Connecting multiple inputs into Lepai 2020A+ cause level of some to drop - AVS Forum
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post #1 of 13 Old 05-14-2013, 10:19 AM - Thread Starter
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Howdy,

Thanks to all for the advice already present, they've helped me delve into the world of sound a little bit. My apologies if this is long

I have a a little Lepai 2020A+ amp, which has two inputs in the back, a 3.5 and RCA, which are both on at the same time.

I'd like to hook up audio out from the tv (RCA), line out from a computer (3.5), and line out from a homelink bluetooth music adapter to the Lepai, using a splitter to hook up two inputs into the 3.5 jack.

I'm able to hook up the computer line out and the TV line out through a splitter into the 3.5 jack, and they play back normally, with the level of one dropping a very tiny bit when the other source is hooked up, not really noticeably.

However, when I try to hook up the bluetooth music reciever to the RCA inputs on the Lepai, so that all three are hooked up at the same time, the level of the TV and Computer inputs is reduced to barely be audible with the volume fully turned up, even when the bluetooth reciever is not playing anything.

When I use the bluetooth reciever to stream music through the amp, however, it plays back at a more normal volume.

Using RCA to 3.5 cables, I've varied what is connected to what, like having the Bluetooth and TV connected to one input port, the Computer to the other, and other such combinations, but it really seems as though connecting the Bluetooth reciever is causing the level of the other inputs to be reduced.

Why might this be happening? I'm just starting to learn about the electronics, but would it be the case that the Bluetooth reciever line out is sucking voltage from the other sources? If so, what is causing it, and how can I fix it? Would increasing the level of the bluetooth reciever using a pre-amp help at all?

Cheers,
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post #2 of 13 Old 05-14-2013, 12:49 PM
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You do not want to connect those outputs together the way you are doing it. What you are doing can damage the devices you are connecting to the amplifier. You are short-circuiting the outputs of the units to each other, and that is a NO-NO!!!!

You need an external switch box so that only one source device is connected to the amplifier at a time.

The Radio Shack 15-313 will allow you to switch between four different audio sources and route them to the amplifier inputs. You need it, or an equivalent switcher. It is around $20.

It has RCA inputs, so you will need adapter cables with 3.5mm on one end and RCA on the other for some connections. Its RCA outputs will go to the amplifier RCA inputs.

Amazon has the CABLESTOGO #28750 for about $17, and it also switches up to four devices. it will also work fine.
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post #3 of 13 Old 05-14-2013, 02:10 PM - Thread Starter
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Hmm. Thanks for that advice. I was hoping to avoid manual switching (i.e. getting up). I've seen some auto sensing video switches, but are there similar devices for audio?

I also wonder why the two inputs on the Lepai are both connected at the same time. If doing so might damage either source, wouldn't that be a serious design flaw? Is there a signal required to do damage? What causes this damage?

Thanks,
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post #4 of 13 Old 06-07-2013, 09:17 PM
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I have the same Lepai amp. What a great bang for the buck. I have it connected to a pair of Bose model 101 outdoor monitors, and the result is, to my ear, as good as the 50 lbs Sansui AU9900 integrated amp I had hooked up before it died.

On to my question. I am wondering, like thelivingna, why and how can the two inputs on the Lepai be "always on"?

Why I wonder this is, I am trying to use a similar setup to thelivingna, but I only have two sources, which are as follows; a desktop PC hooked up through the motherboard 3.5mm output, and a Belkin bluetooth adapter also through a 3.5mm out. My problem is, whenever the bluetooth is plugged in the, PC's volume drops dramatically and becomes "muddled". This is the case regardless of which source I attach to the RCA vs. 3.5mm jack on the amp, and whether the bluetooth is even on. According to both thelivingna (if I understand his setup correctly) and CNET this should work fine, but is not for me. Do I have a faulty amp? Could a line level discrepancy between the PC and bluetooth source be causing the PC's level to drop?

One peculiar behavior I noticed was, if I unplug the bluetooth's power cable, I can leave it fully hooked up to the amp without interference to the PC sound. Could a different bluetooth adapter solve this problem?
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post #5 of 13 Old 08-24-2013, 07:07 AM
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I just got my Lepai 2020A+ set up to. Connected through 3.5mm to a bluetooth receiver and RCAs to my Vizio TV. I have the same problem as you. The volume level through the RCA (TV) is really low. I have to turn the volume all the way up on the Lepai and almost to the top on the TV to get medium volumes. Can't figure out what might be causing this.
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post #6 of 13 Old 08-24-2013, 08:39 AM
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Quote:
Originally Posted by mikeyfoucs View Post

I just got my Lepai 2020A+ set up to. Connected through 3.5mm to a bluetooth receiver and RCAs to my Vizio TV. I have the same problem as you. The volume level through the RCA (TV) is really low. I have to turn the volume all the way up on the Lepai and almost to the top on the TV to get medium volumes. Can't figure out what might be causing this.

Devices with audio outputs have a characteristic called source impedance. It acts like a small-value (example: 1 to 100 ohm) resistor. When you connect multiple sources to the same input, each source ends up being loaded down by the source impedance of the other devices.

A simple way to think of this is that when you hook multiple sources to the same input, they short each other out. Hence the loss of signal.

So, the rule is don't hook multiple outputs to the same input. Instead, use a switch.
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post #7 of 13 Old 11-14-2013, 10:34 AM
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Quote:
Originally Posted by ericdunn01 View Post

One peculiar behavior I noticed was, if I unplug the bluetooth's power cable, I can leave it fully hooked up to the amp without interference to the PC sound. Could a different bluetooth adapter solve this problem?

 

I'm in exactly the same boat.  TV audio and bluetooth adapter audio into the Lepai.  No matter which input on the Lepai I use for which device, the bluetooth output always "wins" -- perhaps because it's a hotter output?  I'd actually like the TV to always "win" when it's on.  The TV output goes totally dead when the TV is turned off -- but apparently the bluetooth adapter always outputs a voltage, even when there's no audio there, but unplugging it from power or from the input allows the TV to play through.

 

Maybe there's some kind of a sensor in the Lepai that "switches" between the two inputs, or maybe the behavior is simply due to the electrical characteristics of the two inputs.  I'm leaning toward there being some kind of sensing, because when I plug in the TV audio with the bluetooth audio running, there's *no change whatsoever* to the bluetooth audio.  Whereas if the TV audio is going and I plug in the bluetooth adapter input, the TV audio is attenuated down to almost nothing.

 

I'd *really* like to be able to be lazy and not have to plug/unplug or install an inline switch for the bluetooth adapter.  I guess one solution would be an "inverse" power switcher -- that would power down the bluetooth adapter whenever it senses the TV is on, and power it back on when the tv is off -- though I don't think such a product exists, though If pressed, I guess I could build one (!) -- that would have the added benefit of not wasting (a tiny amount) of power with the bluetooth adapter when it's not needed.

 

 

If anyone has any ideas, I'd *love* to hear them!

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post #8 of 13 Old 11-14-2013, 10:56 AM
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Quote:
but apparently the bluetooth adapter always outputs a voltage, even when there's no audio there,

uh, no.

The answer is in post #6.
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post #9 of 13 Old 11-14-2013, 11:23 AM
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Quote:
Originally Posted by SAM64 View Post


uh, no.

The answer is in post #6.


Okay, I see your point, though I don't (entirely) understand why the TV audio then works when power is removed from the bluetooth adapter.  I also just tried an experiment where I ran the audio directly from my tablet to the lepai, and the TV audio and tablet audio are (more or less) the same volume, though both attenuate slightly.  So I guess if the impedance is closely matched between the two sources, the interference is minimal?

 

I guess I'll have to find an auto-switch (affordable ones that actually work are like hen's teeth)  -- or build one -- or I guess just install a switch and walk over to the TV when I want to switch inputs...

 

The Lepai 2020+ is so incredible (especially for it's size and the money) I don't think I'll ever go back to a "regular" receiver.

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post #10 of 13 Old 11-14-2013, 11:31 AM
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though I don't (entirely) understand why the TV audio then works when power is removed from the bluetooth adapter.

The bluetooth adapter goes into a high impedance state when power is removed from it.
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post #11 of 13 Old 11-14-2013, 01:11 PM
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Quote:
Originally Posted by SAM64 View Post


The bluetooth adapter goes into a high impedance state when power is removed from it.

 

That makes sense.  I guess it's all about impedance...

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post #12 of 13 Old 11-16-2013, 09:00 AM
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Amazon is selling the "Cables to Go" #28750 Audio/Video selector switch for under $20.

This has input connections for four channels and RCA outputs to go to your amplifier.

That will take care of your problem and allow you to select from up to four sources.
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post #13 of 13 Old 11-18-2013, 08:07 AM
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Thanks for the tip about the $20 switch. That would certainly do it. Or I guess I could buy a cheap mixer, but I just love the look of the system with just the lepai on a tiny shelf tucked under the TV, and I'd prefer to be lazy and not have to touch a physical switch -- though thanks to this forum I do understand what's going on now!
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