Re: Parallel stereo = more output?

John Fields wrote:

On 1 Feb 2006 10:35:35 -0800, meow2222@xxxxxxxxx wrote:

Joseph2k wrote:
meow2222@xxxxxxxxx wrote:

Fred wrote:
GregS wrote:
In article <o1vst19g0dnevqmq5tute0u0e7e934iblq@xxxxxxx>, Steven
Goring <stevegoring@xxxxxxxxx> wrote:
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.

I do not want to use a bridge configuration for design reasons.

Thank you for any advice.

Steven Goring

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.

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.


And when you add series resistors you
lose the advantage you are trying to gain by introducing new losses.

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


Not a good approach.

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?

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.


OP may get 41% more usable
voltage

10% less usable voltage, not 41% more.

but not 41% more usable current;

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


and power dissipation remains as a
limiting factor.

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.

---
???

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
.

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