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Author Topic: Home Theater  (Read 11153 times)

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Online radioman

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Re: Home Theater
« Reply #15 on: February 20, 2016, 03:42PM »
OK, here goes. When interfacing audio components to each other, there are many things to consider.
Impedance: This is the load that one component presents to another. When impedance is matched, gain is consistent, frequency response is flat and noise is more easily controlled.
This being said we come to balanced vs unbalanced connections. In commercial audio, like sound systems in concert venues, balanced systems are almost exclusively used since they fix a multitude of impedance and noise issues, since in a balanced system all component interfaces are based on a standard.
You can use this standard in any audio system and it will have the same effect. The standard allows for balanced and unbalanced connections to "talk" to each other.  Loosely explained, balanced is a low impedance connection, typically 600 ohms,  in which neither side is physically connected to earth ground and unbalanced high impedance, typically around 10K ohms, and one side is hot and the other is a earth ground. Can you see where tying these to each other could be problematic?
Getting clser to the standard involves getting the impedance and physical connections to closely match each other. Sometimes it is a simple as the correct cable or a combination of cable and an adapter. Other times devices called matching transformers, sometimes integreatd into cable and/or connectors are necessary. If your decoder has RCA outs and your SUB amp has a balanced input, you can get a specific adapter for this based on what input connector the sub amp has.
The isolator you used, depending on type may have accomplished some of this and that is why you saw a significant reduction in hum.
Hum can be and is most likely caused by an inadequate ground or what is known as a ground loop. Both of these will be mitigated with a balanced connection.
Lifting a ground on one component or another can reduce noise but it is like a bandaid. By lifting  ground you are eliminating a true path to ground on that device causing a risk of static and lighting damage as well as shock potential if there is an internal component failure.
Give me the model number of the decoder and the SUB amp as well as a diagram of how you are connected and I may be able to make a recommendation on a fix.

Before being a radio guy, in a previous life, I wanted to be an audio engineer. That is actually what I started to go to college for, but got detoured. I still love to play audio man and have built many sound reinforcement systems as well as have worked in the radio and tv field for awhile.

I hope this has shed some light. Complicated subject but not so hard to understand or fix.
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Offline bob

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Re: Home Theater
« Reply #16 on: February 20, 2016, 07:25PM »
Dayton sa1000 amp and a using the lfe output using a Yamaha rx-v677
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Offline bob

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Re: Home Theater
« Reply #17 on: February 20, 2016, 07:42PM »
I did more investigation.  Seems that my dishwasher and fridge are in the same circuit.  Likely the inline isolator is the best possible solution to this hum.  Hoping the power conditioner will pull a miracle.  But the hum is barely noticeable at guapo levels of volume. 

I kind of got the jist of what you wrote.  Originally i was using a straight monster RCA cable for audio connecte to the LFE of the receiver/decoder to the sa1000 lfe input jack.  Then I had to use a splitter to connect the line isolator to the LFE (turn the one connection into two) and then another splitter (turn the two connections into one) into the LFE input of the amp, that is what I have now.  At half the gain the hum is barely noticeable ... I am willing to live with it if the power conditioner does not help.  In the future I think a dedicated circuit for the theater maybe the solution.

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Re: Home Theater
« Reply #18 on: February 20, 2016, 08:51PM »
Since you are splitting the output you might also try a buffer amplifier. It will isolate all the ins and outs and level match them.
I am glad you are tracking it down.
The SA1000 is unbalanced line level only. You could use adapters to make it balanced and therefore increase the signal to noise ratio and noise immunity, but no need if the problem is on the AC power side. I have a power line analyzer if you want to borrow it. Runs on a DOS laptop though  LOL
Let me know how you make out.
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Re: Home Theater
« Reply #19 on: February 20, 2016, 09:31PM »
Is there an easy solution to fixing the buzz issue without floating the ground on a Sampson S1000 amp and a Denon AVR-X2200?

The Denon only has a two prong plug. The Sampson has a three prong that I had to float to get the buzz to stop.

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Re: Home Theater
« Reply #20 on: February 21, 2016, 10:58AM »
S1000 does have a balanced input, denon has a line level high impedance output for sub.
How do you currently have them interconnected?
Specifically what type of cable and connectors?
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Offline bob

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Re: Home Theater
« Reply #21 on: February 21, 2016, 07:48PM »
 :tv2

Project finished

No one would suspect that a monster lurks behind that innocent looking screen.

:D


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Offline cas

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Re: Home Theater
« Reply #22 on: February 21, 2016, 08:56PM »
As someone who studied and build tuned and ported subwoofer enclosures, that whole thing baffles me. It seems so backwards. lol
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Re: Home Theater
« Reply #23 on: February 21, 2016, 09:19PM »
It's connected by an rca to 1/4" old style headphone looking cable (mono), with nothing in between. There is a switch on the amp that bridges the mono input to both channels and each channel has 12" sub connected to it.

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Re: Home Theater
« Reply #24 on: February 21, 2016, 09:22PM »

As someone who studied and build tuned and ported subwoofer enclosures, that whole thing baffles me. It seems so backwards. lol

They can hit super low frequencies that no boxed sub woofer can. Some guys have 4 or 8 subs connected to the manifold. It can get crazy.


Offline bob

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Re: Home Theater
« Reply #25 on: February 22, 2016, 08:25AM »
The great thing of my setup is that my decoder is a 7.2 surround sound.  The subwoofer is on the second LFE port.  Thankfully this mean the sub is not always on and my front ported 12 inch sub is the one driving the action most of the time.  But once in a while when things go boom, or take off like in the movie interstellar the new sub kicks in and wow.  You literally feel the change in air pressure in the room.  I have turned it down somewhat as I am sure that can't be healthy to ones ears.  Now it is still stout, and it complements the front sub to the point it sounds better than any real movie theater I have been to.  Likely because it is a small room and I am in my basement after all. Not much volume of air to play with. 

I followed the specs as close as possible from the article.   Understood maybe 25% of it.  Most of that was just the actual build of the manifold.  I really took a leap of faith, and I got lucky. :D
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Offline xdguy

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Re: Home Theater
« Reply #26 on: February 22, 2016, 09:14AM »
So when is Movie Night?
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Offline bob

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Re: Home Theater
« Reply #27 on: February 22, 2016, 12:09PM »
That is the funny thing.  After building a home theater in an impossible space and spending a good amount of money to make it sound decent, all the movies I can show you can easily view with a $7/month Netflix subscription, and with as good video and sound quality with an iPad plus a good pair of head phones.  No one is really interested, not even my kids anymore, to watch anything down there.  I think the wife watches stuff with me down there out of pitty.  I in the other hand am happy as a pig on shit :D
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Re: Home Theater
« Reply #28 on: February 22, 2016, 12:43PM »
To get the kids down there, you need to put in a concession stand, or at least a popcorn maker.


Now, for the grownups, a fully functioning bar will do.   :wink

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Re: Home Theater
« Reply #29 on: February 22, 2016, 12:57PM »
My home theatre is heavily used, I don't regret the expenditure at all. Luckily I have been able to fight off the urge to upgrade all the time.