Any cheap solution?

[systemerror909]

I've been using this old, early 90's pioneer VSX series reciever for the past six months. Something that has started to bother me over time is this very soft hum I hear that doesn't seem to change much regardless of volume level. With no signal being input, I can crank the volume up all the way and this humm doesn't really get any louder. All along i've figured this hum was due to the 10 channel graphic equilizer, which I can't bypass. The thing introduces a good bit of noise/static when its even slightly bumped from completely flat.

The friend who gave me the reciever tells me that what I'm describing sounds like i'm getting signal from the powerline, and suggests that a power conditioner should get rid of this. Anyone agree/disagree with this, and if this is the problem, are there any cheap ($50 or under) solutions?

Thanks

[ron.eddy]

Is it a hum as in AC frequency or 60hZ or just a general white noise type of sound. I know my old Pioneer (early 90's) reciever/graphic equalizer/tape deck developed some noise over the years and it wasn't from the power. Not to mention I don't know that conditioning the power coming into the receiver will fix AC hum within the reciever anyway, as this would indicate a problem with either the rectification circuitry or a ground loop problem. Unless the receiver has been taken apart and modified it is unlikely to be a ground problem, unless something happened to the wires (assuming there was no noise when you first got it).

You could always buy a power conditioner from Wal-mart (yea, cheap I know) and try it out and if it doesn't work at all just return it! No questions asked.

But it also could be something as simple as your input cables picking up AC noise. Make sure they are not running parallel with any AC lines behind your setup. Also, external AC-DC transformers are a good source of 60Hz noise due to the switching action of the diodes, so make sure none of your input cables are near them. If any of this reduces the hum at all you have probably found your problems. I have had hum introduced through these ways in the past and clearing the wires (or upgrading to better cables) fixed the problem. Thats my 2 cents anyway.

- Ron

[systemerror909]

A few other things that might have been important to include:

The reciever is not grounded (uses standard 2 prong plug) but does have a seperate connection on the back for this purpose. When I set the thing up it seemed like making the connection would be more trouble than its worth, so I never bothered.

Second, I've connected the speakers with "lamp wire" an improvement I thought would be a step up from the smaller gauge "speaker wire" sold at the local hardware store. I've got the speakers bi-wired, with the lengths of wire being somewhere between 10-12 feet long, with the excess wire coiled. Any chance this is picking up any signal?

Lastly, I'm reconsidering the thought that the noise/hum is from my AC connection because it seems like the frequency is too high. AC hum should be around 60hz right? Well the noise is coming from my tweeters, not the mid/bass driver.

[ron.eddy]

Yea, if it is coming from your tweeter than it is almost surely not AC since most tweeters cannot play that low of a frequency. It sounds like it is just a case of the reciever not being very good (it is almost 15 years old after all!). Chances are the reciever's noise floor is above your level of hearing and the speakers you have hooked up are good enough to play below that noise floor, thus your hearing that noise. Unfortunately I doubt there is really much you can do about this that is worth the effort. Better (read newer) recievers have higher signal to noise ratios and this noise cannot usually be heard anymore.

The lamp cord is probably ok for speaker wire and it isnt picking up AC hum anyway since you would be able to hear that in your mid/bass driver. Just to be sure though uncoil the wire and see what happens. Who knows.

There is the possibility that the noise is being introduced by the crossover in your speakers, but if it just started this is probably unlikely. You could hook up an alternate set of speakers to see if it is quiet then, but even then that might simply mean the alternate speakers are not sensitive enough to play the noise.

Perhaps others on this forum will have some better ideas, as I am not all that good at this stuff. But it may just be time to hang up the saddle on that receiever.

[Dominique]

I'm no expert, but as far as I know, a hum from the power line could also include multiples of 60Hz, up to pretty high frequencies.

I just have to think at how capacitors sometimes degrade a lot over time, so a cap which filters the ac, wouldn't do it's job correctly anymore after years, when a big part of it's capacitamce has gone...

[B Cullingford]

Lets use a little logic
Since the noise is not effected by the volume control it is very likely to be due to circuitry after the vol control, this eliminates the preamp section and input cables, it might not eliminate the graphic equaliser (if you had a schematic it would elimiate some of the guessing)
So lets apply one of the tried and true repair sayings - 'fix the obvious problems first'
In this case the scratchy controls. This is probably just dirty controls, a simple temporary fix is to just exercise them (move up and down many times) - the fix is to spray with a contact cleaner and then exercise. If this does not cure the problem there may be dc on the controls from leaky caps, not as easy a fix.
So:
exercise the controls does this help the scrathyness? And if it does does it also fix the noise - a long shot but worth it.
If it is only noise from tweeter then it is probably not 60Hz related but it may be from the AC mains. Do you have any light dimmers, motor speed controllers, and ... who knows what else, try turning these off or with light dimmers fully on usually works. If it is this then maybe a power conditioner would help. Or try a different AC outlet.
In my present setup I have a buzz from only my left channel when a lamp in the dining area is dimmed - some day I'll get to replacing the dimmer, fixing or modifying the preamp (could it be the one amp but not the other?) or finally building a new preamp.

Hope some of this helps, good luck

Bill

[CBS240]

Originally posted by systemerror909
Well the noise is coming from my tweeters, not the mid/bass driver.

Is there anyway to keep the amp on and connected for a second or two when switched off as the filter caps will maintain bias for just a bit after AC is switched off? Then you can see if the noise is related to the power supply and not the circuit or the pot. Better yet, if you have access to an oscilloscope, you can get a much better idea of the nature of the noise. RF oscillations will make noise in tweeters easily. A noisy PS can trigger instability in some circuits.
Also electrolytic caps can absorb moisture over time and change in value sometimes throwing a circuit out of whack. This once happed to an older TV I have. An electrolytic apperently changed value a bit in the corona circuit causing a shift where the colors showed up on the screen. Took me a while to find it, I had to take each one out in that section and test them all.