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Hiss / Noise

38bass

38bass

Dec 7, 2008
99
2
Edmonton, Alberta, Canada.
#1
Hi, I've tried looking at all this FAQ material and still don't see what I'm looking for (Could be blind :hmm:).
I bought an 08 S.W.R. Redhead and holy crap does it ever have a lot of hiss coming out. :confused: If I reach to the back and dial the horn out it's less pronounced (as with the treble control on the front panel too). It does not seem to matter where I plug it in (A.C.) it's always there. This is without any instrument connected, when I plug my Bass in it's even louder :crying:(and yes I've changed the battery in my active bass).
:help:
 
#3
I figured this is a good space to make a comment on amp noise. In my dining room, the main power comes in from the meter under the floor in a crawl space and then down into the basement and the service panel.

The room also has a couple romex runs under the floor along the joices to the rear wall where there are electrical outlets. In the ceiling is a run that provides power to the outside lights and the single ceiling light.

When near ANY of these lines especially the MAIN POWER FEED for the house the bass inductively picks up the hum. When cranked this HUM is massive. By rotating myself and the bass 90 degrees to the power lines I can effectively nearly cancel the 60 cycle hum.

Practice space needs to be without power wiring running above and below where you are standing, it takes a lot of fun out of things.

HISS? That sounds like a severe internal issue especially with nothing plugged into the jack. BOB
 
#5
Swap the ICs in the circuit. There are about 8 of them, TL072. The amalgmated effect through the circuit is quite a bit of noise /hiss.

Use a better spec. IC. eg. NE5532 or OPA equivalent. Your noise floor should drop by about 10dB.
 
#7
rbonner said:
When near ANY of these lines especially the MAIN POWER FEED for the house the bass inductively picks up the hum. When cranked this HUM is massive. By rotating myself and the bass 90 degrees to the power lines I can effectively nearly cancel the 60 cycle hum.
Click to expand...

I wonder if what you're experiencing is inductive pickup from the amplifier power transformer. What kind of amp? I'm surprised that power wiring can give off fields like that, considering that there are two conductors carrying equal and opposite current, very close to each other. But I have definitely experienced the hum pickup from an amp.
 
#8
I'm currently running 4 SVT-4PRO's in parallel each to their own cabinets. My house service is a 200 amp service in PVC not steel and when I stand near or over the service run and the bass is in line with the pipe the hum is about 1/8 th power. When I turn 90 degrees it completely nulls.

This phenominum repeats anywhere along the service run. Why is this so unbelievable? Its AC and basic magnetics. The higher the current flowing through those conductors the higher the field.

I doubt the light duty power runs are being picked up, especially with no current flow through them. But I can't tell as they are all parallel with the main power. When turning 90 degrees across them the signal nulls but this effect even though 15 feet from the main power run could still be happening.

Makes me think though... I have installed nearly 200 power services in houses while working as an electrician. (I worked as an electrician while I was building flight hours to be a professional pilot) and in all those services we used PVC to run all the services. It wasn't until I was watching that GHOSTHUNTERS show on the SCI-FI channel and them walking around with EMF meters. I said yeah right... Come on... Then I started thinking about 60 hz fields and how far they might actually radiate. The more current in the wire the stronger the field and I suppose my house is drawing at least XX amps most of the time with somebody home. I know with the amp running at full power I peak 30 amps per leg on a 250V circuit.

Remember those are parallel conductors not twisted pair in that pipe. There is no common mode rejection without them being a twisted pair.

My PhD is in Physics with my specialty in this sort of thing. My thesis was "Passive reflectors in space communication", funny that I didnt apply the effect until I had it actually happening in my house. But as has been mentioned a guitar pickup is a magnetic antenna, an active pickup is even an amplified antenna... With the amp and speakers the receiver and since 60HZ is audable provides detected output of that antenna. BOB
 
#9
synaesthesia said:
Swap the ICs in the circuit. There are about 8 of them, TL072. The amalgmated effect through the circuit is quite a bit of noise /hiss.

Use a better spec. IC. eg. NE5532 or OPA equivalent. Your noise floor should drop by about 10dB.
Click to expand...

I call BS. The noise floor difference between a TLO72 and the "gourmet" audio opamps is nowhere near that extreme, and it will vary in different implementations. Additionally, there are thousands of devices using TLO72's which do not hiss in the horrible way he describes, so blaming the IC's is misguiding him away from whatever the real problem is.
 
#10
TL072 have been known to get noisey after many years of service (and some abuse). I used some upgraded IC's in my 800rb, more headroom, slightly quieter, better frequency response. The noise difference was not huge over new TL072's, but noticable (-91db TL072, -97db with Burr-Browns).
 
#12
rbonner said:
I'm currently running 4 SVT-4PRO's in parallel each to their own cabinets. My house service is a 200 amp service in PVC not steel and when I stand near or over the service run and the bass is in line with the pipe the hum is about 1/8 th power. When I turn 90 degrees it completely nulls.

This phenominum repeats anywhere along the service run. Why is this so unbelievable? Its AC and basic magnetics. The higher the current flowing through those conductors the higher the field.
Click to expand...
Ah, the service run. That might be the case that I had not considered. I can't remember. Is that a two- or three-wire run from the pole to the house?

I will try it myself, though all of the original wiring in my house is in hard pipe. I have a Fender Mustang with single coil pickups, that really enjoys stray magnetic fields.
 
#13
Actually I'd recommend trying the TLE2072, which is supposed to be the replacement for the TL072. It will be less noisy and has a better chance of being compatible with your amp circuit. It worked with my Thunderfunk when some of the other chips I tried did not work. I think it has to do with the input offset and bias current spec of the TL072 being very low and the other chips being many times higher.

The amount of hiss and noise tolerance, as I have found, varies quite a bit between people. It bugs some more than others. The TLE2072 definitely cut down on the noise and not by a small margin. Noise is added and multiplied by the number of gain stages the signal goes through and by the gain in each stage so by replacing your opamps with quieter ones, you can potentially cut down noise by a significant amount. The reason why the TL072 is acceptable in many circuits noise wise depends on how many gain stage the signal goes through and the tolerance of the end user.
 
#14
The wiring in the pipe is two hots a neutral and a ground wire to the ground rod. Three off the pole. Yes the metallic conduit would be grounded and should shield it to radiation more than mine is doing here. Which is nothing.

My house has an addition on the back, the service is mounted on that addition. To be code the panel has to be within 5' of the actual entrance to the house off the meter. In my case it's about 12 feet. So I have whats called a meter main... Its actually a meter with a MAIN BREAKER and mine has room for 8 circuits in it. Then it comes off that buss and heads for the main 200 amp panel in the basement. It runs 10 feet across the floor joices into the basement and down into the panel a 12 foot run.

Its all OO wire cept the 4ga ground run. Pretty hard to twist those three cables, ha.

Its a real pain working with 2" conduit in that situation when schedule 80 on the outside and schedule 40 PVC on the inside is all that is required. I didnt even think when I installed this stuff that I would be putting the amp which takes up a whole end wall of the dining room in there in the first place.

Lets just say I'm not dancing around in there when playing the thing. As any movement UNNULLS the signal.

I won't be doing anything about it, as when I build the studio I will have a concrete floor in there covered in carpet and won't put any power through it and if I do it will be in conduit and not the power service.

I just wanted to mention to everybody what effects I am having here and amp noise is quite possible due to your environment. Somebody who wasn't electrical or electro-mechanical might not understand what was happening.

I'm just suprised it is so loud... BUT THEN I am amplifying with 4800Watts of amp. Even when just practicing there is the hum there. Fortunately it goes down with the Bass volume knob to very reasonable levels. I also only need to turn one amp on which also cuts the zoom down too.

I will have to pick up another amp head for the 410HLF cab and I can put that in the living room, thats where I had the old combo amp. BOB
 
#15
bongomania said:
Sounds like a QC problem- I'd take it back to the shop, or call SWR service.
Click to expand...
+1 Had an SWR SR and it was whisper quiet; I don't think the LMII was that quiet. They're intended for studio use; have a kill switch for the fan in case you want to mic the cab in the studio. SO - long as you're sure it ain't the house wiring (eg, lug over to a friend's house)...goes back under 5 year warranty.
 
#16
bongomania said:
I call BS. The noise floor difference between a TLO72 and the "gourmet" audio opamps is nowhere near that extreme, and it will vary in different implementations. Additionally, there are thousands of devices using TLO72's which do not hiss in the horrible way he describes, so blaming the IC's is misguiding him away from whatever the real problem is.
Click to expand...

Call it BS if you will. I've modded several SWRs that way with desired results. The NE5532 is hardly a gourmet chip, but used cumulatively in your typical SWR circuit the noise floor drops. I am certainly not advocating a magic chip replacement and am making a suggestion against a known circuit.

So call it or smell as you will but unless you have tried it, stuff the BS up your own nose.
 

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