2 Amps 1 pair of speakers

[fuzz092888]

Is there any danger in connecting two amplifiers to one pair of speakers?

Like say, if I had a pair of speakers with two pairs of binding posts that had a jumper connecting them, could I use one pair of binding posts like this:

Receiver -> Amplifier -> Speakers

While using the other pair like this:

Oppo BDP-95 -> Amplifier -> speakers

Obviously both setups wouldn't be on at the same time, but could this do anything bad to the speakers or the electronics?

 

[markw]

I don't kow the exact electrical principles involved but I believe connecting the outputs of two amplifiers together sounds like a trip to the new amplifier store.

Look for a switch to select one or the other, never both.

 

[fuzz092888]

I figured that would be the case, thanks Mark.

 

[ImcLoud]

why would you want to do that

 

[j_garcia]

That won't work. The 95 is not a preamp, so there is no way to control volume to the amp unless the amp has the ability to do this.

 

[fuzz092888]

why would you want to do that

I have it set up to use my receiver and Outlaw 755 for home theater and TV watching, but I want to use the Oppo for 2 channel only music listening as well and without the receiver in the way. I know I can go pure audio or direct on my receiver, but I'd rather not have to turn it on at all.

That won't work. The 95 is not a preamp, so there is no way to control volume to the amp unless the amp has the ability to do this.

Are you sure? I can adjust the volume with the oppo remote, independent of the receiver or TV or anything else. I think you may be mistaken on this one.

Just gave it a go and you can adjust volume with only the Oppo connected directly to the amp.

 

[j_garcia]

Are you sure? I can adjust the volume with the oppo remote, independent of the receiver or TV or anything else. I think you may be mistaken on this one.

Just gave it a go and you can adjust volume with only the Oppo connected directly to the amp.

My 10yr old Sony CDP has that ability too, but that doesn't mean I am going to connect it directly to one of my amps if I have a unit with a preamp available. That volume control is digital, and my understanding was that there were issues with this function on basically all digital volume controls. The digital control works OK as long as you aren't looking to alter the levels more than a few dB. With a digital volume control, lowering the sound level also slightly degrades the signal, the lower you take it, the more loss there is. So while it will technically work, it also sort of defeats the purpose.

 

[TLS Guy]

Is there any danger in connecting two amplifiers to one pair of speakers?

Like say, if I had a pair of speakers with two pairs of binding posts that had a jumper connecting them, could I use one pair of binding posts like this:

Receiver -> Amplifier -> Speakers

While using the other pair like this:

Oppo BDP-95 -> Amplifier -> speakers

Obviously both setups wouldn't be on at the same time, but could this do anything bad to the speakers or the electronics?

Never connect the outputs of two amps together, even if one is off.

This is really good way to dispose of your equipment.

 

[fuzz092888]

My 10yr old Sony CDP has that ability too, but that doesn't mean I am going to connect it directly to one of my amps if I have a unit with a preamp available. That volume control is digital, and my understanding was that there were issues with this function on basically all digital volume controls. The digital control works OK as long as you aren't looking to alter the levels more than a few dB. With a digital volume control, lowering the sound level also slightly degrades the signal, the lower you take it, the more loss there is. So while it will technically work, it also sort of defeats the purpose.

From what I'm reading over on AVS in the Official BDP-95 thread the way in which oppo has implemented the digital volume control there isn't a perceptible difference in SQ. I think these were probably the most useful posts

Digital volume control in digital domain will have some bits lost on the least significant bits as you lower the volume from 100%. But how it is performed in the 95's DAC and how many bits are lost at what setting is not known. Oppo would have to supply that information. What rdgrimes stated is
Oppo performed extensive tests (what those tests were is also not known) and concluded that their implementation does not degrade the audio quality in any negative way that may be perceptible to the listeners.

Here is an example of how Wadia implemented their old digital volume control without sacrificing audio quality. They don't tell you what they do exactly, I guess that algorithm is proprietary.

http://www.wadia.com/technology/tech..._Control_2.pdf

Let's talk about the Cirrus DACs used in the original BDP83 stereo output. Looking at their datasheet (CS4398), it says they have a "Non-Decimating Volume Control with 1/2 dB Step Size and Soft Ramp". Their functional diagram clearly shows this function is performed by a digital filter, a simple multiplier really, to reduce the volume in 0.5dB increments. This is what Bob meant by the volume control being done within the DAC as opposed to being done in the mediatek decoder. Oppo decided to use 1dB increments or else you'd have to press the remote volume control 'forever' before you hear a discernable change in levels.

Wadia (an excellent and admirable company btw) implements a more complex digital filter with volume control as well(a fancier multipler) to maintain resolution as for as long as possible.

With a 24-bit audio input datastream, multiplied by a high precision coefficient value between 0 and 1, you'd get a number which still is high precision and not simply bit-shifted to the right which results in dropping bits.

This isn't much different than an analog volume control where the output is simply the voltage read from a high quality pot.

So, using the Oppo83/93/95 volume control doesn't have the bad effects on would expect from bit dropping. If you can hear a 1dB difference in levels, good for you. I know i can't for i tried, failed and gave-up.

I'll probably do a little experimenting, but if what they're saying is true I doubt I'd be able to detect a difference. Plus the amp I'm using has gain controls, so I'll just leave them high, negating the need to lower the volume past 80 or so. YMMV