Electric question, isolated circuits

Richard · Sep 14, 2006

I'm not an electrician and didn't stay at a Holiday Inn last night so I wont be doing ANY of this "myself". I'm asking to try to find out if what I want to do is possible, as was suggested by a friend.

Stereo & "hi-fi" sound along with 60hz hum over the speakers is my concern.

Ok, evidently, you can buy an "isotap" on ebay for $10/$20. This plugs into an outlet and via transformer (I think) gives you a built in outlet that is isolated from the household current BUT won't have as much horsepower as the household outlet will. I guess you lose some 'oomph' during the conversion.

I want to plug some tube amplifiers in and was told this 400Va item won't have enough power for them to work properly. BUT, I was also told, if I "only had access" to some 220, I could split it, invert it or otherwise, do some other magic with it.

By inverting it, I'd negate the 60hz hum and be able to step it down to 110V and be happy.

I've never heard of this so this is all very new to me. I've got some SERIOUSLY efficient speakers that will put out something like 110 db with 1 watt of input. Any kind of circuit noise & hum will be an issue for me.

OK, so here's my scenario, my media room in basement is currently open walls so I can run ANY kind of wire anywhere. Also, I can add a second panel box. Actually, I already WANTED to add a second panel box and have this box EXCLUSIVELY wired to the outlets where I was going to plug in my amps, cd player, tv...

(I've got 3 tube amps and 2 solid state amps and 1 HT amp, BEFORE you then add in CD, DVD, EQ, Expander, TV, Sat receiver)

I saw on internet where you can build a larger isotap

Projects update and iformation page

and before I looked into that, I thought... "couldn't I just push it up the food chain and seperate it at the panel?"

So, my basic question is... from my main panel to the sub panel, is there SOME way, or some item to purchase, that will allow the circuits in the sub panel to be isolated, such that I can minimize hum & circuit noise?

BB_TX · Sep 14, 2006

I am not a sound expert or know what an isotap is. But 60 cycles in = 60 cycles out on a typical isolation transformer. Isolation transformers eliminate/reduce electrical "noise" on the AC sine wave. You are not normally changing the frequency of the AC signal, merely smoothing it out. Maybe an isotap changes frequency but I would think your sound equipment would want to be running on 120 v 60 cycle AC power.
Soundguy, where are you????

schmism · Sep 14, 2006

most 60hz hum is due to blead over from the highvoltage wire to the lowvoltage speaker wire. (ie the amp has little to do with it, Unless you have some spectacualr craptiastic amp) this often occurs when the low voltage speaker wire is run physcialy close (or layed ontop of) normal hosehould 120v wireing.
(this also includes cords on the floor and in that rats nest of wireing in the back of the stereo cabinet)

connect some speakers directly to the amp with small speaker cable runs that dont run through the wall/cabinet.

ie pull the amp out, hooke up 2 speakers and a source and see if you have the same problem

RonMar · Sep 14, 2006

An isolation transformer does just that. it isolates. It's output by design is typically the same as it's input.

60 HZ AC hum is either induced or is leaked/not filtered. Induction is usually because the speaker or amp input wireing is too close to the AC supply wireing. Leaked hum is usually due to poor quality or failed filter capacitors on the amp power supply. When you rectify AC into DC, you take a sine wave and flip all the negative going half-cycles upright. This gives you a series of positive half-cycles one after another. This is DC with a terrible "Ripple". That ripple is fed into a capacitor(or bank of caps) which charge up to the peak voltage and resist pulsing. It is kind of like shooting large pulses of water into a barrel from a hose. Once the barrel is full, the water can be drained off in a steady stream even though the input is pulsed. if the caps are poor quality, failed or not the right size for the application, the pulses going in will still make it out to the rest of the circuitry. There are ususlly many other design considerations inside the amplifier to resist the effects of ripple on the source voltage, but if the amp circuits are being fed too much 60HZ ripple, odds are that this ripple will be applied to the output signal.

If the amps are working properly, the best way to reduce electromagnetic interference is to separate the signals. Since the walls are open, keeping as much physical separation between the audio/video lines and the supply power and room power wireing as possible should be fairly easy.

_RaT_ · Sep 15, 2006

RonMar said:
An isolation transformer does just that. it isolates. It's output by design is typically the same as it's input.

60 HZ AC hum is either induced or is leaked/not filtered. Induction is usually because the speaker or amp input wireing is too close to the AC supply wireing. Leaked hum is usually due to poor quality or failed filter capacitors on the amp power supply. When you rectify AC into DC, you take a sine wave and flip all the negative going half-cycles upright. This gives you a series of positive half-cycles one after another. This is DC with a terrible "Ripple". That ripple is fed into a capacitor(or bank of caps) which charge up to the peak voltage and resist pulsing. It is kind of like shooting large pulses of water into a barrel from a hose. Once the barrel is full, the water can be drained off in a steady stream even though the input is pulsed. if the caps are poor quality, failed or not the right size for the application, the pulses going in will still make it out to the rest of the circuitry. There are ususlly many other design considerations inside the amplifier to resist the effects of ripple on the source voltage, but if the amp circuits are being fed too much 60HZ ripple, odds are that this ripple will be applied to the output signal.

If the amps are working properly, the best way to reduce electromagnetic interference is to separate the signals. Since the walls are open, keeping as much physical separation between the audio/video lines and the supply power and room power wireing as possible should be fairly easy.

Great explanation.

gws · Sep 15, 2006

The 60 cycle hum I would bet is not comming directly from the wiring but from a secondary source. It could also be an issue that you dont have a good ground between componets, you have ffluorescent light transformer, touch lamp near by that is injecting noise.

OKnewguy · Sep 15, 2006

I have worked with audio gear for many years now, on the consummer side and the pro side. The easiest precautions to take (which will take care of 99% of the problems) are:
Use isolated ground circuits: this means a sub-panel with a seperate grounding rod. All sounds circuits also should be on the same phase and keep the sub-panel "sound only".
Keep signal level circuits isolated: from power and speaker circuits. Cross signals at 90 degrees if possible and try and never parellel signal to power (keep 12" or more of clearance, 18" is better). Keep all a/v wiring away from anything with a ballast or dimmer or motor. The main thing here is to keep the signals away from any device that switch or changes electricity in any way. I have a wire tracer (inductive amplifier) and when you wave that thing in the air around different devices you would be amazed at all of the emf garbage in the air.
Keep your ground rods grounded, drought can mess up your ground. Your equipment will try and ground any way it can. Hums are often a result of different ground potential between 2 devices. Then the difference travels across the connecting signal wires. Your devices then amplifies it or projects it or what have you depending on what equipment you are using.
This is just a quick brainstorm of hums and buzzes based off of 20 plus years in the A/V industry. If you have any specific questions, please let me know.
I might not know a lot about tractors, but I know about buzzes.
Dave

_RaT_ · Sep 15, 2006

OKnewguy said:
I have worked with audio gear for many years now, on the consummer side and the pro side. The easiest precautions to take (which will take care of 99% of the problems) are:
Use isolated ground circuits: this means a sub-panel with a seperate grounding rod. All sounds circuits also should be on the same phase and keep the sub-panel "sound only".
Keep signal level circuits isolated: from power and speaker circuits. Cross signals at 90 degrees if possible and try and never parellel signal to power (keep 12" or more of clearance, 18" is better). Keep all a/v wiring away from anything with a ballast or dimmer or motor. The main thing here is to keep the signals away from any device that switch or changes electricity in any way. I have a wire tracer (inductive amplifier) and when you wave that thing in the air around different devices you would be amazed at all of the emf garbage in the air.
Keep your ground rods grounded, drought can mess up your ground. Your equipment will try and ground any way it can. Hums are often a result of different ground potential between 2 devices. Then the difference travels across the connecting signal wires. Your devices then amplifies it or projects it or what have you depending on what equipment you are using.
This is just a quick brainstorm of hums and buzzes based off of 20 plus years in the A/V industry. If you have any specific questions, please let me know.
I might not know a lot about tractors, but I know about buzzes.
Dave

Dave I was ready to hammer you on the ground because of potential ground disparities but then read on to see that you had it covered. Your comments are excellent.

OKnewguy · Sep 15, 2006

Thanks for the compliment rat! In thinking aobut this some more, I thought I should warn that ground problems are strange beast. By taking care care of the installation now, you are way ahead of the game. Nothing is worse then fixing ground problems in old buildings with bad grounds, multiple panels and grounds. Good job on doing it right NOW!
Dave