System Sum - at a loss...

[barryb5]

Hi,

So, after electing to add a sub to my setup, I've found I now have some nasty 60 cycle-like hum when I select 'phono' setting on my amp. The hum is only present with the sub connected to my amp i.e. If I unplug the sub, the hum disappears. In fact, even with sub powered off (yet still plugged in) and connected to the amp, the phono channel still has hum present.

I've tried different RCA cables between sub and amp but to no avail. I've also tried using different plugs in different areas of room but also to no avail. On all other inputs, e.g. cd/ optical etc, the sub works fine with no hum present.

A cheater plug tried with both sub and turntable did not elicit results.

My TT is a debut carbon for what it's worth.

To surmise, the turntable/ phono input only has hum present when the sub is connected to the system. The sub on all other inputs causes no hum, and the phono/ turntable without the sub connected produces no hum. Hope that's clear!

Many thanks for any insights, it's driving me nuts...

 

[barryb5]

I should also note ground wires between turntable and amp have been connected properly as well unconnected to examine resulting effect. Note, it's way worse when unconnected!

 

[everettT]

Can you move the sub or phono power cord onto another circuit. Are you using a power strip with both 3 prong and 2 prong plugged into it?

 

[barryb5]

The power strip is all uk 3-pin plugs, bar the sub, which is a 2-pin US going into 3-pin adaptor.Could this be affecting it?

I haven't tried plugging the turntable into another strip - it wouldn't be exactly easy to do or sightly but I'll certainly try it. Thanks for the reply.

 

[Dan Madden]

Fascinating !! Sounds like your sub really does not like the turntable for some reason. How close is the sub to the turntable? A turntable's MM/MC cartridge is a pretty sensitive element. Have you tried plugging the sub's power cord into a completely different power socket than the rest of the system?

 

[barryb5]

Fascinating !! Sounds like your sub really does not like the turntable for some reason. How close is the sub to the turntable? A turntable's MM/MC cartridge is a pretty sensitive element. Have you tried plugging the sub's power cord into a completely different power socket than the rest of the system?

Hi Dan, I have done so, within the same room. The sub is positioned under the turntable, separated by perhaps 2 feet vertically. It's not ideal however living arrangements make it so. I have tried moving it away by up to about six feet just to test your hypothesis, and unfortunately the hum remains...

 

[barryb5]

This, from the sticky on ground hum, seems pertinent to me, however I am unsure how to apply it in real world terms to my set-up (I must confess here to this kind of thing really not being my forte...)

First of all, a ground loop has one and only one causation. It is a voltage potential between grounds. This way currents flow along your audio cables between the grounds, and it does not take much to induce hum. That is the cause, and the ONLY cause.

So ground loop problems are solved by removing and interrupting grounds, and NOT adding them.

So, with this in mind, how might I do this with my set-up? It's fairly simple - a TT, an integrated amp, Chromecast audio, sub, speakers.

 

[Dan Madden]

Even though it made no difference in the hum problem, having the TT so close to the sub is a REALLY bad idea!! Did you try plugging the sub into a different socket??

 

[Latent]

If you have tried all other solutions and swapping power cables in all combinations possible and can't avoid the issue then another method is to get a wireless 2.4ghz audio transmitter for the SUB. This avoids the ground and signal wire connected between the other gear and the SUB so there should be no ground issues then. To test this will work just pull out the signal cable and see if the HUM stops. Other great feature is you are now free to move the sub anywhere you want to get it further away from the turntable which will get vibrations from the sub output which is not ideal.

 

[everettT]

Fascinating !! Sounds like your sub really does not like the turntable for some reason. How close is the sub to the turntable? A turntable's MM/MC cartridge is a pretty sensitive element. Have you tried plugging the sub's power cord into a completely different power socket than the rest of the system?

Even though it made no difference in the hum problem, having the TT so close to the sub is a REALLY bad idea!! Did you try plugging the sub into a different socket??

Your instance about another potential problem does nothing about the OP. Once the product that is causing the loop is identified, then and only then is your suggestion possibly relevant. Run the sub to a different circuit, if there is no hum, hiss, feedback etc, then we can visit placement issues of the table;if any

 

[TLS Guy]

The power strip is all uk 3-pin plugs, bar the sub, which is a 2-pin US going into 3-pin adaptor.Could this be affecting it?

I haven't tried plugging the turntable into another strip - it wouldn't be exactly easy to do or sightly but I'll certainly try it. Thanks for the reply.

I think this is where your problem lies. Why is the sub 2 pin US and the rest of the system UK MK plugs. I assume you are in the UK on the 240 volt system. What sort of adapter are you using?

What strikes me is that hum is only induced in the high gain turntable RIAA circuit.

Now that hum only exists connecting the sub which you say is 2 pin and has no ground.

I strongly suspect that the live and neutral are reversed in your sub hook up.

Neutrals and grounds are connected at the panel.

You need to check that your sub is properly connected to the mains. Reversing the neutral to a switching power supply, or any other double insulated device is very dangerous and will cause problems.

 

[barryb5]

If you have tried all other solutions and swapping power cables in all combinations possible and can't avoid the issue then another method is to get a wireless 2.4ghz audio transmitter for the SUB. This avoids the ground and signal wire connected between the other gear and the SUB so there should be no ground issues then. To test this will work just pull out the signal cable and see if the HUM stops. Other great feature is you are now free to move the sub anywhere you want to get it further away from the turntable which will get vibrations from the sub output which is not ideal.

That's certainly an interesting suggestion - I didn't know of such a device existing, will definitely investigate.

I think this is where your problem lies. Why is the sub 2 pin US and the rest of the system UK MK plugs. I assume you are in the UK on the 240 volt system. What sort of adapter are you using?

What strikes me is that hum is only induced in the high gain turntable RIAA circuit.

Now that hum only exists connecting the sub which you say is 2 pin and has no ground.

I strongly suspect that the live and neutral are reversed in your sub hook up.

Neutrals and grounds are connected at the panel.

You need to check that your sub is properly connected to the mains. Reversing the neutral to a switching power supply, or any other double insulated device is very dangerous and will cause problems.

TLS Guy, the sub is an SVS SB1000. It's a 240v version (bought from their EU dealer - I'm in Ireland which also operates at 230v). It came with a 2-prong plug that I have going into 3 prong adaptor, so I assumed this was now grounding it, perhaps wrongly? Could it be that my adaptor doesn't actually provide the ground? I've tried it without the plug adaptor too (not recommended, I know...) and the result was unchanged.

When you say my live and neutral reversed, what does this mean? For dummies, please! Thanks for the input guys.

 

[herbu]

the sub is an SVS SB1000. It's a 240v version (bought from their EU dealer - I'm in Ireland which also operates at 230v). It came with a 2-prong plug that I have going into 3 prong adaptor

Have you contacted SVS directly, (not the dealer)? They are very helpful and may have some insight.

 

[barryb5]

I have. After a bit of back and forth they laid blame with the TT and reckon the sub is operating as it should be.

 

[TLS Guy]

That's certainly an interesting suggestion - I didn't know of such a device existing, will definitely investigate.


TLS Guy, the sub is an SVS SB1000. It's a 240v version (bought from their EU dealer - I'm in Ireland which also operates at 230v). It came with a 2-prong plug that I have going into 3 prong adaptor, so I assumed this was now grounding it, perhaps wrongly? Could it be that my adaptor doesn't actually provide the ground? I've tried it without the plug adaptor too (not recommended, I know...) and the result was unchanged.

When you say my live and neutral reversed, what does this mean? For dummies, please! Thanks for the input guys.

This is the UK MK plug.

3). Green is the ground.

2). Blue is the neutral. It carries no voltage. This line is connected at the panel to ground. It is NOT a chassis ground!

5). Is the live line, and is fused in the MK plug. It is HOT and the voltage goes 120 volts above neutral and 120 volts below neutral, to give you 240 volts AC. Actually the peak to peak voltage is a little higher than that. 240 volts is the root mean square voltage.

Here is a US AC outlet. It is 120 volt.

Now here is a picture if a US two pronged AC plug that should be on your sub.

Note that the prongs are different and the plug can only be inserted into the outlet one way round.

The prong with the bumps at the end is the neutral and the other live.

So the prong without the bumps should connect to the fused leg 4/5 of the MK plug and the one with the lobes to pin 2 of the MK plug and outlet, in other words the non fused side.

Now much equipment like your sub is not intended to be connected to ground, to avoid ground loops. The equipment is what is known as double insulated. However it is vital that that the correct pins be connected to live and neutral as otherwise there will be problems and a severe electrical hazard, not excluding severe equipment damage under fault conditions and also the possibility of electric shock.

So you need to use an ohm meter to make sure your sub is correctly polarized.

If the plug on your sub is NOT of the polarized non reversing type, then the agent/importer has done something very improper. In addition your adapter that connects to the AC plug must preserve correct polarity.

This is something that it is vital for you to check very carefully.

 

[TLS Guy]

I have. After a bit of back and forth they laid blame with the TT and reckon the sub is operating as it should be.

Nonsense. If the high gain turntable only hums when the sub is connected, there is something wrong with the sub or more likely as explained above an improper connection to the mains.

I suspect that the agents put that AC plug on the sub and they are Wallys. What your sub should have on it is an MK plug that you can not unscrew from the lead and a plastic non conducting ground pin. That is code for European countries that use the excellent MK plugs.

This is the plug your sub should have.

For the benefit of US readers following this thread, the reason for the plastic "ground" pin for double insulated devices is that the MK plug is inherently child proof. The grounding pin is longer than the live and neutral pins. It moves the inside cover that shields the neutral and live pins from children. Nothing can be inserted into the live or neutral sockets unless the longer ground pin is inserted.

Your set up at least is not to code, and is likely not proper, the cause of your problem and is in any event at least a child hazard and probably worse than that.

The improper plug was either put on by SVS or the importer/agent and needs correction.

 

[barryb5]

Appreciate the comprehensive reply, TLS Guy. The plug supplied is of this variety, EU two pin I believe...

https://en.wikipedia.org/wiki/Europlug

An ohm meter is not something I have to hand, though I'll make enquiries to see if I can sort out something. Have a friend who may be able to assist.

Thanks

 

[barryb5]

I should note that the plug lead itself is detachable - I could just replace it with a three pin type detailed above if that's a likely solution?

 

[macddmac]

Does the sub hum without turntable connected and phono selected?
There's a huge thread on AVS dealing with debut hum.
Cheers, Mac

https://www.google.com/search?q=pro+ject+debut+carbon+hum&ie=UTF-8&oe=UTF-8&hl=en-us&client=safari

 

[barryb5]

Thanks Mac, yes, have read about the debut carbon hum problems before, but in this instance it's not the turntable.