Subs, hum and popping

MaxCast · « **on:** 8 Sep 2003, 05:59 pm »

By question is: Do systems that use a passive sub (or two) and a separate 2 channel amp have issues with hum and the turn on thump?

I have a Rava with the Hypex amp and have hooked it up many ways in my system. When I run it through a receiver there is a very slight hum. Tried different receipticals and cheater plugs but to no avail. The hum is only audible next to the speaker and is not much of an issue. I do leave it on all the time to eliminate the power on thump.

When I run it through my Foreplay the hum get worse and again I leave it on to avoid the thump.

So, back to the question. Do systems that use a passive sub (or two) and a separate 2 channel amp have issues with hum and the turn on thump?

Thanks,

Curt · « **Reply #1 on:** 8 Sep 2003, 06:51 pm »

Is the amps power supply analog (transformer, bridge, etc) or a switching power supply?

Curt · « **Reply #2 on:** 8 Sep 2003, 06:58 pm »

My passive sub powered by an external MB-100 has no hum or turn on thump, none what so ever.

All audible hums point to something wrong (ground loop, bad component) or simply a poor design.

MaxCast · « **Reply #3 on:** 8 Sep 2003, 07:40 pm »

Not sure. I can't find the mfgs. home page. This is a link to a discription of the amp
http://www.adireaudio.com/diy_audio/amplifiers/hs200.htm

It seems almost everyone goes through this ground loop hum sometime in their lives, especially with HT and subwoofers. I realy want to have two subs and I was wondering if passive subs with outboard amps have this issue to deal with.

PSP · « **Reply #4 on:** 8 Sep 2003, 07:57 pm »

I have a VMPS New Original Sub, powered by single channel 100w AKSA... no hum and a barely audible turn on thump.

Peter

Curt · « **Reply #5 on:** 8 Sep 2003, 08:17 pm »

Amp description sounds fine, it should be quiet.

Take the ICs out of the sub and plug in a set of shorted RCA plugs in their place then turn it on and see if it hums and thumps out the driver. If not it's not the sub/ amp combo but the upstream components--wires.

Got long unshielded ICs? Maybe running near some power cords? Sounds like your picking up some 60Hz somewhere (the hum) and/or there is a difference in ground potentials between components (could cause the thump). Differences in chassis potentials are usually caused by "leaky" power transformers. An AC volt meter can help find the problem.

Your right, a common problem, and it must be your turn

MaxCast · « **Reply #6 on:** 8 Sep 2003, 09:12 pm »

Quote

Your right, a common problem, and it must be your turn

Thanks for the replies.
A shorted RCA plug. That is a wire going from the center to the outer ring, correct? Do I have to put a resistor in there?

Quote

Differences in chassis potentials are usually caused by "leaky" power transformers. An AC volt meter can help find the problem.

I do have a volt meter. Would you care to give directions?

Curt · « **Reply #7 on:** 9 Sep 2003, 07:26 am »

No resistor is required for shorting the input RCA jack.

When looking for ground loop situations start with the meter in AC volts (start with a high value and work down to a smaller value when trying to make the measurement) and measure between the ground side of the preamps IC (when not connected to the amp) and the amp's input RCA's ground then from chassis to chassis, your just looking for a difference in AC potential (voltage) somewhere in the system that could be generating noise loop currents.

You got to poke around trying to solve these types of problems, good luck.

TIC · « **Reply #8 on:** 9 Sep 2003, 09:39 pm »

Hey MC,

I previously owned a couple of early production HSU VTF-2's that hummed. I spoke with Dr. Hsu and he made a suggestion that solved the hum issue.

I turned the amp mounting upside-down! Literally, I removed the amp and reinstalled it so that the writing was upside-down when viewed from the side!

What this did was move the transformer futher away from the driver in the enclosure.

It worked for me. It is very easy to determine if this is the issue. Just remove the screws that hold the amp in place and flip it around. For convenience, just reinstall a couple of the screws. Now, turn the sub on and listen for a hum. If this resolves the issue, re-insert all of the screws. If the amp is not drilled simetrically, you will need to drill a couple of new screw holes into the enclosure where the amps holes now don't match the original openings.

It's worth a try if you can't find any other resolution...........

Enjoy,

TIC

MaxCast · « **Reply #9 on:** 10 Sep 2003, 10:42 am »

Thanks TIC that is a great idea. But, the Rave is front fireing and the amp in back. I doubt I would gain much distance. Plus the amp has a seal around it as it is a sealed sub. I believe the HSU was down fireing.
Thanks for the suggestion.

I'm actually ok with the receiver hook up (DVD, hi-rez). Most of this hum came with the combination of the Stratos, sub and the Foreplay. It is consistant, doesn't varry with volume.

MaxCast · « **Reply #10 on:** 10 Sep 2003, 03:23 pm »

Would this Van den Hul polarity checker help?

Quote

Due to the fact that most audio equipment in your installation is powered by the mains voltage, an unavoidable hum voltage residual is induced on all cabinets and audio grounds. At all audio devices these residual voltages are of different magnitude (or phase) and will balance out by means of ground currents flowing through the shields of your interconnecting cables.
Generally, these ground currents are in the same order of magnitude as the audio signal currents being transferred (microAmperes), and thus are likely to interfere, thereby reducing transparency and imaging.
With the van den Hul POLARITY CHECKER, you can simply fine-tune your audio system to eliminate, or at least strongly reduce, these residual ground currents and thus improve your system’s performance.

http://www.vandenhul.com/other/c-care.htm#polchckman

Also, I have a 15 amp 2 wire line (three pronged outlet installed) and a 20 amp 3 wire line. Can I connect the ground from the three wire line to the ground on the two wire line? Would this help at all?

Thanks again,

audioengr · « **Reply #11 on:** 10 Sep 2003, 04:14 pm »

Put a cheater plug on the power cord of the sub. If that does not make the hum go away, then you are probably plugged into an outlet with a different phase than the rest of your components.