Parallel stereo = more output?

I didn't look up the specs, but generally you can't do this. They have to have identical poles and stuff, but by adding a little lossy resistance on each output, they may be stable enough to opperated with the resistor legs tied together to form the output.

greg

The output of one channel would see, as a load, the very low output impedance of the other channel. And when you add series resistors you lose the advantage you are trying to gain by introducing new losses. Not a good approach.

Fred

Well, not by much. A fractional ohm resistor might drop efficiency by 10%. (It also provides current protection to some extent, if that matters any with that chip.)

Tim

-- Deep Fryer: a very philosophical monk. Website:

Invert the input signal to one amplifier, then connect the load "bridge-style"... output to output... PROVIDED the TDA2009 can handle the doubled current.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
        Global Warming is God\'s gift to the Blue States ;-)

Only if the 2 amps try to fight each other at some point. Take care that the response across the spectrum is the same with both amps and things are ok.

power doubled then -10%, so no, you get 80% more power.

It does increase output impedance, and the careless may be tempted to do it with unmatched circuits. And if any minor circuit fault changes the closed loop characteristics you can end up with 2 chips trying to cook each other, hence a few more failures. It works though.

NT

The original device is two (stereo) amplifiers on one chip. How much more well matched do you think you are going to get? OP may get 41% more usable voltage but not 41% more usable current; and power dissipation remains as a limiting factor.

--
JosephKK
Gegen dummheit kampfen Die Gotter Selbst, vergebens.  
--Shiller

He only wants 20 W not 40 W, 1.41 times original current into load.

--
JosephKK
Gegen dummheit kampfen Die Gotter Selbst, vergebens.  
--Shiller

He'll have to lower his load impedance as well as paralleling. (Unless the issue was that a single section couldn't support the current needs of his load in the first place.)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
        Global Warming is God\'s gift to the Blue States ;-)

--- Yes. If your load impedance remains constant, the voltage across it will be the same whether it's being driven by one amplifier or two.

Assume a single unity gain amplifier with a 1 volt input driving a 1 ohm load, and the load will be dissipating 1 watt.

Now assume two unity gain amplifiers in parallel being driven with a

1 volt input and driving the same 1 ohm load. The output of both amplifiers will be 1 volt, so the dissipation in the load will be 1 watt, as with the single amplifier.

---

-- John Fields Professional Circuit Designer

--
LOL!

He says (quite clearly, I thought) that he doesn\'t want to use a
bridged configuration, and you suggest that he use a bridged
configuration...

Short term memory starting to fade???

A

GOTO A

Ooops! Guess I didn't read far enough. But paralleling WILL NOT raise available power unless either the single device couldn't support the load current, or you are allowed to reduce load impedance.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
        Global Warming is God\'s gift to the Blue States ;-)

Matched characteristics depends also on the circuit applied to each amp, it is here that people often get into murky water. For example configuring one amp as a gain of -100, with the other as a gain +1 follower. Not best practice, as response at frequency roll off is likely to be different.

10% less usable voltage, not 41% more.

100% more usable current. I wonder if we're talking about 2 different circuits?

As with every amp ever made. But this time, its twice what it was with a single amp, with about 10% then lost to the Rs, so apx 80% power output gain.

NT

Matched characteristics depends also on the circuit applied to each amp, it is here that people often get into murky water. For example configuring one amp as a gain of -100, with the other as a gain +1 follower. Not best practice, as response at frequency roll off is likely to be different.

10% less usable voltage, not 41% more.

100% more usable current. I wonder if we're talking about 2 different circuits?

As with every amp ever made. But this time, its twice what it was with a single amp, with about 10% then lost to the Rs, so apx 80% power output gain.

NT

--
???

Here\'s the essence of the OP\'s post:


" I have a TDA 2009 audio amp chip that does 10W on each channel.

Is there any reason why I cannot connect the output of both channels
in parallel to produce a total 20W output?

Obviously, the same signal would be used to drive both inputs, and
amp output would be mono."

Notice that he made no mention of changing the gains of the
amplifiers, the level of the input signals, or changing the
impedance of the load, so with the same input voltage and load
impedance as in the 10 watt case, the load would obviously dissipate
the same amount of power as in the single amplifier case.

However, if he kept the same load all he\'d have to do to increase
the power to it by a factor of two would be to increase the level of
the input signals to the amplifiers by 1.4, or increase the gain of
both amplifiers by 1.4.

Conversely, if he kept the input signal levels and gains the same as
in the single amplifier case he could double the power into the load
by halving its impedance. I.e., if he had an 8 ohm speaker on it
before, put another 8 ohm speaker in parallel with that one.

Completely correct John, i had misread OP. Same voltage twice the current.

--
JosephKK
Gegen dummheit kampfen Die Gotter Selbst, vergebens.  
--Shiller