Amplifier Hum

[toadtobin]

Just picked up a Crown Amp XLS 402 for 150 bucks used but in like new condition. It's rated 260wpc(1Khz >.5%thd) but I rarely ask for more than 110-115db from my RF-7's so it seemed like a good fit. The amp really opened up my speakers, specifically at the low end. To the point where my sub can no longer keep up w/out sounding muddy at higher spl's. Overall I'm thrilled- however there is a distinct hum/hiss that comes out of my tweeters that correlates with my volume if i have no source material playing. I don't think it could be groud loop hum, since all of my electronics are connected to the same outlet. Do you think this is something that a good line conditioner/better interconnects could clean up, or is it just characteristic of pro amps?

Any ideas would be apprieciated.

Using a Harmon Kardon HK3470 receiver as my preamplifier for now. Hiss was not present when I was using the receiver's onboard amp.

[Guest " "]

don't assume anything....if the amp has a three-prong cord...go down to the hardware store or home depot and buy one of those gray three prong to two prong adapters that have the green wire and plug your amp into it with out connecting the green wire....if the hum goes away...you have a ground issue of some type...

ALso...you should do this with nothing but the speakers connected....nothing at all on any of the inputs.

I once had a situation of a hum that only occured if things with three prongs were connected..even if those things were off.

[HarryO]

One of my PS400's had that same issue. I had to put it on a different power outlet to eliminate the hum. Move the amp power cord and hook up source components one at a time. also make sure your speaker wires are not close to the power cord on the amp. Too many items on the same outlet can cause noise also. You may have to seperate power feeds to your components.

Harry

[toadtobin]

thanks for the suggestions guys. I will have time to tinker later today and I'll let ya know if your advice solved the problem.

[mas]

is it just characteristic of pro amps?

Yes, but only in the really expensive models.

Funny you should ask...

It took the manufacturers years to perfect that feature and each employs their own proprietary circuitry topology which is a highly guarded secret. You will be hard pressed to find this feature in lesser quality units.

[*-)]

[toadtobin]

only in the really expensive models.

Funny you should ask...

It took the manufacturers years to perfect that feature and each employs their own proprietary circuitry topology which is a highly guarded secret. You will be hard pressed to find this feature in lesser quality units.

[*-)]

Grats smartass. I was asking if a small amount of hiss with the volume turned up w/out program material was characteristic in pro amps possibly due to them being rated generally much higher power and used in environments where the higher SPL's render such hiss a non-issue. I was also expecting the possibility of my particular amp being of lower quality. But thanks for the constructive reply. It makes so much sense for me to be asking questions when I already have all of the answers!

[michael hurd]

Pro amps generally require more voltage than a consumer level piece. Try boosting the channel level in you Harman Kardon, and turn the gain down slighlty on the Crown. You may also require a product like the ART Cleanbox. ( device made for boosting up the signal level from consumer to pro-level gear )

Available from most MI / Pro Sound outlets and places like www.partsexpress.com ......

[LarryC]

there is a distinct hum/hiss that comes out of my tweeters that correlates with my volume if i have no source material playing.

Using a Harmon Kardon HK3470 receiver as my preamplifier for now. Hiss was not present when I was using the receiver's onboard amp.

While you need to track down possible hum gremlins as discussed above, the fact that HISS is part of the problem makes me think it's not hum as much as a system gain imbalance issue, i.e., too much gain somewhere in the system. Especially with high-efficiency speakers, it's unlikely that the hiss is coming from the amplifier -- it's more likely your preamp/sound sources. Receivers and integrated amplifiers sort out gain issues internally and don't seem to present such problems.

Michael's suggestion sounds good, try reducing the gain of your Crown to lower the hiss level, and then boost the input level if necessary. I'm a little puzzled that the noise varies with the position of the volume control.

[mas]

only in the really expensive models.

Funny you should ask...

It took the manufacturers years to perfect that feature and each employs their own proprietary circuitry topology which is a highly guarded secret. You will be hard pressed to find this feature in lesser quality units.

[*-)]

Grats smartass. I was asking if a small amount of hiss with the volume turned up w/out program material was characteristic in pro amps possibly due to them being rated generally much higher power and used in environments where the higher SPL's render such hiss a non-issue. I was also expecting the possibility of my particular amp being of lower quality. But thanks for the constructive reply. It makes so much sense for me to be asking questions when I already have all of the answers!

You're welcome.

That's what I thought too.