electrical noise when bridged

[JUV]

Hi All,
I own an Usher R1.5 pwr amp and recently purchased a second amp from my friend, with the intention to run 2x mono amps. The problem i am having is there's the presence of electrical noise some where above 4.5kHz when the amps are bridged. In stereo the noise is none existant even with my ear right up to the speaker. But get this with the amps bridged and i remove any input to them, no noise. It must be the pre amp then right? I remove the pre and connect the cdp to the amps directly and its back again, right its the cdp, swapped this over and its still there. interconnects swapped still there. But the noise comes from both amps bridge with any component connected to them. Could rfi or emi do this or is there more than likely something wrong with the amps? secondly is bi amping or bridged to dual mono better ie bass grip (damping factor) doubled or halfed?

[Zaphod Beeblebrox]

Hi All,
I own an Usher R1.5 pwr amp and recently purchased a second amp from my friend, with the intention to run 2x mono amps. The problem i am having is there's the presence of electrical noise some where above 4.5kHz when the amps are bridged. In stereo the noise is none existant even with my ear right up to the speaker. But get this with the amps bridged and i remove any input to them, no noise. It must be the pre amp then right? I remove the pre and connect the cdp to the amps directly and its back again, right its the cdp, swapped this over and its still there. interconnects swapped still there. But the noise comes from both amps bridge with any component connected to them. Could rfi or emi do this or is there more than likely something wrong with the amps? secondly is bi amping or bridged to dual mono better ie bass grip (damping factor) doubled or halfed?

One question (well two):

* Are the amps designed to be bridged?
* What does the manufacturer say about your problem (Assuming you have bridged the amps according to the manufacturer's reccommendations)?

[JUV]

Yes there is a switch on the back and a wiring diagram near the terminals as well. The distributer is at a loss and the only sevice centre is over east and im in perth. i've tried using standard kettle leads incase it was an earth loop but no glory. and the distributer recommends not taking it to a normal hifi repairer. but they weigh near 40kg each plus the pre amp. it be to much to send east. do you think if it sounds fine in stereo it would be nothing major and a normal hifi repairer would be trust worthy of the job or should i be content and horizontally bi amp the speakers?

Cheers

[Ken]

JUV,

I don’t know the Usher amps, but the appear to be fairly substantial.

I was wondering if the are capable of both Balanced (XLR) and Single ended (RCA) inputs.

If they are, and, you are only using the RCA inputs, have you used shorting pins on the XLR inputs.

I don’t know if this could cause you problem but it would be one less item to consider in fault finding.

Ken

[Zaphod Beeblebrox]

Yes there is a switch on the back and a wiring diagram near the terminals as well. The distributer is at a loss and the only sevice centre is over east and im in perth. i've tried using standard kettle leads incase it was an earth loop but no glory. and the distributer recommends not taking it to a normal hifi repairer. but they weigh near 40kg each plus the pre amp. it be to much to send east. do you think if it sounds fine in stereo it would be nothing major and a normal hifi repairer would be trust worthy of the job or should i be content and horizontally bi amp the speakers?

Cheers

I doubt there is a fault with the amps, as such. I suggest you contact the manufacturer and explain the issue. They may have some ideas.

[Perth-Ed]

Hi JUV,

Be interesting to hear your report back on this.

I can only offer a comparison from my own power amps. In 2 channel mode there is a very low hiss/hum from speakers but i can only hear if place ears near speakers with music paused. In bridged mode the hiss/hum increases maybe 1 - 2 dB (not measured). Certainly nothing that has bothered me. (There may even be a school of thought that says a bit of baseline noise adds a more analogue element, but i wouldn't dare suggest that for fear of this thread veering OT ).

My feeling, not based on any technical knowledge, is the noise you report may just be nature of the amp circuit when bridged. My reading of the owners manual is that bridged mode results in a less effective earthing of the circuit ? ... i could be way wrong though ... which might result in higher baseline noise ? But would expect different circuit implementations to influence.

Zaph and others be kind re my possibly misguided guesses .

Regards,

Ed

[Grumpy]

I did some reading on 'bridged amps' some years a go because i had one (I used it for a passive subwoofer) Most write-ups did mention there could be added noise when 2 bridged amps were used as a stereo set-up. Some do this, some don't
Sorry that's all I know about them except that most bridged amps increase the power output to about triple the normal quoted figures per channel.

[Perth-Ed]

Hi JUV, issue now resolved ?

[JUV]

Wow 2yrs without internet been busy. The buzzing has over the past has been gradually subsiding. Not to sure if im just not hearing it (as in living near an airport) or if its actually getting quieter. I chose to ignore the suspense to findout incase its because i've learnt to live with it. Thank you all. sorry for the late reply...

[Loco57]

Juv,
check a simple thing like lead placement in relation to your power leads, can in some instances induce hum if run in paralel. I run a pair of class A bridged amps and they are totally silent in operation not the slightest mechanical or audible hum. Do you run any sort of power conditioner on your supply? I have noticed with the Shunyata V-Ray unit in line all is very quiet. Trouble is once you hear a problem it tends to multiply until sorted, good luck!