Understanding a Resistive Power Divider for Audio Amplifiers

[FrankJ777]

I have to hook up two audio amplifiers to one audio source. According to the instructions I've been given, I need to build a resistive power divider/splitter with 3 Z0/2 resistors in a wye configuration to connect them. I have to admit that I don't understand why or how the power splitter works. I've taken a few EE courses a while back including xmission lines and circuit analysis, but I'm not sure what approach to take to analyze the power splitter and its function. It seems that to use the wave approach would be wrong as audio wavelengths are so long as compared to RF. Using circuits I & II maximum power transfer approach, I don't see the point of adding the resistive network. I've found schematics on what I need to do. I just want to understand how it works. Hope some one can point me in the right direction.

Thanks

 

[schip666!]

I'm confused... You have one signal source and two amplifiers. If the source is audio-line-level (~1v) and the amplifiers have line level inputs, you can just run the inputs in parallel. But all the talk of resistor networks makes me think that you perhaps have the output of some other amp (which might go to a speaker) as your source? Or maybe a 70v PA distribution system? Can you sketch a schematic to make things clearer for my addled little mind?

I think you are correct in assuming that you don't need to use RF line matching techniques.

 

[FrankJ777]

Here's a a rough diagram of what I'm trying to do. Already the balanced audio from a telephone E&M card is connected to the telephone equipment. I want to also connect the audio line to the Low Z mic input of a public address system amplifier. The resistive network(power divider) on the side is what I'm told to use as a bridge.

I understand the max power transfer theorem, but I don't see how that applies.

I'd really liketo brush up on my understanding, and apply what I've learned before, but I have no idea how to approach this.

Thanks a lot for the patience.

 

[Bob S]

i have done this before, for RG-58, and used a delta connection rather than a wye. But let me discuss your wye.

If both of your loads were 600 ohm, then the forward load impedance at the node would be 0.5( 1.5 Z₀) = 0.75 Z₀ (i.e., 900/2 = 450 ohms). Adding the series Z₀/2 gives me 1.25 Z₀ (i.e., 750 ohms) for the load as seen by the "E&M" source. This is too high. If the mic input impedance is very low, then the E&M sees only 525 ohms. If I put an additional series resistor =Z₀ in the mic input, this would raise the load seen by E&M back up to 750 ohms.

What backward-looking impedance do you want the two output loads (telephone and low-Z mic) to see? What you have is a resistor wye circuit with 3 unknown resistors, and 3 desired input impedances (into the wye). Solve it.

Bob S