DIY Audio Projects Forum

Hum, Buzz and Hiss
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Author:  gofar99 [ 08 Oct 2012, 22:58 ]
Post subject:  Re: Hum, Buzz and Hiss

Hi Mark, Yes hum and noise can come from funny things. In my shop I have to keep projects a little to the right of center on my bench to do sensitive measurements as the proximity to the house wiring will mess them up. If I rotate the project about 60 degrees the hum goes away. Also I just installed two new florescent lights in the ceiling. They are the new type with electronic PS and no ballasts. They send out a huge 43K HZ signal into the AC mains it is so strong it gets through my APC power filter and will cause serious problems with measurements. It will show up as a wide peak about 35 dbv above the average noise (about -95 to -100 dbv). I guess I can do tests by candle light. :D

Good listening

Author:  mwhouston [ 09 Oct 2012, 00:07 ]
Post subject:  Re: Hum, Buzz and Hiss

Good one Bruce (candle light). I know when I built the ZCA, all those years ago, I turned the choke about 30 - 45 degrees off from the Power tranni with the belief the power tranni would induce into the choke otherwise. It seem to work the ZCA is reasonably quiet with only 20,000uf of filtering. And with the choke of course.

Also a lot of my tube builds lately are spread out a fair bit and others remote PSs which I think helps a real lot. With the Silver Dragon only DC enters the amp section. All tubes have DC filament voltages.

Author:  mwhouston [ 14 Oct 2012, 12:33 ]
Post subject:  Re: Hum, Buzz and Hiss

The latest chip amp (LM3875) I built was quite unstable. Through a lot of experimenting to try to get stability I solved the problem with a couple of 4mm X 20mm mild steel bolts. The amp need a small inductor on the output to kill some very high frequency oscillations. These could be heard as a whistling on sibilance and metallic sounds in the upper mid-range. Luckily for me I had made a few turns of 0.4mm pure silver wire the connecting wire from the chip output to binding post only 2" away. I was able to "screw" in the bolt to increase the inductance to something more useful. This has fixed the instability problem and the amp sounds glorious now.

Further steps to help with stability is small bi-pass caps on the feed back resistors and a 150nF cap from speaker binding post to ground, These are yet to be tried.

Author:  mwhouston [ 15 Nov 2012, 19:02 ]
Post subject:  Re: Hum, Buzz and Hiss

I am selling some off my mother's LPs. One collectable is "Elvis Ballads". It is a rare Australia release by J&B. The LP is in pristine condition and so is the cover. I converted it to a 24Bit 96K wav. direct from my phono preamp using a Behinger A2D converter. When I played back the digital copy it had a huge hum.

The A2D has no earthing points so what I did was run a fine wire from the TT earth and wrapped it around the input 6.5mm plug (metal) and plugged it in. This worked by bringing the TT earth and the A2D together. The recording and converted sounds excellent after I ran the Vinyl restoration program over the file filtering out noise below -60db.

Author:  mwhouston [ 15 Dec 2012, 18:27 ]
Post subject:  Re: Hum, Buzz and Hiss

It appears with each new amp or preamp different parts of my house electrical wiring induce clicks into the system. With the recent chip amp, SynergyII\Cu, the house wiring would produce a loud click when I turned off the light in the walk in robes (closet). The new 6N7 preamp picks-up a faint click when I close the fridge door. It seems the fridge light turning off induces a small pulse into the wiring.

Not a amp but a KEF iQ30 speaker (and only one) would click when the house heating turned on and off. I thought there was some residual charge in the amp (6EM7 - Paris amp at the time) that was mysteriously picking-up and electrical pulses and sending them off to the speaker. I disconnected the speaker from the amp to find the clicks, very loud, to continue. Ghost in the machine?? Now with the 807 amp (Luciano) connected to the KEFs no clicks occurs?? Not sure how a speaker can pickup electrical pulse but I suppose the speaker wire is like an areal??

The silver dragon does is not effected by any house appliances nor is the Paris amp. I'm about to complete the C3m preamp. Will the coffee machine become its "click" buddy or maybe the second toilet light switch?

Author:  gofar99 [ 15 Dec 2012, 20:18 ]
Post subject:  Re: Hum, Buzz and Hiss

Hi Mark, it has to be poltergeists. The only way I could get rid of clicks and pops in the stereo was first put it on its own AC circuit and second by using a transformer isolated line filter. Now the problem in my shop seems beyond resolution. Maybe you and I are on exactly opposite places on Earth and there is a phenomenon involving the shifting of the core that causes us grief. :bawling: :D

You can try a trick that sometimes helps. Using a type X2 cap of about 0.1uf and a series resistor of about 100R 1 watt put it across the AC mains near some of the click sources. Since you have 220 VAC you may need to increase the resistor to a higher value if the 100R gets warm.

Good listening

Author:  mwhouston [ 15 Dec 2012, 20:42 ]
Post subject:  Re: Hum, Buzz and Hiss

Funny how each device finds a mains "mate" within the house to which it becomes mutually attached. Every amp I build has power filters. I must say every amp I use power filters on sounds so much better than when I didn't use power filters. Only the first one or two I built didn't have power filters. They only cots a few bucks and very easy to place under the bonnet. They will handle up to 10A so for all my low power tube amps have no impact on mains voltage.

Bruce I must get a direct feed from the switch board. I have two electrician mates so no excuse.

Author:  mwhouston [ 27 Apr 2013, 04:26 ]
Post subject:  Re: Hum, Buzz and Hiss

Spent a few hours with Intermezzo my 1920's tube based amp today to get rid of a slight hum. Follow this thread:

Author:  MikeDavid [ 13 May 2018, 18:52 ]
Post subject:  Re: Hum, Buzz and Hiss

I have built a 4 channel amplifier to use in bi amping my diy hifi 3 way monitors. The amp consists of a large toroidal transformer that powers two yuan-jing 2x150w amp boards. The monitors consist of 7" Seas T18REX coax woofers for mid and high, and 8" Seas H1208 woofers for bass. The coax woofers have their own passive xover and I am using a minidsp 2x4 to crossover the coax and woofer. I have one amp powering the coax, and one amp powering the woofers. My issue is hum when all 4 channels are plugged in. I can have just the coax running and it is quiet, same with the woofers, nut the moment I try to play them at the same time I get hum. Anyone have an idea what is causing the problem? Thank you

Author:  laurie54 [ 14 May 2018, 15:34 ]
Post subject:  Re: Hum, Buzz and Hiss

-- Do you have a separate gnd running to each amp from the input signal point? That makes a gnd loop at the input stage of the amp.
If so, just run one wire (signal) from the first amp to over to the second amp's input and not the gnd wire. The second amp is connected to gnd threw it's power supply gnd already. Hence gnd loop hummmm.

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