Sub tech help please

[admin_exported]

Here's the equipment (at least the important bits for this thread):

Marantz PM6002 amp
Epos M5 speakers
Epos ELS sub

The speakers are biwired to the Speaker A circuit, the sub is wired to Speaker B.

The sub is a new purchase, and today I've been trying to get it set up properly. Whilst in the process of this, I turned off the Speaker A circuit, leaving just the sub, to hear what it was doing. I was surprised to hear, at 9 o'clock on the volume, that some very high frequency sounds were actually coming from inside the casing of the amp. I turned the volume up a little, just to check that my ears weren't deceiving me (they weren't, it was definitely coming from the amp) and then the amp's circuit protection cut in and shut it down (volume now at 10 o'clock).

I haven't been able to try this with the Speaker A circuit turned on, as I live in a flat and it would be a tad loud. Also the speakers would mask any sound that might be coming from the amp, so I wouldn't be able to tell anyway.

Now, having done a bit of research, I can understand why the circuit protection cut in (I think). The manual for the 6002 says this may happen if it's used with speakers less than 8 ohms, and the sub is only 4.

So, I have some questions.

1) Is impedance cumulative, i.e. will driving the speakers and the sub together present a higher overall impedance figure than driving either individually, say 8-12 ohms?

2) What's with those high frequencies coming from the amp?

3) When I finally manage to get a house rather than a crappy new build flat, and turn turn the volume up a bit, will I get the amp's circuit protection kicking in, or will it be fine? I guess this depends on the answer to question 1....

Thanks in advance for any advice.

 

[Anonymous]

That doesn't sound good to me! Music coming from the amp - that's a new one! I take it you weren't using a turntable, because there will obviously be sound coming from the turntable...

As for the circuit protection - NEVER fear about turning the volume up high...there should be no problem in a normal amp - if the protection cuts in, either you have a short circuit somewhere or there is a fault with the amp (or you have very, very hard to drive speakers!)

The PM6002 is a very powerful amplifier and should have no problem driving that sub! But then again, as the sub was wired in parallel, it probably has literally NO impedence so the amplifier is driving nothing...hard! I mess about with my JVC alot and I can drive 4ohm speakers to their death without a single problem with the amp and it is rated at 8-16ohms - I'm not sure about yours though, I'm not that familiar with the amp...somebody else will know!

 

[Anonymous]

Hughes123:That doesn't sound good to me! Music coming from the amp - that's a new one! I take it you weren't using a turntable, because there will obviously be sound coming from the turntable...

As for the circuit protection - NEVER fear about turning the volume up high...there should be no problem in a normal amp - if the protection cuts in, either you have a short circuit somewhere or there is a fault with the amp (or you have very, very hard to drive speakers!)

Nope, this was with the CD player as the front end. There are no short circuits visible, and this music from the amp disappeared when I unhooked the bananas at the sub end, which would seem to confirm there are no short circuits at the amp end causing this.

 

[Andrew Everard]

Yes I think the protest noises were caused by the amp running into effectively zero impedance, and there should be no lasting damage - that's what the protection circuitry is for.

Running the sub in parallel with the main speakers won't create this condition again, and all will be fine.

 

[Anonymous]

Hughes, Andrew, thank you for your help.

 

[Anonymous]

Just had a look around and you can get that sub for half its retail price on some sites, how are you finding it?

 

[Anonymous]

Well, this is my first, and in fact my first experience of, a sub, since none of my friends are remotely interested in hi fi or home cinema. (Maybe I should ditch them and get some new ones...) So treat my comments with suspicion as they are not the words of experience.

I'm getting on with it very well indeed. It seems to integrate well with my main speakers, in that you don't really notice it until you turn it off. I bought it because I could occasionally hear the lower reaches of some music delving below what my M5s could comfortably produce, and the sub is doing a good job of covering this. I'm currently listening to a bit of Groove Armada and the sub is producing a nice punchy support to the low end without booming at all.

Fit and finish is competent, if unremarkable, and although it's definitely not going to win any beauty contests, it feels solidly put together. Absolute bargain at the current price I'd say.

If you're thinking about getting one, either get it delivered or take someone with you to help you cart it from the shop. At 24kg in the box, it's a bit on the unwieldy side. My arms are still aching 2 days later.