What will raising the Va of atransformers provide?

Thanks, Stanwal, excellent explanation.
Class A amps are fully on (conducting 100% of the rated power) most of the time, therefore the power transformer, rectifiers and power supply capacitors must be over-specified, in order to supply the high current demand, stay relatively cool, not buzz or fail.

On the contrary, Class AB amps pass a fraction of the maximum power most of the time, while playing music. On musical peaks, a larger transformer and stiffer power supply MAY help output more peak power.

Some amplifiers are current-limited by the choice of output devices or the size of the heatsinks. In that case a larger transformer would be of little help.
I suggest that the OP contact the amp's designer for guidance.

Larger transformers will have a much larger turn-on current inrush.

Not necessarily bad, but should be considered. Maximum from the wall, even a 20a circuit is what......1800va?

For larger transformer(s) to be effective, this amp will need a dedicated circuit.

Need some more infor. What class is the amp? Listening habbits and speakers will give some idea of actual power needed.

I thought North American power is 120 volts. That means a 15 amp circuit x 120 volts will equal 1800 watts and a 20 amp circuit will equal 2400 watts. If I was going to be using close to the limit for either scenario, I would opt for several dedicated circuits.

Ciao,
Audioquest4life

1. Unless you are upgrading and altering the circuit designs within your amp, the new transformers must have the same turns ratio for voltage in and out. In other words, whatever the original input and output voltages are in your current transformer, that is what it must be for your new transformers. With Higer VA rating, that means for the example I stated above, that the current output will be different.
2. Current in-rush must be considered. you would need a slow start circuit.

I have found more benefit by upgrading my power supplies, larger capacitors, separate power supplies, etc. and upgrading the output transistors and pre-drivers to newer, more linear powerful transistors. I have also added Threshold style heat sinks to my amps and altered the bias accordingly to more class A operation. Amps such as Bedini, Threshold, etc. really benefit from this.

By-the-way, you can bias for various levels of Class A. What most people feel is class A is bias whereby the output drivers are producing rated current with no signal. you can bias to lower amounts also. Say, for example the amp is a 100 WPC amp. Nelson Pass on his web site gives several examples of heat sinking, transformer characteristics, amp design, etc. so take a look at his web site, but, for full class A, this means that the output drivers are biased for current output that equates to 100 WPC for the amp. you can bias for 5 WPC, 10 WPC, 50 WPC, etc. This totally depends on the transformer capacity, other circuit considerations and mostly proper heatsinking. To have true full output class A, you need rediculous heat sinks and they cost a ton of money. This is why most amps are not true full output class A, but are biased to class A for lower wattage.

So, if you really like your amp and want to upgrade it. Try upgrading the power supplies first. Then look into new more linear output transistors and pre-drivers. for tube amps, that is a totally different story.

enjoy

Firstly lets get this Class-A and AB thing sorted out.

Class-A: This is where the transistors that operate both the negative and positive going parts of the waveform are ALWAYS on. The reason why Class-A amplifiers get hot is because the transistors are always ON.

Class AB: is where the transistors are only on half of the time, they switch on and off, cycling between the two halves of the waveform. The good thing here is that the transistors are OFF half the time hence less heat.
The problem now is crossover distortion! This is where the 2 halves 'don't quite meet up properly'.

Stanwal - it has nothing to do with full power or AB varying with demand.

So the question to whether a larger VA rating can improve the audio is YES. This is partly because as the VA rating increases the transformer 'regulation' becomes more efficient. Also (and remember VA = Volt Amperes) as you increase VA your current 'tap' increases allowing your amplifier to draw more current when needed.
If you imagine - a standard desktop computer draws approx 25-35A for a few milli secs when asked to perform a BIG number crunch. - this is the equivalent of a large transient in music (kick drum, bass guitar pluck, timpany on drugs)

How much current does a preamp need????

Well, I'm not a Naim Audio lover BUT if you listen to any of there preamps with their smaller power supplies and go to a bigger power supply the improvement is BIG. This is the same for any amplifier design (A,AB,B etc).
Class-D (again not a fan) improves with larger VA transformer - just ask Hypex

Remember, to get the best from a larger VA rated transformer you must upgrade the rectifiers and filter caps accordingly or else it's bottleneck time.