Ground Loop?

[venomclan]

Hi Guys,
I think I may have a ground loop problem. I recently got a Krell Kav 250a and 250p amp and preamp. When I turn on the 2-channel amp, there is a thump sent through my speakers for a second. What do you think will cause this thump. I had previously had an h/k pa5800 amp and Outlaw Mblocks hooked up with no problems. Is it a ground loop problem? I had heard of others with a similar problem but I don not recall the solution. Any recommendations appreciated. Thanks.
Jeremy

[F1nut]

A ground loop (hum) is an entirely different thing, you don't have that problem. Try doing this, turn on the amp first, wait a minute and then turn on your pre amp. When you turn things off, turn the pre amp off first, then the amp. That should solve the problem.

[gidrah]

Agreed. This is not a ground loop problem. I have an integrated that thumps on power-up. I make sure to turn the speaker switch to "off" before powering on.

[steveinaz]

Many amps have this "thump" you're hearing at power-up, most notably Soundcraftsmen. Perfectly normal. Just stay in the habit of turning your volume all the way down after turning off your system. It's automatic for me as I had Soundcraftsmen amps for 14 yrs.

[venomclan]

Hi Guys,
Thanks for the advise. I have tried a few times to power on the amp first, the speakers thump every time no matter which order I power up. I spoke to Krell and they said it was normal. I am not the concerned with it just as long as it cannot do any damage to my b&w's. Thanks again guys for the input.
Best Regards,
Jeremy

[steveinaz]

The amp will thump each and every time regardless of your "turn-on" sequence; it's a function of the amplifier.

[tryrrthg]

This happens with my amp also, you can just leave you amp on all the time. I've read that you should just leave it on, especially if you use it everyday...

[venomclan]

Hi Guys,
I have heard form many people that leaving the amp on all the time is good. Does an amp eat a lot of electricity when on, but not receiving a signal? My Krell 250a does get warm when left on and so does my preamp 250p. Are there any drawback to leaving the amp on? fire hazards? anything?
Regards,
Jeremy

[steveinaz]

I guess the only drawbacks would be an elevated electric bill and maybe excessive heat. I personally don't do it.

[rlw]

Originally posted by venomclan
[snip, snip]
Are there any drawback to leaving the amp on? fire hazards? anything?
Regards,
Jeremy

Yes. Fire hazard is one of them; it's conceivable that an amp can malfunction and start a fire if left on - and if memory serves me correctly, I've read about it happening to at least one person. Another drawback is that leaving the amp on, and drawing current, keeps it warm - - which dries out the capacitors quicker.

With that said, I leave my amp on quite a bit - I like to fire it up on Thursday, and let it run through the weekend. I find that by Saturday, it's sounding very relaxed.

[anonymouse]

As someone who built amps for a hobby, the thump is mostly likely due to a fairly large capacitor in the output stage of your amp charging at Power on. Yes, that current is going through your speakers as it charges. If your speakers are high wattage, they should not fry, but if your amp is say twice the wattage of your speakers, you may fry em.
The way most consumer receivers and subs avoid this problem is by switching that initial charging current surge into a harmless resistor within the device. The only issue is that involves a mechanical relay switch in the output circuit, which is presumably why high end amps do not do it - they do not want the switch.

Anyway, I am rambling - I hope this helps.

[venomclan]

Hi Guys,
Thanks for the info. Anonymouse you are 100% right. I spoke with Krell and they said my amp has no relay, but also to not leave it on all the time because of the heat it produces. My Krell 250a is rated at 250 watts(8ohm) and 500 watts (4ohm), I am using B&W CDM7NT's for my mains and they are 8ohm speakers rated to handle 150 watts. I hope the power of the amp is not too much. I have heard that Krell power ratings are often underrated, and that my amp might be pushing more power than thought.

I am curious to know at start-up how much power is behind the "thump". Amps usually do not need to output the majority of their power at low volumes or only if there is a sudden need, like an explosion in a movie. Does anyone know how much output the amp puts out when switched on?
Thanks,
Jeremy

[steveinaz]

Don't sweat it brother, just get in the habit of "zeroing" your volume knob after shutdown...

My Soundcraftsmen manual assured me that the thump was both normal and harmless.

[HBombToo]

Originally posted by venomclan
Hi Guys,
Does an amp eat a lot of electricity when on, but not receiving a signal? Regards,
Jeremy

My amp eats 1 amp while idle.:D

Outlaw 770 with massive torroids and caps and at 7 channels what can 1 expect.

HBomb

[polkatese]

I am resurrecting this thread, since my new power amp exhibits the "thumps", since it doesn't employ any muting capacitors to filter, during power on/off.

I am curious if there is documented case(s) in which these thumps cause damage to speakers? annoying? yes, but I can live with that. Turning down the volume to minimum doesn't make it dissapear, and having 7 speakers thumps simultaneously is a bit nerve wrecking..

[phoneisbusy]

The only time I've heard of power on thumps causing damage is in the case of active speakers where there is little or nothing between the amp and the tweeters. Thumps tend to be lower frequency and sending them to an unprotected tweeter will likely cause damage. Speakers with passive crossovers will filter the thump out to the tweeters.

regards

Dave

[McLoki]

My amp thumps on power down to my LSiC, sub, and 4 LSi7's. The amp is much stronger than the speakers are rated for and it does not appear to hurt them in the least. I have not measured the DB of the thump when it turns off but I bet it is about 80db and that should be under 1 watt of power running to them.

It should'nt be a problem.

Michael

[polkatese]

thanks for the info, guys.

[steveinaz]

Won't hurt a thing, relax bubba.