Thorens TD 160 "pop" revisited

Thanks for following up! I am sure future 160 owners will find this useful…

I wanted to provide an update on the solution to the pop which occurred on both opening and closing the power switch on my TD 160. This switch works in tandem with the speed control selector. As many have suggested, I had a snubber installed by a friend who knew just what was needed. ( Thank you Sanjib)  

A 0.1 microfarad/450 vdc capacitor was placed in series with a 100 ohm resistor across the switch. This served to prevent the arc across the air gap. 

Problem solved! The pop is gone completely. Thanks to everyone who contributed. 

I hope this information helps others who encounter this issue. 

Apparently, if left uncorrected it will eventually fry the contacts.

Or worse, damage electronic equipment.

We would like to think that the AC or DC power supplies we use to power our circuits are both clean and well-regulated supplies. However, the switching of AC inductive loads or the switching of DC relay contacts and DC motors as part of a micro-controller project all combine to produce a quality of power supply that is difficult to maintain.

These inductive switching transients occur when some form of inductive or reactive load, such as a motor, a solenoid coil or a relay coil, is suddenly switched off. The rapidly collapsing of its magnetic field induces a transient voltage which becomes superimposed onto the steady-state supply. These inductive switching voltage transients can reach the 1,000’s of volts.

Transients are very steep voltage steps that occur in electrical circuits due to the sudden release of a previously stored energy, either inductive or capacitive, which results in a high voltage transient, or surge being created. This sudden release of energy back into the circuit due to some switching action creates a transient voltage spike in the form of a steep impulse of energy which can in theory be of any infinite value.

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transients are bad as they can damage electronic equipment and therefore need to be suppressed and controlled.

Thank you all for very helpful and thought provoking advice. I'm going to ensure there is a proper snubber circuit including a capacitor and a resistor across the switch. Apparently, if left uncorrected it will eventually fry the contacts.

After it's all done, I'll update with details for the benefit of the next poor soul.  😉

A resistor should be wired in series with the capacitor.

“Snubber” Circuit

A sudden rise in voltage across the switch contact caused by the contact opening will be tempered by the capacitor’s charging action (the capacitor opposing the increase in voltage by drawing current).

The resistor limits the amount of current that the capacitor will discharge through the contact when it closes again. If the resistor were not there, the capacitor might actually make the arcing during contact closure worse than the arcing during contact opening without a capacitor!

Here's some discussion of eliminating the startup pop.

Having owned 5-6 TD160's I recall that the circuits can vary a bit (and I'm pretty certain that mine were all original/stock).

https://www.vinylengine.com/turntable_forum/viewtopic.php?t=76532

DeKay

As a rule turn on, (closure of the ON/OFF switch contacts), does not cause a high voltage transient. Opening the switch contact, (creating an arc), causes the voltage transient.

To protect all the audio electronic equipment from the high voltage transient all equipment would have to be powered off. Not just the power amplifier.

As noted, turn on the TT first. Problem easily solved. Then the other way around when powering down.

A couple of snubber circuits to use. Both circuits are wired in parallel with the switch contacts

First is to wire a capacitor and resistor in series and install the two across the switch contact terminals.

Second method is to install an MOV across the contact of the switch.

Application Note: - Inductive Load Arc Suppression - Littelfuse

Apparently I've been told this is what I'm trying to remedy:

Spark Suppression circuits are designed to reduce arcing and noise generation produced in switches and relays. When a switch or relay is opened, an arc can develop across the contacts, which over time can erode the contacts.

I'll just throw this out there: Turn the TT on first.