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I recently acquired a new, very high-end Swiss-made stereo amplifier. I've tried using the amplifier with three very different SS preamps and four very different sets of interconnects. With any of the ICs and preamps, the amplifier emits 60 Hz hum through the speakers.
Among the (unsuccessful) measures I've taken in my efforts eliminate the hum are the following:
(1) use of various power conditioning products
(2) lifting the ground on the amplifier with a cheater plug (not advisable, I know, but I tried it anyway)
(3) connecting the amplifier and preamplifier with a grounding wire
(4) lifting the ground on the preamplifier
(5) moving the amplifier to different electrical outlets
(6) cutting breakers to everything in the house except the audio room power outlets
(7) plugging amp and preamp into the same outlet
(8) cutting CATV connections to all devices in the home
The only thing that eliminates the hum is disconnecting at least one of the ICs from the amp or preamp. (Inserting shorting plugs in both RCA inputs eliminates any trace of hiss, too, but there's no hum when no RCAs are connected.) The hum persists regardless of whether the connected preamp is plugged into the wall, powered up, or connected to other devices.
I've contacted the manufacturer directly and am waiting for a response. It seems to me that the amplifier must be defective.
Before I send this thing back to Switzerland, does anyone have other ideas about what the problem might be?
Follow Ups:
Mine was also fixed. Evidently rearranged the ground connections. a 5 min mod. The amp sounds great and is dead quite now.
Thanks,
--Ze'ev
PROBLEM solved:
Goldmund/JOB acknowledged a problem with the initial run of JOB 225 amps. The company was very quick to address the problem, and I received mine (in the U.S.) just a couple of days after sending it off to Switzerland.
The sound of this amp without the noise is phenomenal. Many thanks to those who offered advice.
Did this get resolved. I posted a similar problem not realizing this thread was happening. With my unit it's not so much a hum as a low level buzz.
http://www.audioasylum.com/cgi/vt.mpl?f=amp&m=186811
Thanks,
--Ze'ev
Edits: 06/23/13
...is not only to prevent different ground pot. between components, but also to make it possible to reverse hot and neutral. Not all cheater plugs allow this because of the 'blade's width difference.
In Europe you can plug any component in either way, but only one way is optimal and yields least potential from ground to the ground plane of the components.
Try the cheater plug again, and try plugging it in upside down (if the design of the cheater plug allows it, that is there can't be a wider blade on one side and not on the other).
However, some components must be grounded so doing so could be unsafe in the long run (even if the strategy works).
My Naim gear always said 'must be earthed' on the back.
Also, your amplifier may be a fully balanced design and using SE connections might foul that up. What amp is it?
If the amp would invert phase they may have swapped the + - at the RCA??
Or the amp has reversed AC input?
I have a very minor hum in my system. And initially I thought it was the amp/preamp/cables/etc.
Turns out that my CDP has an issue. When I switch "off" the CDP, the hum goes away. When I connect a different CDP, there is no hum.
Just a suggestion.
Thanks, milpai--I've tried this and just about every usual step. Still haven't figured it out. I suspect something is wrong with the amp internally.
that did the same thing, 60 cycle hum through the speakers. I tried everything and nothing worked.
I was in Northern Manitoba and sent the amplifier back to Winnipeg 4 times. The last time, the service department manager checked it himself. He used a small rubber rod to tap on the internal components of the amplifier while it was in operation.
The problem was a heat sink shield that was a bit loose. Once tightened up, there was never another problem.
It was a long, drawn out and very frustrating experience. I hope yours goes better.
Plug the amp and pre into a grounded power strip.
Still hums? Repair the new amplifier.
No hum? begin connecting one source component at a time to the pre and the power strip until hum is present.
If the units are under warranty, first email the manufacturer describing your ground loop/hun issues. He may have solutions better suited to your specific setup.Other than that --- I would not mess with any intermal wiring or adding any component not recommended by this manufacturer.
"Fait Dans Suisse." Signifie D'habitude l'article coûte cher.
It should work to your satisfication. Out of the box.
Edits: 06/16/13
Thanks, Fender--I concur. Manufacturer has not been helpful thus far.
Parfois, vous reçoit meilleur réponse de petit étranger fabrica.
Gut Gluck!
If you touch 1 or both RCA input plugs (while the amp is on/playing) with your fingers --- or even get close with them--- what happens?
a. Nothing
b. The hum goes away.
Observe, before you think. Think before you open your yap. Act on the basis of experience.
(a) Nothing happens.
The noise occurs if and only if both ICs are connected to both input jacks on the amp and to one device on the other end. Makes no difference what the other device is or, as I just discovered, if the ground is lifted on one IC.
I was talking about touching the RCA plugs with your hands while the unit is playing. Does it make the hum go away? That's not the solution. It's an indication of a faulty ground connection (bad joint) somewhere.
Observe, before you think. Think before you open your yap. Act on the basis of experience.
Nope. Problem is still there when I touch RCA plugs with my hands.
Have you tried:
Different IC's?
A different preamp?
A source connected directly to the amp?
Yes, all of the above. No success.
Try a length of 12 or 10 gage Romex, single wire. Strip back 1" on each end and insert inside the center of the RCA female plug only, into the pre and the amp, eliminating the outside ground at both ends. If you still have a hum, there is a problem with the amp.
Opus 104
Yep. I've also tried grounding everything "through" the preamp. No difference.
A basic test
how does it sound with no preamp?
and with no sources?
charles
With no preamp and no sources, it makes no noise.
It makes noise only if there are two RCA cables plugged in, and both are running to the same preamp. Changing out the preamp makes no difference. Unplugging the preamp (or powering up the preamp) makes no difference. If either RCA cable is disconnected, the noise disappears.
It might be interesting to put an ohmmeter between the 2 RCA socket shields on the amp, and between the 2 RCA sockets on the preamp. Most gear has a common ground for both channels. If that's the case, you could try breaking the shield connection on *one* IC at one end (preamp end probably best, but try it both ways and see.) You'd still have a full signal path for both channels and both channels' ICs would be shielded.
If your amp has separate grounds for each channel, see what the amp people have to say.
The third possibility is that either your preamp or amps have separate grounds for the circuit and chassis. If that's the case, talk to them - they should be able to figure out how to get rid of that hum.
If all else fails, hit it with a hammer. It never helps, but can be very satisfying in an expensive sort of way.
WW
New Orthophonic High Fidelity
Please ignore my question about the ohmmeter. The RCA grounds on my amp have continuity, and the RCA grounds on my preamp have continuity.
Just to confirm that I'm understanding correctly, you suggest I cut the ground connection on one of my RCAs to see what happens?
Go ahead and try the cables with the shield connected on one cable only.
An guaranteed absolute fix would be a 1:1 isolation transformer between the amp and preamp.
Rowland Research actually provided sockets in some of their preamp models for just this purpose. A transformer can provide other benefits as well as the elimination of hum.
"the transformers provide true galvanic ground isolation. A virtually infinite impedance between any ground noise and signal is achieved, as well as the buffering – or fire wall – between the output circuitry, and any RF or EMI which could enter the output connectors."
A 'good' transformer may be had for about $30 (Edcor), the 'best' may cost $200+ (Jensen, Lundahl, etc).
I agree with DJK, the Jensen transformers have been the answer to all of my hum and noise problems for many years with a verity of components, both SS and tube. They might seem a bit costly, but they can remove a lot of frustration in set ups.
Good luck, RD
I just tried disconnecting the shield on one IC. No luck.
If I disconnect either interconnect from the amp, the problem disappears. It's a stereo amp, though, so this defeats the purpose of owning it.
Just buy a transformer and be done with the problem.
I'd try lifting the ground at one end of 1 IC. As your grounds are common, you'll still have a full signal path to both channels. If the hum goes away, I can't quite explain it...
And you get no hum with just one IC connected, and you've tried both ICs singly? It's a perplexion.
WW
New Orthophonic High Fidelity
Thanks, Bill. A couple of amateur questions:
What should I see on an ohmmeter if there is a common ground for both channels?
And if I cut the shield connection at one end of an RCA, will the signal be able to pass through the cable?
If the grounds are common, the ohmmeter will read zero across the 2 RCA socket grounds of the unit.
And if they are, lifting the ground at one end of 1 RCA will still let the (common) ground on the other function as the return for the 2 channels.
The other thing to check, just to start to understand what's going on, is to put the ohmmeter on an RCA ground, and on the chassis. If it's zero, which is most common, then the unit uses one ground for both the chassis and circuit. If it's high or infinite, then the unit has separate grounds for the circuit and chassis, which is rarely the case, but might help explain the problem.
WW
New Orthophonic High Fidelity
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