS noise floor with the power switch cable wrapped with some crummy 22AWG strand wire and grounded to the PCB. Considering that's where I was with the power switch not connected I think that's pretty reasonable!

Now, I'm confused why the case of both the 1475 transformer and the 9530 transformer are not connected to ground, the other two smaller cased transformer and inductor are shielded to ground.

Any reason not to solder a wire to the case of these to x-formers and ground them?
 

chrisregent

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Dec 21, 2013
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Transformer case shielding is down to specific requests of the person the transformer is intended for. Souter do seem to not bother grounding the cans because of their intention for the can function but you would have an inter-winding shield that is for RF blocking that would be grounded. from what I have experienced grounding the can is no bad thing but inside a unit it isn't needed unless there are internal issues.
As so shielding requirements for grounding the can vs not grounding the can are different depending on the application.

Essentially you have used screened cable, with the wire wrapped round. For best noise rejection or screening use foil cable but be careful where you ground it.

Remote switching is something i have done a lot of, the use of a module like the TMPS 03-124 is very good, it meets the needs for continuous connection to the mains for low current when "off". Often with modifying terrible racking jobs I use this for a remote mains switch for a higher current supply without having mains to and from the rack. Remember to put a snubbing network on any relay contacts that are switching high voltages or an inrush limiter on transformer power switching.

 

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