Is a parallel amp the same as a balanced amp?

I'm not sure where you found a parallel amp, but it can hardly be the same as a balanced amplifier because the two outputs of a balanced (bridged amplifier) are in series, with the load between them. This increases the total voltage applied to the load.

I can only assume that paralleled amplifiers are just connected in parallel (to raise the total output current capability) with the load connected between that node and the signal common (ground).

So if you need more voltage for the load, use a balanced configuration. If you need more current for the load, use the parallel configuration.

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Regards,

John Popelish

'Balanced input' means it can take a differential signal on a 'cannon mic connector'. 'Parallel' is just a stereo-mono switch that lets one channel drive both amp channels in phase and in parallel. 'Bridge' sticks an inverter in front of one channel so they are out of phase... one red wire is going positive and the other one is going negative.... hook the speakers up to the two red terminals for more ooomph. I've never heard the term 'balanced amp' but it sort of sounds like the bridged definition I just tried to explain. Hope it helped.

"BobG"

** Watch out !!!!

Having a "mono' switch does NOT = parallel operation of the power amps !!!

Only a very few amps ( notably some Crown models ) have the ability to parallel the speaker outputs with safety.

The others will BLOW UP if you dare try it.

** Mostly, yes.

But it only takes one resistor, connected from ch A's output to ch B's inverting input, ( virtual earth point ) to get ch A to drive ch B with equal level & reverse polarity.

** The OP is a f****it - omitting all context from his asinine Q.

..... Phil

Parallel refers to the configuration of an amplifier's output circuit. And now for something completely different.

Balanced refers to the nature of the either input or output signals. Balanced means that the two lines of the output are referenced to each other and not to ground; the input's or load's voltage is measured between two lines and voltages present on either line (as measured to ground) are typically unintentional, undesired and are to be rejected as extraneous. This is good for long runs, e.g. between a mic and an amp input, because noise is mostly referenced to ground and is so theoretically rejected. Whatever noise hits one line also hits the other and so is ideally cancelled.

Unbalanced signals are measured to ground, so are limited to short runs where they won't be susceptible to noise pickup, e.g. between adjacent audio components. (The run to a speaker is typically long, but can get away with an unbalanced line by virture of a speaker's low impedance, making it much, much less susceptible to noise. If someone went crazy and designed a high-impedance speaker circuit, it would benefit from a balanced output, too. Nobody's been that crazy yet.)

As you might guess, a mic input, say, that is both balanced AND low impedance, is the double-whammy for quietness. Professional mic inputs are that way. Cheapo mic inputs are high-impedance and unbalanced, the worst case, so they rely simply on short runs to avoid noise. If you have to carry signals between two buildings that use separate ground systems that may have a small difference between them (or a large one if lightning or other surges strike!), then a balanced system would be preferable so that the signals ignore the ground as much as possible. Whole books are written on signals, grounding and noise reduction tecniques. Many books. They come with magic wands.

h

dmeans that the two lines of the output are referenced to each

Thanks guys for the great input. The "parallel amplifiers" that I am speaking of are for HF PAs and LNAs, and are in parallel with each other and have Wilkinson dividers at their input and output. But the "balanced amplifiers" I have seen are also in parallel, but have a 90=BA hybrid power divider at their input and a 90=BA hybrid power combiner at their output. They look so darn close to each other, both circuit- wise and performance-wise, that it starts to get a bit confusing!

Best,

-Nick

Who would have thought that 'amplifier' without 'rf' in front of it meant audio? Only about 99 out of 100 I bet. Fooled me!

A parallel voltage amplifier can take the form of a 'compound' amplifier, where one provides the power and another provides the signal (cancelling the PA noise), whether the resulting circuit is balanced or not.

An RF PA with a low frequency modulator is another form of parallel amplification, whether the resulting output is balanced or not.

In fact you can't really apply voltages in parallel; they have to be isolated by identifiable impedances. Operating them in series is tricky in concept, but fairly common in practice; directly at low frequencies and magnetically coupled at higher frequencies.

RL

cedmeans that the two lines of the output are referenced to each

Sounds like a continuation from the other thread ... An RF balanced amplifier usually refers to a 180-degree phase split, not 90. The main reason to use a balanced amp is to suppress the 2nd (and other even order) harmonics.

The main reason to use a 90-degree split is to match the amplifier over a broader bandwidth, and to realize a good match at the optimum noise figure (Zopt).

So ... you still didn't answer the question: what linearity do you need?

Frank

Its the same guy looking to build a small pirate TV transmitter, I bet.

Mark

Thanks guys for the great input. The "parallel amplifiers" that I am speaking of are for HF PAs and LNAs, and are in parallel with each other and have Wilkinson dividers at their input and output. But the "balanced amplifiers" I have seen are also in parallel, but have a 90º hybrid power divider at their input and a 90º hybrid power combiner at their output. They look so darn close to each other, both circuit- wise and performance-wise, that it starts to get a bit confusing!

Best,

-Nick

In this context, the balanced amp is usually used to cancel second order harmonics and second order intermod products. By careful matching of the phase shifts, you can get around 40 dB improvements in IP2, sometimes more, along with the 3 dB additional gain of the fundamental. Usually seen when the band is more than an octave wide, because second order intermods generated by 2 signals at the low end will be in-band near the top of the band.

Steve

,

Thanks for all the clarifying answers guys. Now it's finally clear! (Frank, linearity is not an issue for me, since I was just trying to fill in one of the many gaps in my electronics knowledge, and not actually trying to build either a parallel or balanced amplifier).

Best regards,

-Nick