Two Amps Double Output?

[germaniohm]

I want to combine two identical 5 watt, 9 volt amplifiers. Each amplifier will have one microphone. Both amplifiers will share one speaker. I tried but all I got was one amplifier working. When I turned one amplifier off, the other would work. Any ideas or references?

 

[dknguyen]

THe problem is that they aren't really identical and the one with lower output impedance is not letting the one with higher output impedance do any driving. WIthout knowing the amplifier circuit it's hard to say what can be done to match them. Perhaps give each one it's own tuneable series output resistor and fiddle around with it until they match (small resistors to minimize the loss).

 

[Hero999]

They're also have slightly different gains and phase shifts at different frequencies.

You could use a loa value resistor 470mΩ to 1Ω but that would ruin the dampling factor.

 

[audioguru]

An amplifier will not produce 5W when its supply is only 9V.
The amplifier will have a peak-to-peak output of about 7V (or less) which is 2.48V RMS. Then the power in an 8 ohm speaker is only 0.77W.
If the supply is 21V to 24V then the output will be 5W in an 8 ohm speaker.

You cannot parallel amplifiers. They will fight each other. When one tries to make a signal then the other one will say, "No you won't". The amplifiers will kill the supply or be destroyed.

But if you use two amplifiers in a bridge then the output power is almost quadrupled. That is how car radio amplifiers work. They produce 14W in a 4 ohm speaker when the supply is only 13.2V.
Then if one amplifier has a signal then the speaker will play at normal volume. If both amplifiers have a signal then it will be nearly 4 times the power.

Mixing of signals is usually done at the inputs to power amplifiers.

 

[on1aag]

Hi Germaniohm,

There is a possibility to combine two amplifiers to drive one
speaker, you will have to reverse the phase of the signal of one of the amplifiers and connect the speaker between both outputs. That principle is also used in car radio's. The reason why they do this is that you can't get enough output power from amplifiers that operate from low supply voltages e.g. 12 volt or so.
But there is a catch, there always is ! When you do that the output voltage accross the speaker will double and therefore also the output current. The output stages of both amplifiers must be able to supply the double output current and the same goes for the power supply.
The ouput power will quadruple, not just 10 but 20 watts !

on1aag.

ps: Audioguru, you beat me by three minutes.

 

[germaniohm]

How Wrong Of Me

I'm sorry. It was a bad example. Specifically what I want to do is take 2 "Listen Up" devices and connect them to 1 set of headphones to create a "super ear". I tried doing it but one "Listen Up" overwhelmed the other. Is it possible to connect 2 or even 3 "Listen Up" devices to create my "super ear"?

 

[sniper007]

You cannot parallel amplifiers. They will fight each other. When one tries to make a signal then the other one will say, "No you won't". The amplifiers will kill the supply or be destroyed.

Hmm, but wiki say different ?

https://en.wikipedia.org/wiki/Bridged_and_paralleled_amplifiers#Paralleled_amplifier

 

[Mikebits]

Hmm, but wiki say different ?

https://en.wikipedia.org/wiki/Bridged_and_paralleled_amplifiers#Paralleled_amplifier

Not really. Quoted from your Wiki article.

This configuration (ideally or theoretically) requires each amplifier to be exactly identical to the other(s), or they will appear as loads to each other.

Also from your Wiki link.

The gains of the amplifiers must be as closely matched as possible so that the outputs don't try to drive each other when signal is present.

You would just be peeing up a rope trying to match all the needed parameters.

 

[Hero999]

As I said above you might be able to do it if you a low value ballancing resistor but it's pretty pointless.

 

[audioguru]

You said that each amplifier would have one microphone. I assumed that each amplifier would have its own microphone. If you speak into only one microphone then its amplifier would try to make a signal but the other amplifier would try not to produce a signal.

You said that it didn't work when both amplifiers had their outputs connected but it worked whe one amplifier was turned off. Wiki says because one amplifier was the load for the other amplifier. It says you don't want the amplifiers to try to driver each other.

The circuit in Wiki has both amplifiers with the same input.

If the amplifiers worked when connected in parallel then they will not make a Super Ear because the gain would be the same as a single amplifier. Maybe you mean to connect the amplifiers in series to make extremely high gain?

 

[Torben]

Just a random thought, but couldn't you build a mixer which would handle this? Couldn't he use a typical simple mixer circuit (a resistor and cap in series with each input line) into an op-amp, perhaps taking the signal from before the Listen-Ups' power amp output stages?

He'd need to provide a new power amp for this setup to drive the headphones, but that should be simple enough.

Am I just blathering or does that make some kind of sense?


Torben

 

[Mikebits]

Just a random thought, but couldn't you build a mixer which would handle this? Couldn't he use a typical simple mixer circuit (a resistor and cap in series with each input line) into an op-amp, perhaps taking the signal from before the Listen-Ups' power amp output stages?

He'd need to provide a new power amp for this setup to drive the headphones, but that should be simple enough.

Am I just blathering or does that make some kind of sense?
Torben

LOL, That's a real word... I had to look it up. hehe

blath·er (blr) also bleth·er (bl-)
intr.v. blath·ered, blath·er·ing, blath·ers
To talk nonsensically.
n.
Nonsensical talk.

--------------------------------------------------------------------------------

[Old Norse bladhra; see bhl- in Indo-European roots.]

--------------------------------------------------------------------------------

blather·er n.