50Hz hum thru my sub... :(

MikeHunt79 · 21 Jun 2011 at 05:47

Ok, recently I've moved my DIY sub from my computer setup to my HT setup, it's a DIY horn sub which offers good sensitivity, and I'm sure it's not my sub amp (Phonic MAX1500) as with other sources it does not give a 50Hz hum as loud as this.

My HT amp is a Cambridge AUdio Azur, and I'm thinking this is the source of the 50Hz hum, as when I chance from AC3 to PCM the hum goes, and I've tried other sources apart from the Azur and these give less hum.

Is there any way of reducing the hum?

Thanks.

Holwill · 21 Jun 2011 at 07:10

You could look at a ground loop isolator, I run a Motor Factor and have used one of these on my Rel sub inline to stop the humming.

http://www.tech-faq.com/ground-loop-isolator.html

MikeHunt79 · 21 Jun 2011 at 08:11

^Thanks, in fact there is a ground loop isolater in the Phonic amp, I tried setting the switch from 'ground' to 'floating' on the back of the Phonic amp and it did not eliminate the humming.

I'm pretty sure the hum is coming from output of the CA amp, as when I reduce the volume on the Phonic amp, the hum decreases also... I think it may just be a S/N ratio issue.

ANyway, I'm going to try a better interconnect cable, would there be any way of getting a balanced sub output at all as I'm using quite a long (8 metre) interconnect between the two amps?

The 50Hz hum isn't that bad, but a little anooying especially during the quieter scenes in films... so it would be nice to reduce it a little.

Nick1881 · 21 Jun 2011 at 11:19

You could try winding your cable to the sub round some ferrite cores, I read a thread recently where someone was getting interference and that was what someone suggested.

MikeHunt79 · 21 Jun 2011 at 17:02

Nick1881 said:
You could try winding your cable to the sub round some ferrite cores, I read a thread recently where someone was getting interference and that was what someone suggested.

That's not a bad idea actually, I've got a couple of ferrite cores from an old PC psu so I'll give that a go.

Was it the interconnect or the speaker cable itself they wound round the cores?

Nick1881 · 21 Jun 2011 at 22:15

The interconnect AFAIK.

MikeHunt79 · 21 Jun 2011 at 23:22

Nick1881 said:
The interconnect AFAIK.

Thanks, that makes sense. My interconnect is an XLR cable right now which means I'll need a rather large ferrite core in order to fit the plugs thru.

I need to make another interconnect anyway, so when I do I'll be sure to try winding the cable round the ferrite cores a few times before soldering on the plugs.

Finally, I've turned down the sub a little to less window rattling levels, and the hum is a lot less now. You have to be less than 1 metre from the sub now to hear it, so I may just live with it.

It's a real shame that HT amp's don't have a digital output for the subwoofer as this would allow me to use an external DAC with a lower noise floor compared to the CA amp...