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Topic: Wire two amplifiers in series? (Read 7199 times) previous topic - next topic
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Wire two amplifiers in series?

If I have an amplifier that is too weak to properly drive some drivers, can I add another amplifier in between the first amp and the speakers?

I'm dealing with a 2.1 watt amp driving 7.5 watt drivers. I know normally one would remove the 2.1 watt amp and use a larger one, but I'm dealing with components soldered onto a circuit board and don't have that luxury. I would have to tap into the speaker wires.

Cheers.

Re: Wire two amplifiers in series?

Reply #1 –
Its a bad idea. One amp acts as a load for the other- you can wind up blowing both of them.

Re: Wire two amplifiers in series?

Reply #2 –
No you can't. Amp outputs have a low impedance output, effectively working as a current source. And as we know from electronics class, current sources can't be connected in series, except if both have the same value for I (which negates the idea of adding the sources). In all other cases, one source will limit the current of the other.

If your amplifier has a bridge circuit, you can use a stereo amp to drive one channel, the amp needs a dedicated circuit for that, and usually has an extra switch to enable those. This will make each of the two amplifier stages work in a push-pull configuration for just one channel.

You can add amplifiers in parallel. This isn't really advisable, but it does work. However, if these are two different amps, one might always be slightly out of phase of the other, acting like a different voltage source to the other at any given point. Connecting multiple voltage sources is not allowed in parallel, so that again becomes a problem.
Both amps must have preferably zero DC offset, as well as the same gain, so they don't drive each other, either.
You can add small resistors to the output of each of the amps, to facilitate current sharing.
The output impedance of each of the amps will be halved (assuming they are otherwise identical).
So if you have a 2Ω load, each amp will "see" a 4Ω load, if in parallel mode.

The more amps you parallel like that, the more difficult it becomes to sync them up like that, so the real gain actually drops the more amps you use like that.

Re: Wire two amplifiers in series?

Reply #3 –
Thanks for the info! Is there a way to return the audio signal to line level so that I can run it through another amp?

Re: Wire two amplifiers in series?

Reply #4 –
Quote from: Rogue75 on
Thanks for the info! Is there a way to return the audio signal to line level so that I can run it through another amp?
Hmm, this doesn't make much sense. You see, what you're doing, is you'd limit the amplified signal down, so it can be amplified by another amp?

What sort of signal are we talking on the input side?

EDIT:
OK, I've re-read your question and here's this: if those are soldered components on a board, you should be able to identify the darlington circuit of the output stage, the signal before that, should be a line-level signal, if not you should be able to inspect it with a scope. I'd tap into the signal right there. You can add a switch so you can switch between line-out and the amplified signal.

There's a how-ya-doin' kindof way to find the signal behind the darlington: get a 22pF cap, attach it to a stripped cable of a line input of a soundcard. The shielding you connect to to a ground point on the device you're probing: You can now touch the cap to solder pads to see if there's a signal (while playing some music through that device). You should be able to find the signal leaving some sort of IC, etc.

If those are Op-Amps, you should be able to identify them by their part numbers, and simply tap the signal at the point of it entering the IC.

Re: Wire two amplifiers in series?

Reply #5 –
Quote from: Rogue75 on
Is there a way to return the audio signal to line level so that I can run it through another amp?
Line level converter

"0.5db linearity" remains to be seen, but this doesn't sound like a ultra high end system application
Loudspeaker manufacturer

Re: Wire two amplifiers in series?

Reply #6 –
Quote from: polemon on
You can add amplifiers in parallel. This isn't really advisable, but it does work. However, if these are two different amps, one might always be slightly out of phase of the other, acting like a different voltage source to the other at any given point. Connecting multiple voltage sources is not allowed in parallel, so that again becomes a problem.
Both amps must have preferably zero DC offset, as well as the same gain, so they don't drive each other, either.
You can add small resistors to the output of each of the amps, to facilitate current sharing.
The output impedance of each of the amps will be halved (assuming they are otherwise identical).
So if you have a 2Ω load, each amp will "see" a 4Ω load, if in parallel mode.

The more amps you parallel like that, the more difficult it becomes to sync them up like that, so the real gain actually drops the more amps you use like that.

Wow my understanding of electronics is rusty. I was in fact trying to wire them in parallel. Thanks for the info!

Re: Wire two amplifiers in series?

Reply #7 –
If you're willing to mod your device anyway, just tap into the signal before the darlington output stage, you'll end up with a far more efficient and better engineered result.

Re: Wire two amplifiers in series?

Reply #8 –
Another option is to use the amp in bridge if the amp isn't using it already.

Re: Wire two amplifiers in series?

Reply #9 –
Quote from: ajinfla on
Quote from: Rogue75 on
Is there a way to return the audio signal to line level so that I can run it through another amp?
Line level converter

"0.5db linearity" remains to be seen, but this doesn't sound like a ultra high end system application

I was so impressed by the commercial alternatives that I designed and built some of my own. The raw materials come from "passive direct box" products, some of which have very nice transformers, which can be upgraded further by replacing the transformer with the equivalent from Jensen (shown in the picture).  Note: the picture was taken before the need for the 1K 2 watt resistor became apparent. Be sure to follow the schematic.

Re: Wire two amplifiers in series?

Reply #10 –
Quote from: Arnold B. Krueger on
I was so impressed by the commercial alternatives that I designed and built some of my own. The raw materials come from "passive direct box" products, some of which have very nice transformers, which can be upgraded further by replacing the transformer with the equivalent from Jensen (shown in the picture).  Note: the picture was taken before the need for the 1K 2 watt resistor became apparent. Be sure to follow the schematic.
Maybe Ralph can now post the Hifi tube version
Loudspeaker manufacturer

Re: Wire two amplifiers in series?

Reply #11 –
Quote from: Arnold B. Krueger on
I was so impressed by the commercial alternatives that I designed and built some of my own. The raw materials come from "passive direct box" products, some of which have very nice transformers, which can be upgraded further by replacing the transformer with the equivalent from Jensen (shown in the picture).  Note: the picture was taken before the need for the 1K 2 watt resistor became apparent. Be sure to follow the schematic.
Nice re-use of Cat5 wires. But that soldering job on the binding posts, dude...

Should be noted, that a level converter like this, is basically a DI-Box with a different transformer. All passive level converters basically work the same. DI-Boxes often contain baluns, too, but other than that, it's just a transformer in a box.

Re: Wire two amplifiers in series?

Reply #12 –
Quote from: polemon on
Quote from: Arnold B. Krueger on
I was so impressed by the commercial alternatives that I designed and built some of my own. The raw materials come from "passive direct box" products, some of which have very nice transformers, which can be upgraded further by replacing the transformer with the equivalent from Jensen (shown in the picture).  Note: the picture was taken before the need for the 1K 2 watt resistor became apparent. Be sure to follow the schematic.
Nice re-use of Cat5 wires. But that soldering job on the binding posts, dude...

Should be noted, that a level converter like this, is basically a DI-Box with a different transformer. All passive level converters basically work the same. DI-Boxes often contain baluns, too, but other than that, it's just a transformer in a box.

in your rush to judge the curde prototype-level workmanship my first prototype you seem to have failed to notice that as my quoted text above says, the converter was built out of parts of direct boxes. This makes your technical comments moot on the grounds that they are just paraphrases of what I already said.  Interesting coincidence that the  impedances and turns ratios for direct boxes work so well in this application as well.
 

Re: Wire two amplifiers in series?

Reply #13 –
Quote from: ajinfla on
Quote from: Arnold B. Krueger on
I was so impressed by the commercial alternatives that I designed and built some of my own. The raw materials come from "passive direct box" products, some of which have very nice transformers, which can be upgraded further by replacing the transformer with the equivalent from Jensen (shown in the picture).  Note: the picture was taken before the need for the 1K 2 watt resistor became apparent. Be sure to follow the schematic.
Maybe Ralph can now post the Hifi tube version

The Jensen is the HiFi tube version...